.LL164 JSR WaitForPPUToFinish ; Wait until both bitplanes of the screen have been ; sent to the PPU, so the screen is fully updated and ; there is no more data waiting to be sent to the PPU JSR HideStardust ; Hide the stardust sprites JSR HideExplosionBurst ; Hide the four sprites that make up the explosion burst JSR MakeHyperSound ; Make the hyperspace sound LDA #128 ; This value is not used in the following, so this has STA K+2 ; no effect LDA #72 ; This value is not used in the following, so this has STA K+3 ; no effect LDA #64 ; Set XP to use as a counter for each frame of the STA XP ; hyperspace effect, so we run the following loop 64 ; times for an animation of 64 frames ; We now draw 64 frames of hyperspace effect, looping ; back to hype1 for each new frame .hype1 JSR CheckPauseButton ; Check whether the pause button has been pressed or an ; icon bar button has been chosen, and process pause or ; unpause if a pause-related button has been pressed JSR DORND ; Set X to a random number between 0 and 15 AND #15 TAX LDA hyperspaceColour,X ; Set the visible colour to entry number X from the STA visibleColour ; hyperspaceColour table, so this sets the hyperspace ; colour randomly to one of the colours in the table JSR FlipDrawingPlane ; Flip the drawing bitplane so we draw into the bitplane ; that isn't visible on-screen LDA XP ; Set STP = XP mod 32 AND #31 ; STA STP ; So over the course of the 64 iterations around the ; loop, STP starts at 0, then counts down from 31 to 0, ; and then counts down from 31 to 1 again ; ; The higher the value of STP, the closer together the ; lines in the hyperspace effect, so this makes the ; lines move further away as the effect progresses, ; giving a feeling of moving through hyperspace LDA #8 ; Set X1 = 8 so we draw horizontal lines from STA X1 ; x-coordinate 8 on the left of the screen LDA #248 ; Set X2 = 248 so we draw horizontal lines to STA X2 ; x-coordinate 248 on the right of the screen ; We now draw the lines in the hyperspace effect (with ; lines in the top half of the screen and the same ; lines, reflected, in the bottom half), looping back ; to hype2 for each new line ; ; STP gets incremented by 16 for each line, so STP is ; set to the starting point (in the range 0 to 31), plus ; 16 for the first line, plus 32 for the second line, ; and so on until we get to 90, at which point we stop ; drawing lines for this frame ; ; As STP increases, the lines get closer to the middle ; of the screen, so this loop draws the lines, starting ; with the lines furthest from the centre and working in ; towards the centre .hype2 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure ; the PPU to use nametable 0 and pattern table 0 LDA STP ; Set STP = STP + 16 CLC ; ADC #16 ; And set A to the new value of STP STA STP CMP #90 ; If A >= 90, jump to hype3 to move on to the next frame BCS hype3 ; (so we stop drawing lines in this frame) STA Q ; Set Q to the new value of STP ; We now calculate how far this horizontal line is from ; the centre of the screen in a vertical direction, with ; the result being lines that are closer together, the ; closer they are to the centre ; ; We space out the lines using a reciprocal algorithm, ; where the distance of line n from the centre is ; proportional to 1/n, so the lines get spaced roughly ; in the proportions of 1/2, 1/3, 1/4, 1/5 and so on, so ; the lines bunch closer together as n increases ; ; STP also includes the iteration number, modded so it ; runs from 31 to 0, so over the course of the animation ; the lines move away from the centre line, as the ; iteration decreases and the value of R below increases LDA #8 ; Set A = 8 to use in the following division JSR LL28 ; Call LL28 to calculate: ; ; R = 256 * A / Q ; = 256 * 8 / STP ; ; So R is the vertical distance of the current line from ; the centre of the screen ; ; The minimum value of STP is 16 and the maximum is 89 ; (the latter being enforced by the comparison above), ; so R ranges from 128 to 23 LDA R ; Set K+1 = R - 20 SEC ; SBC #20 ; This sets the range of values in K+1 to 108 to 3 STA K+1 ; We can now use K+1 as the vertical distance of this ; line from the centre of the screen, to give us an ; effect