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477 lines
9.6 KiB
ArmAsm
477 lines
9.6 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 2009-10-25
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; Clips line coordinates to the screen coordinates and calls tgi_line
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;
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.import umul16x16r32, udiv32by16r16
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.import negax
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.include "tgi-kernel.inc"
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.include "zeropage.inc"
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.macpack longbranch
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;----------------------------------------------------------------------------
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; Data
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.bss
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; Outcodes for both ends
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tgi_clip_o1: .res 1
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tgi_clip_o2: .res 1
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; Line deltas
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tgi_clip_d: .res 1
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tgi_clip_dx: .res 2
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tgi_clip_dy: .res 2
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tgi_clip_sign: .res 1
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;----------------------------------------------------------------------------
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; Calculate outcodes for both ends of the line
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;
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.code
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.proc outcode1
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ldy #0
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jsr tgi_outcode
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sta tgi_clip_o1
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rts
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.endproc
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.code
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.proc outcode2
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ldy #<(tgi_clip_y2 - tgi_clip_y1)
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jsr tgi_outcode
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sta tgi_clip_o2
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rts
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.endproc
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;----------------------------------------------------------------------------
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; Negate tgi_clip_dxy
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;
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.code
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.proc negate
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lda tgi_clip_dx,y
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eor #$FF
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clc
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adc #1
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sta tgi_clip_dx,y
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lda tgi_clip_dx+1,y
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eor #$FF
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adc #$00
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sta tgi_clip_dx+1,y
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rts
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.endproc
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;----------------------------------------------------------------------------
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; Calculate the absolute values of dx and dy and store the combined sign in
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; tgi_clip_sign
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;
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.code
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.proc calcdeltas
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lda tgi_clip_x2
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sec
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sbc tgi_clip_x1
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sta tgi_clip_dx
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lda tgi_clip_x2+1
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sbc tgi_clip_x1+1
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sta tgi_clip_dx+1
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sta tgi_clip_sign
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bpl @L1
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ldy #0
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jsr negate
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@L1: lda tgi_clip_y2
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sec
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sbc tgi_clip_y1
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sta tgi_clip_dy
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lda tgi_clip_y2+1
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sbc tgi_clip_y1+1
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sta tgi_clip_dy+1
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eor tgi_clip_sign
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sta tgi_clip_sign
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bit tgi_clip_dy+1
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bpl @L9
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ldy #(tgi_clip_dy - tgi_clip_dx)
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jmp negate
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@L9: rts
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.endproc
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;----------------------------------------------------------------------------
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; Helper routine. Generate the absolute value of y/a and calculate the sign
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; of the final result
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;
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.code
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.proc prepare_coord
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tax ; Remember high byte
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eor tgi_clip_sign
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sta tmp1 ; Sign of result
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tya
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cpx #0 ; Check sign
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bpl @L1
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jsr negax
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@L1: sta ptr1
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stx ptr1+1
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rts
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.endproc
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;----------------------------------------------------------------------------
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; Helper routine. Move the value in eax to ptr1:ptr2
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;
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.code
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.proc move_intermediate_result
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sta ptr1
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stx ptr1+1
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ldy sreg
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sty ptr2
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ldy sreg+1
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sty ptr2+1
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rts
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.endproc
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;----------------------------------------------------------------------------
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; Multiplicate value in y/a by dy, then divide by dx.
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;
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.code
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.proc muldiv_dydx
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; Generate the absolute value of y/a and calculate the sign of the final
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; result
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jsr prepare_coord
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; All values are positive now (dx/dy have been made positive in calcdeltas)
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; and the sign of the final result is on tmp1, so we can use unsigned
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; operations and apply the final result later, after rounding.
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lda tgi_clip_dy
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ldx tgi_clip_dy+1 ; rhs
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jsr umul16x16r32 ; Multiplicate
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; Move the result of the multiplication into ptr1:ptr2
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jsr move_intermediate_result
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; Load divisor and divide
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lda tgi_clip_dx
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ldx tgi_clip_dx+1
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jsr udiv32by16r16
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; Check the sign of the final result and negate it if nessary
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done: bit tmp1
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jmi negax
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rts
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.endproc
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;----------------------------------------------------------------------------
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; Multiplicate value in y/a by dx, then divide by dy.
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;
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.code
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.proc muldiv_dxdy
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; Generate the absolute value of y/a and calculate the sign of the final
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; result
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jsr prepare_coord
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; All values are positive now (dx/dy have been made positive in calcdeltas)
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; and the sign of the final result is on tmp1, so we can use unsigned
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; operations and apply the final result later, after rounding.
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lda tgi_clip_dx
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ldx tgi_clip_dx+1 ; rhs
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jsr umul16x16r32 ; Multiplicate
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; Move the result of the multiplication into ptr1:ptr2
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jsr move_intermediate_result
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; Load divisor and divide
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lda tgi_clip_dy
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ldx tgi_clip_dy+1
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jsr udiv32by16r16
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; Check the sign of the final result and negate it if nessary
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jmp muldiv_dydx::done
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.endproc
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;----------------------------------------------------------------------------
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; Clip a line using Cohen Sutherland
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;
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.code
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.proc tgi_clippedline
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; Set a flag that we have no deltas calculated
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lda #0
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sta tgi_clip_d
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; Generate outcodes
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jsr outcode1
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jsr outcode2
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; if ((tgi_clip_o1 | tgi_clip_o2) == 0) {
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; tgi_line (x1, y1, x2, y2);
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; }
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Loop: lda tgi_clip_o1
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ora tgi_clip_o2
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bne L1
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; Copy the coordinates into ptr1-4 and draw the line
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ldx #7
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L0: lda tgi_clip_x1,x
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sta ptr1,x
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dex
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bpl L0
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jmp tgi_line
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; if ((tgi_clip_o1 & tgi_clip_o2) != 0) reject;
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L1: lda tgi_clip_o1
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and tgi_clip_o2
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beq L2
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rts ; Nothing to draw
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; We must clip. If we haven't already done so, calculate dx/dy.
