CODE_E% = P% LOAD_E% = LOAD% + P% - CODE%ELITE E FILE.cpl LDX #5 \ First we need to back up the seeds in QQ15, so set up \ a counter in X to cover three 16-bit seeds (i.e. \ 6 bytes) .TT53 LDA QQ15,X \ Copy byte X from QQ15 to QQ19 STA QQ19,X DEX \ Decrement the loop counter BPL TT53 \ Loop back for the next byte to back up LDY #3 \ Step 1: Now that the seeds are backed up, we can \ start the name-generation process. We will either \ need to loop three or four times, so for now set \ up a counter in Y to loop four times BIT QQ15 \ Check bit 6 of s0_lo, which is stored in QQ15 BVS P%+3 \ If bit 6 is set then skip over the next instruction DEY \ Bit 6 is clear, so we only want to loop three times, \ so decrement the loop counter in Y STY T \ Store the loop counter in T .TT55 LDA QQ15+5 \ Step 2: Load s2_hi, which is stored in QQ15+5, and AND #%00011111 \ extract bits 0-4 by AND'ing with %11111 BEQ P%+7 \ If all those bits are zero, then skip the following \ two instructions to go to step 3 ORA #%10000000 \ We now have a number in the range 1-31, which we can \ easily convert into a two-letter token, but first we \ need to add 128 (or set bit 7) to get a range of \ 129-159 JSR TT27 \ Print the two-letter token in A JSR TT54 \ Step 3: twist the seeds in QQ15 DEC T \ Decrement the loop counter BPL TT55 \ Loop back for the next two letters LDX #5 \ We have printed the system name, so we can now \ restore the seeds we backed up earlier. Set up a \ counter in X to cover three 16-bit seeds (i.e. 6 \ bytes) .TT56 LDA QQ19,X \ Copy byte X from QQ19 to QQ15 STA QQ15,X DEX \ Decrement the loop counter BPL TT56 \ Loop back for the next byte to restore RTS \ Once all the seeds are restored, return from the \ subroutineName: cpl [Show more] Type: Subroutine Category: Universe Summary: Print the selected system name Deep dive: Generating system names Galaxy and system seedsContext: See this subroutine on its own page References: This subroutine is called as follows: * cour_count calls cpl * HME2 calls cpl * TT102 calls cpl * TT23 calls cpl * TT27 calls cpl * ypl calls cpl
Print control code 3 (the selected system name, i.e. the one in the crosshairs in the Short-range Chart)..cmn JSR MT19 \ Call MT19 to capitalise the next letter (i.e. set \ Sentence Case for this word only) LDY #0 \ Set up a counter in Y, starting from 0 .QUL4 LDA NA%,Y \ The commander's name is stored at NA%, so load the \ Y-th character from NA% CMP #13 \ If we have reached the end of the name, return from BEQ ypl-1 \ the subroutine (ypl-1 points to the RTS below) JSR TT26 \ Print the character we just loaded INY \ Increment the loop counter BNE QUL4 \ Loop back for the next character RTS \ Return from the subroutineName: cmn [Show more] Type: Subroutine Category: Status Summary: Print the commander's nameContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls cmn
Print control code 4 (the commander's name).
Other entry points: cmn-1 Contains an RTS.ypl JSR TT62 \ Call TT62 below to swap the three 16-bit seeds in \ QQ2 and QQ15 (before the swap, QQ2 contains the seeds \ for the current system, while QQ15 contains the seeds \ for the selected system) JSR cpl \ Call cpl to print out the system name for the seeds \ in QQ15 (which now contains the seeds for the current \ system) \ Now we fall through into the TT62 subroutine, which \ will swap QQ2 and QQ15 once again, so everything goes \ back into the right place, and the RTS at the end of \ TT62 will return from the subroutine .TT62 LDX #5 \ Set up a counter in X for the three 16-bit seeds we \ want to swap (i.e. 6 bytes) .TT78 LDA QQ15,X \ Swap byte X between QQ2 and QQ15 LDY QQ2,X STA QQ2,X STY QQ15,X DEX \ Decrement the loop counter BPL TT78 \ Loop back for the next byte to swap RTS \ Once all bytes are swapped, return from the \ subroutineName: ypl [Show more] Type: Subroutine Category: Universe Summary: Print the current system nameContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls ypl * cmn calls via ypl-1
Print control code 2 (the current system name).
Other entry points: ypl-1 Contains an RTS.tal CLC \ We don't want to print the galaxy number with a \ decimal point, so clear the C flag for pr2 to take as \ an argument LDX GCNT \ Load the current galaxy number from GCNT into X INX \ Add 1 to the galaxy number, as the galaxy numbers \ are 0-7 internally, but we want to display them as \ galaxy 1 through 8 JMP pr2 \ Jump to pr2, which prints the number in X to a width \ of 3 figures, left-padding with spaces to a width of \ 3, and return from the subroutine using a tail callName: tal [Show more] Type: Subroutine Category: Universe Summary: Print the current galaxy numberContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls tal
Print control code 1 (the current galaxy number, right-aligned to width 3)..fwl LDA #105 \ Print recursive token 105 ("FUEL") followed by a JSR TT68 \ colon LDX QQ14 \ Load the current fuel level from QQ14 SEC \ We want to print the fuel level with a decimal point, \ so set the C flag for pr2 to take as an argument JSR pr2 \ Call pr2, which prints the number in X to a width of \ 3 figures (i.e. in the format x.x, which will always \ be exactly 3 characters as the maximum fuel is 7.0) LDA #195 \ Print recursive token 35 ("LIGHT YEARS") followed by JSR plf \ a newline .PCASH LDA #119 \ Print recursive token 119 ("CASH:" then control code BNE TT27 \ 0, which prints cash levels, then " CR" and newline)Name: fwl [Show more] Type: Subroutine Category: Status Summary: Print fuel and cash levelsContext: See this subroutine on its own page References: This subroutine is called as follows: * TT213 calls fwl * TT27 calls fwl
Print control code 5 ("FUEL: ", fuel level, " LIGHT YEARS", newline, "CASH:", control code 0)..csh LDX #3 \ We are going to use the BPRNT routine to print out \ the current amount of cash, which is stored as a \ 32-bit number at location CASH. BPRNT prints out \ the 32-bit number stored in K, so before we call \ BPRNT, we need to copy the four bytes from CASH into \ K, so first we set up a counter in X for the 4 bytes .pc1 LDA CASH,X \ Copy byte X from CASH to K STA K,X DEX \ Decrement the loop counter BPL pc1 \ Loop back for the next byte to copy LDA #9 \ We want to print the cash amount using up to 9 digits STA U \ (including the decimal point), so store this in U \ for BRPNT to take as an argument SEC \ We want to print the cash amount with a decimal point, \ so set the C flag for BRPNT to take as an argument JSR BPRNT \ Print the amount of cash to 9 digits with a decimal \ point LDA #226 \ Print recursive token 66 (" CR") followed by a \ newline by falling through into plfName: csh [Show more] Type: Subroutine Category: Status Summary: Print the current amount of cashContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls csh
Print control code 0 (the current amount of cash, right-aligned to width 9, followed by " CR" and a newline)..plf JSR TT27 \ Print the text token in A JMP TT67 \ Jump to TT67 to print a newline and return from the \ subroutine using a tail call.TT68 JSR TT27 \ Print the text token in A and fall through into TT73 \ to print a colonName: TT68 [Show more] Type: Subroutine Category: Text Summary: Print a text token followed by a colonContext: See this subroutine on its own page References: This subroutine is called as follows: * fwl calls TT68 * TT146 calls TT68 * TT213 calls TT68 * TT25 calls TT68
Arguments: A The text token to be printed.TT73 LDA #':' \ Set A to ASCII ":" and fall through into TT27 to \ actually print the colonName: TT73 [Show more] Type: Subroutine Category: Text Summary: Print a colonContext: See this subroutine on its own page References: This subroutine is called as follows: * crlf calls TT73.TT27 TAX \ Copy the token number from A to X. We can then keep \ decrementing X and testing it against zero, while \ keeping the original token number intact in A; this \ effectively implements a switch statement on the \ value of the token BEQ csh \ If token = 0, this is control code 0 (current amount \ of cash and newline), so jump to csh to print the \ amount of cash and return from the subroutine using \ a tail call BMI TT43 \ If token > 127, this is either a two-letter token \ (128-159) or a recursive token (160-255), so jump \ to TT43 to process tokens DEX \ If token = 1, this is control code 1 (current galaxy BEQ tal \ number), so jump to tal to print the galaxy number and \ return from the subroutine using a tail call DEX \ If token = 2, this is control code 2 (current system BEQ ypl \ name), so jump to ypl to print the current system name \ and return from the subroutine using a tail call DEX \ If token > 3, skip the following instruction BNE P%+5 JMP cpl \ This token is control code 3 (selected system name) \ so jump to cpl to print the selected system name \ and return from the subroutine using a tail call DEX \ If token = 4, this is control code 4 (commander BEQ cmn \ name), so jump to cmn to print the commander name \ and return from the subroutine using a tail call DEX \ If token = 5, this is control code 5 (fuel, newline, BEQ fwl \ cash, newline), so jump to fwl to print the fuel level \ and return from the subroutine using a tail call \ --- Mod: Code removed for Elite-A: ------------------> \DEX \ If token > 6, skip the following three instructions \BNE P%+7 \ \LDA #%10000000 \ This token is control code 6 (switch to Sentence \STA QQ17 \ Case), so set bit 7 of QQ17 to switch to Sentence Case \RTS \ and return from the subroutine as we are done \ \DEX \ If token > 8, skip the following two instructions \DEX \BNE P%+5 \ \STX QQ17 \ This token is control code 8 (switch to ALL CAPS), so \RTS \ set QQ17 to 0 to switch to ALL CAPS and return from \ \ the subroutine as we are done \ --- And replaced by: --------------------------------> DEX \ If token = 6, this is control code 6 (switch to BEQ vdu_80 \ Sentence Case), so jump to vdu_80 to do just that DEX \ If token <> 8, jump to l_31d2 to skip the following DEX \ four instructions BNE l_31d2 \ If we get here, then token = 8 (switch to ALL CAPS) \ and X = 0, which we now use to set the value of QQ17 \ below EQUB &2C \ Skip the next instruction by turning it into \ &2C &A2 &80, or BIT &80A2, which does nothing apart \ from affect the flags .vdu_80 LDX #%10000000 \ Set bit 7 of X, so when we set QQ17 below, we switch \ standard tokens to Sentence Case STX QQ17 \ This token is control code 8 (switch to ALL CAPS), so RTS \ set QQ17 to 0 to switch to ALL CAPS and return from \ the subroutine as we are done .l_31d2 \ --- End of replacement ------------------------------> DEX \ If token = 9, this is control code 9 (tab to column BEQ crlf \ 21 and print a colon), so jump to crlf CMP #96 \ By this point, token is either 7, or in 10-127. BCS ex \ Check token number in A and if token >= 96, then the \ token is in 96-127, which is a recursive token, so \ jump to ex, which prints recursive tokens in this \ range (i.e. where the recursive token number is \ correct and doesn't need correcting) CMP #14 \ If token < 14, skip the following two instructions BCC P%+6 CMP #32 \ If token < 32, then this means token is in 14-31, so BCC qw \ this is a recursive token that needs 114 adding to it \ to get the recursive token number, so jump to qw \ which will do this \ By this point, token is either 7 (beep) or in 10-13 \ (line feeds and carriage returns), or in 32-95 \ (ASCII letters, numbers and punctuation) LDX QQ17 \ Fetch QQ17, which controls letter case, into X BEQ TT74 \ If QQ17 = 0, then ALL CAPS is set, so jump to TT74 \ to print this character as is (i.e. as a capital) BMI TT41 \ If QQ17 has bit 7 set, then we are using Sentence \ Case, so jump to TT41, which will print the \ character in upper or lower case, depending on \ whether this is the first letter in a word BIT QQ17 \ If we get here, QQ17 is not 0 and bit 7 is clear, so BVS TT46 \ either it is bit 6 that is set, or some other flag in \ QQ17 is set (bits 0-5). So check whether bit 6 is set. \ If it is, then ALL CAPS has been set (as bit 7 is \ clear) but bit 6 is still indicating that the next \ character should be printed in lower case, so we need \ to fix this. We do this with a jump to TT46, which \ will print this character in upper case and clear bit \ 6, so the flags are consistent with ALL CAPS going \ forward \ If we get here, some other flag is set in QQ17 (one \ of bits 0-5 is set), which shouldn't happen in this \ version of Elite. If this were the case, then we \ would fall through into TT42 to print in lower case, \ which is how printing all words in lower case could \ be supported (by setting QQ17 to 1, say)Name: TT27 [Show more] Type: Subroutine Category: Text Summary: Print a text token Deep dive: Printing text tokensContext: See this subroutine on its own page References: This subroutine is called as follows: * cour_dock calls TT27 * cpl calls TT27 * DETOK2 calls TT27 * EQSHP calls TT27 * ex calls TT27 * fwl calls TT27 * JMTB calls TT27 * mes9 calls TT27 * MT17 calls TT27 * n_name calls TT27 * NLIN3 calls TT27 * plf calls TT27 * prq calls TT27 * qv calls TT27 * sell_yn calls TT27 * spc calls TT27 * status_equip calls TT27 * TT151 calls TT27 * TT162 calls TT27 * TT208 calls TT27 * TT210 calls TT27 * TT219 calls TT27 * TT22 calls TT27 * TT25 calls TT27 * TT43 calls TT27 * TT60 calls TT27 * TT67 calls TT27 * TT68 calls TT27 * TT70 calls TT27 * TTX66 calls TT27 * cour_buy calls via vdu_80 * EQSHP calls via vdu_80 * status_equip calls via vdu_80 * TITLE calls via vdu_80 * TT102 calls via vdu_80 * TT167 calls via vdu_80 * TT219 calls via vdu_80 * TT23 calls via vdu_80
Print a text token (i.e. a character, control code, two-letter token or recursive token).
