CODE_H% = P% LOAD_H% = LOAD% + P% - CODE%ELITE H FILE Produces the binary file ELTH.bin that gets loaded by elite-checksum.py..MVEIT LDA INWK+31 ; If bits 5 or 7 of ship byte #31 are set, jump to MV30 AND #%10100000 ; as the ship is either exploding or has been killed, so BNE MV30 ; we don't need to tidy its orientation vectors or apply ; tactics LDA MCNT ; Fetch the main loop counter EOR XSAV ; Fetch the slot number of the ship we are moving, EOR AND #15 ; with the loop counter and apply mod 15 to the result. BNE MV3 ; The result will be zero when "counter mod 15" matches ; the slot number, so this makes sure we call TIDY 12 ; times every 16 main loop iterations, like this: ; ; Iteration 0, tidy the ship in slot 0 ; Iteration 1, tidy the ship in slot 1 ; Iteration 2, tidy the ship in slot 2 ; ... ; Iteration 11, tidy the ship in slot 11 ; Iteration 12, do nothing ; Iteration 13, do nothing ; Iteration 14, do nothing ; Iteration 15, do nothing ; Iteration 16, tidy the ship in slot 0 ; ... ; ; and so on JSR TIDY ; Call TIDY to tidy up the orientation vectors, to ; prevent the ship from getting elongated and out of ; shape due to the imprecise nature of trigonometry ; in assembly languageName: MVEIT (Part 1 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Tidy the orientation vectors Deep dive: Program flow of the ship-moving routine Scheduling tasks with the main loop counterContext: See this subroutine on its own page References: This subroutine is called as follows: * BRIEF calls MVEIT * ESCAPE calls MVEIT * Main flight loop (Part 6 of 16) calls MVEIT * PAS1 calls MVEIT * TITLE calls MVEIT
This routine has multiple stages. This stage does the following: * Tidy the orientation vectors for one of the ship slots
Arguments: INWK The current ship/planet/sun's data block XSAV The slot number of the current ship/planet/sun TYPE The type of the current ship/planet/sun.MV3 LDX TYPE ; If the type of the ship we are moving is positive, BPL P%+5 ; i.e. it is not a planet (types 128 and 130) or sun ; (type 129), then skip the following instruction JMP MV40 ; This item is the planet or sun, so jump to MV40 to ; move it, which ends by jumping back into this routine ; at MV45 (after all the rotation, tactics and scanner ; code, which we don't need to apply to planets or suns) LDA INWK+32 ; Fetch the ship's byte #32 (AI flag) into A BPL MV30 ; If bit 7 of the AI flag is clear, then if this is a ; ship or missile it is dumb and has no AI, and if this ; is the space station it is not hostile, so in both ; cases skip the following as it has no tactics CPX #MSL ; If the ship is a missile, skip straight to MV26 to BEQ MV26 ; call the TACTICS routine, as we do this every ; iteration of the main loop for missiles only LDA MCNT ; Fetch the main loop counter EOR XSAV ; Fetch the slot number of the ship we are moving, EOR AND #7 ; with the loop counter and apply mod 8 to the result. BNE MV30 ; The result will be zero when "counter mod 8" matches ; the slot number mod 8, so this makes sure we call ; TACTICS 12 times every 8 main loop iterations, like ; this: ; ; Iteration 0, apply tactics to slots 0 and 8 ; Iteration 1, apply tactics to slots 1 and 9 ; Iteration 2, apply tactics to slots 2 and 10 ; Iteration 3, apply tactics to slots 3 and 11 ; Iteration 4, apply tactics to slot 4 ; Iteration 5, apply tactics to slot 5 ; Iteration 6, apply tactics to slot 6 ; Iteration 7, apply tactics to slot 7 ; Iteration 8, apply tactics to slots 0 and 8 ; ... ; ; and so on .MV26 JSR TACTICS ; Call TACTICS to apply AI tactics to this ship .MV30 JSR SCAN ; Draw the ship on the scanner, which has the effect of ; removing it, as it's already at this point and hasn't ; yet movedName: MVEIT (Part 2 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Call tactics routine, remove ship from scanner Deep dive: Scheduling tasks with the main loop counterContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * Apply tactics to ships with AI enabled (by calling the TACTICS routine) * Remove the ship from the scanner, so we can move itLDA INWK+27 ; Set Q = the ship's speed byte #27 * 4 ASL A ASL A STA Q LDA INWK+10 ; Set A = |nosev_x_hi| AND #%01111111 JSR FMLTU ; Set R = A * Q / 256 STA R ; = |nosev_x_hi| * speed / 64 LDA INWK+10 ; If nosev_x_hi is positive, then: LDX #0 ; JSR MVT1-2 ; (x_sign x_hi x_lo) = (x_sign x_hi x_lo) + R ; ; If nosev_x_hi is negative, then: ; ; (x_sign x_hi x_lo) = (x_sign x_hi x_lo) - R ; ; So in effect, this does: ; ; (x_sign x_hi x_lo) += nosev_x_hi * speed / 64 LDA INWK+12 ; Set A = |nosev_y_hi| AND #%01111111 JSR FMLTU ; Set R = A * Q / 256 STA R ; = |nosev_y_hi| * speed / 64 LDA INWK+12 ; If nosev_y_hi is positive, then: LDX #3 ; JSR MVT1-2 ; (y_sign y_hi y_lo) = (y_sign y_hi y_lo) + R ; ; If nosev_y_hi is negative, then: ; ; (y_sign y_hi y_lo) = (y_sign y_hi y_lo) - R ; ; So in effect, this does: ; ; (y_sign y_hi y_lo) += nosev_y_hi * speed / 64 LDA INWK+14 ; Set A = |nosev_z_hi| AND #%01111111 JSR FMLTU ; Set R = A * Q / 256 STA R ; = |nosev_z_hi| * speed / 64 LDA INWK+14 ; If nosev_y_hi is positive, then: LDX #6 ; JSR MVT1-2 ; (z_sign z_hi z_lo) = (z_sign z_hi z_lo) + R ; ; If nosev_z_hi is negative, then: ; ; (z_sign z_hi z_lo) = (z_sign z_hi z_lo) - R ; ; So in effect, this does: ; ; (z_sign z_hi z_lo) += nosev_z_hi * speed / 64Name: MVEIT (Part 3 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Move ship forward according to its speedContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * Move the ship forward (along the vector pointing in the direction of travel) according to its speed: (x, y, z) += nosev_hi * speed / 64LDA INWK+27 ; Set A = the ship's speed in byte #24 + the ship's CLC ; acceleration in byte #28 ADC INWK+28 BPL P%+4 ; If the result is positive, skip the following ; instruction LDA #0 ; Set A to 0 to stop the speed from going negative LDY #15 ; We now fetch byte #15 from the ship's blueprint, which ; contains the ship's maximum speed, so set Y = 15 to ; use as an index CMP (XX0),Y ; If A < the ship's maximum speed, skip the following BCC P%+4 ; instruction LDA (XX0),Y ; Set A to the ship's maximum speed STA INWK+27 ; We have now calculated the new ship's speed after ; accelerating and keeping the speed within the ship's ; limits, so store the updated speed in byte #27 LDA #0 ; We have added the ship's acceleration, so we now set STA INWK+28 ; it back to 0 in byte #28, as it's a one-off changeName: MVEIT (Part 4 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Apply acceleration to ship's speed as a one-offContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * Apply acceleration to the ship's speed (if acceleration is non-zero), and then zero the acceleration as it's a one-off changeLDX ALP1 ; Fetch the magnitude of the current roll into X, so ; if the roll angle is alpha, X contains |alpha| LDA INWK ; Set P = ~x_lo (i.e. with all its bits flipped) so that EOR #%11111111 ; we can pass x_lo to MLTU2 below) STA P LDA INWK+1 ; Set A = x_hi JSR MLTU2-2 ; Set (A P+1 P) = (A ~P) * X ; = (x_hi x_lo) * alpha STA P+2 ; Store the high byte of the result in P+2, so we now ; have: ; ; P(2 1 0) = (x_hi x_lo) * alpha LDA ALP2+1 ; Fetch the flipped sign of the current roll angle alpha EOR INWK+2 ; from ALP2+1 and EOR with byte #2 (x_sign), so if the ; flipped roll angle and x_sign have the same sign, A ; will be positive, else it will be negative. So A will ; contain the sign bit of x_sign * flipped alpha sign, ; which is the opposite to the sign of the above result, ; so we now have: ; ; (A P+2 P+1) = - (x_sign x_hi x_lo) * alpha / 256 LDX #3 ; Set (A P+2 P+1) = (y_sign y_hi y_lo) + (A P+2 P+1) JSR MVT6 ; = y - x * alpha / 256 STA K2+3 ; Set K2(3) = A = the sign of the result LDA P+1 ; Set K2(1) = P+1, the low byte of the result STA K2+1 EOR #%11111111 ; Set P = ~K2+1 (i.e. with all its bits flipped) so STA P ; that we can pass K2+1 to MLTU2 below) LDA P+2 ; Set K2(2) = A = P+2 STA K2+2 ; So we now have result 1 above: ; ; K2(3 2 1) = (A P+2 P+1) ; = y - x * alpha / 256 LDX BET1 ; Fetch the magnitude of the current pitch into X, so ; if the pitch angle is beta, X contains |beta| JSR MLTU2-2 ; Set (A P+1 P) = (A ~P) * X ; = K2(2 1) * beta STA P+2 ; Store the high byte of the result in P+2, so we now ; have: ; ; P(2 1 0) = K2(2 1) * beta LDA K2+3 ; Fetch the sign of the above result in K(3 2 1) from EOR BET2 ; K2+3 and EOR with BET2, the sign of the current pitch ; rate, so if the pitch and K(3 2 1) have the same sign, ; A will be positive, else it will be negative. So A ; will contain the sign bit of K(3 2 1) * beta, which is ; the same as the sign of the above result, so we now ; have: ; ; (A P+2 P+1) = K2(3 2 1) * beta / 256 LDX #6 ; Set (A P+2 P+1) = (z_sign z_hi z_lo) + (A P+2 P+1) JSR MVT6 ; = z + K2 * beta / 256 STA INWK+8 ; Set z_sign = A = the sign of the result LDA P+1 ; Set z_lo = P+1, the low byte of the result STA INWK+6 EOR #%11111111 ; Set P = ~z_lo (i.e. with all its bits flipped) so that STA P ; we can pass z_lo to MLTU2 below) LDA P+2 ; Set z_hi = P+2 STA INWK+7 ; So we now have result 2 above: ; ; (z_sign z_hi z_lo) = (A P+2 P+1) ; = z + K2 * beta / 256 JSR MLTU2 ; MLTU2 doesn't change Q, and Q was set to beta in ; the previous call to MLTU2, so this call does: ; ; (A P+1 P) = (A ~P) * Q ; = (z_hi z_lo) * beta STA P+2 ; Set P+2 = A = the high byte of the result, so we ; now have: ; ; P(2 1 0) = (z_hi z_lo) * beta LDA K2+3 ; Set y_sign = K2+3 STA INWK+5 EOR BET2 ; EOR y_sign with BET2, the sign of the current pitch EOR INWK+8 ; rate, and z_sign. If the result is positive jump to BPL MV43 ; MV43, otherwise this means beta * z and y have ; different signs, i.e. P(2 1) and K2(3 2 1) have ; different signs, so we need to add them in order to ; calculate K2(2 1) - P(2 1) LDA P+1 ; Set (y_hi y_lo) = K2(2 1) + P(2 1) ADC K2+1 STA INWK+3 LDA P+2 ADC K2+2 STA INWK+4 JMP MV44 ; Jump to MV44 to continue the calculation .MV43 LDA K2+1 ; Reversing the logic above, we need to subtract P(2 1) SBC P+1 ; and K2(3 2 1) to calculate K2(2 1) - P(2 1), so this STA INWK+3 ; sets (y_hi y_lo) = K2(2 1) - P(2 1) LDA K2+2 SBC P+2 STA INWK+4 BCS MV44 ; If the above subtraction did not underflow, then ; jump to MV44, otherwise we need to negate the result LDA #1 ; Negate (y_sign y_hi y_lo) using two's complement, SBC INWK+3 ; first doing the low bytes: STA INWK+3 ; ; y_lo = 1 - y_lo LDA #0 ; Then the high bytes: SBC INWK+4 ; STA INWK+4 ; y_hi = 0 - y_hi LDA INWK+5 ; And finally flip the sign in y_sign EOR #%10000000 STA INWK+5 .MV44 ; So we now have result 3 above: ; ; (y_sign y_hi y_lo) = K2(2 1) - P(2 1) ; = K2 - beta * z LDX ALP1 ; Fetch the magnitude of the current roll into X, so ; if the roll angle is alpha, X contains |alpha| LDA INWK+3 ; Set P = ~y_lo (i.e. with all its bits flipped) so that EOR #$FF ; we can pass y_lo to MLTU2 below) STA P LDA INWK+4 ; Set A = y_hi JSR MLTU2-2 ; Set (A P+1 P) = (A ~P) * X ; = (y_hi y_lo) * alpha STA P+2 ; Store the high byte of the result in P+2, so we now ; have: ; ; P(2 1 0) = (y_hi y_lo) * alpha LDA ALP2 ; Fetch the correct sign of the current roll angle alpha EOR INWK+5 ; from ALP2 and EOR with byte #5 (y_sign), so if the ; correct roll angle and y_sign have the same sign, A ; will be positive, else it will be negative. So A will ; contain the sign bit of x_sign * correct alpha sign, ; which is the same as the sign of the above result, ; so we now have: ; ; (A P+2 P+1) = (y_sign y_hi y_lo) * alpha / 256 LDX #0 ; Set (A P+2 P+1) = (x_sign x_hi x_lo) + (A P+2 P+1) JSR MVT6 ; = x + y * alpha / 256 STA INWK+2 ; Set x_sign = A = the sign of the result LDA P+2 ; Set x_hi = P+2, the high byte of the result STA INWK+1 LDA P+1 ; Set x_lo = P+1, the low byte of the result STA INWK ; So we now have result 4 above: ; ; x = x + alpha * y ; ; and the rotation of (x, y, z) is doneName: MVEIT (Part 5 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Rotate ship's location by our pitch and roll Deep dive: Rotating the universeContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * Rotate the ship's location in space by the amount of pitch and roll of our ship. See below for a deeper explanation of this routine.MV45 LDA DELTA ; Set R to our speed in DELTA STA R LDA #%10000000 ; Set A to zeroes but with bit 7 set, so that (A R) is ; a 16-bit number containing -R, or -speed LDX #6 ; Set X to the z-axis so the call to MVT1 does this: JSR MVT1 ; ; (z_sign z_hi z_lo) = (z_sign z_hi z_lo) + (A R) ; = (z_sign z_hi z_lo) - speed LDA TYPE ; If the ship type is not the sun (129) then skip the AND #%10000001 ; next instruction, otherwise return from the subroutine CMP #129 ; as we don't need to rotate the sun around its origin. BNE P%+3 ; Having both the AND and the CMP is a little odd, as ; the sun is the only ship type with bits 0 and 7 set, ; so the AND has no effect and could be removed RTS ; Return from the subroutine, as the ship we are moving ; is the sun and doesn't need any of the followingName: MVEIT (Part 6 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Move the ship in space according to our speedContext: See this subroutine on its own page References: This subroutine is called as follows: * MV40 calls via MV45
This routine has multiple stages. This stage does the following: * Move the ship in space according to our speed (we already moved it according to its own speed in part 3). We do this by subtracting our speed (i.e. the distance we travel in this iteration of the loop) from the other ship's z-coordinate. We subtract because they appear to be "moving" in the opposite direction to us, and the whole MVEIT routine is about moving the other ships rather than us (even though we are the one doing the moving).
