Applecorn/FDRAW.CIRCLE.S

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2021-09-18 01:06:24 +00:00
********************************
* *
* Fast Apple II Graphics *
* By Andy McFadden *
* Version 0.3, Aug 2015 *
* *
* Circle rendering *
* (Included by FDRAW.S) *
* *
* Developed with Merlin-16 *
* *
********************************
* TODO: if USE_FAST is 0, replace the outline circle
* plot code with calls to DrawPoint (or maybe a
* common sub-function so we don't trash the input
* parameters). Saves a little space.
********************************
*
* Draw a circle. The radius is in in_rad, and
* the center is at in_x0l+in_x0h,in_y0.
*
********************************
DrawCircle
lda #$20 ;JSR
cmp _cp08 ;configured for outline?
beq :okay
jsr fixcplot
:okay
jmp calc_circle
********************************
*
* Draw filled circle.
*
********************************
FillCircle
lda #$2c ;BIT
cmp _cp08 ;configured for fill?
beq :okay
jsr fixcplot
:okay
jsr calc_circle
jmp FillRaster
* Calculate a circle, using Bresenham's algorithm. The
* results are placed into the rasterization buffers.
*
* in_rad must be from 0 to 255. The x/y center
* coordinates must be on the screen, but the circle
* can extend off the edge.
*
* The computed values are stored in the rasterization
* tables. For an outline circle, we also plot the
* points immediately.
do USE_FAST ;*****
* local storage -- not used often enough to merit DP
circ_8bit ds 1
circ_clip ds 1
fin ;*****
calc_circle
max_fast_rad equ 41
]cxl equ zloc0
]cxh equ zloc1
]cy equ zloc2
]dlo equ zloc3
]dhi equ zloc4
]xsav equ zloc5
]ysav equ zloc6
]min_x equ zloc7 ;min/max offsets from center
]max_x equ zloc8 ;(min is above center, max
]min_y equ zloc9 ; is below)
]max_y equ zloc10
]hitmp equ zloc11
* only used by hplot for outline circles
]hbasl equ zptr0
]andmask equ zloc11 ;overlaps with ]hitmp
]savxreg equ zloc12
]savyreg equ zloc13
* Special-case radius=0. It removes an annoying
* edge case (first y-- becomes 0xff, but 6502 cmp
* is unsigned).
lda in_rad
bne :notzero
ldy in_y0
sty rast_top
sty rast_bottom
lda in_x0l
sta rastx0l,y
sta rastx1l,y
lda in_x0h
sta rastx0h,y
sta rastx1h,y
rts
* Use different version of function for small
* circles, because we can do it all in 8 bits.
:notzero
do USE_FAST ;*****
ldy #$01
cmp #max_fast_rad ;in_rad in Acc
blt :use_fast
dey
:use_fast sty circ_8bit
fin ;*****
lda in_x0l ;copy center to DP for speed
sta ]cxl
lda in_x0h
sta ]cxh
lda in_y0
sta ]cy
* Compute min/max values, based on offset from center.
* These are compared against offset-from-center x/y.
* We need tight bounds on Y because we use it to
* compute the rast_render top/bottom. Getting tight
* bounds on X is not so important, but we still need
* it for the no-clip optimization.
ldx #$04 ;count edges needing clip
lda #NUM_ROWS-1 ;191
sec
sbc ]cy ;maxY = 191-cy
cmp in_rad
blt :ylimok
lda in_rad ;clamp to radius
dex
:ylimok sta ]max_y ;maxY = 191-cy
lda ]cy ;minY = cy
cmp in_rad
blt :ylimok2
lda in_rad ;clamp to radius
dex
:ylimok2 sta ]min_y
lda ]cxh
beq :xlimlo
* Examples (note #<NUM_COLS-1 is 279-256 = 23):
* cx=265 (cxh=1 cxl=11), 23-11=14, chk rad
lda #<NUM_COLS-1 ;maxX = 279-cx
sec
sbc ]cxl
cmp in_rad
blt :xlimhok
lda in_rad ;clamp to radius
dex
:xlimhok sta ]max_x
lda in_rad ;min X always out of range
dex ; so just clamp to radius
sta ]min_x
jmp :xlimdone
* Examples:
* For cx=0 to 24, we can never pass right edge (our
* maximum radius is 255).
