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spiral: more gratuitous code commenting
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@ -6,7 +6,7 @@
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; Lovebyte 2024
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; Spiral plus some bass notes in 31 bytes
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; Spiral plus some bass notes in 31 bytes on Apple II
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; You can enter it directly onto your Apple II with the following:
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; CALL -151
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@ -16,8 +16,6 @@
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; zero page locations
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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 ; overlaps our code, but it's OK
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; as it's modified after the HGR2
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@ -30,52 +28,60 @@ HGR_ROTATION = $FE ; IMPORTANT! set this right!
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HGR2 = $F3D8
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HPOSN = $F411
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XDRAW0 = $F65D
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XDRAW1 = $F661
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HPLOT0 = $F457
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spiraling_shape:
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jsr HGR2 ; Set Hi-resolution (140x192) mode
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; HGR2 means use PAGE2 and no text at bottom
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jsr HGR2 ; Set Hi-resolution (280x192) mode
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; HGR2 means use PAGE2 ($4000)
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; and no text at bottom
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; Y=0, A=0 after this call
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; A and Y are 0 here.
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; X is left behind by the boot process?
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; A and Y are always 0 here.
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; we can't rely on X (left behind by the boot process?)
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tiny_loop:
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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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tay ; set Y to 0 (A always 0 here)
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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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jsr HPOSN ; set screen position to xpos= (Y,X) ypos=(A)
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; so xpos = (Y*256)+X, ypos = (A)
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; as side effect saves X,Y,A to zero page
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; after returning Y = orig X/7
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; A and X are ??
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ldx #<our_shape ; load $E2DF
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ldy #>our_shape ;
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ldx #<our_shape ; load pointer to $E2DF
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ldy #>our_shape ;
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inc HGR_ROTATION ; rotate the line, also make it larger
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lda #1 ; HGR_ROTATION is HERE ($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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sta HGR_SCALE ; and save as SCALE size
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jsr XDRAW0 ; XDRAW 1 AT X,Y
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jsr XDRAW0 ; similary to BASIC 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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; XDRAW0 entry point expects
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; shape poitner in X/Y
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; and rotation in A
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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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beq tiny_loop ; bra (branch always)
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; 1 byte shorter than a JMP
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; o/~ No way to stop o/~
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