spiral: update code comments
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@ -10,10 +10,13 @@
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GBASL = $26
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GBASH = $27
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HGR_SCALE = $E7
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HGR_COLLISION = $EA
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HGR_COLLISION = $EA ; overlaps our code, but it's OK
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; as it's modified after the HGR2
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; runs
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HGR_ROTATION = $FE ; IMPORTANT! set this right!
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; we get this for free by loading
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; our code into $E9 in zero page
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; ROM locations
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HGR2 = $F3D8
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HPOSN = $F411
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@ -29,10 +32,14 @@ spiraling_shape:
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; X is left behind by the boot process?
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tiny_loop:
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bit $C030
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bit $C030 ; click the speaker for some sound
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tay ; ldy #0 ; A always 0 here
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ldx #140
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lda #96
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ldx #140 ; center spiral on the screen
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; this is expensive
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lda #96 ; but otherwise doesn't look right
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jsr HPOSN ; set screen position to X= (y,x) Y=(a)
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; saves X,Y,A to zero page
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; after Y= orig X/7
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@ -40,21 +47,33 @@ tiny_loop:
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ldx #<our_shape ; load $E2DF
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ldy #>our_shape ;
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inc HGR_ROTATION
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inc HGR_ROTATION ; rotate the line, also make it larger
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lda #1 ; HGR_ROTATION is HERE ($FE)
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; we also use it for scale
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and #$7f ; cut off before it gets too awful
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sta HGR_SCALE
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jsr XDRAW0 ; XDRAW 1 AT X,Y
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; XDRAW does an exclusive-or shape table
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; draw, so it draws the spiral first, then
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; undraws it on the second pass
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; Both A and X are 0 at exit
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; Z flag set on exit
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; Y varies
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beq tiny_loop ; bra
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our_shape = $E2DF
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; o/~ No way to stop o/~
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our_shape = $E2DF ; location in the Applesoft ROM
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; that holds $11,$F0,$03,$20,$00
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; which makes a nice line in shape table
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; (it points into the code for the FRE()
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; BASIC routine but that's not important)
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