99 lines
2 KiB
ArmAsm
99 lines
2 KiB
ArmAsm
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; Ullrich von Bassewitz, 2009-10-25
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; Generates clipping outcodes for Cohen Sutherland and others.
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;
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.include "tgi-kernel.inc"
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.include "zeropage.inc"
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;----------------------------------------------------------------------------
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; Data
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.bss
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; Clipping coordinates.
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tgi_clip_x1: .res 2
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tgi_clip_y1: .res 2
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tgi_clip_x2: .res 2
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tgi_clip_y2: .res 2
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;----------------------------------------------------------------------------
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; Generate a Cohen Sutherland outcode
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;
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; void outcode ()
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; {
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; unsigned char o = 0;
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; if (Y < 0) {
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; o = TGI_CLIP_BOTTOM;
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; } else if (Y >= yres) {
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; o = TGI_CLIP_TOP;
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; }
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; if (X < 0) {
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; o |= TGI_CLIP_LEFT;
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; } else if (X >= xres) {
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; o |= TGI_CLIP_RIGHT;
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; }
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; return o;
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; }
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;
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; The function return the outcode in A and the flags for the outcode are
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; correctly set.
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;
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.code
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.proc tgi_outcode
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lda #TGI_CLIP_NONE
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sta tmp1
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; Check Y coordinate
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lda tgi_clip_y1+1,y ; High byte of Y1
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bmi L2 ; Jump if bottom clip
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ldx tgi_clip_y1,y ; Low byte of Y1
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cpx _tgi_yres
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sbc _tgi_yres+1
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bvs L1
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eor #$80
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L1: bpl L4
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lda #TGI_CLIP_TOP ; Top clipping necessary
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bne L3
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L2: lda #TGI_CLIP_BOTTOM
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L3: sta tmp1 ; Save temp outcode
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; Check X coordinate
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L4: lda tgi_clip_x1+1,y ; High byte of X1
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bmi L7 ; Jump if left clip
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ldx tgi_clip_x1,y ; Low byte of X1
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cpx _tgi_xres
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sbc _tgi_xres+1
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bvs L5
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eor #$80
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L5: bmi L6
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; No right or left clipping necessary
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lda tmp1
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rts
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; Need right clipping
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L6: lda #TGI_CLIP_RIGHT
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ora tmp1
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rts
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; Need left clipping
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L7: lda #TGI_CLIP_LEFT
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ora tmp1
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rts
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.endproc
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