; Lo-res cycle-counting water transparency hack ; by deater (Vince Weaver) ; Zero Page FRAMEBUFFER = $00 ; $00 - $0F YPOS = $10 YPOS_SIN = $11 CH = $24 CV = $25 GBASL = $26 GBASH = $27 BASL = $28 BASH = $29 MASK = $2E COLOR = $30 FRAME = $60 BLARGH = $69 DRAW_PAGE = $EE LASTKEY = $F1 PADDLE_STATUS = $F2 XPOS = $F3 TEMP = $FA TEMPY = $FB INL = $FC INH = $FD OUTL = $FE OUTH = $FF ; Soft Switches KEYPRESS= $C000 KEYRESET= $C010 SET_GR = $C050 ; Enable graphics FULLGR = $C052 ; Full screen, no text PAGE0 = $C054 ; Page0 PAGE1 = $C055 ; Page1 LORES = $C056 ; Enable LORES graphics PADDLE_BUTTON0 = $C061 PADDL0 = $C064 PTRIG = $C070 ; ROM routines TEXT = $FB36 ;; Set text mode HOME = $FC58 ;; Clear the text screen WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us waterfall_demo: ;=================== ; init screen jsr TEXT jsr HOME bit KEYRESET bit PAGE0 ;=================== ; init vars lda #4 sta DRAW_PAGE sta XPOS ;============================= ; Load foreground to graphic page1 (apple page2) lda #$0c sta BASH lda #$00 sta BASL ; load image to $c00 lda #waterfall_page1 sta GBASH jsr load_rle_gr jsr gr_copy_to_current ; copy to page1 ;============================= ; Load bg to memory lda #$0c sta BASH lda #$00 sta BASL ; load image to $c00 lda #waterfall_page2 sta GBASH jsr load_rle_gr ;============================== ; setup graphics for vapor lock ;============================== ; Clear Page0 lda #$0 sta DRAW_PAGE lda #$44 jsr clear_gr ; Make screen half green lda #$11 ldy #24 jsr clear_page_loop ;===================================================== ; attempt vapor lock ; by reading the "floating bus" we can see most recently ; written value of the display ; we look for $55 (which is the grey line) ;===================================================== ; See: ; Have an Apple Split by Bob Bishop ; Softalk, October 1982 ; Challenges: each scan line scans 40 bytes. ; The blanking happens at the *beginning* ; So 65 bytes are scanned, starting at adress of the line - 25 ; the scan takes 8 cycles, look for 4 repeats of the value ; to avoid false positive found if the horiz blanking is mirroring ; the line (max 3 repeats in that case) vapor_lock_loop: ; first make sure we have all zeroes LDA #$11 zxloop: LDX #$04 wiloop: CMP $C051 BNE zxloop DEX BNE wiloop LDA #$44 ; now look for our border color (4 times) zloop: LDX #$04 qloop: CMP $C051 BNE zloop DEX BNE qloop ; found first line of black after green, at up to line 26 on screen ; so we want roughly 22 lines * 4 = 88*65 = 5720 + 4550 = 10270 ; - 65 (for the scanline we missed) = 10205 - 12 = 10193 jsr gr_copy_to_current ; 6+ 9292 ; 10193 - 9298 = 895 ; Fudge factor (unknown) -30 = 865 ; GR part bit LORES ; 4 bit SET_GR ; 4 bit FULLGR ; 4 ; Try X=88 Y=2 cycles=893 R2 nop ldy #2 ; 2 loopA: ldx #88 ; 2 loopB: dex ; 2 bne loopB ; 2nt/3 dey ; 2 bne loopA ; 2nt/3 jmp display_loop .align $100 ;================================================ ; Display Loop ;================================================ ; each scan line 65 cycles ; 1 cycle each byte (40cycles) + 25 for horizontal ; Total of 12480 cycles to draw screen ; Vertical blank = 4550 cycles (70 scan lines) ; Total of 17030 cycles to get back to where was ; We want to alternate between page1 and page2 every 65 cycles ; vblank = 4550 cycles to do scrolling ; 2 + 48*( (4+2+25*(2+3)) + (4+2+23*(2+3)+4+5)) + 9) ; 48*[(6+125)-1] + [(6+115+10)-1] display_loop: ldy #96 ; 2 outer_loop: bit PAGE0 ; 4 ldx #12 ; 65 cycles with PAGE0 ; 2 page0_loop: ; delay 61+bit dex ; 2 bne page0_loop ; 2/3 ; bit(4) -1(fallthrough) + loop*5 -1(fallthrouh)+4 extra = 61 ; 5L = 55 bit PAGE1 ; 4 ldx #11 ; 65 cycles with PAGE1 ; 2 ; page1_loop: ; delay 115+(7 loop)+4 (bit)+4(extra) dex ; 2 bne page1_loop ; 2/3 dey ; 2 bne outer_loop ; 2/3 ;====================================================== ; We have 4550 cycles in the vblank, use them wisely ;====================================================== ; do_nothing should be 4550 ; +1 fallthrough from above ; -2 display loop setup ; -6 jsr to do_nothing ; -10 check for keypress ; -2252 copy screen ; -2214 draw sprite ; ============= ; 67 jsr do_nothing ; 6 ;========================= ; Clear background ;========================= jsr gr_copy_row22 ; 6+ 2246 ;========= ; 2252 ;========================== ; draw sprite ;========================== ; 13 + 11 + 2190 = 2214 ; beq bird_walking ; ; 2 lda #>bird_rider_stand_right ; 2 sta INH ; 3 lda #bird_rider_walk_right ; 2 ; sta INH ; 3 ; lda #