mirror of
https://github.com/deater/dos33fsprogs.git
synced 2024-11-01 16:04:55 +00:00
243 lines
3.1 KiB
ArmAsm
243 lines
3.1 KiB
ArmAsm
; Bresenham Lines
|
|
|
|
; by Vince `deater` Weaver <vince@deater.net>
|
|
|
|
; based on pseudo-code from
|
|
; https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
|
|
|
|
|
|
|
|
.include "zp.inc"
|
|
.include "hardware.inc"
|
|
|
|
; 174 -- initial
|
|
; 170 -- inline init
|
|
; 166 -- inline step
|
|
; 161 -- merge absolute_value/negative code
|
|
; 159 -- merging init X/Y paths
|
|
; 156 -- more merging X/Y init
|
|
; 154 -- note PLOT doesn't touch Y
|
|
; 152 -- merge into common_inc
|
|
; 151 -- share an RTS
|
|
; 150 -- use X when plotting
|
|
; 147 -- count down instead of up
|
|
; 144 -- mess around with how count set
|
|
; 142 -- who needs COUNT anyway
|
|
; 139 -- inline draw_line
|
|
|
|
B_X1 = $F0
|
|
B_Y1 = $F1
|
|
B_X2 = $F2
|
|
B_Y2 = $F3
|
|
B_DX = $F4
|
|
B_DY = $F5
|
|
B_SX = $F6
|
|
B_SY = $F7
|
|
B_ERR = $F8
|
|
|
|
lines_bot:
|
|
|
|
jsr SETGR ; set lo-res 40x40 mode
|
|
; A=$D0 afterward
|
|
|
|
restart:
|
|
lda #36
|
|
sta B_Y2
|
|
lines_loop:
|
|
pha
|
|
sta B_X2
|
|
sta B_Y1
|
|
|
|
jsr NEXTCOL
|
|
|
|
lda #0
|
|
sta B_X1
|
|
|
|
;====================================
|
|
; inline draw_line
|
|
;====================================
|
|
|
|
|
|
|
|
;============================
|
|
; draw line
|
|
; from x1,y1 to x2,y2
|
|
;============================
|
|
draw_line:
|
|
|
|
; from wikipedia
|
|
|
|
; dx = abs(x2 - x1)
|
|
; sx = x1 < x2 ? 1 : -1
|
|
; dy = -abs(y2 - y1)
|
|
; sy = y1 < y2 ? 1 : -1
|
|
; err = dx+dy
|
|
|
|
init_bresenham:
|
|
|
|
; dx = abs(x2-x1)
|
|
; sx = x1<x2 ? 1 : -1
|
|
|
|
tax ; know this is zero from above
|
|
; ldx #0
|
|
jsr do_abs
|
|
|
|
; dy = -abs(y2-y1)
|
|
; sy = y1 < y2 ? 1 : -1
|
|
|
|
inx
|
|
jsr do_abs
|
|
jsr neg ; dy = -abs(y2-y1)
|
|
|
|
; err = dx+dy
|
|
; B_DY is in A already
|
|
clc
|
|
adc B_DX
|
|
sta B_ERR
|
|
|
|
;======================
|
|
; iterative plot points
|
|
|
|
line_loop:
|
|
|
|
; plot X1,Y1
|
|
|
|
ldy B_X1
|
|
ldx B_Y1
|
|
txa
|
|
jsr PLOT ; PLOT AT Y,A (A colors output, Y preserved)
|
|
|
|
; check if hit end
|
|
|
|
; ldy B_X1
|
|
cpy B_X2
|
|
bne line_no_end
|
|
|
|
; lda B_Y1
|
|
cpx B_Y2
|
|
beq end_inline_draw_line
|
|
line_no_end:
|
|
|
|
;========================
|
|
; step bresenham
|
|
;========================
|
|
|
|
; err2 = 2*err
|
|
lda B_ERR
|
|
asl
|
|
pha ; save err2 for later
|
|
|
|
ldx #0 ; setup for common_inc
|
|
|
|
; if err2 >= dy:
|
|
; err = err + dy
|
|
; x1 = x1 + sx
|
|
|
|
|
|
; B_ERR already in A
|
|
cmp B_DY ; check equal first
|
|
beq do_x
|
|
|
|
clc ; signed compare
|
|
sbc B_DY
|
|
bvc blah2
|
|
eor #$80
|
|
blah2:
|
|
bmi skip_x ; ble
|
|
|
|
do_x:
|
|
lda B_DY
|
|
jsr common_inc
|
|
skip_x:
|
|
|
|
|
|
|
|
inx ; setup common inc
|
|
|
|
; if err2 <= dx:
|
|
; err = err + dx
|
|
; y1 = y1 + sy
|
|
pla ; restore err2
|
|
|
|
clc ; signed compare
|
|
sbc B_DX
|
|
bvc blah
|
|
eor #$80
|
|
blah:
|
|
bpl skip_y
|
|
|
|
do_y:
|
|
lda B_DX
|
|
jsr common_inc
|
|
|
|
skip_y:
|
|
|
|
jmp line_loop
|
|
|
|
;=============================
|
|
;end inline draw_line
|
|
;=============================
|
|
|
|
; jsr draw_line
|
|
|
|
end_inline_draw_line:
|
|
|
|
pla
|
|
sec
|
|
sbc #4 ; update count
|
|
|
|
bpl lines_loop
|
|
bmi restart
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
;=====================================
|
|
; common increment
|
|
;=====================================
|
|
common_inc:
|
|
|
|
clc
|
|
adc B_ERR
|
|
sta B_ERR
|
|
|
|
lda B_X1,X
|
|
clc
|
|
adc B_SX,X
|
|
sta B_X1,X
|
|
done_line:
|
|
rts
|
|
|
|
|
|
;=====================================
|
|
; init, do the abs and sx calculations
|
|
; x=0, for X
|
|
; x=1, for Y
|
|
;=====================================
|
|
do_abs:
|
|
sec
|
|
lda B_X1,X
|
|
sbc B_X2,X ; A = x1 - x2
|
|
|
|
bmi is_neg
|
|
|
|
ldy #$ff
|
|
bmi neg_done
|
|
|
|
is_neg:
|
|
ldy #$1
|
|
neg:
|
|
eor #$ff
|
|
clc
|
|
adc #1
|
|
|
|
neg_done:
|
|
sty B_SX,X
|
|
sta B_DX,X
|
|
rts
|
|
|
|
jmp lines_bot
|