* cx=3, 23-3=20 + carry set --> bad, must use rad
* cx=24, 23-24=255 + carry clear --> ok, chk rad
* cx=255, 23-255=24 + carry clear --> ok, chk rad
:xlimlo
lda #<NUM_COLS-1 ;maxX = 279-cx
sec
sbc ]cxl
bcs :xuserad
cmp in_rad
blt :xlimok
:xuserad lda in_rad ;clamp to radius
dex
:xlimok sta ]max_x
lda ]cxl ;minX = (cx > 255) ?
cmp in_rad
blt :xlimok2
lda in_rad ;clamp to radius
dex
:xlimok2 sta ]min_x
:xlimdone
do USE_FAST ;*****
stx circ_clip
fin ;*****
* set top/bottom rows for rasterizer
lda ]cy
clc
adc ]max_y
sta rast_bottom
lda ]cy
sec
sbc ]min_y
sta rast_top
DO 0 ;debug debug debug
LDA ]min_x ;save a copy where the
STA $0380 ; monitor won't trash it
LDA ]max_x
STA $0381
LDA ]min_y
STA $0382
LDA ]max_y
STA $0383
FIN
* Set initial conditions for Bresenham.
ldx #0 ;:x = 0
stx ]xsav
ldy in_rad ;:y = rad
sty ]ysav
lda #1 ;:d = 1 - rad
sec
sbc ]ysav ;in_rad
sta ]dlo
bcs :hizero ;C==1 if in_rad<=1
ldx #$ff ;C was 0, make neg
:hizero stx ]dhi
*
* Outer loop -- plot 8 points, then update values.
*
circ_loop
do USE_FAST ;*****
lda circ_clip
beq ncypy
jmp with_clip
* Quick version, no clipping required
* row cy+y: cx-x and cx+x
ncypy
lda ]ysav
clc
adc ]cy
tay ;y-coord in Y-reg
lda ]cxl
sec
sbc ]xsav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp00 jsr cplotl
lda ]cxl
clc
adc ]xsav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp01 jsr cplotrn
* row cy-y: cx-x and cx+x
ncymy
lda ]cy
sec
sbc ]ysav
tay ;y-coord in Y-reg
lda ]cxl
sec
sbc ]xsav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp02 jsr cplotl
lda ]cxl
clc
adc ]xsav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp03 jsr cplotrn
* row cy+x: cx-y and cx+y
ncypx
lda ]xsav ;off bottom?
clc
adc ]cy
tay ;y-coord in Y-reg
lda ]cxl
sec
sbc ]ysav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp04 jsr cplotl
lda ]cxl
clc
adc ]ysav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp05 jsr cplotrn
* row cy-x: cx-y and cx+y
ncymx
lda ]cy
sec
sbc ]xsav
tay ;y-coord in Y-reg
lda ]cxl
sec
sbc ]ysav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp06 jsr cplotl
lda ]cxl
clc
adc ]ysav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp07 jsr cplotrn
* CLICK
jmp circ_plot_done
fin ;***** (USE_FAST)
*
* Same thing, but this time clipping edges.
*
with_clip
* row cy+y: cx-x and cx+x
ccypy
lda ]ysav ;off bottom?
cmp ]max_y
beq :cypy_ok
bge cypy_skip ;completely off screen
:cypy_ok clc
adc ]cy
tay ;y-coord in Y-reg
ldx ]xsav ;handle cx-x
cpx ]min_x
blt :cxmx_ok
beq :cxmx_ok
lda #0 ;clip at 0
sta rastx0l,y
sta rastx0h,y
beq cxmx_done0 ;always
BREAK
:cxmx_ok lda ]cxl
sec
sbc ]xsav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp08 jsr cplotl
cxmx_done0
cpx ]max_x ;handle cx+x
blt :cxpx_ok
beq :cxpx_ok
lda #<NUM_COLS-1
sta rastx1l,y
lda #>NUM_COLS-1
sta rastx1h,y
bne cxpx_done0 ;always
BREAK
:cxpx_ok lda ]cxl
clc
adc ]xsav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp09 jsr cplotr
cxpx_done0
cypy_skip
* row cy-y: cx-x and cx+x
ccymy
lda ]ysav ;off top?
