autumn: comment code
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Vince Weaver
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autumn/autumn.s
278
autumn/autumn.s
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@ -1,12 +1,7 @@
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; Autumn, based on the code in Hellmood's Autumn
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; by deater (Vince Weaver) <vince@deater.net>
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; Zero Page
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BASL = $28
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BASH = $29
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H2 = $2C
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;COLOR = $30
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; Zero Page Addresses
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XCOORDL = $F0
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XCOORDH = $F1
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@ -19,155 +14,194 @@ EBP4 = $F7
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COLORL = $F8
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COLORH = $F9
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TEMP = $FA
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TEMPY = $FB
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FRAME = $FC
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TEMPX = $FD
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; Soft Switches
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KEYPRESS= $C000
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KEYRESET= $C010
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SET_GR = $C050 ; Enable graphics
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FULLGR = $C052 ; Full screen, no text
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PAGE0 = $C054 ; Page0
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PAGE1 = $C055 ; Page1
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LORES = $C056 ; Enable LORES graphics
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; ROM routines
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; Some of these are in the Applesoft ROMs so need at least an Apple II+
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; or later to run
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PLOT = $F800 ; plot, horiz=y, vert=A (A trashed, XY Saved)
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SETCOL = $F864
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TEXT = $FB36 ;; Set text mode
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BASCALC = $FBC1
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SETGR = $FB40
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HOME = $FC58 ;; Clear the text screen
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WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
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HLINE = $F819
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TEXT = $FB36 ; Set text mode
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HGR2 = $F3D8 ; Set full-screen hi-res mode using page 2 ($4000)
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; 280x192 6-colors
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HPLOT0 = $F457 ; Plot point, (Y,X) = Horizontal, (A=Vertical)
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HCOLOR = $F6EC ; Set color in X, must be 0..7
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HGR2 = $F3D8
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HPLOT0 = $F457 ; (Y,X) = Horizontal, (A=Vertical)
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HCOLOR = $F6EC ; color in x, must be 0..7
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autumn:
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;===================
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; init screen
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jsr HGR2 ; 3
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ldx #0
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stx XCOORDL
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stx YCOORDL
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stx XCOORDH
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stx YCOORDH
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stx EBP1
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stx EBP2
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stx EBP3
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stx EBP4
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stx COLORH
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; init screen ; Instruction Length
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jsr HGR2 ; 3
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lda #$4f
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sta COLORL
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; init vars to zero. Apple II doesn't clear RAM
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; some of these might not be necessary
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; should make this a loop
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ldx #0 ; 2
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stx XCOORDL ; 2
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stx YCOORDL ; 2
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stx XCOORDH ; 2
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stx YCOORDH ; 2
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stx EBP1 ; 2
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stx EBP2 ; 2
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stx EBP3 ; 2
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stx EBP4 ; 2
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stx COLORH ; 2
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; not necessary? on x86 is probably the
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; result of the VESA BIOS call
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; lda #$4f
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; sta COLORL
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autumn_forever:
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clc
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rol COLORL ; shl %ax
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rol COLORH
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; 16-bit shift of color
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; 2nd is a rotate as asl doesn't shift in cary
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asl COLORL ; 2 ; shl %ax
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rol COLORH ; 2
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ldx XCOORDL
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ldy XCOORDH ; save old X
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; put old X value to X/Y
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; push/pop is 1 byte each but have to get
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; value into accumulator first
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ldx XCOORDL ; 2
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ldy XCOORDH ; 2
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sec
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lda XCOORDL
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sbc YCOORDL ; X=X-Y
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sta XCOORDL
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lda XCOORDH
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sbc YCOORDH
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sta XCOORDH
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; 16-bit subtraction x=x-y
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; need to set carry before subtraction on 6502
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sec ; 1
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lda XCOORDL ; 2
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sbc YCOORDL ; 2
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sta XCOORDL ; 2
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lda XCOORDH ; 2
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sbc YCOORDH ; 2
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sta XCOORDH ; 2
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cmp #$80
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ror XCOORDH ; asr X
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ror XCOORDL
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; 16-bit arithmatic shift right of X
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; 6502 has no asr instruction
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; cmp #$80 sets carry if high bit set
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cmp #$80 ; 2
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ror XCOORDH ; 2
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ror XCOORDL ; 2
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clc
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txa
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adc YCOORDL ; y=y+oldx
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sta YCOORDL
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tya
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adc YCOORDH
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sta YCOORDH
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; 16-bit add, y=y+oldx
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clc ; 1
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txa ; 1
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adc YCOORDL ; 2
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sta YCOORDL ; 2
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tya ; 2
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adc YCOORDH ; 2
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sta YCOORDH ; 2
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cmp #$80
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ror YCOORDH ; asr Y
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ror YCOORDL
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; 16-bit arithmatic shift right of y-coord
