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Old 28 January 2005, 09:47   #9
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Join Date: Dec 2002
Location: England
Posts: 940
Originally Posted by Bamiga2002
Both Slam Tilt & Pinball Illusions don't flicker in hires laced modes when screen is still but when the screen scrolls...aargh! It's not updated correctly, i can see the lines going over each other, producing ugly scrolling effect.
This is caused by the flickerfixer. Basically, each time the screen redraws in interlace mode, only half of the scanlines get drawn. The display alternates between drawing the odd and even lines, whilst the persistence of the display makes it appear that they are both drawn at the same time. So:

Frame 1
1 -----------
3 -----------
5 -----------

Frame 2
2 -----------
4 -----------

The sequence then repeats. The flicker fixer buffers the last frame drawn and sends it to the display with the current frame, thus the entire display is drawn in one pass. However, as the buffered frame is older than the newer frame, it lags behind - hence moving objects seem to tear horizontally, and scrolling looks strange.
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