75 lines
1.7 KiB
ArmAsm
75 lines
1.7 KiB
ArmAsm
;;drawing line from 2 cordinates
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.proc line_down_inv
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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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.include "line.inc"; Defines memory positions, ex X_pos
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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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;;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 $FD ; for pixel_draw
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;; V = 2*(dy -dx)
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;; where: dy = Y_end - Y_start, dx = X_end - X_start
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LDA X_end
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SEC
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SBC X_pos
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STA >V
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STA >dx_2; >dx_2 = dx. Needed for dx_2 (not for V)
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LDA Y_end
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SEC
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SBC Y_pos
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STA dy
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SEC
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SBC >V
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STA >V; <V = dy - dx
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mult_16 >V, <V; V = 2*(dy -dx)
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;dx_2 = dx*2
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mult_16 >dx_2, <dx_2
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;;D = 2*dy - dx + 2*255
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;;Our D is bigger then wikipedia because D is unsigned.
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LDA >dx_2
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STA >D
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LDA <dx_2
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STA <D
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Add_16 >D, <D, #$ff, #$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 < %00000010 00000000: case_2
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;;else case 1.
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Lag_16 >D, <D, #$00, #$02, case_2
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case_1:
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INC 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*dx
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JMP for_y
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end:
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RTS
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.endproc
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