.SIGHT LDA #%101 ; Call SETL1 to set the 6510 input/output port to the JSR SETL1 ; following: ; ; * LORAM = 1 ; * HIRAM = 0 ; * CHAREN = 1 ; ; This sets the entire 64K memory map to RAM except for ; the I/O memory map at $D000-$DFFF, which gets mapped ; to registers in the VIC-II video controller chip, the ; SID sound chip, the two CIA I/O chips, and so on ; ; See the memory map at the top of page 264 in the ; Programmer's Reference Guide LDY VIEW ; Fetch the laser power for our new view LDA LASER,Y BEQ SIG3 ; If it is zero (i.e. there is no laser fitted to this ; view), jump to SIG3 with A = 0 to skip displaying the ; laser sights ; We now set the sprite pointer for sprite 0 so that it ; points to the correct sprite definition for the ; current laser type, so we can display sprite 0 in the ; middle of the space view to show the laser sights LDY #SPOFF% ; The first sprite definition at offset SPOFF% contains ; the sights for the pulse laser, so we start by setting ; Y to the sprite pointer for the first sprite, which is ; for the pulse laser (the sprites are defined in ; elite-sprite.asm) ; The second sprite definition is the beam laser sight, ; the third is the military laser sight and the fourth ; is the mining laser sprite, so we now increment Y (if ; required) to point to the correct sprite definition ; for the current laser type CMP #POW ; If the laser power in A is equal to a pulse laser, BEQ SIG1 ; jump to SIG1 with Y pointing to the first sprite ; definition INY ; Increment Y to point to the beam laser sight in the ; second sprite definition CMP #POW+128 ; If the laser power in A is equal to a beam laser, BEQ SIG1 ; jump to SIG1 with Y pointing to the second sprite ; definition INY ; Increment Y to point to the military laser sight in ; the third sprite definition CMP #Armlas ; If the laser power in A is equal to a military laser, BEQ SIG1 ; jump to SIG1 with Y pointing to the third sprite ; definition INY ; Increment Y to point to the mining laser sight in the ; fourth sprite definition .SIG1 STY $63F8 ; Set the pointer for sprite 0 in the text view to Y ; ; The sprite pointer for sprite 0 is at $63F8 for the ; text view because screen RAM for the text view is ; at $6000 to $63FF, and the sprite pointers always ; live in the last eight bytes of screen RAM, so that's ; from $63F8 to $63FF for sprites 0 to 7 STY $67F8 ; Set the pointer for sprite 0 in the space view to Y ; ; The sprite pointer for sprite 0 is at $67F8 for the ; space view because screen RAM for the space view is ; at $6400 to $67FF, and the sprite pointers always ; live in the last eight bytes of screen RAM, so that's ; from $67F8 to $67FF for sprites 0 to 7 LDA sightcol-SPOFF%,Y ; Fetch the colour from the sightcol table, subtracting ; SPOFF% from Y so we have Y = 0 for pulse lasers ; through to Y = 3 for mining lasers (as we set Y to ; SPOFF% + laser number above) STA VIC+$27 ; Set VIC register $27 to set the colour for sprite 0 to ; the value in A, so the laser sights are shown in the ; correct colour from the sightcol table LDA #1 ; Set A = 1 to store in T to denote that we need to show ; the laser sights .SIG3 STA T ; Store A in T, so T will be 0 if we jumped here without ; wanting to show the laser sights, or 1 if we do want ; to show the laser sights LDA TRIBBLE+1 ; Set A to bits 4-6 of the high byte of TRIBBLE(1 0) AND #%01111111 ; LSR A ; TRIBBLE(1 0) is the number of Trumbles in the hold, LSR A ; and the maximum value of the high byte is $7F, so this LSR A ; sets A to the number of Trumbles in the hold, scaled LSR A ; to the range 0 to %111 (or 0 to 7) ;LSR A ; These instructions are commented out in the original ;ORA #3 ; source TAX ; Copy A into X, so X is now in the range 0 to 7 LDA TRIBTA,X ; Look up the X-th entry in the TRIBTA table, which will ; change X from 7 to 6, but leave X alone otherwise ; (this is a pretty inefficient way to do this, so ; presumably the TRIBTA table approach was used during ; development to fine-tune the relationship between ; Trumble counts and the number of sprites) STA TRIBCT ; Store A in TRIBCT to record the number of Trumble ; sprites to show on-screen, which is in the range 0 to ; 6 (as the six sprites from 2 to 7 are allocated to the ; Trumbles) LDA TRIBMA,X ; The TRIBMA table contains sprite-enable flags for use ; with VIC register $15, where the byte at position X ; contains the correct bits for enabling sprites 2 to 7, ; according to the number of Trumble sprites we want to ; enable, so TRIBMA+2 enables two sprites (2 and 3) for ; example, while TRIBMA+5 enables five sprites (2 to 6) ; ; The Trumble sprites are sprites 2 to 7, so the table ; contains values with bits 0 and 1 clear ; ; So this sets A to the correct sprite-enable mask for ; the set of Trumble sprites that we want to enable ORA T ; T contains 1 if we want to show laser sights or 0 if ; we don't, so this sets bit 0 of A so we show sprite 0 ; if there are laser sights ; ; Both T and the value from TRIBMA have bit 1 clear, so ; this will also disable the explosion sprite if it's ; being shown (which is fine as the explosion sprite is ; only shown fleetingly) STA VIC+$15 ; Set VIC register $15 to enable each of the eight ; sprites, with sprite 0 enabled (bit 0) if there are ; laser sights, and sprites 2 to 7 (bits 2 to 7) enabled ; according to the number of Trumbles in the hold LDA #%100 ; Call SETL1 to set the 6510 input/output port to the JMP SETL1 ; following: ; ; * LORAM = 0 ; * HIRAM = 0 ; * CHAREN = 1 ; ; and return from the subroutine using a tail call ; ; This sets the entire 64K memory map to RAM ; ; See the memory map at the top of page 265 in the ; Programmer's Reference GuideName: SIGHT [Show more] Type: Subroutine Category: Flight Summary: Draw the laser crosshairsContext: See this subroutine in context in the source code References: This subroutine is called as follows: * LOOK1 calls SIGHT
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Configuration variable Armlas = INT(128.5 + 1.5*POW)
Military laser power
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Configuration variable POW = 15
Pulse laser power
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Subroutine SETL1 (category: Utility routines)
Set the 6510 input/output port register to control the memory map
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Label SIG1 is local to this routine
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Label SIG3 is local to this routine
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Configuration variable SPOFF% = (SPRITELOC% - SCBASE) / 64
Sprite pointers are defined as the offset from the start of the VIC-II screen bank to start of the sprite definitions, divided by 64, so SPOFF% is the offset for the first sprite definition at SPRITELOC%
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Variable TRIBMA (category: Missions)
A table for converting the number of Trumbles in the hold into a sprite-enable flag to use with VIC register $15
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Variable TRIBTA (category: Missions)
A table for converting the number of Trumbles in the hold into a number of sprites in the range 0 to 6
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Configuration variable VIC = $D000
Registers for the VIC-II video controller chip, which are memory-mapped to the 46 bytes from $D000 to $D02E (see page 454 of the Programmer's Reference Guide)
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Variable sightcol (category: Drawing lines)
Colours for the crosshair sights on the different laser types