Arguments: A The text token to be printed
Other entry points: vdu_80 Switch standard tokens to Sentence Case.TT42 CMP #'A' \ If A < ASCII "A", then this is punctuation, so jump BCC TT44 \ to TT26 (via TT44) to print the character as is, as \ we don't care about the character's case CMP #'Z'+1 \ If A >= (ASCII "Z" + 1), then this is also BCS TT44 \ punctuation, so jump to TT26 (via TT44) to print the \ character as is, as we don't care about the \ character's case ADC #32 \ Add 32 to the character, to convert it from upper to \ lower case .TT44 JMP TT26 \ Print the character in AName: TT42 [Show more] Type: Subroutine Category: Text Summary: Print a letter in lower caseContext: See this subroutine on its own page References: This subroutine is called as follows: * TT45 calls TT42 * TT41 calls via TT44
Arguments: A The character to be printed. Can be one of the following: * 7 (beep) * 10-13 (line feeds and carriage returns) * 32-95 (ASCII capital letters, numbers and punctuation)
Other entry points: TT44 Jumps to TT26 to print the character in A (used to enable us to use a branch instruction to jump to TT26).TT41 \ If we get here, then QQ17 has bit 7 set, so we are in \ Sentence Case BIT QQ17 \ If QQ17 also has bit 6 set, jump to TT45 to print BVS TT45 \ this character in lower case \ If we get here, then QQ17 has bit 6 clear and bit 7 \ set, so we are in Sentence Case and we need to print \ the next letter in upper case CMP #'A' \ If A < ASCII "A", then this is punctuation, so jump BCC TT74 \ to TT26 (via TT44) to print the character as is, as \ we don't care about the character's case PHA \ Otherwise this is a letter, so store the token number TXA \ Set bit 6 in QQ17 (X contains the current QQ17) ORA #%1000000 \ so the next letter after this one is printed in lower STA QQ17 \ case PLA \ Restore the token number into A BNE TT44 \ Jump to TT26 (via TT44) to print the character in A \ (this BNE is effectively a JMP as A will never be \ zero)Name: TT41 [Show more] Type: Subroutine Category: Text Summary: Print a letter according to Sentence CaseContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls TT41
The rules for printing in Sentence Case are as follows: * If QQ17 bit 6 is set, print lower case (via TT45) * If QQ17 bit 6 is clear, then: * If character is punctuation, just print it * If character is a letter, set QQ17 bit 6 and print letter as a capital
Arguments: A The character to be printed. Can be one of the following: * 7 (beep) * 10-13 (line feeds and carriage returns) * 32-95 (ASCII capital letters, numbers and punctuation) X Contains the current value of QQ17 QQ17 Bit 7 is set.qw ADC #114 \ This is a recursive token in the range 0-95, so add BNE ex \ 114 to the argument to get the token number 128-145 \ and jump to ex to print itName: qw [Show more] Type: Subroutine Category: Text Summary: Print a recursive token in the range 128-145Context: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls qw
Print a recursive token where the token number is in 128-145 (so the value passed to TT27 is in the range 14-31).
Arguments: A A value from 128-145, which refers to a recursive token in the range 14-31.crlf LDA #21 \ Set the X-column in XC to 21 STA XC BNE TT73 \ Jump to TT73, which prints a colon (this BNE is \ effectively a JMP as A will never be zero)Name: crlf [Show more] Type: Subroutine Category: Text Summary: Tab to column 21 and print a colonContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls crlf
Print control code 9 (tab to column 21 and print a colon). The subroutine name is pretty misleading, as it doesn't have anything to do with carriage returns or line feeds..TT45 \ If we get here, then QQ17 has bit 6 and 7 set, so we \ are in Sentence Case and we need to print the next \ letter in lower case CPX #255 \ If QQ17 = 255 then printing is disabled, so return BEQ TT48 \ from the subroutine (as TT48 contains an RTS) CMP #'A' \ If A >= ASCII "A", then jump to TT42, which will BCS TT42 \ print the letter in lowercase \ Otherwise this is not a letter, it's punctuation, so \ this is effectively a word break. We therefore fall \ through to TT46 to print the character and set QQ17 \ to ensure the next word starts with a capital letterName: TT45 [Show more] Type: Subroutine Category: Text Summary: Print a letter in lower caseContext: See this subroutine on its own page References: This subroutine is called as follows: * TT41 calls TT45
This routine prints a letter in lower case. Specifically: * If QQ17 = 255, abort printing this character as printing is disabled * If this is a letter then print in lower case * Otherwise this is punctuation, so clear bit 6 in QQ17 and print
Arguments: A The character to be printed. Can be one of the following: * 7 (beep) * 10-13 (line feeds and carriage returns) * 32-95 (ASCII capital letters, numbers and punctuation) X Contains the current value of QQ17 QQ17 Bits 6 and 7 are set.TT46 PHA \ Store the token number TXA \ Clear bit 6 in QQ17 (X contains the current QQ17) so AND #%10111111 \ the next letter after this one is printed in upper STA QQ17 \ case PLA \ Restore the token number into A \ Now fall through into TT74 to print the characterName: TT46 [Show more] Type: Subroutine Category: Text Summary: Print a character and switch to capitalsContext: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls TT46
Print a character and clear bit 6 in QQ17, so that the next letter that gets printed after this will start with a capital letter.
Arguments: A The character to be printed. Can be one of the following: * 7 (beep) * 10-13 (line feeds and carriage returns) * 32-95 (ASCII capital letters, numbers and punctuation) X Contains the current value of QQ17 QQ17 Bits 6 and 7 are set.TT74 JMP TT26 \ Print the character in A.TT43 CMP #160 \ If token >= 160, then this is a recursive token, so BCS TT47 \ jump to TT47 below to process it AND #127 \ This is a two-letter token with number 128-159. The ASL A \ set of two-letter tokens is stored in a lookup table \ at QQ16, with each token taking up two bytes, so to \ convert this into the token's position in the table, \ we subtract 128 (or just clear bit 7) and multiply \ by 2 (or shift left) TAY \ Transfer the token's position into Y so we can look \ up the token using absolute indexed mode LDA QQ16,Y \ Get the first letter of the token and print it JSR TT27 LDA QQ16+1,Y \ Get the second letter of the token CMP #'?' \ If the second letter of the token is a question mark BEQ TT48 \ then this is a one-letter token, so just return from \ the subroutine without printing (as TT48 contains an \ RTS) JMP TT27 \ Print the second letter and return from the \ subroutine .TT47 SBC #160 \ This is a recursive token in the range 160-255, so \ subtract 160 from the argument to get the token \ number 0-95 and fall through into ex to print itName: TT43 [Show more] Type: Subroutine Category: Text Summary: Print a two-letter token or recursive token 0-95Context: See this subroutine on its own page References: This subroutine is called as follows: * TT27 calls TT43
Print a two-letter token, or a recursive token where the token number is in 0-95 (so the value passed to TT27 is in the range 160-255).
