87 lines
1.7 KiB
ArmAsm
87 lines
1.7 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 X_pos <= X_end, Y_pos <= Y_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 = $08
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D = $0a0b
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;;Set values
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LDA #$00
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STA $FD ; for pixel_draw
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;example values ~~~~~ SHOULD BE PRECOMPILED
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LDA #$00
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STA X_pos
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STA Y_pos
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LDA #$40
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STA X_end
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LDA #$a0
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STA Y_end
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;;~~~~~~~~~~
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;;2*dx = 2*(X_end -X_pos)
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LDA X_end
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SEC
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SBC X_pos
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STA >dx_2
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LDA #$00
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STA <dx_2
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mult_16 >dx_2, <dx_2
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;;dy = (Y_end -Y_pos)
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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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;;D = 2*dx - dy + 2*255. 0 <=D <= 4*255
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;;Our D is bigger then wikipedia to not use negative numbers
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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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;;We wont use dy, only 2*dy from now on
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dy_2 = $0809 ;Lets reuse dy register ($08)
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LDA #$00
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STA <dy_2
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mult_16 >dy_2, <dy_2
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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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INC X_pos
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;; D = D - 2*dx
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Sub_16 >D, <D, >dy_2, <dy_2
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case_2:
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;;D = D + 2*dy
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Add_16 >D, <D, >dx_2, <dx_2
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last:
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JMP for_y
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end:
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.endproc
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