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hgr: lines: got 16-bit bresenham working

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This commit is contained in:
Vince Weaver 2021-07-27 15:29:08 -04:00
parent 87b44bb7f3
commit 068ed6a85b
1 changed files with 88 additions and 36 deletions
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124
graphics/hgr/lines/lines.s
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@ -10,7 +10,14 @@
HGR_COLOR = $E4
HGR_PAGE = $E6
X1_L = $A0
X1_H = $A1
Y1 = $A2
X2_L = $A3
X2_H = $A4
Y2 = $A5
B_ERR2_L = $EE
B_ERR2_H = $EF
B_X1_L = $F0
B_X1_H = $F1
B_Y1 = $F2
@ -56,31 +63,31 @@ reset:
ldx #0
stx COUNT
stx B_X1_H
stx B_X1_L
stx B_Y1
stx X1_H ; 0:0,0
stx X1_L
stx Y1
stx B_X2_H
stx B_X2_L
stx X2_H ; 0:0,191
stx X2_L
lda #191
sta B_Y2
sta Y2
left_lines_loop:
jsr draw_line
lda B_Y1
lda Y1
clc
adc #8
sta B_Y1
sta Y1
lda B_X2_L ; 280/24 = 140/12 = 70/6 = 11
lda X2_L ; 280/24 = 140/12 = 70/6 = 11
clc
adc #11
sta B_X2_L
sta X2_L
bcc noc
inc B_X2_H
inc X2_H
noc:
inc COUNT
inc FRAME
@ -100,28 +107,28 @@ end:
; want x2,y2 to go from 264,192 to 264,0
ldx #0
stx B_Y1
stx Y1
ldx B_X2_L
stx B_X1_L
ldx B_X2_H
stx B_X1_H
ldx X2_L
stx X1_L
ldx X2_H
stx X1_H
right_lines_loop:
jsr draw_line
lda B_Y2
lda Y2
sec
sbc #8
sta B_Y2
sta Y2
lda B_X1_L
lda X1_L
sec
sbc #11
sta B_X1_L
sta X1_L
bcs noc2
dec B_X1_H
dec X1_H
noc2:
dec COUNT
inc FRAME
@ -147,6 +154,20 @@ draw_line:
jsr HCOLOR1 ; set color
lda X1_L
sta B_X1_L
lda X1_H
sta B_X1_H
lda Y1
sta B_Y1
lda X2_L
sta B_X2_L
lda X2_H
sta B_X2_H
lda Y2
sta B_Y2
; from wikipedia
@ -202,7 +223,7 @@ do_abs_y:
lda B_Y1
sbc B_Y2 ; A = y1 - y2
sta B_DY_L
lda #0
lda #0 ; need to sign extend?
sbc #0
sta B_DY_H
@ -216,6 +237,7 @@ yneg:
adc #1
sta B_DY_L
lda B_DY_H
eor #$ff
adc #0
sta B_DY_H
@ -272,24 +294,30 @@ line_no_end:
; err2 = 2*err
lda B_ERR_L
asl
rol B_ERR_H
sta B_ERR2_L
lda B_ERR_H
sta B_ERR2_H
clc
rol B_ERR2_L
rol B_ERR2_H
; if err2 >= dy:
; err = err + dy
; x1 = x1 + sx
; http://6502.org/tutorials/compare_beyond.html#5
; 16 bit signed compare
lda B_ERR_L ; ERR2-DY
lda B_ERR2_L ; ERR2-DY
cmp B_DY_L
lda B_ERR_H
lda B_ERR2_H
sbc B_DY_H
bvc blah
eor #$80 ; N eor V
blah:
bmi check_dx
bmi check_dx ; branch if less than
; FIXME: convert ERR2 back to ERR
; err = err + dy
clc
lda B_ERR_L
@ -299,28 +327,50 @@ blah:
adc B_DY_H
sta B_ERR_H
lda B_X1_L
adc B_SX
; x1 = x1 + sx
clc
lda B_SX
bmi x1_neg
x1_pos:
adc B_X1_L
sta B_X1_L
lda B_X1_H
adc #0
sta B_X1_H
jmp check_dx
x1_neg:
adc B_X1_L
sta B_X1_L
lda B_X1_H
adc #$ff
sta B_X1_H
check_dx:
; if err2 <= dx:
; err = err + dx
; y1 = y1 + sy
lda B_DX_L
cmp B_ERR2_L
bne check_less
lda B_DX_H
cmp B_ERR2_H
beq doit
check_less:
; 16 bit signed compare
lda B_ERR_L ; ERR2-DX
cmp B_DX_L
lda B_ERR_H
sbc B_DX_H
lda B_DX_L
cmp B_ERR2_L
lda B_DX_H
sbc B_ERR2_H
bvc blah2
eor #$80 ; N eor V
blah2:
bmi skip_y
bmi skip_y ; if minus than dx<err2 (i.e. err2>=dx)
; err = err + dx
doit:
clc
lda B_ERR_L
adc B_DX_L
@ -329,6 +379,8 @@ blah2:
adc B_DX_H
sta B_ERR_H
; y1 = y1 + sy
clc
lda B_Y1
adc B_SY
sta B_Y1