Arguments: A One of the following: * 128-159 (two-letter token) * 160-255 (the argument to TT27 that refers to a recursive token in the range 0-95).ex TAX \ Copy the token number into X \ --- Mod: Code removed for Elite-A: ------------------> \LDA #LO(QQ18) \ Set V(1 0) to point to the recursive token table at \STA V \ location QQ18 \LDA #HI(QQ18) \STA V+1 \ \LDY #0 \ Set a counter Y to point to the character offset \ \ as we scan through the table \ --- And replaced by: --------------------------------> LDY #LO(QQ18) \ Set V(1 0) to point to the recursive token table at STY V \ location QQ18, and because QQ18 starts on a page LDA #HI(QQ18) \ boundary, the lower byte of the address is 0, so this STA V+1 \ also sets Y = 0, which we can now use as a counter to \ point to the character offset as we scan through the \ table \ --- End of replacement ------------------------------> TXA \ Copy the token number back into A, so both A and X \ now contain the token number we want to print BEQ TT50 \ If the token number we want is 0, then we have \ already found the token we are looking for, so jump \ to TT50, otherwise start working our way through the \ null-terminated token table until we find the X-th \ token .TT51 LDA (V),Y \ Fetch the Y-th character from the token table page \ we are currently scanning BEQ TT49 \ If the character is null, we've reached the end of \ this token, so jump to TT49 INY \ Increment character pointer and loop back around for BNE TT51 \ the next character in this token, assuming Y hasn't \ yet wrapped around to 0 INC V+1 \ If it has wrapped round to 0, we have just crossed BNE TT51 \ into a new page, so increment V+1 so that V points \ to the start of the new page .TT49 INY \ Increment the character pointer BNE TT59 \ If Y hasn't just wrapped around to 0, skip the next \ instruction INC V+1 \ We have just crossed into a new page, so increment \ V+1 so that V points to the start of the new page .TT59 DEX \ We have just reached a new token, so decrement the \ token number we are looking for BNE TT51 \ Assuming we haven't yet reached the token number in \ X, look back up to keep fetching characters .TT50 \ We have now reached the correct token in the token \ table, with Y pointing to the start of the token as \ an offset within the page pointed to by V, so let's \ print the recursive token. Because recursive tokens \ can contain other recursive tokens, we need to store \ our current state on the stack, so we can retrieve \ it after printing each character in this token TYA \ Store the offset in Y on the stack PHA LDA V+1 \ Store the high byte of V (the page containing the PHA \ token we have found) on the stack, so the stack now \ contains the address of the start of this token LDA (V),Y \ Load the character at offset Y in the token table, \ which is the next character of this token that we \ want to print EOR #RE \ Tokens are stored in memory having been EOR'd with the \ value of RE - which is 35 for all versions of Elite \ except for NES, where RE is 62 - so we repeat the \ EOR to get the actual character to print JSR TT27 \ Print the text token in A, which could be a letter, \ number, control code, two-letter token or another \ recursive token PLA \ Restore the high byte of V (the page containing the STA V+1 \ token we have found) into V+1 PLA \ Restore the offset into Y TAY INY \ Increment Y to point to the next character in the \ token we are printing BNE P%+4 \ If Y is zero then we have just crossed into a new INC V+1 \ page, so increment V+1 so that V points to the start \ of the new page LDA (V),Y \ Load the next character we want to print into A BNE TT50 \ If this is not the null character at the end of the \ token, jump back up to TT50 to print the next \ character, otherwise we are done printing .TT48 RTS \ Return from the subroutineName: ex [Show more] Type: Subroutine Category: Text Summary: Print a recursive token Deep dive: Printing text tokensContext: See this subroutine on its own page References: This subroutine is called as follows: * qw calls ex * TT27 calls ex * LL9 (Part 1 of 12) calls via TT48 * LL9 (Part 9 of 12) calls via TT48 * TT43 calls via TT48 * TT45 calls via TT48
This routine works its way through the recursive text tokens that are stored in tokenised form in the table at QQ18, and when it finds token number A, it prints it. Tokens are null-terminated in memory and fill three pages, but there is no lookup table as that would consume too much memory, so the only way to find the correct token is to start at the beginning and look through the table byte by byte, counting tokens as we go until we are in the right place. This approach might not be terribly speed efficient, but it is certainly memory-efficient.
Arguments: A The recursive token to be printed, in the range 0-148
Other entry points: TT48 Contains an RTS\ --- Mod: Code removed for Elite-A: ------------------> \.EX2 \ \LDA INWK+31 \ Set bits 5 and 7 of the ship's byte #31 to denote that \ORA #%10100000 \ the ship is exploding and has been killed \STA INWK+31 \ \RTS \ Return from the subroutine \ \.DOEXP \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: DOEXP, Removed [Show more] Type: Subroutine Category: Drawing ships Summary: Draw an exploding ship Deep dive: Drawing explosion clouds Generating random numbersContext: See this subroutine on its own page References: No direct references to this subroutine in this source file.WPSHPS LDX #0 \ Set up a counter in X to work our way through all the \ ship slots in FRIN .WSL1 LDA FRIN,X \ Fetch the ship type in slot X BEQ WS2 \ If the slot contains 0 then it is empty and we have \ checked all the slots (as they are always shuffled \ down in the main loop to close up and gaps), so jump \ to WS2 as we are done BMI WS1 \ If the slot contains a ship type with bit 7 set, then \ it contains the planet or the sun, so jump down to WS1 \ to skip this slot, as the planet and sun don't appear \ on the scanner JSR GINF \ Call GINF to get the address of the data block for \ ship slot X and store it in INF LDY #31 \ We now want to copy the first 32 bytes from the ship's \ data block into INWK, so set a counter in Y .WSL2 LDA (INF),Y \ Copy the Y-th byte from the data block pointed to by STA INWK,Y \ INF into the Y-th byte of INWK workspace DEY \ Decrement the counter to point at the next byte BPL WSL2 \ Loop back to WSL2 until we have copied all 32 bytes STX XSAV \ Store the ship slot number in XSAV while we call SCAN LDX XSAV \ Restore the ship slot number from XSAV into X LDY #31 \ Clear bits 3, 4 and 6 in the ship's byte #31, which LDA (INF),Y \ stops drawing the ship on-screen (bit 3), hides it AND #%10100111 \ from the scanner (bit 4) and stops any lasers firing STA (INF),Y \ (bit 6) .WS1 INX \ Increment X to point to the next ship slot BNE WSL1 \ Loop back up to process the next slot (this BNE is \ effectively a JMP as X will never be zero) .WS2 LDX #&FF \ Set LSX2 = LSY2 = &FF to clear the ball line heap STX LSX2 STX LSY2 \ Fall through into FLFLLS to reset the LSO blockName: WPSHPS [Show more] Type: Subroutine Category: Dashboard Summary: Clear the scanner, reset the ball line and sun line heapsContext: See this subroutine on its own page References: This subroutine is called as follows: * RES2 calls WPSHPS
Remove all ships from the scanner, reset the sun line heap at LSO, and reset the ball line heap at LSX2 and LSY2..FLFLLS LDY #2*Y-1 \ #Y is the y-coordinate of the centre of the space \ view, so this sets Y as a counter for the number of \ lines in the space view (i.e. 191), which is also the \ number of lines in the LSO block LDA #0 \ Set A to 0 so we can zero-fill the LSO block .SAL6 STA LSO,Y \ Set the Y-th byte of the LSO block to 0 DEY \ Decrement the counter BNE SAL6 \ Loop back until we have filled all the way to LSO+1 DEY \ Decrement Y to value of &FF (as we exit the above loop \ with Y = 0) STY LSX \ Set the first byte of the LSO block, which has its own \ label LSX, to &FF, to indicate that the sun line heap \ is empty RTS \ Return from the subroutineName: FLFLLS [Show more] Type: Subroutine Category: Drawing suns Summary: Reset the sun line heapContext: See this subroutine on its own page References: This subroutine is called as follows: * TT23 calls FLFLLS
Reset the sun line heap at LSO by zero-filling it and setting the first byte to &FF.
Returns: A A is set to 0\ --- Mod: Code removed for Elite-A: ------------------> \.DET1 \ \LDA #6 \ Set A to 6 so we can update 6845 register R6 below \ \SEI \ Disable interrupts so we can update the 6845 \ \STA VIA+&00 \ Set 6845 register R6 to the value in X. Register R6 \STX VIA+&01 \ is the "vertical displayed" register, which sets the \ \ number of rows shown on the screen \ \CLI \ Re-enable interrupts \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: DET1, Removed [Show more] Type: Subroutine Category: Drawing the screen Summary: Show or hide the dashboard (for when we die)Context: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine sets the screen to show the number of text rows given in X. It is used when we are killed, as reducing the number of rows from the usual 31 to 24 has the effect of hiding the dashboard, leaving a monochrome image of ship debris and explosion clouds. Increasing the rows back up to 31 makes the dashboard reappear, as the dashboard's screen memory doesn't get touched by this process.
Arguments: X The number of text rows to display on the screen (24 will hide the dashboard, 31 will make it reappear)
Returns: A A is set to 6\ --- Mod: Code removed for Elite-A: ------------------> \DEX \ If we get here then we just incremented the shield \ \ value back around to zero, so decrement it back down \ \ to 255 so it stays at the maximum value of 255 \ \RTS \ Return from the subroutine \ \.SHD \ \INX \ Increment the shield value \ \BEQ SHD-2 \ If the shield value is 0 then this means it was 255 \ \ before, which is the maximum value, so jump to SHD-2 \ \ to bring it back down to 255 and return without \ \ draining our energy banks \ \ \ Otherwise fall through into DENGY to drain our energy \ \ to pay for all this shield charging \ --- End of removed code ----------------------------->Name: SHD, Removed [Show more] Type: Subroutine Category: Flight Summary: Charge a shield and drain some energy from the energy banksContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Charge up a shield, and if it needs charging, drain some energy from the energy banks.
Arguments: X The value of the shield to recharge\ --- Mod: Code removed for Elite-A: ------------------> \.DENGY \ \DEC ENERGY \ Decrement the energy banks in ENERGY \ \PHP \ Save the flags on the stack \ \BNE P%+5 \ If the energy levels are not yet zero, skip the \ \ following instruction \ \INC ENERGY \ The minimum allowed energy level is 1, and we just \ \ reached 0, so increment ENERGY back to 1 \ \PLP \ Restore the flags from the stack, so we return with \ \ the Z flag from the DEC instruction above \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: DENGY, Removed [Show more] Type: Subroutine Category: Flight Summary: Drain some energy from the energy banksContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Returns: Z flag Set if we have no energy left, clear otherwise\ --- Mod: Code removed for Elite-A: ------------------> \.SPS3 \ \LDA K%+1,X \ Copy x_hi into K3+X \STA K3,X \ \LDA K%+2,X \ Set A = Y = x_sign \TAY \ \AND #%01111111 \ Set K3+1 = |x_sign| \STA K3+1,X \ \TYA \ Set K3+2 = the sign of x_sign \AND #%10000000 \STA K3+2,X \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: SPS3, Removed [Show more] Type: Subroutine Category: Maths (Geometry) Summary: Copy a space coordinate from the K% block into K3Context: See this subroutine on its own page References: No direct references to this subroutine in this source file
Copy one of the space coordinates of the planet, sun or space station into the corresponding location in the temporary variable K3. The high byte and absolute value of the sign byte are copied into the first two K3 bytes, and the sign of the sign byte is copied into the highest K3 byte. The comments below are written for copying the planet's x-coordinate into K3(2 1 0).
Arguments: X Determines where to copy the coordinate to: * X = 0 copies the coordinate into K3(2 1 0) * X = 3 copies the coordinate into K3(5 4 3) * X = 6 copies the coordinate into K3(8 7 6) Y Determines which coordinate to copy: * Y = 0 copies (x_sign, x_hi) of planet * Y = 3 copies (y_sign, y_hi) of planet * Y = 6 copies (z_sign, z_hi) of planet * Y = NI% + 0 copies (x_sign, x_hi) of sun/station * Y = NI% + 3 copies (y_sign, y_hi) of sun/station * Y = NI% + 6 copies (z_sign, z_hi) of sun/station
Returns: X X is incremented by 3 to point to the next coordinate Y Y is incremented by 3 to point to the next coordinate.GINF TXA \ Set Y = X * 2 ASL A TAY LDA UNIV,Y \ Get the high byte of the address of the X-th ship STA INF \ from UNIV and store it in INF LDA UNIV+1,Y \ Get the low byte of the address of the X-th ship STA INF+1 \ from UNIV and store it in INF RTS \ Return from the subroutineName: GINF [Show more] Type: Subroutine Category: Universe Summary: Fetch the address of a ship's data block into INFContext: See this subroutine on its own page References: This subroutine is called as follows: * NWSHP calls GINF * WPSHPS calls GINF
Get the address of the data block for ship slot X and store it in INF. This address is fetched from the UNIV table, which stores the addresses of the 13 ship data blocks in workspace K%.
Arguments: X The ship slot number for which we want the data block address.NWSHP STA T \ Store the ship type in location T LDX #0 \ Before we can add a new ship, we need to check \ whether we have an empty slot we can put it in. To do \ this, we need to loop through all the slots to look \ for an empty one, so set a counter in X that starts \ from the first slot at 0. When ships are killed, then \ the slots are shuffled down by the KILLSHP routine, so \ the first empty slot will always come after the last \ filled slot. This allows us to tack the new ship's \ data block and ship line heap onto the end of the \ existing ship data and heap, as shown in the memory \ map below .NWL1 LDA FRIN,X \ Load the ship type for the X-th slot BEQ NW1 \ If it is zero, then this slot is empty and we can use \ it for our new ship, so jump down to NW1 INX \ Otherwise increment X to point to the next slot CPX #NOSH \ If we haven't reached the last slot yet, loop back up BCC NWL1 \ to NWL1 to check the next slot (note that this means \ only slots from 0 to #NOSH - 1 are populated by this \ routine, but there is one more slot reserved in FRIN, \ which is used to identify the end of the slot list \ when shuffling the slots down in the KILLSHP routine) .NW3 CLC \ Otherwise we don't have an empty slot, so we can't RTS \ add a new ship, so clear the C flag to indicate that \ we have not managed to create the new ship, and return \ from the subroutine .NW1 \ If we get here, then we have found an empty slot at \ index X, so we can go ahead and create our new ship. \ We do that by creating a ship data block at INWK and, \ when we are done, copying the block from INWK into \ the K% workspace (specifically, to INF) JSR GINF \ Get the address of the data block for ship slot X \ (which is in workspace K%) and store it in INF LDA T \ If the type of ship that we want to create is BMI NW2 \ negative, then this indicates a planet or sun, so \ jump down to NW2, as the next section sets up a ship \ data block, which doesn't apply to planets and suns, \ as they don't have things like shields, missiles, \ vertices and edges \ This is a ship, so first we need to set up various \ pointers to the ship blueprint we will need. The \ blueprints for each ship type in Elite are stored \ in a table at location XX21, so refer to the comments \ on that variable for more details on the data we're \ about to access ASL A \ Set Y = ship type * 2 TAY LDA XX21-2,Y \ The ship blueprints at XX21 start with a lookup STA XX0 \ table that points to the individual ship blueprints, \ so this fetches the low byte of this particular ship \ type's blueprint and stores it in XX0 LDA XX21-1,Y \ Fetch the high byte of this particular ship type's STA XX0+1 \ blueprint and store it in XX0+1, so XX0(1 0) now \ contains the address of this ship's blueprint CPY #2*SST \ If the ship type is a space station (SST), then jump BEQ NW6 \ to NW6, skipping the heap space steps below, as the \ space station has its own line heap at LSO (which it \ shares with the sun) \ We now want to allocate space for a heap that we can \ use to store the lines we draw for our new ship (so it \ can easily be erased from the screen again). SLSP \ points to the start of the current heap space, and we \ can extend it downwards with the heap for our new ship \ (as the heap space always ends just before the WP \ workspace) LDY #5 \ Fetch ship blueprint byte #5, which contains the LDA (XX0),Y \ maximum heap size required for plotting the new ship, STA T1 \ and store it in T1 LDA SLSP \ Take the 16-bit address in SLSP and subtract T1, SEC \ storing the 16-bit result in INWK(34 33), so this now SBC T1 \ points to the start of the line heap for our new ship STA INWK+33 LDA SLSP+1 SBC #0 STA INWK+34 \ We now need to check that there is enough free space \ for both this new line heap and the new data block \ for our ship. In memory, this is the layout of the \ ship data blocks and ship line heaps: \ \ +-----------------------------------+ &0F34 \ | | \ | WP workspace | \ | | \ +-----------------------------------+ &0D40 = WP \ | | \ | Current ship line heap | \ | | \ +-----------------------------------+ SLSP \ | | \ | Proposed heap for new ship | \ | | \ +-----------------------------------+ INWK(34 33) \ | | \ . . \ . . \ . . \ . . \ . . \ | | \ +-----------------------------------+ INF + NI% \ | | \ | Proposed data block for new ship | \ | | \ +-----------------------------------+ INF \ | | \ | Existing ship data blocks | \ | | \ +-----------------------------------+ &0900 = K% \ \ So, to work out if we have enough space, we have to \ make sure there is room between the end of our new \ ship data block at INF + NI%, and the start of the \ proposed heap for our new ship at the address we \ stored in INWK(34 33). Or, to put it another way, we \ and to make sure that: \ \ INWK(34 33) > INF + NI% \ \ which is the same as saying: \ \ INWK+33 - INF > NI% \ \ because INWK is in zero page, so INWK+34 = 0 LDA INWK+33 \ Calculate INWK+33 - INF, again using 16-bit SBC INF \ arithmetic, and put the result in (A Y), so the high TAY \ byte is in A and the low byte in Y. The subtraction LDA INWK+34 \ works because the previous subtraction will never SBC INF+1 \ underflow, so we know the C flag is set BCC NW3+1 \ If we have an underflow from the subtraction, then \ INF > INWK+33 and we definitely don't have enough \ room for this ship, so jump to NW3+1, which returns \ from the subroutine (with the C flag already cleared) BNE NW4 \ If the subtraction of the high bytes in A is not \ zero, and we don't have underflow, then we definitely \ have enough space, so jump to NW4 to continue setting \ up the new ship CPY #NI% \ Otherwise the high bytes are the same in our BCC NW3+1 \ subtraction, so now we compare the low byte of the \ result (which is in Y) with NI%. This is the same as \ doing INWK+33 - INF > NI% (see above). If this isn't \ true, the C flag will be clear and we don't have \ enough space, so we jump to NW3+1, which returns \ from the subroutine (with the C flag already cleared) .NW4 LDA INWK+33 \ If we get here then we do have enough space for our STA SLSP \ new ship, so store the new bottom of the ship line LDA INWK+34 \ heap (i.e. INWK+33) in SLSP, doing both the high and STA SLSP+1 \ low bytes .NW6 LDY #14 \ Fetch ship blueprint byte #14, which contains the LDA (XX0),Y \ ship's energy, and store it in byte #35 STA INWK+35 LDY #19 \ Fetch ship blueprint byte #19, which contains the LDA (XX0),Y \ number of missiles and laser power, and AND with %111 AND #%00000111 \ to extract the number of missiles before storing in STA INWK+31 \ byte #31 LDA T \ Restore the ship type we stored above .NW2 STA FRIN,X \ Store the ship type in the X-th byte of FRIN, so the \ this slot is now shown as occupied in the index table TAX \ Copy the ship type into X BMI P%+5 \ If the ship type is negative (planet or sun), then \ skip the following instruction INC MANY,X \ Increment the total number of ships of type X LDY #NI%-1 \ The final step is to copy the new ship's data block \ from INWK to INF, so set up a counter for NI% bytes \ in Y .NWL3 LDA INWK,Y \ Load the Y-th byte of INWK and store in the Y-th byte STA (INF),Y \ of the workspace pointed to by INF DEY \ Decrement the loop counter BPL NWL3 \ Loop back for the next byte until we have copied them \ all over SEC \ We have successfully created our new ship, so set the \ C flag to indicate success RTS \ Return from the subroutineName: NWSHP [Show more] Type: Subroutine Category: Universe Summary: Add a new ship to our local bubble of universeContext: See this subroutine on its own page References: This subroutine is called as follows: * BRIEF calls NWSHP * TITLE calls NWSHP
This creates a new block of ship data in the K% workspace, allocates a new block in the ship line heap at WP, adds the new ship's type into the first empty slot in FRIN, and adds a pointer to the ship data into UNIV. If there isn't enough free memory for the new ship, it isn't added.
Arguments: A The type of the ship to add (see variable XX21 for a list of ship types)
Returns: C flag Set if the ship was successfully added, clear if it wasn't (as there wasn't enough free memory) INF Points to the new ship's data block in K%\ --- Mod: Code removed for Elite-A: ------------------> \.NwS1 \ \LDA INWK,X \ Load the X-th byte of INWK into A and flip bit 7, \EOR #%10000000 \ storing the result back in the X-th byte of INWK \STA INWK,X \ \INX \ Add 2 to X \INX \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: NwS1, Removed [Show more] Type: Subroutine Category: Universe Summary: Flip the sign and double an INWK byteContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Flip the sign of the INWK byte at offset X, and increment X by 2. This is used by the space station creation routine at NWSPS.
Arguments: X The offset of the INWK byte to be flipped
Returns: X X is incremented by 2\ --- Mod: Code removed for Elite-A: ------------------> \.ABORT \ \LDX #&FF \ Set X to &FF, which is the value of MSTG when we have \ \ no target lock for our missile \ \ \ Fall through into ABORT2 to set the missile lock to \ \ the value in X, which effectively disarms the missile \ --- End of removed code ----------------------------->Name: ABORT, Removed [Show more] Type: Subroutine Category: Dashboard Summary: Disarm missiles and update the dashboard indicatorsContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Arguments: Y The new status of the leftmost missile indicator\ --- Mod: Code removed for Elite-A: ------------------> \.ABORT2 \ \STX MSTG \ Store the target of our missile lock in MSTG \ \LDX NOMSL \ Call MSBAR to update the leftmost indicator in the \JSR MSBAR \ dashboard's missile bar, which returns with Y = 0 \ \STY MSAR \ Set MSAR = 0 to indicate that the leftmost missile \ \ is no longer seeking a target lock \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: ABORT2, Removed [Show more] Type: Subroutine Category: Dashboard Summary: Set/unset the lock target for a missile and update the dashboardContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Set the lock target for the leftmost missile and update the dashboard.
