.HAS1 JSR ZINF \ Call ZINF to reset the INWK ship workspace and reset \ the orientation vectors, with nosev pointing out of \ the screen, so this puts the ship flat on the \ horizontal deck (the y = 0 plane) with its nose \ pointing towards us LDA XX15 \ Set z_lo = XX15 STA INWK+6 LSR A \ Set the sign bit of x_sign to bit 0 of A ROR INWK+2 LDA XX15+1 \ Set x_hi = XX15+1 STA INWK LSR A \ Set z_hi = 1 + bit 0 of XX15+1 LDA #1 ADC #0 STA INWK+7 LDA #%10000000 \ Set bit 7 of y_sign, so y is negative STA INWK+5 STA RAT2 \ Set RAT2 = %10000000, so the yaw calls in HAL5 below \ are negative LDA #&B \ Set the ship line heap pointer in INWK(35 34) to point STA INWK+34 \ to &0B00 JSR DORND \ We now perform a random number of small angle (3.6 STA XSAV \ degree) rotations to spin the ship on the deck while \ keeping it flat on the deck (a bit like spinning a \ bottle), so we set XSAV to a random number between 0 \ and 255 for the number of small yaw rotations to \ perform, so the ship could be pointing in any \ direction by the time we're done .HAL5 LDX #21 \ Rotate (sidev_x, nosev_x) by a small angle (yaw) LDY #9 JSR MVS5 LDX #23 \ Rotate (sidev_y, nosev_y) by a small angle (yaw) LDY #11 JSR MVS5 LDX #25 \ Rotate (sidev_z, nosev_z) by a small angle (yaw) LDY #13 JSR MVS5 DEC XSAV \ Decrement the yaw counter in XSAV BNE HAL5 \ Loop back to yaw a little more until we have yawed \ by the number of times in XSAV LDY XX15+2 \ Set Y = XX15+2, the ship type of the ship we need to \ draw BEQ HA1 \ If Y = 0, return from the subroutine (as HA1 contains \ an RTS) \ We now work our way through the ship blueprints table \ for the hanger, counting valid blueprints until we \ have found the Y-th valid blueprint (we do this as the \ hanger blueprint table at XX21 is not fully populated, \ so the Y-th ship is not necessarily at position Y) LDX #4 \ We can start looking from ship blueprint 3, because we \ don't show ship 1 (missile) or ship 2 (space station) \ in the hanger. Setting X to 4, which then gets \ incremented to 6, will start us at XX21(5 4), which is \ the address of ship blueprint 3 (escape pod) .hloop INX \ Increment X by 2 to point to the next blueprint in the INX \ table LDA XX21-2,X \ Set XX0(1 0) to the X-th address in the ship blueprint STA XX0 \ address lookup table at XX21, so XX0(1 0) now points LDA XX21-1,X \ to the blueprint for the ship we need to draw STA XX0+1 BEQ hloop \ If the high byte of the blueprint address is 0, then \ the blueprint for this ship is not available, so jump \ back to hloop to try the next ship along in the table DEY \ We have found a valid blueprint, so decrement the ship \ number that we are looking for in Y BNE hloop \ If Y is not yet zero, we still haven't found the Y-th \ valid blueprint, so loop back to hloop to try the next \ ship along in the table LDY #1 \ Set Q = ship byte #1 LDA (XX0),Y STA Q INY \ Set R = ship byte #2 LDA (XX0),Y \ STA R \ so (R Q) contains the ship's targetable area, which is \ a square number JSR LL5 \ Set Q = SQRT(R Q) LDA #100 \ Set y_lo = (100 - Q) / 2 SBC Q \ LSR A \ so the bigger the ship's targetable area, the smaller STA INWK+3 \ the magnitude of the y-coordinate, so because we set \ y_sign to be negative above, this means smaller ships \ are drawn lower down, i.e. closer to the ground, while \ larger ships are drawn higher up, as you would expect 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 language JMP LL9 \ Jump to LL9 to display the ship and return from the \ subroutine using a tail call .HA1 RTS \ Return from the subroutineName: HAS1 [Show more] Type: Subroutine Category: Ship hanger Summary: Draw a ship in the ship hangerContext: See this subroutine in context in the source code References: This subroutine is called as follows: * HALL calls HAS1

The ship's position within the hanger is determined by the arguments and the size of the ship's targetable area, as follows: * The x-coordinate is (x_sign x_hi 0) from the arguments, so the ship can be left of centre or right of centre * The y-coordinate is negative and is lower down the screen for smaller ships, so smaller ships are drawn closer to the ground (because they are) * The z-coordinate is positive, with both z_hi (which is 1 or 2) and z_lo coming from the arguments Arguments: XX15 Bits 0-7 = Ship's z_lo Bit 0 = Ship's x_sign XX15+1 Bits 0-7 = Ship's x_hi Bit 0 = Ship's z_hi (1 if clear, or 2 if set) XX15+2 Non-zero = Ship type to draw 0 = Don't draw anything

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Subroutine DORND (category: Utility routines)

Generate random numbers

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Label HA1 is local to this routine

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Label HAL5 is local to this routine

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Subroutine LL5 (category: Maths (Arithmetic))

Calculate Q = SQRT(R Q)

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Subroutine LL9 (Part 1 of 12) (category: Drawing ships)

Draw ship: Check if ship is exploding, check if ship is in front

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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 TIDY (category: Maths (Geometry))

Orthonormalise the orientation vectors for a ship

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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 flight in Elite-A

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Subroutine ZINF (category: Utility routines)

Reset the INWK workspace and orientation vectors

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Label hloop is local to this routine