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https://github.com/lscharen/iigs-game-engine.git
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65 lines
2.3 KiB
ArmAsm
65 lines
2.3 KiB
ArmAsm
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; A list of dirty tiles that need to be updated in a given frame
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DirtyTileCount ds 2
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DirtyTiles ds TILE_STORE_SIZE ; At most this many tiles can possibly be update at once
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_ClearDirtyTiles
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bra :hop
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:loop
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jsr _PopDirtyTile
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:hop
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lda DirtyTileCount
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bne :loop
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rts
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; Append a new dirty tile record
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;
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; A = result of _GetTileStoreOffset for X, Y
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;
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; The main purpose of this function is to
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;
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; 1. Avoid marking the same tile dirty multiple times, and
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; 2. Pre-calculating all of the information necessary to render the tile
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_PushDirtyTile
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tax
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; alternate entry point if the x-register is already set
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_PushDirtyTileX
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ldal TileStore+TS_DIRTY,x
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bne :occupied2
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inc ; any non-zero value will work
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stal TileStore+TS_DIRTY,x ; and is 1 cycle faster than loading a constant value
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txa
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ldx DirtyTileCount ; 4
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sta DirtyTiles,x ; 6
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inx ; 2
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inx ; 2
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stx DirtyTileCount ; 4 = 18
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rts
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:occupied2
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txa ; Make sure TileStore offset is returned in the accumulator
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rts
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; Remove a dirty tile from the list and return it in state ready to be rendered. It is important
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; that the core rendering functions *only* use _PopDirtyTile to get a list of tiles to update,
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; because this routine merges the tile IDs stored in the Tile Store with the Sprite
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; information to set the TILE_SPRITE_BIT. This is the *only* place in the entire code base that
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; applies this bit to a tile descriptor.
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_PopDirtyTile
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ldy DirtyTileCount
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bne _PopDirtyTile2
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rts
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_PopDirtyTile2 ; alternate entry point
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dey
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dey
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sty DirtyTileCount ; remove last item from the list
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ldx DirtyTiles,y ; load the offset into the Tile Store
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lda #$FFFF
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stal TileStore+TS_DIRTY,x ; clear the occupied backlink
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rts
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