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143 lines
1.6 KiB
ArmAsm
143 lines
1.6 KiB
ArmAsm
; Bresenham Lines
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; by Vince `deater` Weaver <vince@deater.net>
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; http://www.retroprogramming.com/2016/05/divide-and-conquer-line-algorithm-for.html
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.include "zp.inc"
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.include "hardware.inc"
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; 144 -- initial working implementation
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;B_X1 = $F0
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;B_Y1 = $F1
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;B_X2 = $F2
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;B_Y2 = $F3
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COUNT = $F9
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X1 = $1000
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Y1 = $1100
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X2 = $1200
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Y2 = $1300
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MIDX = $1400
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MIDY = $1500
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lines:
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jsr SETGR ; set lo-res 40x40 mode
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; A=$D0 afterward
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restart:
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lda #0
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sta COUNT
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lines_loop:
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jsr NEXTCOL
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lda #0
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sta X1
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lda #36
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sta Y2
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lda COUNT
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cmp #10
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;end:
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beq restart
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asl
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asl
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sta Y1
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sta X2
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jsr draw_line
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inc COUNT
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jmp lines_loop
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;============================
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; draw line
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; from x1,y1 to x2,y2
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;============================
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draw_line:
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ldx #0
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draw_recurse:
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;int draw ( ax, ay, bx, by )
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;{
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; int midx, midy;
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; midx = ( ax+bx ) / 2;
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; midy = ( ay+by ) / 2;
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; if ( midx != ax && midy != ay )
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; {
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; draw( midx, midy, ax, ay );
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; draw( bx, by, midx, midy );
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; plot( midx, midy );
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; }
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;}
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clc
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lda X1,X
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adc X2,X
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lsr
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sta MIDX,X
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tay
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clc
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lda Y1,X
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adc Y2,X
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lsr
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sta MIDY,X
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; plot midx,midy
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jsr PLOT ;; PLOT AT Y,A (A colors output, Y preserved)
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; check if done
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lda MIDX,X
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cmp X1,X
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bne recurse
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lda MIDY,X
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cmp Y1,X
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beq done_draw_line
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recurse:
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; draw( midx, midy, ax, ay);
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lda MIDX,X
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sta X1+1,X
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lda MIDY,X
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sta Y1+1,X
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lda X1,X
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sta X2+1,X
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lda Y1,X
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sta Y2+1,X
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inx
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jsr draw_recurse
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; draw( bx, by, midx, midy );
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lda X2,X
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sta X1+1,X
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lda Y2,X
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sta Y1+1,X
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lda MIDX,X
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sta X2+1,X
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lda MIDY,X
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sta Y2+1,X
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inx
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jsr draw_recurse
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done_draw_line:
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dex
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rts
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