84 lines
1.8 KiB
ArmAsm
84 lines
1.8 KiB
ArmAsm
;drawing line from 2 cordinates
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.proc line
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;;# (X_pos, Y_pos) #
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;;# * #
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;;# * #
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;;# * #
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;;# (X_end, Y_end) #
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;;NOTE THAT Y_pos <= Y_end, X_pos >= X_end. Min 45deg!
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;;Not values but register position in memory
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X_end = $04
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Y_end = $05
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X_pos = $FC
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Y_pos = $FB
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dx_2 = $0607
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dy = $0c
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V = $0809
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D = $0a0b
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;example values ~~~~~ SHOULD BE PRECOMPILED
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LDA #$60
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STA X_pos
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STA Y_pos
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LDA #$50
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STA X_end
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LDA #$90
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STA Y_end
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;;~~~~~~~~~~
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;We need to clear this memory
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LDA #$00
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STA <V
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STA <dx_2
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STA $FD ; for pixel_draw
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;; V = 2*(dy -dx)
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;; where: dy = Y_pos - Y_end, dx = X_end - X_start
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LDA X_pos
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SEC
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SBC X_end
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STA >V
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STA >dx_2; >dy_2 = dy. Needed for dy_2 (not for V)
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LDA Y_end
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SEC
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SBC Y_pos
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STA dy
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SEC
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SBC >V
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STA >V; <V = dx - dy
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mult_16 >V, <V; V = 2*(dx -dy)
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;dy_2 = dy*2
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mult_16 >dx_2, <dx_2
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;;D = 2*dx - dy + 2*255
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;;Our D is bigger then wikipedia because D is unsigned.
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LDA >dx_2
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STA >D
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LDA <dx_2
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STA <D
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Add_16 >D, <D, #$00, #$01
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Sub_16 >D, <D, dy, #$00
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for_y:
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jsr pixel_draw
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;;Increment Y until Y_pos = Y_end and X_pos = X_end
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INC Y_pos
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LDY Y_pos
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CPY Y_end
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BEQ end
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;;If D < %00000001 11111111 <==> >D ==0, then: case_2
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LDA <D; if <D > 0 then: case_1
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CMP #$00
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BEQ case_2
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case_1:
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DEC X_pos
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Sub_16 >D, <D, >V, <V; D = D - V
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JMP for_y
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case_2:
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Add_16 >D, <D, >dx_2, <dx_2;D = D + 2*dy
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JMP for_y
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end:
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.endproc
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