cmp ]min_y
beq :cymy_ok
bge cymy_skip
:cymy_ok lda ]cy
sec
sbc ]ysav
tay ;y-coord in Y-reg
ldx ]xsav ;handle cx-x
cpx ]min_x
blt :cxmx_ok
beq :cxmx_ok
lda #0 ;clip at 0
sta rastx0l,y
sta rastx0h,y
beq cxmx_done1 ;always
BREAK
:cxmx_ok lda ]cxl
sec
sbc ]xsav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp10 jsr cplotl
cxmx_done1
cpx ]max_x ;handle cx+x
blt :cxpx_ok
beq :cxpx_ok
lda #<NUM_COLS-1
sta rastx1l,y
lda #>NUM_COLS-1
sta rastx1h,y
bne cxpx_done1 ;always
BREAK
:cxpx_ok lda ]cxl
clc
adc ]xsav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp11 jsr cplotr
cxpx_done1
cymy_skip
* row cy+x: cx-y and cx+y
ccypx
lda ]xsav ;off bottom?
cmp ]max_y
beq :cypx_ok
bge cypx_skip
:cypx_ok clc
adc ]cy
tay ;y-coord in Y-reg
ldx ]ysav ;handle cx-y
cpx ]min_x
blt :cxmy_ok
beq :cxmy_ok
lda #0 ;clip at 0
sta rastx0l,y
sta rastx0h,y
beq cxmy_done2 ;always
BREAK
:cxmy_ok lda ]cxl
sec
sbc ]ysav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp12 jsr cplotl
cxmy_done2
cpx ]max_x ;handle cx+y
blt :cxpy_ok
beq :cxpy_ok
lda #<NUM_COLS-1
sta rastx1l,y
lda #>NUM_COLS-1
sta rastx1h,y
bne cxpy_done2 ;always
BREAK
:cxpy_ok lda ]cxl
clc
adc ]ysav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp13 jsr cplotr
cxpy_done2
cypx_skip
* row cy-x: cx-y and cx+y
ccymx
lda ]xsav ;off top?
cmp ]min_y
beq :cymx_ok
bge cymx_skip
:cymx_ok lda ]cy
sec
sbc ]xsav
tay ;y-coord in Y-reg
ldx ]ysav ;handle cx-y
cpx ]min_x
blt :cxmy_ok
beq :cxmy_ok
lda #0 ;clip at 0
sta rastx0l,y
sta rastx0h,y
beq cxmy_done3 ;always
BREAK
:cxmy_ok lda ]cxl
sec
sbc ]ysav
sta rastx0l,y
lda ]cxh
sbc #$00
sta rastx0h,y
_cp14 jsr cplotl
cxmy_done3
cpx ]max_x ;handle cx+y
blt :cxpy_ok
beq :cxpy_ok
lda #<NUM_COLS-1
sta rastx1l,y
lda #>NUM_COLS-1
sta rastx1h,y
bne cxpy_done3 ;always
BREAK
:cxpy_ok lda ]cxl
clc
adc ]ysav
sta rastx1l,y
lda ]cxh
adc #$00
sta rastx1h,y
_cp15 jsr cplotr
cxpy_done3
cymx_skip
circ_plot_done
* Update X/Y/D. Up to about radius=41 we can maintain
* 'd' in an 8-bit register.
do USE_FAST ;*****
lda circ_8bit
beq circ_slow
*
* Bresenham update, with 8-bit 'd'.