where the horizontal lines spread out as they ; get away from the centre, and which move away from the ; centre as the animation progresses, with the movement ; being bigger the further away the line ; ; We now draw this line twice, once above the centre and ; once below the centre, so the lines in the top and ; bottom parts of the screen are mirrored, and the ; overall effect is of hyperspacing forwards, sandwiched ; between two horizontal planes, one above and one below LDA halfScreenHeight ; Set A = halfScreenHeight - K+1 SBC K+1 ; ; So A is the y-coordinate of the line in the top half ; of the screen BCC hype2 ; If A <= 0 then the line is off the top of the screen, BEQ hype2 ; so jump to hype2 to move on to the next line TAY ; Set Y = A, to use as the y-coordinate for this line ; in the hyperspace effect JSR HLOIN ; Draw a horizontal line from (X1, Y) to (X2, Y) INC X2 ; The HLOIN routine decrements X2, so increment it back ; to its original value LDA K+1 ; Set A = halfScreenHeight + K+1 CLC ; ADC halfScreenHeight ; So A is the y-coordinate of the line in the bottom ; half of the screen TAY ; Set Y = A, to use as the y-coordinate for this line ; in the hyperspace effect JSR HLOIN ; Draw a horizontal line from (X1, Y) to (X2, Y) INC X2 ; The HLOIN routine decrements X2, so increment it back ; to its original value JMP hype2 ; Loop back to hype2 to draw the next horizontal line ; in this iteration .hype3 JSR DrawBitplaneInNMI ; Configure the NMI to send the drawing bitplane to the ; PPU after drawing the box edges and setting the next ; free tile number DEC XP ; Decrement the frame counter in XP BNE hype1 ; Loop back to hype1 to draw the next frame of the ; animation, until the frame counter runs down to 0 JMP WaitForPPUToFinish ; Wait until both bitplanes of the screen have been ; sent to the PPU, so the screen is fully updated and ; there is no more data waiting to be sent to the PPU, ; and return from the subroutine using a tail callName: LL164 [Show more] Type: Subroutine Category: Flight Summary: Make the hyperspace sound and draw the hyperspace tunnelContext: See this subroutine in context in the source code References: This subroutine is called as follows: * LL164_b6 calls LL164
This routine does a similar job to the routine of the same name in the BBC Master version of Elite, but the code is significantly different.
[X]
Subroutine CheckPauseButton (category: Icon bar)
Check whether the pause button has been pressed or an icon bar button has been chosen, and process pause/unpause if required
[X]
Subroutine DORND (category: Maths (Arithmetic))
Generate random numbers
[X]
Subroutine DrawBitplaneInNMI (category: Drawing the screen)
Configure the NMI to send the drawing bitplane to the PPU after drawing the box edges and setting the next free tile number
[X]
Subroutine FlipDrawingPlane (category: Drawing the screen)
Flip the drawing bitplane
[X]
Subroutine HLOIN (Part 1 of 5) (category: Drawing lines)
Draw a horizontal line from (X1, Y) to (X2, Y) using EOR logic
[X]
Subroutine HideExplosionBurst (category: Drawing ships)
Hide the four sprites that make up the explosion burst that flashes up when a ship explodes
[X]
Subroutine HideStardust (category: Stardust)
Hide the stardust sprites
[X]
Subroutine LL28 (category: Maths (Arithmetic))
Calculate R = 256 * A / Q
[X]
Subroutine MakeHyperSound (category: Sound)
Make the hyperspace sound
[X]
Macro SETUP_PPU_FOR_ICON_BAR (category: PPU)
If the PPU has started drawing the icon bar, configure the PPU to use nametable 0 and pattern table 0
[X]
Subroutine WaitForPPUToFinish (category: PPU)
Wait until the NMI handler has finished updating both bitplanes, so the screen is no longer refreshing
[X]
Variable halfScreenHeight in workspace ZP
Half the height of the drawable part of the screen in pixels (can be 72, 77 or 104 pixels)
[X]
Label hype1 is local to this routine
[X]
Label hype2 is local to this routine
[X]
Label hype3 is local to this routine
[X]
Variable hyperspaceColour (category: Flight)
The different colours that can be used for the hyperspace effect
[X]
Variable visibleColour in workspace ZP
Contains the colour to use for pixels that are visible in palette 0, e.g. $2C for cyan