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Re: How to determine a single pixels alpha?

On Sunday, September 30, 2001, at 04:12 PM, Peter Ammon wrote:


Try alpha=*(pixels + [bitmap pixelsWide]*[bitmap samplesPerPixel]*(int)aPoint.y + (int)aPoint.x * [bitmap samplesPerPixel] + 3);

I'm not just picking on Peter here, but how about:

alpha=*(pixels + [bitmap bytesPerRow]*(int)aPoint.y + (int)aPoint.x * [bitmap samplesPerPixel] + 3)

It's not a good idea to assume that bytesPerRow is always equal width*bytesPerPixel. It's also probably not wise to assume that samples==bytes, either, but fixing that is left as an exercise for the reader. ;)

-Ken

Kenneth Dyke, email@hidden (personal), email@hidden (work)
Sr. Mad Scientist, MacOS X OpenGL Group, Apple Computer, Inc.
C++ is to C as Lung Cancer is to Lung

References: 
 >Re: How to determine a single pixels alpha? (From: Peter Ammon <email@hidden>)



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