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From: Brian on 22 Mar 2010 07:56
Win32 API and C

I have three stationary overlapping circles on the screen. Their
colours are constantly changing.

To plot the circles I BitBlt each circle into a single bitmap which I
then bitblt onto the screen.

When BitBlt'ing each circle onto the single bitmap I use a raster code
of SRCPAINT. This code OR's the colours in overlapping regions with
the result, for example, that if a red circle partially overlaps a green
circle the overlap region is coloured yellow.

The process I have just described works well, and in the expected
manner, for much of the time, but sometimes the overlap regions are
incorrectly coloured, and also from time to time the colours in the
overlapping regions flicker.

My graphics card is NVidia GeForce4 MX4000, and I have tried compiling
with Visual C++ Version 6 and also with Visual Studio .Net, 2003, with
the same result from both.

I have also tried all the obvious matters, such as providing a pause
between successive BitBlt's, but again this makes no improvement.

Any comments would be gratefull received.

Brian











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