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L2: lda tgi_clip_d ; Deltas alreay calculated?
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bne HaveDeltas ; Jump if yes
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inc tgi_clip_d
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jsr calcdeltas
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; Check if X1/Y1 needs clipping
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HaveDeltas:
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lda tgi_clip_o1
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jeq L10
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; Need to clip X1/Y1
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lsr a ; Check for TGI_CLIP_LEFT
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bcc L3
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; tgi_clip_y1 += (0 - tgi_clip_x1) * tgi_clip_dy / tgi_clip_dx;
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; tgi_clip_x1 = 0;
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lda #$00
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tax
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beq L4
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L3: lsr a ; Check for TGI_CLIP_RIGHT
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bcc L5
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; tgi_clip_y1 += (tgi_xmax - tgi_clip_x1) * tgi_clip_dy / tgi_clip_dx;
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; tgi_clip_x1 = tgi_xmax;
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lda _tgi_xmax
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ldx _tgi_xmax+1
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L4: tay
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sec
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sbc tgi_clip_x1
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sty tgi_clip_x1
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tay
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txa
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sbc tgi_clip_x1+1
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stx tgi_clip_x1+1
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jsr muldiv_dydx
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clc
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adc tgi_clip_y1
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sta tgi_clip_y1
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txa
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adc tgi_clip_y1+1
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sta tgi_clip_y1+1
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;
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lda tgi_clip_o1
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lsr a
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lsr a
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L5: lsr a ; Check for TGI_CLIP_BOTTOM
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bcc L6
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; tgi_clip_x1 = (0 - tgi_clip_y1) * tgi_clip_dx / tgi_clip_dy;
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; tgi_clip_y1 = 0;
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lda #$00
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tax
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beq L7
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L6: lsr a ; Check for TGI_CLIP_TOP
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bcc L8
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; tgi_clip_x1 += (tgi_ymax - tgi_clip_y1) * tgi_clip_dx / tgi_clip_dy;
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; tgi_clip_y1 = ymax;
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lda _tgi_ymax
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ldx _tgi_ymax+1
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L7: tay
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sec
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sbc tgi_clip_y1
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sty tgi_clip_y1
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tay
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txa
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sbc tgi_clip_y1+1
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stx tgi_clip_y1+1
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jsr muldiv_dxdy
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clc
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adc tgi_clip_x1
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sta tgi_clip_x1
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txa
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adc tgi_clip_x1+1
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sta tgi_clip_x1+1
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; We need to recalculate outcode1 in this case
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L8: jsr outcode1
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; Check if X2/Y2 needs clipping
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L10: lda tgi_clip_o2
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jeq Loop
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; Need to clip X2/Y2
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lsr a ; Check for TGI_CLIP_LEFT
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bcc L11
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; tgi_clip_y2 += (0 - tgi_clip_x2) * tgi_clip_dy / tgi_clip_dx;
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; tgi_clip_x2 = 0;
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lda #$00
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tax
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beq L12
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L11: lsr a ; Check for TGI_CLIP_RIGHT
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bcc L13
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; tgi_clip_y2 += (tgi_xmax - tgi_clip_x2) * tgi_clip_dy / tgi_clip_dx;
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; tgi_clip_x2 = tgi_xmax;
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lda _tgi_xmax
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ldx _tgi_xmax+1
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L12: tay
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sec
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sbc tgi_clip_x2
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sty tgi_clip_x2
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tay
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txa
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sbc tgi_clip_x2+1
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stx tgi_clip_x2+1
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jsr muldiv_dydx
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clc
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adc tgi_clip_y2
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sta tgi_clip_y2
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txa
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adc tgi_clip_y2+1
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sta tgi_clip_y2+1
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;
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lda tgi_clip_o2
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lsr a
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lsr a
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L13: lsr a ; Check for TGI_CLIP_BOTTOM
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bcc L14
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; tgi_clip_x2 += (0 - tgi_clip_y2) * tgi_clip_dx / tgi_clip_dy;
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; tgi_clip_y2 = 0;
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lda #$00
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tax
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beq L15
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L14: lsr a ; Check for TGI_CLIP_TOP
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bcc L16
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; tgi_clip_x2 += (tgi_ymax - tgi_clip_y2) * tgi_clip_dx / tgi_clip_dy;
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; tgi_clip_y2 = tgi_ymax;
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lda _tgi_ymax
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ldx _tgi_ymax+1
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L15: tay
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sec
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sbc tgi_clip_y2
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sty tgi_clip_y2
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tay
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txa
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sbc tgi_clip_y2+1
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stx tgi_clip_y2+1
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jsr muldiv_dxdy
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clc
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adc tgi_clip_x2
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sta tgi_clip_x2
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txa
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adc tgi_clip_x2+1
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sta tgi_clip_x2+1
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; We need to recalculate outcode2 in this case
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L16: jsr outcode2
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; Try again
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jmp Loop
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.endproc
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