Arguments: X The slot number of the ship to lock our missile onto, or &FF to remove missile lock Y The new colour of the missile indicator: * &00 = black (no missile) * &0E = red (armed and locked) * &E0 = yellow/white (armed) * &EE = green/cyan (disarmed)\ --- Mod: Code removed for Elite-A: ------------------> \.SPBLB \ \LDA #24*8 \ The space station bulb is in character block number 24 \ \ with each character taking 8 bytes, so this sets the \ \ low byte of the screen address of the character block \ \ we want to draw to \ \LDX #LO(SPBT) \ Set (Y X) to point to the character definition in SPBT \LDY #HI(SPBT) \ \ \ Fall through into BULB to draw the space station bulb \ --- End of removed code ----------------------------->Name: SPBLB, Removed [Show more] Type: Subroutine Category: Dashboard Summary: Light up the space station indicator ("S") on the dashboardContext: See this subroutine on its own page References: No direct references to this subroutine in this source file\ --- Mod: Code removed for Elite-A: ------------------> \.BULB \ \STA SC \ Store the low byte of the screen address in SC \ \STX P+1 \ Set P(2 1) = (Y X) \STY P+2 \ \LDA #&7D \ Set A to the high byte of the screen address, which is \ \ &7D as the bulbs are both in the character row from \ \ &7D00 to &7DFF \ \JMP RREN \ Call RREN to print the character definition pointed to \ \ by P(2 1) at the screen address pointed to by (A SC), \ \ returning from the subroutine using a tail call \ --- End of removed code ----------------------------->Name: BULB, Removed [Show more] Type: Subroutine Category: Dashboard Summary: Draw an indicator bulb on the dashboardContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Arguments: A The y-coordinate of the bulb as a low-byte screen address offset within screen page &7D (as both bulbs are on this character row in the dashboard) (Y X) The address of the character definition of the bulb to be drawn (i.e. ECBT for the E.C.M. bulb, or SPBT for the space station bulb)
Other entry points: BULB-2 Set the Y screen address\ --- Mod: Code removed for Elite-A: ------------------> \.SPBT \ \EQUB %11100000 \ x x x . \EQUB %11100000 \ x x x . \EQUB %10000000 \ x . . . \EQUB %11100000 \ x x x . \EQUB %11100000 \ x x x . \EQUB %00100000 \ . . x . \EQUB %11100000 \ x x x . \EQUB %11100000 \ x x x . \ --- End of removed code ----------------------------->Name: SPBT, Removed [Show more] Type: Variable Category: Dashboard Summary: The bitmap definition for the space station indicator bulbContext: See this variable on its own page References: No direct references to this variable in this source file
The bitmap definition for the space station indicator's "S" bulb that gets displayed on the dashboard. Each pixel is in mode 5 colour 2 (%10), which is yellow/white..MSBAR TXA \ Set T = X * 8 ASL A ASL A ASL A STA T \ --- Mod: Code removed for Elite-A: ------------------> \LDA #49 \ Set SC = 49 - T \SBC T \ = 48 + 1 - (X * 8) \STA SC \ --- And replaced by: --------------------------------> LDA #41 \ Set SC = 41 - T SBC T \ = 40 + 1 - (X * 8) STA SC \ = 48 + 1 - ((X + 1) * 8) \ \ This is the same calculation as in the disc version's \ MSBAR routine, but because the missile number in the \ Elite-A version is in the range 0-3 rather than 1-3, \ we subtract from 41 instead of 49 to get the screen \ address \ --- End of replacement ------------------------------> \ So the low byte of SC(1 0) contains the row address \ for the rightmost missile indicator, made up as \ follows: \ \ * 48 (character block 7, as byte #7 * 8 = 48), the \ character block of the rightmost missile \ \ * 1 (so we start drawing on the second row of the \ character block) \ \ * Move left one character (8 bytes) for each count \ of X, so when X = 0 we are drawing the rightmost \ missile, for X = 1 we hop to the left by one \ character, and so on LDA #&7E \ Set the high byte of SC(1 0) to &7E, the character row STA SCH \ that contains the missile indicators (i.e. the bottom \ row of the screen) TYA \ Set A to the correct colour, which is a 3-pixel wide \ mode 5 character row in the correct colour (for \ example, a green block has Y = &EE, or %11101110, so \ the missile blocks are 3 pixels wide, with the \ fourth pixel on the character row being empty) LDY #5 \ We now want to draw this line five times, so set a \ counter in Y .MBL1 STA (SC),Y \ Draw the 3-pixel row, and as we do not use EOR logic, \ this will overwrite anything that is already there \ (so drawing a black missile will delete what's there) DEY \ Decrement the counter for the next row BNE MBL1 \ Loop back to MBL1 if have more rows to draw RTS \ Return from the subroutineName: MSBAR [Show more] Type: Subroutine Category: Dashboard Summary: Draw a specific indicator in the dashboard's missile barContext: See this subroutine on its own page References: This subroutine is called as follows: * msblob calls MSBAR
Each indicator is a rectangle that's 3 pixels wide and 5 pixels high. If the indicator is set to black, this effectively removes a missile. Note that there are only four missile indicators on the dashboard, but in Elite-A our ship can have up to 7 missiles, in which case the leftmost missile indicator is used for the next missile to use, and the extra missiles are implied rather than displayed.
Arguments: X The number of the missile indicator to update (counting from right to left and starting at 0 rather than 1, so indicator NOMSL - 1 is the leftmost indicator) Y The colour of the missile indicator: * &00 = black (no missile) * &0E = red (armed and locked) * &E0 = yellow/white (armed) * &EE = green/cyan (disarmed)
Returns: X X is preserved Y Y is set to 0.PLF3 \ This is called from below to negate X and set A to \ &FF, for when the new sun's centre is off the bottom \ of the screen (so we don't need to draw its bottom \ half) \ \ This happens when the y-coordinate of the centre of \ the sun is bigger than the y-coordinate of the bottom \ of the space view TXA \ Negate X using two's complement, so X = ~X + 1 EOR #%11111111 CLC ADC #1 TAX .PLF17 \ This is called from below to set A to &FF, for when \ the new sun's centre is right on the bottom of the \ screen (so we don't need to draw its bottom half) LDA #&FF \ Set A = &FF BNE PLF5 \ Jump to PLF5 (this BNE is effectively a JMP as A is \ never zero) .SUN LDA #1 \ Set LSX = 1 to indicate the sun line heap is about to STA LSX \ be filled up JSR CHKON \ Call CHKON to check whether any part of the new sun's \ circle appears on-screen, and if it does, set P(2 1) \ to the maximum y-coordinate of the new sun on-screen LDA #0 \ Set A = 0 LDX K \ Set X = K = radius of the new sun CPX #96 \ If X >= 96, set the C flag and rotate it into bit 0 ROL A \ of A, otherwise rotate a 0 into bit 0 CPX #40 \ If X >= 40, set the C flag and rotate it into bit 0 ROL A \ of A, otherwise rotate a 0 into bit 0 CPX #16 \ If X >= 16, set the C flag and rotate it into bit 0 ROL A \ of A, otherwise rotate a 0 into bit 0 \ By now, A contains the following: \ \ * If radius is 96-255 then A = %111 = 7 \ \ * If radius is 40-95 then A = %11 = 3 \ \ * If radius is 16-39 then A = %1 = 1 \ \ * If radius is 0-15 then A = %0 = 0 \ \ The value of A determines the size of the new sun's \ ragged fringes - the bigger the sun, the bigger the \ fringes .PLF18 STA CNT \ Store the fringe size in CNT \ We now calculate the highest pixel y-coordinate of the \ new sun, given that P(2 1) contains the 16-bit maximum \ y-coordinate of the new sun on-screen LDA #2*Y-1 \ #Y is the y-coordinate of the centre of the space \ view, so this sets Y to the y-coordinate of the bottom \ of the space view LDX P+2 \ If P+2 is non-zero, the maximum y-coordinate is off BNE PLF2 \ the bottom of the screen, so skip to PLF2 with A set \ to the y-coordinate of the bottom of the space view CMP P+1 \ If A < P+1, the maximum y-coordinate is underneath the BCC PLF2 \ dashboard, so skip to PLF2 with A set to the \ y-coordinate of the bottom of the space view LDA P+1 \ Set A = P+1, the low byte of the maximum y-coordinate \ of the sun on-screen BNE PLF2 \ If A is non-zero, skip to PLF2 as it contains the \ value we are after LDA #1 \ Otherwise set A = 1, the top line of the screen .PLF2 STA TGT \ Set TGT to A, the maximum y-coordinate of the sun on \ screen \ We now calculate the number of lines we need to draw \ and the direction in which we need to draw them, both \ from the centre of the new sun LDA #2*Y-1 \ Set (A X) = y-coordinate of bottom of screen - K4(1 0) SEC \ SBC K4 \ Starting with the low bytes TAX LDA #0 \ And then doing the high bytes, so (A X) now contains SBC K4+1 \ the number of lines between the centre of the sun and \ the bottom of the screen. If it is positive then the \ centre of the sun is above the bottom of the screen, \ if it is negative then the centre of the sun is below \ the bottom of the screen BMI PLF3 \ If A < 0, then this means the new sun's centre is off \ the bottom of the screen, so jump up to PLF3 to negate \ the height in X (so it becomes positive), set A to &FF \ and jump down to PLF5 BNE PLF4 \ If A > 0, then the new sun's centre is at least a full \ screen above the bottom of the space view, so jump \ down to PLF4 to set X = radius and A = 0 INX \ Set the flags depending on the value of X DEX BEQ PLF17 \ If X = 0 (we already know A = 0 by this point) then \ jump up to PLF17 to set A to &FF before jumping down \ to PLF5 CPX K \ If X < the radius in K, jump down to PLF5, so if BCC PLF5 \ X >= the radius in K, we set X = radius and A = 0 .PLF4 LDX K \ Set X to the radius LDA #0 \ Set A = 0 .PLF5 STX V \ Store the height in V STA V+1 \ Store the direction in V+1 LDA K \ Set (A P) = K * K JSR SQUA2 STA K2+1 \ Set K2(1 0) = (A P) = K * K LDA P STA K2 \ By the time we get here, the variables should be set \ up as shown in the header for part 3 belowName: SUN (Part 1 of 4) [Show more] Type: Subroutine Category: Drawing suns Summary: Draw the sun: Set up all the variables needed to draw the sun Deep dive: Drawing the sunContext: See this subroutine on its own page References: This subroutine is called as follows: * TT23 calls SUN
Draw a new sun with radius K at pixel coordinate (K3, K4), removing the old sun if there is one. This routine is used to draw the sun, as well as the star systems on the Short-range Chart. The first part sets up all the variables needed to draw the new sun.
