202 lines
2.8 KiB
ArmAsm
202 lines
2.8 KiB
ArmAsm
; Tunnel, based on the code in Hellmood's Memories
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; by deater (Vince Weaver) <vince@deater.net>
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; first try = 160 bytes, 14 seconds/frame
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; Zero Page
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COLOR = $30
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XCOORD = $F0
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YCOORD = $F1
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DEPTH = $F2
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VALUE = $F6
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M1 = $F7
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M2 = $F8
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FRAME = $F9
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TEMP = $FA
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; Soft Switches
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KEYPRESS= $C000
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KEYRESET= $C010
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SET_GR = $C050 ; Enable graphics
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FULLGR = $C052 ; Full screen, no text
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; ROM routines
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PLOT = $F800 ; plot, horiz=y, vert=A (A trashed, XY Saved)
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SETCOL = $F864
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SETGR = $FB40
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tunnel:
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;===================
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; init screen
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jsr SETGR ; 3
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bit FULLGR ; 3
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tunnel_forever:
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inc FRAME ; 2
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ldx #47 ; 2
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yloop:
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ldy #39 ; 2
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xloop:
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; Xcoord = (x-10)*4
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sec ; 1
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tya ; 1
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sbc #10 ; 2
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asl ; 1
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asl ; 1
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sta XCOORD ; 2
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; Ycoord = (y-10)*4
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sec ; 1
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txa ; 1
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sbc #10 ; 2
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asl ; 1
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asl ; 1
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; center
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sbc #24
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sta YCOORD ; 2
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; set depth to -9 (move backwards)
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lda #$f7 ; 2
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sta DEPTH ; 2
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fx5_loop:
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; get ycoord
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lda YCOORD ; 2
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; 8x8 signed multiply of M1*DEPTH
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;sta M1 ; 2
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jsr imul ; 3
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; lda M2 ; 2
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sta VALUE ; high result in A ; 2
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; get xcoord
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lda XCOORD ; 2
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; add distance to projection (bend right)
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clc ; 1
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adc DEPTH ; 2
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;sta M1 ; 2
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; 8x8 signed multiply of M1*DEPTH
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jsr imul ; 3
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; do the calculation
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dec DEPTH ; 2
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beq putpixel ; 2 ; is this needed?
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; load the yprojection
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lda VALUE ; 2
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; xor with the xprojection
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eor M2 ; 2
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; center walls around 0
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clc ; 1
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adc #$4 ; 2
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; test with -8, see if wall hit
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sta VALUE ; 2
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and #$f8 ; 2
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beq fx5_loop ; 2
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putpixel:
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; adjust color by frame and set
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sec ; 1
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lda DEPTH ; 2
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sbc FRAME ; 2
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eor VALUE ; 2
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and #$7 ; 2
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;adc #$20
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jsr SETCOL ; 3
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txa ; A==Y1 ; 1
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jsr PLOT ; (X2,Y1) ; 3
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dey ; 1
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bpl xloop ; 2
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dex ; 1
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bpl yloop ; 2
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bmi tunnel_forever ; 2
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;=================================================
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; A = M1
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; DEPTH (preserve) is M2
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imul:
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stx TEMP ; save as we trash it
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sta M1 ; get values in right place
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lda DEPTH
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sta M2
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eor M1 ; calc if we need to adjust at end
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; (++ vs +- vs -+ vs --)
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php ; save status on stack
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; if M1 negative, negate it
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lda M1
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bpl m1_positive
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eor #$ff
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clc
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adc #0
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m1_positive:
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sta M1
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; if M2 negative, naegate it
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lda M2
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bpl m2_positive
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eor #$ff
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clc
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adc #0
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m2_positive:
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sta M2
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;==================
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; unsigned multiply
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; factors in M1 and M2
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lda #0
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ldx #$8
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lsr M1
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clc
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imul_loop:
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bcc no_add
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clc
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adc M2
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no_add:
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ror
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ror M1
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dex
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bne imul_loop
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sta M2
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; done, high result in factor2, low result in factor1
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; adjust to be signed
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; if m1 and m2 positive, good
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; if m1 and m2 negative, good
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; otherwise, negate result
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plp ; restore saved pos/neg value
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bpl done_result
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negate_result:
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sec
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lda #0
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sbc M1
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lda #0
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sbc M2
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done_result:
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sta M2
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ldx TEMP
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rts
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