pandocs icon indicating copy to clipboard operation
pandocs copied to clipboard

Get Tile step during the FIFO needs correction / improvement

Open datapaganism opened this issue 4 years ago • 1 comments

If the current tile is a window tile, the X coordinate for the window tile is used, otherwise the following formula is used to calculate the X coordinate: ((SCX / 8) + fetcher’s X coordinate) & $1F. Because of this formula, fetcherX can be between 0 and 31.

fetcher's X and fetcherX are too similar and cause confusion.

Suggestion : rename fetcher's X coordinate to X_tile_number or something similar. Also provide a range, since it is not inferred from the variable name, i.e. 0 - 31 (fetcher's X advances once every 8 pixel fetch).

If the current tile is a window tile, the Y coordinate for the window tile is used, otherwise the following formula is used to calculate the Y coordinate: (currentScanline + SCY) & 255. Because of this formula, fetcherY can be between 0 and 159.

currentScanline (same as LY?) ranges between 0 - 143 (visable), SCY ranges between 0 - 255, fetcherY therefore must be between 0 and 255 instead of 159.

Suggestion : change the range of fetcherY

datapaganism avatar Oct 12 '21 16:10 datapaganism

Note: being covered by my reworking of this article.

ISSOtm avatar Oct 12 '21 17:10 ISSOtm