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cc65/libsrc/tgi/tgi_clippedline.s

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9.6 KiB
ArmAsm

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