Other entry points: MV45 Rejoin the MVEIT routine after the rotation, tactics and scanner codeLDY #9 ; Apply our pitch and roll rotations to the current JSR MVS4 ; ship's nosev vector LDY #15 ; Apply our pitch and roll rotations to the current JSR MVS4 ; ship's roofv vector LDY #21 ; Apply our pitch and roll rotations to the current JSR MVS4 ; ship's sidev vectorName: MVEIT (Part 7 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Rotate ship's orientation vectors by pitch/roll Deep dive: Orientation vectors Pitching and rollingContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * Rotate the ship's orientation vectors according to our pitch and roll As with the previous step, this is all about moving the other ships rather than us (even though we are the one doing the moving). So we rotate the current ship's orientation vectors (which defines its orientation in space), by the angles we are "moving" the rest of the sky through (alpha and beta, our roll and pitch), so the ship appears to us to be stationary while we rotate.LDA INWK+30 ; Fetch the ship's pitch counter and extract the sign AND #%10000000 ; into RAT2 STA RAT2 LDA INWK+30 ; Fetch the ship's pitch counter and extract the value AND #%01111111 ; without the sign bit into A BEQ MV8 ; If the pitch counter is 0, then jump to MV8 to skip ; the following, as the ship is not pitching CMP #%01111111 ; If bits 0-6 are set in the pitch counter (i.e. the ; ship's pitch is not damping down), then the C flag ; will be set by this instruction SBC #0 ; Set A = A - 0 - (1 - C), so if we are damping then we ; reduce A by 1, otherwise it is unchanged ORA RAT2 ; Change bit 7 of A to the sign we saved in RAT2, so ; the updated pitch counter in A retains its sign STA INWK+30 ; Store the updated pitch counter in byte #30 LDX #15 ; Rotate (roofv_x, nosev_x) by a small angle (pitch) LDY #9 JSR MVS5 LDX #17 ; Rotate (roofv_y, nosev_y) by a small angle (pitch) LDY #11 JSR MVS5 LDX #19 ; Rotate (roofv_z, nosev_z) by a small angle (pitch) LDY #13 JSR MVS5 .MV8 LDA INWK+29 ; Fetch the ship's roll counter and extract the sign AND #%10000000 ; into RAT2 STA RAT2 LDA INWK+29 ; Fetch the ship's roll counter and extract the value AND #%01111111 ; without the sign bit into A BEQ MV5 ; If the roll counter is 0, then jump to MV5 to skip the ; following, as the ship is not rolling CMP #%01111111 ; If bits 0-6 are set in the roll counter (i.e. the ; ship's roll is not damping down), then the C flag ; will be set by this instruction SBC #0 ; Set A = A - 0 - (1 - C), so if we are damping then we ; reduce A by 1, otherwise it is unchanged ORA RAT2 ; Change bit 7 of A to the sign we saved in RAT2, so ; the updated roll counter in A retains its sign STA INWK+29 ; Store the updated pitch counter in byte #29 LDX #15 ; Rotate (roofv_x, sidev_x) by a small angle (roll) LDY #21 JSR MVS5 LDX #17 ; Rotate (roofv_y, sidev_y) by a small angle (roll) LDY #23 JSR MVS5 LDX #19 ; Rotate (roofv_z, sidev_z) by a small angle (roll) LDY #25 JSR MVS5Name: MVEIT (Part 8 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Rotate ship about itself by its own pitch/roll Deep dive: Orientation vectors Pitching and rolling by a fixed angleContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * If the ship we are processing is rolling or pitching itself, rotate it and apply damping if required.MV5 LDA INWK+31 ; Fetch the ship's exploding/killed state from byte #31 AND #%10100000 ; If we are exploding or removing this ship then jump to BNE MVD1 ; MVD1 to remove it from the scanner permanently LDA INWK+31 ; Set bit 4 to keep the ship visible on the scanner ORA #%00010000 STA INWK+31 JMP SCAN ; Display the ship on the scanner, returning from the ; subroutine using a tail call .MVD1 LDA INWK+31 ; Clear bit 4 to hide the ship on the scanner AND #%11101111 STA INWK+31 RTS ; Return from the subroutineName: MVEIT (Part 9 of 9) [Show more] Type: Subroutine Category: Moving Summary: Move current ship: Redraw on scanner, if it hasn't been destroyedContext: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine has multiple stages. This stage does the following: * If the ship is exploding or being removed, hide it on the scanner * Otherwise redraw the ship on the scanner, now that it's been movedAND #%10000000 ; Clear bits 0-6 of A .MVT1 ASL A ; Set the C flag to the sign bit of the delta, leaving ; delta_hi << 1 in A STA S ; Set S = delta_hi << 1 ; ; This also clears bit 0 of S LDA #0 ; Set T = just the sign bit of delta (in bit 7) ROR A STA T LSR S ; Set S = delta_hi >> 1 ; = |delta_hi| ; ; This also clear the C flag, as we know that bit 0 of ; S was clear before the LSR EOR INWK+2,X ; If T EOR x_sign has bit 7 set, then x_sign and delta BMI MV10 ; have different signs, so jump to MV10 ; At this point, we know x_sign and delta have the same ; sign, that sign is in T, and S contains |delta_hi|, ; so now we want to do: ; ; (x_sign x_hi x_lo) = (x_sign x_hi x_lo) + (S R) ; ; and then set the sign of the result to the same sign ; as x_sign and delta LDA R ; First we add the low bytes, so: ADC INWK,X ; STA INWK,X ; x_lo = x_lo + R LDA S ; Then we add the high bytes: ADC INWK+1,X ; STA INWK+1,X ; x_hi = x_hi + S LDA INWK+2,X ; And finally we add any carry into x_sign, and if the ADC #0 ; sign of x_sign and delta in T is negative, make sure ORA T ; the result is negative (by OR'ing with T) STA INWK+2,X RTS ; Return from the subroutine .MV10 ; If we get here, we know x_sign and delta have ; different signs, with delta's sign in T, and ; |delta_hi| in S, so now we want to do: ; ; (x_sign x_hi x_lo) = (x_sign x_hi x_lo) - (S R) ; ; and then set the sign of the result according to ; the signs of x_sign and delta LDA INWK,X ; First we subtract the low bytes, so: SEC ; SBC R ; x_lo = x_lo - R STA INWK,X LDA INWK+1,X ; Then we subtract the high bytes: SBC S ; STA INWK+1,X ; x_hi = x_hi - S LDA INWK+2,X ; And finally we subtract any borrow from bits 0-6 of AND #%01111111 ; x_sign, and give the result the opposite sign bit to T SBC #0 ; (i.e. give it the sign of the original x_sign) ORA #%10000000 EOR T STA INWK+2,X BCS MV11 ; If the C flag is set by the above SBC, then our sum ; above didn't underflow and is correct - to put it ; another way, (x_sign x_hi x_lo) >= (S R) so the result ; should indeed have the same sign as x_sign, so jump to ; MV11 to return from the subroutine ; Otherwise our subtraction underflowed because ; (x_sign x_hi x_lo) < (S R), so we now need to flip the ; subtraction around by using two's complement to this: ; ; (S R) - (x_sign x_hi x_lo) ; ; and then we need to give the result the same sign as ; (S R), the delta, as that's the dominant figure in the ; sum LDA #1 ; First we subtract the low bytes, so: SBC INWK,X ; STA INWK,X ; x_lo = 1 - x_lo LDA #0 ; Then we subtract the high bytes: SBC INWK+1,X ; STA INWK+1,X ; x_hi = 0 - x_hi LDA #0 ; And then we subtract the sign bytes: SBC INWK+2,X ; ; x_sign = 0 - x_sign AND #%01111111 ; Finally, we set the sign bit to the sign in T, the ORA T ; sign of the original delta, as the delta is the STA INWK+2,X ; dominant figure in the sum .MV11 RTS ; Return from the subroutineName: MVT1 [Show more] Type: Subroutine Category: Moving Summary: Calculate (x_sign x_hi x_lo) = (x_sign x_hi x_lo) + (A R)Context: See this subroutine on its own page References: This subroutine is called as follows: * MVEIT (Part 6 of 9) calls MVT1 * SFS2 calls MVT1 * MVEIT (Part 3 of 9) calls via MVT1-2
Add the signed delta (A R) to a ship's coordinate, along the axis given in X. Mathematically speaking, this routine translates the ship along a single axis by a signed delta. Taking the example of X = 0, the x-axis, it does the following: (x_sign x_hi x_lo) = (x_sign x_hi x_lo) + (A R) (In practice, MVT1 is only ever called directly with A = 0 or 128, otherwise it is always called via MVT-2, which clears A apart from the sign bit. The routine is written to cope with a non-zero delta_hi, so it supports a full 16-bit delta, but it appears that delta_hi is only ever used to hold the sign of the delta.) The comments below assume we are adding delta to the x-axis, though the axis is determined by the value of X.
Arguments: (A R) The signed delta, so A = delta_hi and R = delta_lo X Determines which coordinate axis of INWK to change: * X = 0 adds the delta to (x_lo, x_hi, x_sign) * X = 3 adds the delta to (y_lo, y_hi, y_sign) * X = 6 adds the delta to (z_lo, z_hi, z_sign)
Other entry points: MVT1-2 Clear bits 0-6 of A before entering MVT1.MVS4 LDA ALPHA ; Set Q = alpha (the roll angle to rotate through) STA Q LDX INWK+2,Y ; Set (S R) = nosev_y STX R LDX INWK+3,Y STX S LDX INWK,Y ; These instructions have no effect as MAD overwrites STX P ; X and P when called, but they set X = P = nosev_x_lo LDA INWK+1,Y ; Set A = -nosev_x_hi EOR #%10000000 JSR MAD ; Set (A X) = Q * A + (S R) STA INWK+3,Y ; = alpha * -nosev_x_hi + nosev_y STX INWK+2,Y ; ; and store (A X) in nosev_y, so this does: ; ; nosev_y = nosev_y - alpha * nosev_x_hi STX P ; This instruction has no effect as MAD overwrites P, ; but it sets P = nosev_y_lo LDX INWK,Y ; Set (S R) = nosev_x STX R LDX INWK+1,Y STX S LDA INWK+3,Y ; Set A = nosev_y_hi JSR MAD ; Set (A X) = Q * A + (S R) STA INWK+1,Y ; = alpha * nosev_y_hi + nosev_x STX INWK,Y ; ; and store (A X) in nosev_x, so this does: ; ; nosev_x = nosev_x + alpha * nosev_y_hi STX P ; This instruction has no effect as MAD overwrites P, ; but it sets P = nosev_x_lo LDA BETA ; Set Q = beta (the pitch angle to rotate through) STA Q LDX INWK+2,Y ; Set (S R) = nosev_y STX R LDX INWK+3,Y STX S LDX INWK+4,Y STX P ; This instruction has no effect as MAD overwrites P, ; but it sets P = nosev_y LDA INWK+5,Y ; Set A = -nosev_z_hi EOR #%10000000 JSR MAD ; Set (A X) = Q * A + (S R) STA INWK+3,Y ; = beta * -nosev_z_hi + nosev_y STX INWK+2,Y ; ; and store (A X) in nosev_y, so this does: ; ; nosev_y = nosev_y - beta * nosev_z_hi STX P ; This instruction has no effect as MAD overwrites P, ; but it sets P = nosev_y_lo LDX INWK+4,Y ; Set (S R) = nosev_z STX R LDX INWK+5,Y STX S LDA INWK+3,Y ; Set A = nosev_y_hi JSR MAD ; Set (A X) = Q * A + (S R) STA INWK+5,Y ; = beta * nosev_y_hi + nosev_z STX INWK+4,Y ; ; and store (A X) in nosev_z, so this does: ; ; nosev_z = nosev_z + beta * nosev_y_hi RTS ; Return from the subroutineName: MVS4 [Show more] Type: Subroutine Category: Moving Summary: Apply pitch and roll to an orientation vector Deep dive: Orientation vectors Pitching and rollingContext: See this subroutine on its own page References: This subroutine is called as follows: * MVEIT (Part 7 of 9) calls MVS4
Apply pitch and roll angles alpha and beta to the orientation vector in Y. Specifically, this routine rotates a point (x, y, z) around the origin by pitch alpha and roll beta, using the small angle approximation to make the maths easier, and incorporating the Minsky circle algorithm to make the rotation more stable (though more elliptic). If that paragraph makes sense to you, then you should probably be writing this commentary! For the rest of us, there's a detailed explanation of all this in the deep dive on "Pitching and rolling".
