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