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kieranhj / pop-beeb

Prince of Persia port to BBC Master
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Graphical glitch with falling floor #45

Closed kieranhj closed 6 years ago

kieranhj commented 6 years ago

On first screen, when the falling floor drops there are a couple of pixels that end up different between the two buffers, so flicker on & off.

Not sure what is causing this as all wipes etc. are supposed to last two frames to cover this. Needs investigating.

kieranhj commented 6 years ago

Suspect this is something to do with masking and the plot with AND functions.

kieranhj commented 6 years ago

Turns out it was nothing to do with the AND plot functions and actually two bugs in one.

Firstly the FAST STA and AND functions weren't plotting correctly if there had been a previous CROP. (This only happens because on Beeb the regular STA & AND lay functions are diverted to the FAST implementation, which is different to Apple II.)

Secondly there was a tiny cut & paste error with one of the sprites in the Dungeon BG set - turns out one of the frames that appears to be a duplicate is actually one line smaller (but then fixed in code) for reasons that only Jordan will know!!