Creating a Transparent Bitmap with GDI?

I want to implement a layering system in my application and was thinking of creating a bunch of transparent bitmaps, adding content to them then blitting 开发者_如何学Pythonthem on top of each other, how can this be done without setting each pixel to (0,0,0,0). I'm using Pure win32, not MFC, thanks.

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What do you mean by transparent?

If you are looking for partial (to full) transparency, then AlphaBlend is the GDI API to use. Loading bitmaps with alpha is tricky - The only format the base windows API supports for loading bitmaps with alpha is a 32bpp .BMP file with an alpha channel in the top 8 bits of each byte - and the lower bytes should to be pre-multiplied.

It is possible to use GDI+ to load a variety of image formats with alpha - PNG is probably the best to go for, and blit onto a 32bpp DIBSection so you can use AlphaBlend and plain-old GDI functions.

If you want a simple transparency mask rather than a full alpha channel you can use TransparentBlt along with a color key to mask out areas of a bitmap when blitting it.

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GDI does not support transparency in bitmaps and in general. Consider using GDI+.