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lovebyte: sierzoom: update the comments to explain things a bit better

This commit is contained in:
Vince Weaver 2021-03-25 18:58:45 -04:00
parent e83a9e6d6c
commit fe720a30fa
1 changed files with 30 additions and 6 deletions
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36
demos/lovebyte2021/sierzoom/sierzoom.s
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@ -1,13 +1,12 @@
; sierpinski-like demo
; 128 byte sierpinski-like rotozoomer intro
; based on the code from Hellmood's Memories demo
; by Vince `deater` Weaver <vince@deater.net>
; for Lovebyte 2021
; the simple sierpinski you more or less just plot
; for a simple sierpinski you more or less just plot
; X AND Y
; Hellmood's you plot something more or less like
; COLOR = ( (Y-(X*T)) & (X+(Y*T) ) & 0xf0
; where T is an incrementing frame value
@ -15,6 +14,30 @@
; to get speed on 6502/Apple II we change the multiplies to
; a series of 16-bit 8.8 fixed point adds
; instead of multiplying X*T and Y*T you know that since you start at 0,0
; they both start at 0, and you can find X*T by just having an XT
; value that starts at 0 and add T to it as you move across the
; screen which is the same result as calculating X*T over and over
; you can do the same thing with Y*T
; t=0;
;
; draw_frame:
;
; y_t=0;
; for(y=0;y<48;y++) {
; y_t+=t;
; x_t=0;
; for(x=0;x<40;x++) {
; color= ((x+y_t) & (y-x_t))&0xf0;
; plot(x,y);
; x_t+=t;
; }
; }
; t++;
; goto draw_frame;
; 140 bytes -- bot demo version
; 137 bytes -- remove & jump
@ -76,7 +99,7 @@ sier_outer:
ldx #0 ; YY starts at 0
stx YY_TL
stx YY_TL ; YY_T also starts at 0
stx YY_TH
sier_yloop:
@ -116,8 +139,9 @@ draw_page_smc:
; reset XX to 0
ldy #0 ; XX
sty XX_TL
ldy #0 ; XX=0
sty XX_TL ; XX_T also 0
sty XX_TH
sier_xloop: