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lovebyte: sierzoom: more comments
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@ -1,4 +1,5 @@
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; 128 byte sierpinski-like rotozoomer intro
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; 122 byte sierpinski-like rotozoomer intro
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; for Apple II lo-res 40x48 mode
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; based on the code from Hellmood's Memories demo
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; by Vince `deater` Weaver <vince@deater.net>
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@ -92,8 +93,8 @@ sier:
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bit LORES ; drop down to lo-res
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; lda #0 ; start with multiplier 0
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; sta T_L
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; sta T_H
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; sta T_L ; since we are executing in zero page we
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; sta T_H ; don't need to init these
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sier_outer:
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@ -105,8 +106,8 @@ sier_outer:
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sier_yloop:
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; calc YY_T (8.8 fixed point add)
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; save space by skipping clc as it's only a slight variation w/o
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; clc
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; clc ; save byte by ignoring carry (slightly
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; changes results but not by much)
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lda YY_TL
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adc T_L
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sta YY_TL
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@ -114,21 +115,15 @@ sier_yloop:
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adc T_H
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sta YY_TH
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txa ; YY ; plot call needs Y/2
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txa ; YY ; plot call needs Y/2
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lsr
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php
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php ; save the bit we shifted into carry
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; bcc even_mask
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; ldy #$f0
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; .byte $2C ; bit hack
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;even_mask:
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; ldy #$0f
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; sty MASK
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jsr GBASCALC ; take Y-coord/2 in A, put address in GBASL/H
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; ( A trashed, C clear)
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jsr GBASCALC ; take Y-coord/2 in A, put address in GBASL/H ( a trashed, C clear)
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lda GBASH
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lda GBASH ; adjust GBASH for draw page
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draw_page_smc:
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adc #0
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sta GBASH ; adjust for PAGE1/PAGE2 ($400/$800)
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@ -150,15 +145,16 @@ sier_xloop:
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; SAVED = XX+(Y*T)
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; clc
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tya ; XX
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adc YY_TH
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sta SAVED
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; clc ; skip setting carry to save byte
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tya ; XX lives in Y
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adc YY_TH
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sta SAVED ; save XX+YY_T
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; calc XX*T
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; clc
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lda XX_TL
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; clc ; skip setting carry to save byte
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lda XX_TL ; XX_T=XX_T+T
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adc T_L
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sta XX_TL
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lda XX_TH
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@ -167,7 +163,7 @@ sier_xloop:
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; calc (YY-X_T)
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txa ; lda YY
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txa ; YY lives in X
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sec
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sbc XX_TH
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@ -207,7 +203,7 @@ blah_smc:
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inc T_H
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no_carry:
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; speed up the zoom as it goes
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; speed up the zoom as time goes on
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inc blah_smc+1
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@ -223,7 +219,8 @@ done_page:
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eor #$4 ; flip draw page between $400/$800
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sta draw_page_smc+1 ; DRAW_PAGE
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jmp sier_outer ; what can we branch on?
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jmp sier_outer ; can't guarantee a flag value for a 2-byte
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; branch :(
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T_L: .byte $00
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T_H: .byte $00
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