Arguments: K The new sun's radius K3(1 0) Pixel x-coordinate of the centre of the new sun K4(1 0) Pixel y-coordinate of the centre of the new sun SUNX(1 0) The x-coordinate of the vertical centre axis of the old sun (the one currently on-screen)LDY #2*Y-1 \ Set Y = y-coordinate of the bottom of the screen, \ which we use as a counter in the following routine to \ redraw the old sun LDA SUNX \ Set YY(1 0) = SUNX(1 0), the x-coordinate of the STA YY \ vertical centre axis of the old sun that's currently LDA SUNX+1 \ on-screen STA YY+1 .PLFL2 CPY TGT \ If Y = TGT, we have reached the line where we will BEQ PLFL \ start drawing the new sun, so there is no need to \ keep erasing the old one, so jump down to PLFL LDA LSO,Y \ Fetch the Y-th point from the sun line heap, which \ gives us the half-width of the old sun's line on this \ line of the screen BEQ PLF13 \ If A = 0, skip the following call to HLOIN2 as there \ is no sun line on this line of the screen JSR HLOIN2 \ Call HLOIN2 to draw a horizontal line on pixel line Y, \ with centre point YY(1 0) and half-width A, and remove \ the line from the sun line heap once done .PLF13 DEY \ Decrement the loop counter BNE PLFL2 \ Loop back for the next line in the line heap until \ we have either gone through the entire heap, or \ reached the bottom row of the new sunName: SUN (Part 2 of 4) [Show more] Type: Subroutine Category: Drawing suns Summary: Draw the sun: Start from the bottom of the screen and erase the old sun line by line Deep dive: Drawing the sunContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This part erases the old sun, starting at the bottom of the screen and working upwards until we reach the bottom of the new sun..PLFL LDA V \ Set (T P) = V * V JSR SQUA2 \ = V^2 STA T LDA K2 \ Set (R Q) = K^2 - V^2 SEC \ SBC P \ First calculating the low bytes STA Q LDA K2+1 \ And then doing the high bytes SBC T STA R STY Y1 \ Store Y in Y1, so we can restore it after the call to \ LL5 JSR LL5 \ Set Q = SQRT(R Q) \ = SQRT(K^2 - V^2) \ \ So Q contains the half-width of the new sun's line at \ height V from the sun's centre - in other words, it \ contains the half-width of the sun's line on the \ current pixel row Y LDY Y1 \ Restore Y from Y1 JSR DORND \ Set A and X to random numbers AND CNT \ Reduce A to a random number in the range 0 to CNT, \ where CNT is the fringe size of the new sun CLC \ Set A = A + Q ADC Q \ \ So A now contains the half-width of the sun on row \ V, plus a random variation based on the fringe size BCC PLF44 \ If the above addition did not overflow, skip the \ following instruction LDA #255 \ The above overflowed, so set the value of A to 255 \ So A contains the half-width of the new sun on pixel \ line Y, changed by a random amount within the size of \ the sun's fringe .PLF44 LDX LSO,Y \ Set X to the line heap value for the old sun's line \ at row Y STA LSO,Y \ Store the half-width of the new row Y line in the line \ heap BEQ PLF11 \ If X = 0 then there was no sun line on pixel row Y, so \ jump to PLF11 LDA SUNX \ Set YY(1 0) = SUNX(1 0), the x-coordinate of the STA YY \ vertical centre axis of the old sun that's currently LDA SUNX+1 \ on-screen STA YY+1 TXA \ Transfer the line heap value for the old sun's line \ from X into A JSR EDGES \ Call EDGES to calculate X1 and X2 for the horizontal \ line centred on YY(1 0) and with half-width A, i.e. \ the line for the old sun LDA X1 \ Store X1 and X2, the ends of the line for the old sun, STA XX \ in XX and XX+1 LDA X2 STA XX+1 LDA K3 \ Set YY(1 0) = K3(1 0), the x-coordinate of the centre STA YY \ of the new sun LDA K3+1 STA YY+1 LDA LSO,Y \ Fetch the half-width of the new row Y line from the \ line heap (which we stored above) JSR EDGES \ Call EDGES to calculate X1 and X2 for the horizontal \ line centred on YY(1 0) and with half-width A, i.e. \ the line for the new sun BCS PLF23 \ If the C flag is set, the new line doesn't fit on the \ screen, so jump to PLF23 to just draw the old line \ without drawing the new one \ At this point the old line is from XX to XX+1 and the \ new line is from X1 to X2, and both fit on-screen. We \ now want to remove the old line and draw the new one. \ We could do this by simply drawing the old one then \ drawing the new one, but instead Elite does this by \ drawing first from X1 to XX and then from X2 to XX+1, \ which you can see in action by looking at all the \ permutations below of the four points on the line and \ imagining what happens if you draw from X1 to XX and \ X2 to XX+1 using EOR logic. The six possible \ permutations are as follows, along with the result of \ drawing X1 to XX and then X2 to XX+1: \ \ X1 X2 XX____XX+1 -> +__+ + + \ \ X1 XX____X2____XX+1 -> +__+__+ + \ \ X1 XX____XX+1 X2 -> +__+__+__+ \ \ XX____X1____XX+1 X2 -> + +__+__+ \ \ XX____XX+1 X1 X2 -> + + +__+ \ \ XX____X1____X2____XX+1 -> + +__+ + \ \ They all end up with a line between X1 and X2, which \ is what we want. There's probably a mathematical proof \ of why this works somewhere, but the above is probably \ easier to follow. \ \ We can draw from X1 to XX and X2 to XX+1 by swapping \ XX and X2 and drawing from X1 to X2, and then drawing \ from XX to XX+1, so let's do this now LDA X2 \ Swap XX and X2 LDX XX STX X2 STA XX JSR HLOIN \ Draw a horizontal line from (X1, Y1) to (X2, Y1) .PLF23 \ If we jump here from the BCS above when there is no \ new line this will just draw the old line LDA XX \ Set X1 = XX STA X1 LDA XX+1 \ Set X2 = XX+1 STA X2 .PLF16 JSR HLOIN \ Draw a horizontal line from (X1, Y1) to (X2, Y1) .PLF6 DEY \ Decrement the line number in Y to move to the line \ above BEQ PLF8 \ If we have reached the top of the screen, jump to PLF8 \ as we are done drawing (the top line of the screen is \ the border, so we don't draw there) LDA V+1 \ If V+1 is non-zero then we are doing the top half of BNE PLF10 \ the new sun, so jump down to PLF10 to increment V and \ decrease the width of the line we draw DEC V \ Decrement V, the height of the sun that we use to work \ out the width, so this makes the line get wider, as we \ move up towards the sun's centre BNE PLFL \ If V is non-zero, jump back up to PLFL to do the next \ screen line up DEC V+1 \ Otherwise V is 0 and we have reached the centre of the \ sun, so decrement V+1 to -1 so we start incrementing V \ each time, thus doing the top half of the new sun .PLFLS JMP PLFL \ Jump back up to PLFL to do the next screen line up .PLF11 \ If we get here then there is no old sun line on this \ line, so we can just draw the new sun's line LDX K3 \ Set YY(1 0) = K3(1 0), the x-coordinate of the centre STX YY \ of the new sun's line LDX K3+1 STX YY+1 JSR EDGES \ Call EDGES to calculate X1 and X2 for the horizontal \ line centred on YY(1 0) and with half-width A, i.e. \ the line for the new sun BCC PLF16 \ If the line is on-screen, jump up to PLF16 to draw the \ line and loop round for the next line up LDA #0 \ The line is not on-screen, so set the line heap for STA LSO,Y \ line Y to 0, which means there is no sun line here BEQ PLF6 \ Jump up to PLF6 to loop round for the next line up \ (this BEQ is effectively a JMP as A is always zero) .PLF10 LDX V \ Increment V, the height of the sun that we use to work INX \ out the width, so this makes the line get narrower, as STX V \ we move up and away from the sun's centre CPX K \ If V <= the radius of the sun, we still have lines to BCC PLFLS \ draw, so jump up to PLFL (via PLFLS) to do the next BEQ PLFLS \ screen line upName: SUN (Part 3 of 4) [Show more] Type: Subroutine Category: Drawing suns Summary: Draw the sun: Continue to move up the screen, drawing the new sun line by line Deep dive: Drawing the sunContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This part draws the new sun. By the time we get to this point, the following variables should have been set up by parts 1 and 2:
Arguments: V As we draw lines for the new sun, V contains the vertical distance between the line we're drawing and the centre of the new sun. As we draw lines and move up the screen, we either decrement (bottom half) or increment (top half) this value V+1 This determines which half of the new sun we are drawing as we work our way up the screen, line by line: * 0 means we are drawing the bottom half, so the lines get wider as we work our way up towards the centre, at which point we will move into the top half, and V+1 will switch to &FF * &FF means we are drawing the top half, so the lines get smaller as we work our way up, away from the centre TGT The maximum y-coordinate of the new sun on-screen (i.e. the screen y-coordinate of the bottom row of the new sun) CNT The fringe size of the new sun K2(1 0) The new sun's radius squared, i.e. K^2 Y The y-coordinate of the bottom row of the new sunLDA SUNX \ Set YY(1 0) = SUNX(1 0), the x-coordinate of the STA YY \ vertical centre axis of the old sun that's currently LDA SUNX+1 \ on-screen STA YY+1 .PLFL3 LDA LSO,Y \ Fetch the Y-th point from the sun line heap, which \ gives us the half-width of the old sun's line on this \ line of the screen BEQ PLF9 \ If A = 0, skip the following call to HLOIN2 as there \ is no sun line on this line of the screen JSR HLOIN2 \ Call HLOIN2 to draw a horizontal line on pixel line Y, \ with centre point YY(1 0) and half-width A, and remove \ the line from the sun line heap once done .PLF9 DEY \ Decrement the line number in Y to move to the line \ above BNE PLFL3 \ Jump up to PLFL3 to redraw the next line up, until we \ have reached the top of the screen .PLF8 \ If we get here, we have successfully made it from the \ bottom line of the screen to the top, and the old sun \ has been replaced by the new one CLC \ Clear the C flag to indicate success in drawing the \ sun LDA K3 \ Set SUNX(1 0) = K3(1 0) STA SUNX LDA K3+1 STA SUNX+1 .RTS2 RTS \ Return from the subroutineName: SUN (Part 4 of 4) [Show more] Type: Subroutine Category: Drawing suns Summary: Draw the sun: Continue to the top of the screen, erasing the old sun line by line Deep dive: Drawing the sunContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This part erases any remaining traces of the old sun, now that we have drawn all the way to the top of the new sun.
Other entry points: RTS2 Contains an RTS\ --- Mod: Code removed for Elite-A: ------------------> \.CIRCLE \ \LDA #0 \ Set LSX2 = 0 to indicate that the ball line heap is \STA LSX2 \ not empty, as we are about to fill it \ \LDX K \ Set X = K = radius \ \LDA #8 \ Set A = 8 \ \CPX #8 \ If the radius < 8, skip to PL89 \BCC PL89 \ \LSR A \ Halve A so A = 4 \ \CPX #60 \ If the radius < 60, skip to PL89 \BCC PL89 \ \LSR A \ Halve A so A = 2 \ \.PL89 \ \STA STP \ Set STP = A. STP is the step size for the circle, so \ \ the above sets a smaller step size for bigger circles \ \ \ Fall through into CIRCLE2 to draw the circle with the \ \ correct step size \ --- End of removed code ----------------------------->Name: CIRCLE, Removed [Show more] Type: Subroutine Category: Drawing circles Summary: Draw a circle for the planet Deep dive: Drawing circlesContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
Draw a circle with the centre at (K3, K4) and radius K. Used to draw the planet's main outline.