Arguments: Y Determines which of the INWK orientation vectors to transform: * Y = 9 rotates nosev: (nosev_x, nosev_y, nosev_z) * Y = 15 rotates roofv: (roofv_x, roofv_y, roofv_z) * Y = 21 rotates sidev: (sidev_x, sidev_y, sidev_z).MVT6 TAY ; Store argument A into Y, for later use EOR INWK+2,X ; Set A = A EOR x_sign BMI MV50 ; If the sign is negative, i.e. A and x_sign have ; different signs, jump to MV50 ; The signs are the same, so we can add the two ; arguments and keep the sign to get the result LDA P+1 ; First we add the low bytes: CLC ; ADC INWK,X ; P+1 = P+1 + x_lo STA P+1 LDA P+2 ; And then the high bytes: ADC INWK+1,X ; STA P+2 ; P+2 = P+2 + x_hi TYA ; Restore the original A argument that we stored earlier ; so that we keep the original sign RTS ; Return from the subroutine .MV50 LDA INWK,X ; First we subtract the low bytes: SEC ; SBC P+1 ; P+1 = x_lo - P+1 STA P+1 LDA INWK+1,X ; And then the high bytes: SBC P+2 ; STA P+2 ; P+2 = x_hi - P+2 BCC MV51 ; If the last subtraction underflowed, then the C flag ; will be clear and x_hi < P+2, so jump to MV51 to ; negate the result TYA ; Restore the original A argument that we stored earlier EOR #%10000000 ; but flip bit 7, which flips the sign. We do this ; because x_hi >= P+2 so we want the result to have the ; same sign as x_hi (as it's the dominant side in this ; calculation). The sign of x_hi is x_sign, and x_sign ; has the opposite sign to A, so we flip the sign in A ; to return the correct result RTS ; Return from the subroutine .MV51 LDA #1 ; Our subtraction underflowed, so we negate the result SBC P+1 ; using two's complement, first with the low byte: STA P+1 ; ; P+1 = 1 - P+1 LDA #0 ; And then the high byte: SBC P+2 ; STA P+2 ; P+2 = 0 - P+2 TYA ; Restore the original A argument that we stored earlier ; as this is the correct sign for the result. This is ; because x_hi < P+2, so we want to return the same sign ; as P+2, the dominant side RTS ; Return from the subroutineName: MVT6 [Show more] Type: Subroutine Category: Moving Summary: Calculate (A P+2 P+1) = (x_sign x_hi x_lo) + (A P+2 P+1)Context: See this subroutine on its own page References: This subroutine is called as follows: * MVEIT (Part 5 of 9) calls MVT6
Do the following calculation, for the coordinate given by X (so this is what it does for the x-coordinate): (A P+2 P+1) = (x_sign x_hi x_lo) + (A P+2 P+1) A is a sign bit and is not included in the calculation, but bits 0-6 of A are preserved. Bit 7 is set to the sign of the result.
Arguments: A The sign of P(2 1) in bit 7 P(2 1) The 16-bit value we want to add the coordinate to X The coordinate to add, as follows: * If X = 0, add to (x_sign x_hi x_lo) * If X = 3, add to (y_sign y_hi y_lo) * If X = 6, add to (z_sign z_hi z_lo)
Returns: A The sign of the result (in bit 7).MV40 LDA ALPHA ; Set Q = -ALPHA, so Q contains the angle we want to EOR #%10000000 ; roll the planet through (i.e. in the opposite STA Q ; direction to our ship's roll angle alpha) LDA INWK ; Set P(1 0) = (x_hi x_lo) STA P LDA INWK+1 STA P+1 LDA INWK+2 ; Set A = x_sign JSR MULT3 ; Set K(3 2 1 0) = (A P+1 P) * Q ; ; which also means: ; ; K(3 2 1) = (A P+1 P) * Q / 256 ; = x * -alpha / 256 ; = - alpha * x / 256 LDX #3 ; Set K(3 2 1) = (y_sign y_hi y_lo) + K(3 2 1) JSR MVT3 ; = y - alpha * x / 256 LDA K+1 ; Set K2(2 1) = P(1 0) = K(2 1) STA K2+1 STA P LDA K+2 ; Set K2+2 = K+2 STA K2+2 STA P+1 ; Set P+1 = K+2 LDA BETA ; Set Q = beta, the pitch angle of our ship STA Q LDA K+3 ; Set K+3 to K2+3, so now we have result 1 above: STA K2+3 ; ; K2(3 2 1) = K(3 2 1) ; = y - alpha * x / 256 ; We also have: ; ; A = K+3 ; ; P(1 0) = K(2 1) ; ; so combined, these mean: ; ; (A P+1 P) = K(3 2 1) ; = K2(3 2 1) JSR MULT3 ; Set K(3 2 1 0) = (A P+1 P) * Q ; ; which also means: ; ; K(3 2 1) = (A P+1 P) * Q / 256 ; = K2(3 2 1) * beta / 256 ; = beta * K2 / 256 LDX #6 ; K(3 2 1) = (z_sign z_hi z_lo) + K(3 2 1) JSR MVT3 ; = z + beta * K2 / 256 LDA K+1 ; Set P = K+1 STA P STA INWK+6 ; Set z_lo = K+1 LDA K+2 ; Set P+1 = K+2 STA P+1 STA INWK+7 ; Set z_hi = K+2 LDA K+3 ; Set A = z_sign = K+3, so now we have: STA INWK+8 ; ; (z_sign z_hi z_lo) = K(3 2 1) ; = z + beta * K2 / 256 ; So we now have result 2 above: ; ; z = z + beta * K2 EOR #%10000000 ; Flip the sign bit of A to give A = -z_sign JSR MULT3 ; Set K(3 2 1 0) = (A P+1 P) * Q ; = (-z_sign z_hi z_lo) * beta ; = -z * beta LDA K+3 ; Set T to the sign bit of K(3 2 1 0), i.e. to the sign AND #%10000000 ; bit of -z * beta STA T EOR K2+3 ; If K2(3 2 1 0) has a different sign to K(3 2 1 0), BMI MV1 ; then EOR'ing them will produce a 1 in bit 7, so jump ; to MV1 to take this into account ; If we get here, K and K2 have the same sign, so we can ; add them together to get the result we're after, and ; then set the sign afterwards LDA K ; We now do the following sum: CLC ; ADC K2 ; (A y_hi y_lo -) = K(3 2 1 0) + K2(3 2 1 0) ; ; starting with the low bytes (which we don't keep) ; ; The CLC has no effect because MULT3 clears the C ; flag, so this instruction could be removed (as it is ; in the cassette version, for example) LDA K+1 ; We then do the middle bytes, which go into y_lo ADC K2+1 STA INWK+3 LDA K+2 ; And then the high bytes, which go into y_hi ADC K2+2 STA INWK+4 LDA K+3 ; And then the sign bytes into A, so overall we have the ADC K2+3 ; following, if we drop the low bytes from the result: ; ; (A y_hi y_lo) = (K + K2) / 256 JMP MV2 ; Jump to MV2 to skip the calculation for when K and K2 ; have different signs .MV1 LDA K ; If we get here then K2 and K have different signs, so