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plasma: more code comments

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This commit is contained in:
Vince Weaver 2021-01-09 23:25:43 -05:00
parent f119774703
commit 2f044a1633
1 changed files with 34 additions and 21 deletions
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49
graphics/gr/plasma/plasma.s
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@ -1,4 +1,4 @@
; do a (hopefully fast) plasma
; do a (hopefully fast) plasma type demo
; 151 -- original
; 137 -- optimize generation
@ -31,12 +31,16 @@ SAVEY = $FF
; Clear screen and setup graphics
;================================
jsr SETGR
bit FULLGR
jsr SETGR ; set lo-res 40x40 mode
bit FULLGR ; make it 40x48
;col = ( 16.0 + (sintable[xx&0xf])
; + 16.0 + (sintable[yy&0xf])
; ) / 2;
; color = ( 8.0 + 8*sin(x) + 8.0 + 8*sin(y) )/2
; becomes
; color = ( 16 + (sintable[xx&0xf]) + (sintable[yy&0xf])) / 2;
; we only create a 16x16 texture, which we pattern across 40x48 screen
create_lookup:
ldy #15
@ -44,7 +48,7 @@ create_yloop:
ldx #15
create_xloop:
clc
lda #15
lda #15 ; 8+8 (but 15 works better)
adc sinetable,X
adc sinetable,Y
lsr
@ -68,8 +72,10 @@ forever_loop:
cycle_colors:
; cycle colors
; X if $FF when arriving here
; can't do palette rotate on Apple II so faking it here
; just incrementing every entry in texture by 1
; X if $FF when arriving here
; ldx #0
inx ; make X 0
cycle_loop:
@ -78,10 +84,12 @@ cycle_loop:
bne cycle_loop
plot_frame:
; set which page
; flip page
; set/flip pages
; we want to flip pages and then draw to the offscreen one
flip_pages:
; ldx #0 ; x already 0
@ -94,7 +102,11 @@ done_page:
eor #$4 ; flip draw page between $400/$800
sta draw_page_smc+1 ; DRAW_PAGE
; plot frame
; plot current frame
; scan whole 40x48 screen and plot each point based on
; lookup table colors
plot_frame:
ldx #47 ; YY=47 (count backwards)
@ -107,19 +119,20 @@ plot_yloop:
asl
sta CTEMP ; save for later
txa
lsr
txa ; get Y in accumulator
lsr ; call actually wants Ycoord/2
php
jsr GBASCALC ; point GBASL/H to address in (A is ycoord)
php ; save shifted-off low bit in C for later
jsr GBASCALC ; point GBASL/H to address in (A is ycoord/2)
; after, A is GBASL, C is clear
lda GBASH
lda GBASH ; adjust to be PAGE1/PAGE2 ($400 or $800)
draw_page_smc:
adc #0
sta GBASH
plp
plp ; restore C, indicating odd/even row
lda #$0f ; setup mask for odd/even line
bcc plot_mask