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Re: Painter bug? [message #31540 is a reply to message #31538]

Sat, 12 March 2011 19:17

mirek
Messages: 13975
Registered: November 2005

Ultimate Member

I am afraid this is unavoidable problem caused by antialiasing and subpixel accuracy... (and this would appear in most similiar systems. My guess is if you would put something like this to .pdf or .svg, you would get artifact as well).

Think:

At the beggining there is a white color of background - 255,255,255. Now the y is "half" of pixel, so we have to mix the color of polygon with this white with "alpha" 0.5. So if the color is black, there will now be 127, 127, 127 in canvas.

Ok, then paint another polygon, again whe have "half" of pixel, say the color is black, so we again have to apply it with "alpha" 0.5. Result: 64, 64, 64... (but should have been 0,0,0)

So it is a 'feature', not a bug. You have to account for it.

More on this e.g. here (AGG related):

http://thread.gmane.org/gmane.comp.graphics.agg/2359/focus=2 367

Mirek

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