SEC ; instead of adding, we need to subtract to get the SBC K2 ; result we want, like this: ; ; (A y_hi y_lo -) = K(3 2 1 0) - K2(3 2 1 0) ; ; starting with the low bytes (which we don't keep) LDA K+1 ; We then do the middle bytes, which go into y_lo SBC K2+1 STA INWK+3 LDA K+2 ; And then the high bytes, which go into y_hi SBC K2+2 STA INWK+4 LDA K2+3 ; Now for the sign bytes, so first we extract the sign AND #%01111111 ; byte from K2 without the sign bit, so P = |K2+3| STA P LDA K+3 ; And then we extract the sign byte from K without the AND #%01111111 ; sign bit, so A = |K+3| SBC P ; And finally we subtract the sign bytes, so P = A - P STA P ; By now we have the following, if we drop the low bytes ; from the result: ; ; (A y_hi y_lo) = (K - K2) / 256 ; ; so now we just need to make sure the sign of the ; result is correct BCS MV2 ; If the C flag is set, then the last subtraction above ; didn't underflow and the result is correct, so jump to ; MV2 as we are done with this particular stage LDA #1 ; Otherwise the subtraction above underflowed, as K2 is SBC INWK+3 ; the dominant part of the subtraction, so we need to STA INWK+3 ; negate the result using two's complement, starting ; with the low bytes: ; ; y_lo = 1 - y_lo LDA #0 ; And then the high bytes: SBC INWK+4 ; STA INWK+4 ; y_hi = 0 - y_hi LDA #0 ; And finally the sign bytes: SBC P ; ; A = 0 - P ORA #%10000000 ; We now force the sign bit to be negative, so that the ; final result below gets the opposite sign to K, which ; we want as K2 is the dominant part of the sum .MV2 EOR T ; T contains the sign bit of K, so if K is negative, ; this flips the sign of A STA INWK+5 ; Store A in y_sign ; So we now have result 3 above: ; ; y = K2 + K ; = K2 - beta * z LDA ALPHA ; Set A = alpha STA Q LDA INWK+3 ; Set P(1 0) = (y_hi y_lo) STA P LDA INWK+4 STA P+1 LDA INWK+5 ; Set A = y_sign JSR MULT3 ; Set K(3 2 1 0) = (A P+1 P) * Q ; = (y_sign y_hi y_lo) * alpha ; = y * alpha LDX #0 ; Set K(3 2 1) = (x_sign x_hi x_lo) + K(3 2 1) JSR MVT3 ; = x + y * alpha / 256 LDA K+1 ; Set (x_sign x_hi x_lo) = K(3 2 1) STA INWK ; = x + y * alpha / 256 LDA K+2 STA INWK+1 LDA K+3 STA INWK+2 ; So we now have result 4 above: ; ; x = x + y * alpha JMP MV45 ; We have now finished rotating the planet or sun by ; our pitch and roll, so jump back into the MVEIT ; routine at MV45 to apply all the other movementsName: MV40 [Show more] Type: Subroutine Category: Moving Summary: Rotate the planet or sun's location in space by the amount of pitch and roll of our ship Deep dive: Rotating the universeContext: See this subroutine on its own page References: This subroutine is called as follows: * MVEIT (Part 2 of 9) calls MV40
We implement this using the same equations as in part 5 of MVEIT, where we rotated the current ship's location by our pitch and roll. Specifically, the calculation is as follows: 1. K2 = y - alpha * x 2. z = z + beta * K2 3. y = K2 - beta * z 4. x = x + alpha * y See the deep dive on "Rotating the universe" for more details on the above..Checksum SEC ; Set the C flag, so it gets included in the checksum LDY #0 ; Set Y = 0, to act as a byte counter STY V ; Set V = 0 LDX #$10 ; Set X = $10, so we start with (X Y) = $1000 LDA (SC),Y ; This has no effect, as A is overwritten by the next ; instruction TXA ; Set A = $10 .CHKLoop STX V+1 ; Set V(1 0) = (X 0) STY T ; Set T = Y ADC (V),Y ; Set A = A + C + contents of (V(1 0) + Y) ; = A + C + contents of ((X 0) + Y) ; = A + C + contents of (X Y) EOR T ; Set A = A EOR Y SBC V+1 ; Set A = A - (1 - C) - X DEY ; Decrement the loop counter to process the next byte BNE CHKLoop ; Loop back until we have done the whole page INX ; Increment the page counter to point to the next page CPX #$A0 ; Loop back to do the next page until X = $A0, when BCC CHKLoop ; (X Y) = $A000 CMP S%-1 ; Compare the calculated checksum in A with the checksum ; stored in S%-1 BNE Checksum ; If the checksum we just calculated does not match ; the value in location S%-1, jump to Checksum to enter ; an infinite loop, which crashes the game RTS ; Return from the subroutineName: Checksum [Show more] Type: Subroutine Category: Copy protection Summary: Checksum the code from $1000 to $9FFF and check against S%-1Context: See this subroutine on its own page References: No direct references to this subroutine in this source file
This routine is not used in this version of Elite. It is left over from the 650s Second Processor version..PLUT LDX VIEW ; Load the current view into X: ; ; 0 = front ; 1 = rear ; 2 = left ; 3 = right BEQ PU2-1 ; If the current view is the front view, return from the ; subroutine (PU2-1 contains an RTS), as the geometry in ; INWK is already correct .PU1 DEX ; Decrement the view, so now: ; ; 0 = rear ; 1 = left ; 2 = right BNE PU2 ; If the current view is left or right, jump to PU2, ; otherwise this is the rear view, so continue on LDA INWK+2 ; Flip the sign of x_sign EOR #%10000000 STA INWK+2 LDA INWK+8 ; Flip the sign of z_sign EOR #%10000000 STA INWK+8 LDA INWK+10 ; Flip the sign of nosev_x_hi EOR #%10000000 STA INWK+10 LDA INWK+14 ; Flip the sign of nosev_z_hi EOR #%10000000 STA INWK+14 LDA INWK+16 ; Flip the sign of roofv_x_hi EOR #%10000000 STA INWK+16 LDA INWK+20 ; Flip the sign of roofv_z_hi EOR #%10000000 STA INWK+20 LDA INWK+22 ; Flip the sign of sidev_x_hi EOR #%10000000 STA INWK+22 LDA INWK+26 ; Flip the sign of roofv_z_hi EOR #%10000000 STA INWK+26 RTS ; Return from the subroutine .PU2 ; We enter this with X set to the view, as follows: ; ; 1 = left ; 2 = right LDA #0 ; Set RAT2 = 0 (left view) or -1 (right view) CPX #2 ROR A STA RAT2 EOR #%10000000 ; Set RAT = -1 (left view) or 0 (right view) STA RAT LDA INWK ; Swap x_lo and z_lo LDX INWK+6 STA INWK+6 STX INWK LDA INWK+1 ; Swap x_hi and z_hi LDX INWK+7 STA INWK+7 STX INWK+1 LDA INWK+2 ; Swap x_sign and z_sign EOR RAT ; If left view, flip sign of new z_sign TAX ; If right view, flip sign of new x_sign LDA INWK+8 EOR RAT2 STA INWK+2 STX INWK+8 LDY #9 ; Swap nosev_x_lo and nosev_z_lo JSR PUS1 ; Swap nosev_x_hi and nosev_z_hi ; If left view, flip sign of new nosev_z_hi ; If right view, flip sign of new nosev_x_hi LDY #15 ; Swap roofv_x_lo and roofv_z_lo JSR PUS1 ; Swap roofv_x_hi and roofv_z_hi ; If left view, flip sign of new roofv_z_hi ; If right view, flip sign of new roofv_x_hi LDY #21 ; Swap sidev_x_lo and sidev_z_lo ; Swap sidev_x_hi and sidev_z_hi ; If left view, flip sign of new sidev_z_hi ; If right view, flip sign of new sidev_x_hi .PUS1 LDA INWK,Y ; Swap the low x and z bytes for the vector in Y: LDX INWK+4,Y ; STA INWK+4,Y ; * For Y = 9 swap nosev_x_lo and nosev_z_lo STX INWK,Y ; * For Y = 15 swap roofv_x_lo and roofv_z_lo ; * For Y = 21 swap sidev_x_lo and sidev_z_lo LDA INWK+1,Y ; Swap the high x and z bytes for the offset in Y: EOR RAT ; TAX ; * If left view, flip sign of new z-coordinate LDA INWK+5,Y ; * If right view, flip sign of new x-coordinate EOR RAT2 STA INWK+1,Y STX INWK+5,Y ; Fall through into LOOK1 to return from the subroutineName: PLUT [Show more] Type: Subroutine Category: Flight Summary: Flip the coordinate axes for the four different views Deep dive: Flipping axes between space viewsContext: See this subroutine on its own page References: This subroutine is called as follows: * Main flight loop (Part 11 of 16) calls PLUT
This routine flips the relevant geometric axes in INWK depending on which view we are looking through (front, rear, left, right)..LO2 RTS ; Return from the subroutine .LQ STX VIEW ; Set the current space view to X JSR TT66 ; Clear the top part of the screen, draw a border box, ; and set the current view type in QQ11 to 0 (space ; view) JSR SIGHT ; Draw the laser crosshairs JMP NWSTARS ; Set up a new stardust field and return from the ; subroutine using a tail call .LOOK1 LDA #0 ; Set A = 0, the type number of a space view JSR DOVDU19 ; Switch to the palette for the space view, though this ; doesn't actually do anything in this version of Elite LDY QQ11 ; If the current view is not a space view, jump up to LQ BNE LQ ; to set up a new space view CPX VIEW ; If the current view is already of type X, jump to LO2 BEQ LO2 ; to return from the subroutine (as LO2 contains an RTS) STX VIEW ; Change the current space view to X JSR TT66 ; Clear the top part of the screen, draw a border box, ; and set the current view type in QQ11 to 0 (space ; view) JSR FLIP ; Swap the x- and y-coordinates of all the stardust ; particles and redraw the stardust field JSR WPSHPS ; Wipe all the ships from the scanner and mark them all ; as not being shown on-screen ; And fall through into SIGHT to draw the laser ; crosshairsName: LOOK1 [Show more] Type: Subroutine Category: Flight Summary: Initialise the space viewContext: See this subroutine on its own page References: This subroutine is called as follows: * MJP calls LOOK1 * TT102 calls LOOK1 * TT110 calls LOOK1 * WARP calls LOOK1
Initialise the space view, with the direction of view given in X. This clears the upper screen and draws the laser crosshairs, if the view in X has lasers fitted. It also wipes all the ships from the scanner, so we can recalculate ship positions for the new view (they get put back in the main flight loop).
Arguments: X The space view to set: * 0 = front * 1 = rear * 2 = left * 3 = right
Other entry points: LO2 Contains an RTS.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 on its own page References: This subroutine is called as follows: * LOOK1 calls SIGHT.TRIBTA EQUB 0 EQUB 1 EQUB 2 EQUB 3 EQUB 4 EQUB 5 EQUB 6 EQUB 6Name: TRIBTA [Show more] Type: Variable Category: Missions Summary: A table for converting the number of Trumbles in the hold into a number of sprites in the range 0 to 6Context: See this variable on its own page References: This variable is used as follows: * SIGHT uses TRIBTA.TRIBMA EQUB %00000000 ; Disable sprites 2 to 7 EQUB %00000100 ; Enable sprite 2 EQUB %00001100 ; Enable sprites 2 to 3 EQUB %00011100 ; Enable sprites 2 to 4 EQUB %00111100 ; Enable sprites 2 to 5 EQUB %01111100 ; Enable sprites 2 to 6 EQUB %11111100 ; Enable sprites 2 to 7 EQUB %11111100 ; Enable sprites 2 to 7Name: TRIBMA [Show more] Type: Variable Category: Missions Summary: A table for converting the number of Trumbles in the hold into a sprite-enable flag to use with VIC register $15Context: See this variable on its own page References: This variable is used as follows: * SIGHT uses TRIBMA.TT66 STA QQ11 ; Set the current view type in QQ11 to A ; Fall through into TTX66 to clear the screen and draw a ; border boxName: TT66 [Show more] Type: Subroutine Category: Drawing the screen Summary: Clear the screen and set the current view typeContext: See this subroutine on its own page References: This subroutine is called as follows: * BRIEF calls TT66 * DEATH calls TT66 * HFS2 calls TT66 * LOOK1 calls TT66 * MJP calls TT66 * MT9 calls TT66 * PAUSE calls TT66 * qv calls TT66 * TITLE calls TT66 * TRADEMODE calls TT66 * TT18 calls TT66 * TT22 calls TT66 * TT23 calls TT66
Clear the top part of the screen, draw a border box, and set the current view type in QQ11 to A.