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cmp #$80 ; 2
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ror YCOORDH ; 2
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ror YCOORDL ; 2
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; 32 bit rotate of low bit of Y
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ror EBP1
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ror EBP2
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ror EBP3
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ror EBP4 ; ror bottom bit of Y through 32 bits
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; 32 bit rotate of low bit shifted out of Y-coordinate
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ror EBP1 ; 2
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ror EBP2 ; 2
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ror EBP3 ; 2
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ror EBP4 ; 2
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bcs label_11f
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; branch if carry set
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bcs label_11f ; 2
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clc
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lda COLORL
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adc #1
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sta COLORL
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lda COLORH
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adc #0
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sta COLORH
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; 16-bit increment of color
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; no need to clear carry as we wouldn't be
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; here if it wasn't
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inc COLORL ; 2
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bne no_oflo ; 2
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inc COLORH ; 2
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no_oflo:
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clc
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lda XCOORDL
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adc #$80
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sta XCOORDL ; X+=0x80
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lda XCOORDH
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adc #$0
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sta XCOORDH
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; 16-bit add of X-coord by 0x80
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; this keeps the drawing roughly to the 280x192 screen
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; carry should still be clear (inc doesn't set it)
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lda XCOORDL ; 2
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adc #$80 ; 2
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sta XCOORDL ; 2
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lda XCOORDH ; 2
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adc #$0 ; 2
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sta XCOORDH ; 2
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sec
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lda YCOORDL
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eor #$FF
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adc #$0 ; Y=-Y
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sta YCOORDL
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lda YCOORDH
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eor #$FF
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adc #$0
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sta YCOORDH
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; 16-bit negate of Y-coord
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sec ; 1
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lda YCOORDL ; 2
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eor #$FF ; 2
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adc #$0 ; 2
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sta YCOORDL ; 2
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lda YCOORDH ; 2
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eor #$FF ; 2
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adc #$0 ; 2
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sta YCOORDH ; 2
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label_11f:
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; lda COLOR
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; and #$fc
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; eor #$12
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; sta COLOR
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; skipping the color manipulation done here by original
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lda YCOORDH
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bmi autumn_forever ; if negative, loop
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; if ycoord negative, loop
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lda YCOORDH ; 2
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bmi autumn_forever ; 2
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; if top bits of xcoord, loop
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lda XCOORDH ; 2
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and #$f0 ; 2
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bne autumn_forever ; 2
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lda XCOORDH
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and #$f0
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bne autumn_forever
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put_pixel:
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lda COLORL
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and #$7
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beq black1
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cmp #$4
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bne not_black2
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lda #$5
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bne not_black2
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black1:
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lda #$1
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; get color mapping
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; using lookup table for now whil trying to find best
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lda COLORL ; 2
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and #$7 ; 2
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tay ; 1
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ldx color_lookup,Y ; 3 (could be 2 if we had in zero page)
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not_black2:
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tax
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jsr HCOLOR
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; actually set the color
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jsr HCOLOR ; 3
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ldx XCOORDL
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ldy XCOORDH
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lda YCOORDL
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jsr HPLOT0
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; set up paramaters for HPLOT call
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ldx XCOORDL ; 2
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ldy XCOORDH ; 2
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lda YCOORDL ; 2
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jsr HPLOT0 ; 3
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jmp autumn_forever ; 3
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lda KEYPRESS ; 3 ; see if key pressed
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; bpl autumn_forever ; loop if not
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bmi exit_to_prompt ; 2 ; jump target too far away
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jmp autumn_forever ; 3 ; if we get under 128 bytes
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; can use the smaller jump
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exit_to_prompt:
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jsr TEXT ; 3 ; return to text mode
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jmp $3D0 ; 3 ; return to Applesoft prompt
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; Apple II Hi-Res Colors
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; It's all NTSC artifacting and complex
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; There can be color-class at a 3.5 pixel level
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; And adjacent on pixels make white, adjacent off make black
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; Simplistic summary, you can have these 8 colors (6 unique)
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; 0 = Black0
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; 1 = Green
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; 2 = Purple
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; 3 = White0
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; 4 = Black1
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; 5 = Orange
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; 6 = Blue
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; 7 = White2
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color_lookup:
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; my default, colorful palette
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; .byte $01,$01,$02,$03, $05,$05,$06,$07
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; orange and gren palette
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.byte $01,$01,$03,$05, $05,$05,$01,$07
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; "Leaves"
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; TOP-LEFT ?? CENTER-TOP TOP-RIGHT LEFT ?? CENTER-BOTTOM ??
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