Arguments: K The planet's radius K3(1 0) Pixel x-coordinate of the centre of the planet K4(1 0) Pixel y-coordinate of the centre of the planet.CIRCLE2 LDX #&FF \ Set FLAG = &FF to reset the ball line heap in the call STX FLAG \ to the BLINE routine below INX \ Set CNT = 0, our counter that goes up to 64, counting STX CNT \ segments in our circle .PLL3 LDA CNT \ Set A = CNT JSR FMLTU2 \ Call FMLTU2 to calculate: \ \ A = K * sin(A) \ = K * sin(CNT) LDX #0 \ Set T = 0, so we have the following: STX T \ \ (T A) = K * sin(CNT) \ \ which is the x-coordinate of the circle for this count LDX CNT \ If CNT < 33 then jump to PL37, as this is the right CPX #33 \ half of the circle and the sign of the x-coordinate is BCC PL37 \ correct EOR #%11111111 \ This is the left half of the circle, so we want to ADC #0 \ flip the sign of the x-coordinate in (T A) using two's TAX \ complement, so we start with the low byte and store it \ in X (the ADC adds 1 as we know the C flag is set) LDA #&FF \ And then we flip the high byte in T ADC #0 STA T TXA \ Finally, we restore the low byte from X, so we have \ now negated the x-coordinate in (T A) CLC \ Clear the C flag so we can do some more addition below .PL37 ADC K3 \ We now calculate the following: STA K6 \ \ K6(1 0) = (T A) + K3(1 0) \ \ to add the coordinates of the centre to our circle \ point, starting with the low bytes LDA K3+1 \ And then doing the high bytes, so we now have: ADC T \ STA K6+1 \ K6(1 0) = K * sin(CNT) + K3(1 0) \ \ which is the result we want for the x-coordinate LDA CNT \ Set A = CNT + 16 CLC ADC #16 JSR FMLTU2 \ Call FMLTU2 to calculate: \ \ A = K * sin(A) \ = K * sin(CNT + 16) \ = K * cos(CNT) TAX \ Set X = A \ = K * cos(CNT) LDA #0 \ Set T = 0, so we have the following: STA T \ \ (T X) = K * cos(CNT) \ \ which is the y-coordinate of the circle for this count LDA CNT \ Set A = (CNT + 15) mod 64 ADC #15 AND #63 CMP #33 \ If A < 33 (i.e. CNT is 0-16 or 48-64) then jump to BCC PL38 \ PL38, as this is the bottom half of the circle and the \ sign of the y-coordinate is correct TXA \ This is the top half of the circle, so we want to EOR #%11111111 \ flip the sign of the y-coordinate in (T X) using two's ADC #0 \ complement, so we start with the low byte in X (the TAX \ ADC adds 1 as we know the C flag is set) LDA #&FF \ And then we flip the high byte in T, so we have ADC #0 \ now negated the y-coordinate in (T X) STA T CLC \ Clear the C flag so the addition at the start of BLINE \ will work .PL38 JSR BLINE \ Call BLINE to draw this segment, which also increases \ CNT by STP, the step size CMP #65 \ If CNT >= 65 then skip the next instruction BCS P%+5 JMP PLL3 \ Jump back for the next segment CLC \ Clear the C flag to indicate success RTS \ Return from the subroutineName: CIRCLE2 [Show more] Type: Subroutine Category: Drawing circles Summary: Draw a circle (for the planet or chart) Deep dive: Drawing circlesContext: See this subroutine on its own page References: This subroutine is called as follows: * HFS1 calls CIRCLE2 * TT128 calls CIRCLE2
Draw a circle with the centre at (K3, K4) and radius K. Used to draw the planet and the chart circles.
Arguments: STP The step size for the circle K The circle's radius K3(1 0) Pixel x-coordinate of the centre of the circle K4(1 0) Pixel y-coordinate of the centre of the circle
Returns: C flag The C flag is cleared\ --- Mod: Code removed for Elite-A: ------------------> \.WP1 \ \LDA #1 \ Set LSP = 1 to reset the ball line heap pointer \STA LSP \ \LDA #&FF \ Set LSX2 = &FF to indicate the ball line heap is empty \STA LSX2 \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: WP1, Removed [Show more] Type: Subroutine Category: Drawing planets Summary: Reset the ball line heapContext: See this subroutine on its own page References: No direct references to this subroutine in this source file\ --- Mod: Code removed for Elite-A: ------------------> \.WPLS \ \LDA LSX \ If LSX < 0, the sun line heap is empty, so return from \BMI PL44 \ the subroutine (as PL44 contains a CLC and RTS) \ \LDA SUNX \ Set YY(1 0) = SUNX(1 0), the x-coordinate of the \STA YY \ vertical centre axis of the sun that's currently on \LDA SUNX+1 \ screen \STA YY+1 \ \LDY #2*Y-1 \ #Y is the y-coordinate of the centre of the space \ \ view, so this sets Y as a counter for the number of \ \ lines in the space view (i.e. 191), which is also the \ \ number of lines in the LSO block \ \.WPL2 \ \LDA LSO,Y \ Fetch the Y-th point from the sun line heap, which \ \ gives us the half-width of the sun's line on this line \ \ of the screen \ \BEQ P%+5 \ If A = 0, skip the following call to HLOIN2 as there \ \ is no sun line on this line of the screen \ \JSR HLOIN2 \ Call HLOIN2 to draw a horizontal line on pixel line Y, \ \ with centre point YY(1 0) and half-width A, and remove \ \ the line from the sun line heap once done \ \DEY \ Decrement the loop counter \ \BNE WPL2 \ Loop back for the next line in the line heap until \ \ we have gone through the entire heap \ \DEY \ This sets Y to &FF, as we end the loop with Y = 0 \ \STY LSX \ Set LSX to &FF to indicate the sun line heap is empty \ \RTS \ Return from the subroutine \ --- End of removed code ----------------------------->Name: WPLS, Removed [Show more] Type: Subroutine Category: Drawing suns Summary: Remove the sun from the screen Deep dive: Drawing the sunContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
We do this by redrawing it using the lines stored in the sun line heap when the sun was originally drawn by the SUN routine.
Arguments: SUNX(1 0) The x-coordinate of the vertical centre axis of the sun
Other entry points: WPLS-1 Contains an RTS.EDGES STA T \ Set T to the line's half-length in argument A CLC \ We now calculate: ADC YY \ STA X2 \ (A X2) = YY(1 0) + A \ \ to set X2 to the x-coordinate of the right end of the \ line, starting with the low bytes LDA YY+1 \ And then adding the high bytes ADC #0 BMI ED1 \ If the addition is negative then the calculation has \ overflowed, so jump to ED1 to return a failure BEQ P%+6 \ If the high byte A from the result is 0, skip the \ next two instructions, as the result already fits on \ the screen LDA #254 \ The high byte is positive and non-zero, so we went STA X2 \ past the right edge of the screen, so clip X2 to the \ x-coordinate of the right edge of the screen LDA YY \ We now calculate: SEC \ SBC T \ (A X1) = YY(1 0) - argument A STA X1 \ \ to set X1 to the x-coordinate of the left end of the \ line, starting with the low bytes LDA YY+1 \ And then subtracting the high bytes SBC #0 BNE ED3 \ If the high byte subtraction is non-zero, then skip \ to ED3 CLC \ Otherwise the high byte of the subtraction was zero, \ so the line fits on-screen and we clear the C flag to \ indicate success RTS \ Return from the subroutine .ED3 BPL ED1 \ If the addition is positive then the calculation has \ underflowed, so jump to ED1 to return a failure LDA #2 \ The high byte is negative and non-zero, so we went STA X1 \ past the left edge of the screen, so clip X1 to the \ x-coordinate of the left edge of the screen .PL44 CLC \ The line does fit on-screen, so clear the C flag to \ indicate success RTS \ Return from the subroutine .ED1 LDA #0 \ Set the Y-th byte of the LSO block to 0 STA LSO,Y \ The line does not fit on the screen, so fall through \ into PL21 to set the C flag to indicate this resultName: EDGES [Show more] Type: Subroutine Category: Drawing lines Summary: Draw a horizontal line given a centre and a half-widthContext: See this subroutine on its own page References: This subroutine is called as follows: * HLOIN2 calls EDGES * SUN (Part 3 of 4) calls EDGES * CHKON calls via PL44
Set X1 and X2 to the x-coordinates of the ends of the horizontal line with centre x-coordinate YY(1 0), and length A in either direction from the centre (so a total line length of 2 * A). In other words, this line: X1 YY(1 0) X2 +-----------------+-----------------+ <- A -> <- A -> The resulting line gets clipped to the edges of the screen, if needed. If the calculation doesn't overflow, we return with the C flag clear, otherwise the C flag gets set to indicate failure and the Y-th LSO entry gets set to 0.
Arguments: A The half-length of the line YY(1 0) The centre x-coordinate
Returns: C flag Clear if the line fits on-screen, set if it doesn't X1, X2 The x-coordinates of the clipped line LSO+Y If the line doesn't fit, LSO+Y is set to 0 Y Y is preserved
Other entry points: PL44 Clear the C flag and return from the subroutine.PL21 SEC \ Set the C flag to indicate an overflow RTS \ Return from the subroutineName: PL21 [Show more] Type: Subroutine Category: Drawing planets Summary: Return from a planet/sun-drawing routine with a failure flagContext: See this subroutine on its own page References: This subroutine is called as follows: * CHKON calls PL21
Set the C flag and return from the subroutine. This is used to return from a planet- or sun-drawing routine with the C flag indicating an overflow in the calculation..CHKON LDA K3 \ Set A = K3 + K CLC ADC K LDA K3+1 \ Set A = K3+1 + 0 + any carry from above, so this ADC #0 \ effectively sets A to the high byte of K3(1 0) + K: \ \ (A ?) = K3(1 0) + K \ \ so A is the high byte of the x-coordinate of the right \ edge of the circle BMI PL21 \ If A is negative then the right edge of the circle is \ to the left of the screen, so jump to PL21 to set the \ C flag and return from the subroutine, as the whole \ circle is off-screen to the left LDA K3 \ Set A = K3 - K SEC SBC K LDA K3+1 \ Set A = K3+1 - 0 - any carry from above, so this SBC #0 \ effectively sets A to the high byte of K3(1 0) - K: \ \ (A ?) = K3(1 0) - K \ \ so A is the high byte of the x-coordinate of the left \ edge of the circle BMI PL31 \ If A is negative then the left edge of the circle is \ to the left of the screen, and we already know the \ right edge is either on-screen or off-screen to the \ right, so skip to PL31 to move on to the y-coordinate \ checks, as at least part of the circle is on-screen in \ terms of the x-axis BNE PL21 \ If A is non-zero, then the left edge of the circle is \ to the right of the screen, so jump to PL21 to set the \ C flag and return from the subroutine, as the whole \ circle is off-screen to the right .PL31 LDA K4 \ Set P+1 = K4 + K CLC ADC K STA P+1 LDA K4+1 \ Set A = K4+1 + 0 + any carry from above, so this ADC #0 \ does the following: \ \ (A P+1) = K4(1 0) + K \ \ so A is the high byte of the y-coordinate of the \ bottom edge of the circle BMI PL21 \ If A is negative then the bottom edge of the circle is \ above the top of the screen, so jump to PL21 to set \ the C flag and return from the subroutine, as the \ whole circle is off-screen to the top STA P+2 \ Store the high byte in P+2, so now we have: \ \ P(2 1) = K4(1 0) + K \ \ i.e. the maximum y-coordinate of the circle on-screen \ (which we return) LDA K4 \ Set X = K4 - K SEC SBC K TAX LDA K4+1 \ Set A = K4+1 - 0 - any carry from above, so this SBC #0 \ does the following: \ \ (A X) = K4(1 0) - K \ \ so A is the high byte of the y-coordinate of the top \ edge of the circle BMI PL44 \ If A is negative then the top edge of the circle is \ above the top of the screen, and we already know the \ bottom edge is either on-screen or below the bottom \ of the screen, so skip to PL44 to clear the C flag and \ return from the subroutine using a tail call, as part \ of the circle definitely appears on-screen BNE PL21 \ If A is non-zero, then the top edge of the circle is \ below the bottom of the screen, so jump to PL21 to set \ the C flag and return from the subroutine, as the \ whole circle is off-screen to the bottom CPX #2*Y-1 \ If we get here then A is zero, which means the top \ edge of the circle is within the screen boundary, so \ now we need to check whether it is in the space view \ (in which case it is on-screen) or the dashboard (in \ which case the top of the circle is hidden by the \ dashboard, so the circle isn't on-screen). We do this \ by checking the low byte of the result in X against \ 2 * #Y - 1, and returning the C flag from this \ comparison. The constant #Y is the y-coordinate of the \ mid-point of the space view, so 2 * #Y - 1, the \ y-coordinate of the bottom pixel row of the space \ view. So this does the following: \ \ * The C flag is set if coordinate (A X) is below the \ bottom row of the space view, i.e. the top edge of \ the circle is hidden by the dashboard \ \ * The C flag is clear if coordinate (A X) is above \ the bottom row of the space view, i.e. the top \ edge of the circle is on-screen RTS \ Return from the subroutineName: CHKON [Show more] Type: Subroutine Category: Drawing circles Summary: Check whether any part of a circle appears on the extended screenContext: See this subroutine on its own page References: This subroutine is called as follows: * SUN (Part 1 of 4) calls CHKON
Arguments: K The circle's radius K3(1 0) Pixel x-coordinate of the centre of the circle K4(1 0) Pixel y-coordinate of the centre of the circle