*
ldx ]xsav
lda ]dlo
bmi :dneg
txa ;:d = d + ((x-y)*4) +5
sec
sbc ]ysav ;x <= y, may be neg or 0
asl
asl
clc ;can't know carry
adc #5
clc ;still don't want carry
adc ]dlo
sta ]dlo
dec ]ysav ;:y--
jmp :loopbot
:dneg txa ;:d = d + (x*4) +3
asl
asl ;x always pos, C=0
DO 0
BCC :TEST ;debug
BREAK ;debug
:TEST ;debug
FIN
adc #3
adc ]dlo
sta ]dlo
:loopbot
inx ;:x++
stx ]xsav
cpx ]ysav
beq :again
bge circ_done
:again jmp circ_loop
fin ;*****
*
* Bresenham update, with 16-bit 'd'
*
circ_slow
CLICK
ldx ]xsav
lda ]dhi
bmi :dneg
lda ]dlo
clc
adc #5
sta ]dlo
bcc :noinc
inc ]dhi
:noinc
txa ;:d = d + ((x-y)*4) +5
ldy #$00
sty ]hitmp
sec
sbc ]ysav ;x <= y, may be neg or 0
beq :xeqy ;if x==y, nothing to add
ldy #$ff
sty ]hitmp
asl
rol ]hitmp
asl
rol ]hitmp
clc
adc ]dlo
sta ]dlo
lda ]dhi
adc ]hitmp
sta ]dhi
:xeqy
dec ]ysav ;:y--
jmp :loopbot
:dneg lda ]dlo ;:d = d + (x*4) + 3
clc
adc #3
sta ]dlo
bcc :noinc2
inc ]dhi
:noinc2 txa
ldy #0 ;x always positive
sty ]hitmp
asl
rol ]hitmp
asl
rol ]hitmp
clc ;not needed?
adc ]dlo
sta ]dlo
lda ]dhi
adc ]hitmp
sta ]dhi
:loopbot
inx ;:x++
stx ]xsav
cpx ]ysav
beq :again
bge circ_done
:again jmp circ_loop
circ_done rts
* Plot a point for outline circle rendering.
*
* X and Y must be preserved. Y holds the current line
* number.
*
* Most DP locations are in use -- see the variable
* declarations at the start of the circle function.
* cplotl is the entry point for the leftmost point.
cplotl
stx ]savxreg
sty ]savyreg
lda ylooklo,y
sta ]hbasl
lda ylookhi,y
_pg_or2 ora #$20
sta ]hbasl+1
* Convert the X coordinate into byte/bit.
ldx rastx0l,y ;x coord, lo
lda rastx0h,y ;>= 256?
beq :lotabl ;no, use the low table
ldy div7hi,x
lda mod7hi,x
bpl cplotcom ;always
BREAK ;debug
:lotabl ldy div7lo,x
lda mod7lo,x
jmp cplotcom
* cplotr is the entry point for the rightmost point.
* We use rastx1 instead of rastx0.
cplotr
lda ylooklo,y
sta ]hbasl
lda ylookhi,y
_pg_or3 ora #$20
sta ]hbasl+1
* If we just plotted the left point on the same line,
* we can skip the Y-lookup by jumping here.
cplotrn
stx ]savxreg
sty ]savyreg
ldx rastx1l,y ;x coord, lo
lda rastx1h,y ;>= 256?
beq :lotabl ;no, use the low table
ldy div7hi,x
lda mod7hi,x
bpl cplotcom ;always
BREAK ;debug
:lotabl ldy div7lo,x
lda mod7lo,x
* Plot the point. The byte offset (0-39) is in Y,
* the bit offset (0-6) is in A.
cplotcom
tax
lda colorline,y ;start with color pattern
eor (]hbasl),y ;flip all bits
and andmask,x ;clear other bits
eor (]hbasl),y ;restore ours, set theirs
sta (]hbasl),y
ldx ]savxreg
ldy ]savyreg
rts
* Reconfigure calc_circle to either JSR to cplotl/r,
* or just BIT the address (a 4-cycle no-op). The
* desired instruction is in A.
fixcplot
do USE_FAST ;*****
sta _cp00
sta _cp01
sta _cp02
sta _cp03
sta _cp04
sta _cp05
sta _cp06
sta _cp07
fin ;*****
sta _cp08
sta _cp09
sta _cp10
sta _cp11
sta _cp12
sta _cp13
sta _cp14
sta _cp15
rts