Arguments: A The type of the new current view (see QQ11 for a list of view types).TTX66 JSR MT2 ; Switch to Sentence Case when printing extended tokens ;JSR PBZE ; These instructions are commented out in the original ;JSR HBZE ; source LDA #0 ; Reset the ball line heap pointer at LSP ;STA LBUP ; STA LSP ; The STA instruction is commented out in the original ; source LDA #%10000000 ; Set bit 7 of QQ17 to switch to Sentence Case STA QQ17 STA DTW2 ; Set bit 7 of DTW2 to indicate we are not currently ; printing a word JSR FLFLLS ; Call FLFLLS to reset the LSO block ;LDA #YELLOW ; These instructions are commented out in the original ;JSR DOCOL ; source LDA #0 ; Set LAS2 = 0 to stop any laser pulsing STA LAS2 STA DLY ; Set the delay in DLY to 0, to indicate that we are ; no longer showing an in-flight message, so any new ; in-flight messages will be shown instantly STA de ; Clear de, the flag that appends " DESTROYED" to the ; end of the next text token, so that it doesn't LDA #1 ; Move the text cursor to column 1 STA XC STA YC ; Move the text cursor to row 1 JSR TTX66K ; Clear the top part of the screen and draw a yellow ; border LDX QQ22+1 ; Fetch into X the number that's shown on-screen during ; the hyperspace countdown BEQ OLDBOX ; If the counter is zero then we are not counting down ; to hyperspace, so jump to OLDBOX to skip the next ; instruction JSR ee3 ; Print the 8-bit number in X at text location (0, 1), ; i.e. print the hyperspace countdown in the top-left ; corner .OLDBOX LDA #1 ; Move the text cursor to column 1 JSR DOYC LDA QQ11 ; If this is not a space view, jump to tt66 to skip BNE tt66 ; displaying the view name LDA #11 ; Move the text cursor to row 11 JSR DOXC LDA VIEW ; Load the current view into A: ; ; 0 = front ; 1 = rear ; 2 = left ; 3 = right ORA #$60 ; OR with $60 so we get a value of $60 to $63 (96 to 99) JSR TT27 ; Print recursive token 96 to 99, which will be in the ; range "FRONT" to "RIGHT" JSR TT162 ; Print a space LDA #175 ; Print recursive token 15 ("VIEW ") JSR TT27 .tt66 LDX #1 ; Move the text cursor to column 1, row 1 STX XC STX YC DEX ; Set QQ17 = 0 to switch to ALL CAPS STX QQ17 RTS ; Return from the subroutineName: TTX66 [Show more] Type: Subroutine Category: Drawing the screen Summary: Clear the top part of the screen and draw a border boxContext: See this subroutine on its own page References: This subroutine is called as follows: * TT18 calls TTX66
Clear the top part of the screen (the space view) and draw a border box along the top and sides.PRINT "ELITE H" PRINT "Assembled at ", ~CODE_H% PRINT "Ends at ", ~P% PRINT "Code size is ", ~(P% - CODE_H%) PRINT "Execute at ", ~LOAD% PRINT "Reload at ", ~LOAD_H% PRINT "S.ELTH ", ~CODE_H%, " ", ~P%, " ", ~LOAD%, " ", ~LOAD_H% SAVE "3-assembled-output/ELTH.bin", CODE_H%, P%, LOAD%Save ELTH.bin
[X]
Configuration variable Armlas
Military laser power
[X]
Subroutine Checksum (category: Copy protection)
Checksum the code from $1000 to $9FFF and check against S%-1
[X]
Subroutine DOVDU19 (category: Drawing the screen)
Implement the #SETVDU19 command (change mode 1 palette)
[X]
Subroutine DOXC (category: Text)
Move the text cursor to a specific column
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Subroutine DOYC (category: Text)
Move the text cursor to a specific row
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Variable DTW2 (category: Text)
A flag that indicates whether we are currently printing a word
[X]
Subroutine FLFLLS (category: Drawing suns)
Reset the sun line heap
[X]
Subroutine FLIP (category: Stardust)
Reflect the stardust particles in the screen diagonal and redraw the stardust field
[X]
Subroutine FMLTU (category: Maths (Arithmetic))
Calculate A = A * Q / 256
[X]
The ball line heap pointer, which contains the number of the first free byte after the end of the LSX2 and LSY2 heaps (see the deep dive on The ball line heap for details)
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Subroutine MAD (category: Maths (Arithmetic))
Calculate (A X) = Q * A + (S R)
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Subroutine MLTU2 (category: Maths (Arithmetic))
Calculate (A P+1 P) = (A ~P) * Q
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Configuration variable MSL
Ship type for a missile
[X]
Subroutine MT2 (category: Text)
Switch to Sentence Case when printing extended tokens
[X]
Subroutine MULT3 (category: Maths (Arithmetic))
Calculate K(3 2 1 0) = (A P+1 P) * Q
[X]
Label MV26 in subroutine MVEIT (Part 2 of 9)
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Label MV3 in subroutine MVEIT (Part 2 of 9)
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Label MV30 in subroutine MVEIT (Part 2 of 9)
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Subroutine MV40 (category: Moving)
Rotate the planet or sun's location in space by the amount of pitch and roll of our ship
[X]
Label MV43 in subroutine MVEIT (Part 5 of 9)
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Label MV44 in subroutine MVEIT (Part 5 of 9)
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Entry point MV45 in subroutine MVEIT (Part 6 of 9) (category: Moving)
Rejoin the MVEIT routine after the rotation, tactics and scanner code
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Label MV5 in subroutine MVEIT (Part 9 of 9)
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Label MV8 in subroutine MVEIT (Part 8 of 9)
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Label MVD1 in subroutine MVEIT (Part 9 of 9)
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Subroutine MVS4 (category: Moving)
Apply pitch and roll to an orientation vector
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Subroutine MVS5 (category: Moving)
Apply a 3.6 degree pitch or roll to an orientation vector
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Subroutine MVT1 (category: Moving)
Calculate (x_sign x_hi x_lo) = (x_sign x_hi x_lo) + (A R)
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Subroutine MVT3 (category: Moving)
Calculate K(3 2 1) = (x_sign x_hi x_lo) + K(3 2 1)
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Subroutine MVT6 (category: Moving)
Calculate (A P+2 P+1) = (x_sign x_hi x_lo) + (A P+2 P+1)
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Subroutine NWSTARS (category: Stardust)
Initialise the stardust field
[X]
Configuration variable POW
Pulse laser power
[X]
[X]
Subroutine S% (category: Loader)
Checksum, decrypt and unscramble the main game code, and start the game
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Subroutine SCAN (category: Dashboard)
Display the current ship on the scanner
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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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Subroutine SIGHT (category: Flight)
Draw the laser crosshairs
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Configuration variable SPOFF%
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%
[X]
Subroutine TACTICS (Part 2 of 7) (category: Tactics)
Apply tactics: Escape pod, station, lone Thargon, safe-zone pirate
[X]
Subroutine TIDY (category: Maths (Geometry))
Orthonormalise the orientation vectors for a ship
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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
[X]
Subroutine TT162 (category: Text)
Print a space
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Subroutine TT27 (category: Text)
Print a text token
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Subroutine TT66 (category: Drawing the screen)
Clear the screen and set the current view type
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Subroutine TTX66K (category: Drawing the screen)
Clear the whole screen or just the space view (as appropriate), draw a border box, and if required, show the dashboard
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Configuration variable VIC
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)
[X]
Subroutine WPSHPS (category: Dashboard)
Clear the scanner, reset the ball line and sun line heaps
[X]
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
[X]
Subroutine ee3 (category: Flight)
Print the hyperspace countdown in the top-left of the screen
[X]
Variable sightcol (category: Drawing lines)
Colours for the crosshair sights on the different laser types