base:dysp_d017
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Table of Contents
D.Y.S.P. using $d017
Introduction
D.Y.S.P. stands for Different Y Sprite Positioning. Normally only used to refer to a sprite movement in the side borders. At least that's how I understand it, moving sprites around without opening the borders isn't really VIC-magic, now is it?
Anyway, a DYSP can be done in many ways, the way I'm describing below is probably the easiest way, since it keeps the timing for each raster line constant by 'cheating' with $d017 manipulation.
Assembling the code
The code below is in [[http://tass64.sourceforge.net/]64tass] format, and can be assembled using:
64tass -C -a -o dysp.prg dysp.asm
, assuming one would copy and paste the code into a file called 'dysp.asm'.
The Problem
Moving sprites into the side border is fairly easy, but requires cycle exact timing. There are plenty of articles here which explain this. Using a constant Y-position for the sprites makes timing the code easy, the problem arises when we want to have variable Y-positions for each sprite, this screws with our timing.
There's a multitude of ways to solve this, I'll be describing what I consider the easiest and 'cheating' way of doing it. We use sprite stretching via $d017 to keep our timing constant.
The Code
; vim: set et ts=8 sw=8 sts=8 syntax=64tass : ; ; Simple, 'cheated', sideborder D.Y.S.P., using $d017 stretching to allow for ; different Y-positions of each sprite. Since we're using $d017 to stretch the ; first and last line of the sprite over the whole area, we can only use 19 ; lines high sprites, the first and last line must be clear so we won't see ; the $d017 stretcher effect. ; ; With some extra $d011 manipulation, this routine can be used for a ; line cruncher. My line cruncher part in 'Doolittle/Focus' uses this technique ; to display a swinging logo during the line crunching. ; ; 2016-04-22 ; Music, comment out, or adjust to taste music_sid ="/home/compyx/c64/HVSC/MUSICIANS/J/JCH/Training.sid" music_init = $1000 music_play = $1003 ; BASIC SYS line * = $0801 .word (+), 2016 .null $9e, ^start + .word 0 ; Entry point: generate sprite and set up IRQ start jsr $fda3 jsr $fd15 sei jsr create_sprite ldx #7 - lda #$0340/64 sta $07f8,x lda spr_colors,x sta $d027,x dex bpl - lda #0 jsr music_init lda #$35 sta $01 lda #$7f sta $dc0d sta $dd0d lda #0 sta $3fff sta $dc0e lda #$01 sta $d01a lda #$1b sta $d011 lda #$2d ldx #<irq1 ldy #>irq1 sta $d012 stx $fffe sty $ffff ldx #<break ldy #>break stx $fffa sty $fffb stx $fffc sty $fffd bit $dc0d bit $dd0d inc $d019 cli jmp * ; make sure timing loops don't cross page boundaries .align 256 ; 'double IRQ' technique to stabilize raster irq1 pha txa pha tya pha lda #$2e ldx #<irq2 ldy #>irq2 sta $d012 stx $fffe sty $ffff lda #1 inc $d019 tsx cli nop nop nop nop nop nop nop nop nop nop nop irq2 txs ldx #8 - dex bne - bit $ea lda $d012 cmp $d012 beq + + ; stable raster here ; set sprite positions lda #$32 ; constant, the Y-movement is done with $d017 magic sta $d001 sta $d003 sta $d005 sta $d007 sta $d009 sta $d00b sta $d00d sta $d00f x0 lda #$00 sta $d000 x1 lda #$18 sta $d002 x2 lda #$30 sta $d004 x3 lda #$48 sta $d006 x4 lda #$60 sta $d008 x5 lda #$78 sta $d00a x6 lda #$90 sta $d00c x7 lda #$a8 sta $d00e xmsb lda #$00 sta $d010 lda #$00 sta $d01c sta $d01d lda #$ff sta $d015 ldx #09 - dex bne - nop nop nop jsr stretcher lda #$1b sta $d011 lda #0 sta $d015 sta $d021 dec $d020 jsr clear_d017_table dec $d020 jsr sinus_x jsr sinus_y dec $d020 jsr update_d017_table lda #0 sta $d020 lda #$f9 ldx #<irq3 ldy #>irq3 sta $d012 stx $fffe sty $ffff lda #1 sta $d019 pla tay pla tax pla break rti irq3 pha txa pha tya pha ldx #3 ; open top/bottom borders to allow us to open the - dex ; side borders earlier in the $d017 stretcher bne - stx $d011 ldx #40 - dex bne - lda #$1b sta $d011 dec $d020 jsr music_play lda #0 sta $d020 lda #$2d ldx #<irq1 ldy #>irq1 sta $d012 stx $fffe sty $ffff lda #1 sta $d019 pla tay pla tax pla rti ; Create a single sprite at $0340 create_sprite ldx #0 - lda sprite,x sta $0340,x inx cpx #63 bne - rts ; Clear the $d017 'stretcher' table by storing $ff in it ; ; We later mask out bits in this table with the $d017 update routine clear_d017_table lda #$ff ldx #$3f - sta d017_table,x dex bpl - rts ; Update the $d017 'stretcher' table ; ; This is what creates the D.Y.S.P. effect ; ; For each sprite, we get its Y-position and mask out the proper bits in the ; $d017 table. We only mask out bits for 19 lines, line 0 and line 20 are ; always stretched to keep the timing in the loop constant update_d017_table ; sprite 0 ldx siny_table + 0 ldy #18 - lda d017_table,x and #%11111110 sta d017_table,x inx dey bpl - ; sprite 1 ldx siny_table + 1 ldy #18 - lda d017_table,x and #%11111101 sta d017_table,x inx dey bpl - ldx siny_table + 2 ldy #18 - lda d017_table,x and #%11111011 sta d017_table,x inx dey bpl - ldx siny_table + 3 ldy #18 - lda d017_table,x and #%11110111 sta d017_table,x inx dey bpl - ldx siny_table + 4 ldy #18 - lda d017_table,x and #%11101111 sta d017_table,x inx dey bpl - ldx siny_table + 5 ldy #18 - lda d017_table,x and #%11011111 sta d017_table,x inx dey bpl - ldx siny_table + 6 ldy #18 - lda d017_table,x and #%10111111 sta d017_table,x inx dey bpl - ; sprite 7 ldx siny_table + 7 ldy #18 - lda d017_table,x and #%01111111 sta d017_table,x inx dey bpl - rts ; X-movement parameters, two sinus tables added together sinx_idx1 .byte 0 sinx_idx2 .byte 64 sinx_adc1 .byte 8 sinx_adc2 .byte 5 sinx_spd1 .byte $fe sinx_spd2 .byte $03 xmsb_temp .byte 0 ; Calculate the X-movement of the sprites sinus_x lda #0 sta xmsb_temp ; temporary storage for $d010 ldx sinx_idx1 ldy sinx_idx2 lda sinus256,x clc adc sinus88,y sta x0 + 1 bcc + lda xmsb_temp ora #1 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x1 + 1 bcc + lda xmsb_temp ora #2 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x2 + 1 bcc + lda xmsb_temp ora #4 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x3 + 1 bcc + lda xmsb_temp ora #8 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x4 + 1 bcc + lda xmsb_temp ora #16 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x5 + 1 bcc + lda xmsb_temp ora #32 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x6 + 1 bcc + lda xmsb_temp ora #64 sta xmsb_temp + txa clc adc sinx_adc1 tax tya clc adc sinx_adc2 tay lda sinus256,x clc adc sinus88,y sta x7 + 1 bcc + lda xmsb_temp ora #128 sta xmsb_temp + lda xmsb_temp sta xmsb + 1 lda sinx_idx1 clc adc sinx_spd1 sta sinx_idx1 lda sinx_idx2 clc adc sinx_spd2 sta sinx_idx2 rts ; Y-movement parameters, a single sinus, for now siny_table .fill 8, 0 siny_idx .byte 0 siny_adc .byte 16 siny_spd .byte 2 sinus_y ldy #0 ldx siny_idx - lda sinus40,x clc adc #1 sta siny_table,y txa clc adc siny_adc tax iny cpy #8 bne - lda siny_idx clc adc siny_spd sta siny_idx rts ; Colors for the sprites spr_colors .byte 1, 7, 13, 15, 14, 4, 6, 9 ; Example sprite sprite .byte 0, 0, 0 .byte %00000000, %00000000, %00000000 .byte %00000000, %11111111, %00000000 .byte %00000111, %11111111, %11100000 .byte %00011111, %11000001, %11111000 .byte %00111111, %10000000, %11100000 .byte %01111111, %00000000, %00000000 .byte %01111111, %00000000, %00000000 .byte %11111111, %00000000, %00000000 .byte %11111111, %00000000, %00000000 .byte %11111111, %00000000, %00000000 .byte %11111111, %00000000, %00000000 .byte %11111111, %00000000, %00000000 .byte %01111111, %00000000, %00000000 .byte %01111111, %00000000, %11100000 .byte %00111111, %10000000, %11111000 .byte %00011111, %11000011, %11111000 .byte %00000111, %11111111, %11100000 .byte %00000000, %11111111, %00000000 .byte %00000000, %00000000, %00000000 .byte 0, 0, 0 ; make sure we don't cross a page in the stretcher or its data .align 256 ; The $d017 stretcher ; ; Basically an FLD with $d017 manipulation and open borders: we use the FLD ; effect to inhibit bad lines, giving us 63 cycles on each rasterline, of which ; a lot of cycles get eaten by the sprites ; ; At each line we set Y-stretch to false, immediately followed by true, which ; causes a line of a sprite to be stretched indefinately. When we set the ; Y-stretch to false at a line (after the initial false condition), we allow ; the VIC to update its position in the sprite matrix, thus displaying a line ; of a sprite ; ; This loop can be unrolled and optimized to allow for raster splits, if ; desired stretcher ldy #0 ldx #0 - sty $d017 ; set Y-stretch to false lda d017_table,x ; set Y-stretch to true for selected sprites sta $d017 lda d011_table + 0,x bit $ea nop nop dec $d016 ; open side border and do FLD to inhibit sta $d011 ; bad lines inc $d016 inx cpx #64 bne - rts ; Table with values for $d017 in the stretcher d017_table .fill 64, $ff ; Values for $d011 in the stretcher d011_table - = range(0, 64, 1) .byte <(-) & 7 | $10 ; Don't overwrite music with code/data .cerror * > $0fff, "code section too long" ; Link music * = $1000 .binary music_sid, $7e * = $2000 ; Sinus for X-movement sinus256 .byte 127.5 + 128 * sin(range(256) * rad(360.0/256)) sinus88 .byte 42.5 + 43 * sin(range(256) * rad(360.0/256)) ; Sinus for Y-movement sinus40 .byte 19.5 + 20 * sin(range(256) * rad(360.0/256))
base/dysp_d017.1461323363.txt.gz · Last modified: 2016-04-22 13:09 by compyx