Returns: C flag Clear if any part of the circle appears on-screen, set if none of the circle appears on-screen (A X) Minimum y-coordinate of the circle on-screen (i.e. the y-coordinate of the top edge of the circle) P(2 1) Maximum y-coordinate of the circle on-screen (i.e. the y-coordinate of the bottom edge of the circle).TT17 JSR DOKEY \ Scan the keyboard for flight controls and pause keys, \ (or the equivalent on joystick) and update the key \ logger, setting KL to the key pressed LDA JSTK \ If the joystick is not configured, jump down to TJ1, BEQ TJ1 \ otherwise we move the cursor with the joystick LDA JSTX \ Fetch the joystick roll, ranging from 1 to 255 with \ 128 as the centre point EOR #&FF \ Flip the sign so A = -JSTX, because the joystick roll \ works in the opposite way to moving a cursor on-screen \ in terms of left and right JSR TJS1 \ Call TJS1 just below to set A to a value between -2 \ and +2 depending on the joystick roll value (moving \ the stick sideways) TYA \ Copy Y to A TAX \ Copy A to X, so X contains the joystick roll value LDA JSTY \ Fetch the joystick pitch, ranging from 1 to 255 with \ 128 as the centre point, and fall through into TJS1 to \ set Y to the joystick pitch value (moving the stick up \ and down) .TJS1 TAY \ Store A in Y LDA #0 \ Set the result, A = 0 CPY #16 \ If Y >= 16 set the C flag, so A = A - 1 SBC #0 CPY #64 \ If Y >= 64 set the C flag, so A = A - 1 SBC #0 CPY #192 \ If Y >= 192 set the C flag, so A = A + 1 ADC #0 CPY #224 \ If Y >= 224 set the C flag, so A = A + 1 ADC #0 TAY \ Copy the value of A into Y LDA KL \ Set A to the value of KL (the key pressed) RTS \ Return from the subroutine .TJ1 LDA KL \ Set A to the value of KL (the key pressed) LDX #0 \ Set the initial values for the results, X = Y = 0, LDY #0 \ which we now increase or decrease appropriately CMP #&19 \ If left arrow was pressed, set X = X - 1 BNE P%+3 DEX CMP #&79 \ If right arrow was pressed, set X = X + 1 BNE P%+3 INX CMP #&39 \ If up arrow was pressed, set Y = Y + 1 BNE P%+3 INY CMP #&29 \ If down arrow was pressed, set Y = Y - 1 BNE P%+3 DEY STX T \ Set T to the value of X, which contains the joystick \ roll value LDX #0 \ Scan the keyboard to see if the SHIFT key is currently JSR DKS4 \ being pressed, returning the result in A and X BPL TJe \ If SHIFT is not being pressed, skip to TJe ASL T \ SHIFT is being held down, so quadruple the value of T ASL T \ (i.e. SHIFT moves the cursor at four times the speed \ when using the joystick) TYA \ Fetch the joystick pitch value from Y into A ASL A \ SHIFT is being held down, so quadruple the value of A ASL A \ (i.e. SHIFT moves the cursor at four times the speed \ when using the joystick) TAY \ Transfer the amended value of A back into Y .TJe LDX T \ Fetch the amended value of T back into X LDA KL \ Set A to the value of KL (the key pressed) RTS \ Return from the subroutineName: TT17 [Show more] Type: Subroutine Category: Keyboard Summary: Scan the keyboard for cursor key or joystick movementContext: See this subroutine on its own page References: This subroutine is called as follows: * Main game loop (Part 5 of 6) calls TT17
Scan the keyboard and joystick for cursor key or stick movement, and return the result as deltas (changes) in x- and y-coordinates as follows: * For joystick, X and Y are integers between -2 and +2 depending on how far the stick has moved * For keyboard, X and Y are integers between -1 and +1 depending on which keys are pressed
Returns: A The key pressed, if the arrow keys were used X Change in the x-coordinate according to the cursor keys being pressed or joystick movement, as an integer (see above) Y Change in the y-coordinate according to the cursor keys being pressed or joystick movement, as an integer (see above).ping LDX #1 \ We want to copy the X- and Y-coordinates of the \ current system in (QQ0, QQ1) to the selected system's \ coordinates in (QQ9, QQ10), so set up a counter to \ copy two bytes .pl1 LDA QQ0,X \ Load byte X from the current system in QQ0/QQ1 STA QQ9,X \ Store byte X in the selected system in QQ9/QQ10 DEX \ Decrement the loop counter BPL pl1 \ Loop back for the next byte to copy RTS \ Return from the subroutineName: ping [Show more] Type: Subroutine Category: Universe Summary: Set the selected system to the current systemContext: See this subroutine on its own page References: This subroutine is called as follows: * BR1 (Part 2 of 2) calls ping * TT102 calls pingPRINT "ELITE E" PRINT "Assembled at ", ~CODE_E% PRINT "Ends at ", ~P% PRINT "Code size is ", ~(P% - CODE_E%) PRINT "Execute at ", ~LOAD% PRINT "Reload at ", ~LOAD_E% PRINT "S.T.ELTE ", ~CODE_E%, " ", ~P%, " ", ~LOAD%, " ", ~LOAD_E% \SAVE "3-assembled-output/T.ELTE.bin", CODE_E%, P%, LOAD%Save ELTE.bin
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Subroutine BLINE (category: Drawing circles)
Draw a circle segment and add it to the ball line heap
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Subroutine BPRNT (category: Text)
Print a 32-bit number, left-padded to a specific number of digits, with an optional decimal point
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Subroutine CHKON (category: Drawing circles)
Check whether any part of a circle appears on the extended screen
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Subroutine DKS4 (category: Keyboard)
Scan the keyboard to see if a specific key is being pressed
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Subroutine DOKEY (category: Keyboard)
Scan for the joystick
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Subroutine DORND (category: Maths (Arithmetic))
Generate random numbers
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Subroutine EDGES (category: Drawing lines)
Draw a horizontal line given a centre and a half-width
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Subroutine FMLTU2 (category: Maths (Arithmetic))
Calculate A = K * sin(A)
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Subroutine GINF (category: Universe)
Fetch the address of a ship's data block into INF
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Subroutine HLOIN (category: Drawing lines)
Draw a horizontal line from (X1, Y1) to (X2, Y1)
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Subroutine HLOIN2 (category: Drawing lines)
Remove a line from the sun line heap and draw it on-screen
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Subroutine LL5 (category: Maths (Arithmetic))
Calculate Q = SQRT(R Q)
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Subroutine MT19 (category: Text)
Capitalise the next letter
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Configuration variable NA%
The address of the data block for the last saved commander, as set in elite-loader.asm
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Configuration variable NI%
The number of bytes in each ship's data block (as stored in INWK and K%)
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Configuration variable NOSH
The maximum number of ships in our local bubble of universe
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Subroutine PL21 (category: Drawing planets)
Return from a planet/sun-drawing routine with a failure flag
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Label PLF10 in subroutine SUN (Part 3 of 4)
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Label PLF11 in subroutine SUN (Part 3 of 4)
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Label PLF13 in subroutine SUN (Part 2 of 4)
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Label PLF16 in subroutine SUN (Part 3 of 4)
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Label PLF17 in subroutine SUN (Part 1 of 4)
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Label PLF2 in subroutine SUN (Part 1 of 4)
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Label PLF23 in subroutine SUN (Part 3 of 4)
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Label PLF3 in subroutine SUN (Part 1 of 4)
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Label PLF4 in subroutine SUN (Part 1 of 4)
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Label PLF44 in subroutine SUN (Part 3 of 4)
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Label PLF5 in subroutine SUN (Part 1 of 4)
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Label PLF6 in subroutine SUN (Part 3 of 4)
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Label PLF8 in subroutine SUN (Part 4 of 4)
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Label PLF9 in subroutine SUN (Part 4 of 4)
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Label PLFL in subroutine SUN (Part 3 of 4)
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Label PLFL2 in subroutine SUN (Part 2 of 4)
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Label PLFL3 in subroutine SUN (Part 4 of 4)
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Label PLFLS in subroutine SUN (Part 3 of 4)
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Variable QQ16 (category: Text)
The two-letter token lookup table
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Configuration variable QQ18
The address of the text token table, as set in elite-loader.asm
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Configuration variable RE
The obfuscation byte used to hide the recursive tokens table from crackers viewing the binary code
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Subroutine SQUA2 (category: Maths (Arithmetic))
Calculate (A P) = A * A
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Configuration variable SST
Ship blueprint position for the space station
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Subroutine TT26 (category: Text)
Print a character at the text cursor, with support for verified text in extended tokens
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Subroutine TT27 (category: Text)
Print a text token
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Subroutine TT41 (category: Text)
Print a letter according to Sentence Case
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Subroutine TT42 (category: Text)
Print a letter in lower case
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Subroutine TT43 (category: Text)
Print a two-letter token or recursive token 0-95
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Subroutine TT45 (category: Text)
Print a letter in lower case
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Subroutine TT46 (category: Text)
Print a character and switch to capitals
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Subroutine TT54 (category: Universe)
Twist the selected system's seeds
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Subroutine TT67 (category: Text)
Print a newline
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Subroutine TT68 (category: Text)
Print a text token followed by a colon
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Subroutine TT73 (category: Text)
Print a colon
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Subroutine TT74 (category: Text)
Print a character
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Variable UNIV (category: Universe)
Table of pointers to the local universe's ship data blocks
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Temporary storage, used to store the address of a ship blueprint. For example, it is used when we add a new ship to the local bubble in routine NWSHP, and it contains the address of the current ship's blueprint as we loop through all the nearby ships in the main flight loop
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Variable XX21 (category: Drawing ships)
Ship blueprints lookup table for the ship hangar
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Configuration variable Y
The centre y-coordinate of the 256 x 192 space view
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Subroutine cmn (category: Status)
Print the commander's name
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Subroutine cpl (category: Universe)
Print the selected system name
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Subroutine crlf (category: Text)
Tab to column 21 and print a colon
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Subroutine csh (category: Status)
Print the current amount of cash
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Subroutine ex (category: Text)
Print a recursive token
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Subroutine fwl (category: Status)
Print fuel and cash levels
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Subroutine plf (category: Text)
Print a text token followed by a newline
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Subroutine pr2 (category: Text)
Print an 8-bit number, left-padded to 3 digits, and optional point
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Subroutine qw (category: Text)
Print a recursive token in the range 128-145
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Subroutine tal (category: Universe)
Print the current galaxy number
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Subroutine ypl (category: Universe)
Print the current system name