133 lines
2.6 KiB
ArmAsm
133 lines
2.6 KiB
ArmAsm
; Tiny Xdraw
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; repeatedly draws an image from an Apple II shape table
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; can arbitrarily point to any memory location as a source of these
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; some look amazing but depend on random machine state
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; to be deterministic you should probably stick to
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; $E7-$F0 (the program itself)
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; $D000-$FFFF (the ROMs)
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; shapetables are a bit complicated to explain here, but they are a
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; series of bytes ending with a $00
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; (note if you point to a zero, it will be interpreted as an
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; action not an end)
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; each byte specifies up to 3 actions, DRAW + UP DOWN LEFT RIGHT or
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; NODRAW + UP DOWN LEFT RIGHT
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; It is vector scaling with SCALE we hardcode to $20 and rotation
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; which gets set to 0 after the first iteration, (which is
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; why the first shape has arbitrary rotation and gets left)
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; we are xdrawing so it will XOR with the current pixels on the screen
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; NUP=0 UP=4 zz yyy xxx , does xxx yyy zz
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; NRT=1 RT=5
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; NDN=2 DN=6
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; NLT=3 LT=7
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; zero page locations
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HGR_SHAPE = $1A
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HGR_SHAPE2 = $1B
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HGR_BITS = $1C
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GBASL = $26
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GBASH = $27
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A5H = $45
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XREG = $46
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YREG = $47
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; C0-CF should be clear
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; D0-DF?? D0-D5 = HGR scratch?
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HGR_DX = $D0 ; HGLIN
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HGR_DX2 = $D1 ; HGLIN
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HGR_DY = $D2 ; HGLIN
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HGR_QUADRANT = $D3
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HGR_E = $D4
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HGR_E2 = $D5
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HGR_X = $E0
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HGR_X2 = $E1
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HGR_Y = $E2
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HGR_COLOR = $E4
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HGR_HORIZ = $E5
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HGR_SCALE = $E7
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HGR_SHAPE_TABLE = $E8
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HGR_SHAPE_TABLE2= $E9
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HGR_COLLISIONS = $EA
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HGR_ROTATION = $F9
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FRAME = $FC
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XPOS = $FD
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YPOS = $FF
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KEYPRESS = $C000
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KEYRESET = $C010
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; ROM calls
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HGR2 = $F3D8
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HGR = $F3E2
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HPOSN = $F411
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XDRAW0 = $F65D
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XDRAW1 = $F661
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RESTORE = $FF3F
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.zeropage
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.globalzp rot_smc
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tiny_xdraw:
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jsr HGR2 ; Hi-res, full screen ; 3
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; Y=0, A=0 after this call
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; we load at $E7 which is HGR_SCALE, so HGR_SCALE gets
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; the value of the above JSR instruction ($20)
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; A and Y are 0 here.
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; X is left behind by the boot process?
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txa
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jsr HPOSN ; set screen position to X= (y,x) Y=(a)
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; saves X,Y,A to zero page
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; after Y= orig X/7
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; A and X are ??
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tiny_loop:
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; values for shape table
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; Y X
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; 00 E7 = neat
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; 00 EB = OK
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; 00 EF = good
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; F0 01 = cool, let's go with it
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smc2:
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; ldy #$d0 ; point to top byte of shape address
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ldy #$d3 ; point to top byte of shape address
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smc1:
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ldx #$00 ; point to bottom byte of shape address
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; ROT in A
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; this will be 0 2nd time through loop, arbitrary otherwise
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lda #0 ; ROT=0
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jsr XDRAW0 ; XDRAW 1 AT X,Y
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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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lda KEYPRESS
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bpl tiny_loop
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; key pressed
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bit KEYRESET
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jsr HGR2
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inc smc1+1
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bne tiny_loop
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inc smc2+1
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jmp tiny_loop ; bra
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