Creating an OpenGL texture with alpha using NSBitmapImageRep

I am loading a PNG using:

theImage = [NSBitmapImageRep imageRepWithContentsOfFile:imagePath];

from which I can successfully create a gl texture and render correctly without any transparency. However, when I switch blending on using:

glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE);

The texture renders with the correct transparent background, but the开发者_运维百科 image colours are incorrect.

I have tried several options in the blend function, GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_DST_ALPHA, etc.

I was taught maybe I need to reorder the bits in the image data, maybe the channels have been mixed up, but I would not expect it to render correctly when blending is off in that case.

Alternatively, I could use libPNG I guess, but I would like to try using a NSBitmapImageRep if it is possible.

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How about supplying a screenshot?

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Anyway, your blending function is wrong either way for simple transparency channel blending. It should be either

• normal alpha: glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)

or

• premultiplied alpha: glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA)