2020-11-30 12:38:20 +00:00
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; Direct page locations used by the engine
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2021-08-05 13:20:38 +00:00
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ScreenHeight equ 0 ; Height of the playfield in scan lines
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ScreenWidth equ 2 ; Width of the playfield in bytes
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ScreenY0 equ 4 ; First vertical line on the physical screen of the playfield
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ScreenY1 equ 6 ; End of playfield on the physical screen. If the height is 20 and Y0 is
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ScreenX0 equ 8 ; 100, then ScreenY1 = 120.
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ScreenX1 equ 10
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ScreenTileHeight equ 12 ; Height of the playfield in 8x8 blocks
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ScreenTileWidth equ 14 ; Width of the playfield in 8x8 blocks
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StartX equ 16 ; Which code buffer byte is the left edge of the screen. Range = 0 to 167
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StartY equ 18 ; Which code buffer line is the top of the screen. Range = 0 to 207
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EngineMode equ 20 ; Defined the mode/capabilities that are enabled
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; bit 0: 0 = Single Background, 1 = Parallax
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DirtyBits equ 22 ; Identify values that have changed between frames
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BG1DataBank equ 24 ; Data bank that holds BG1 layer data
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BG1AltBank equ 26 ; Alternate BG1 bank
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BlitterDP equ 28 ; Direct page address the holder blitter data
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OldStartX equ 30
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OldStartY equ 32
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LastPatchOffset equ 34 ; Offset into code field that was patched with BRA instructions
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StartXMod164 equ 36
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StartYMod208 equ 38
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BG1StartX equ 40 ; Logical offset of the second background
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BG1StartXMod164 equ 42
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BG1StartY equ 44
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BG1StartYMod208 equ 46
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OldBG1StartX equ 48
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OldBG1StartY equ 50
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BG1OffsetIndex equ 52
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BG0TileOriginX equ 54 ; Coordinate in the tile map that corresponds to the top-left corner
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BG0TileOriginY equ 56
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OldBG0TileOriginX equ 58
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OldBG0TileOriginY equ 60
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BG1TileOriginX equ 62 ; Coordinate in the tile map that corresponds to the top-left corner
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BG1TileOriginY equ 64
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OldBG1TileOriginX equ 66
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OldBG1TileOriginY equ 68
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TileMapWidth equ 70
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TileMapHeight equ 72
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TileMapPtr equ 74
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Next equ 78
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BankLoad equ 128
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blttmp equ 192 ; 32 bytes of local cache/scratch space
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tmp8 equ 224
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tmp9 equ 226
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tmp10 equ 228
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tmp11 equ 230
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tmp12 equ 232
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tmp13 equ 234
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tmp14 equ 236
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tmp15 equ 238
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tmp0 equ 240 ; 16 bytes of temporary space to be used as scratch
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tmp1 equ 242
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tmp2 equ 244
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tmp3 equ 246
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tmp4 equ 248
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tmp5 equ 250
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tmp6 equ 252
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tmp7 equ 254
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DIRTY_BIT_BG0_X equ $0001
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DIRTY_BIT_BG0_Y equ $0002
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DIRTY_BIT_BG1_X equ $0004
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DIRTY_BIT_BG1_Y equ $0008
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