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I need to imitate Photoshop blending modes ("multiply", "screen" etc.) in my OpenGL ES 1.1 code (without shaders).

There are some docs on how to do this with HLSL:

I need at least working Screen mode.

Are there any implementations on fixed pipeline I may look at?

bobobobo
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Alexander Gladysh
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    [This](http://www.pegtop.net/delphi/articles/blendmodes/) page has _a lot_ of detail on how each blend mode works (with diagrams) – bobobobo Apr 04 '13 at 23:22

4 Answers4

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Most photoshop blend-modes are based upon the Porter-Duff blendmodes.

These requires that all your images (textures, renderbuffer) are in premultiplied color-space. This is usually done by multiplying all pixel-values with the alpha-value before storing them in a texture. E.g. a full transparent pixel will look like black in non-premultiplied color space. If you're unfamiliar with this color-space spend an hour or two reading about it on the web. It's a neat and good concept and required for photoshop-like compositions.

Anyway - once you have your images in that format you can enable SCREEN using: 

glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_COLOR)

The full MULTIPLY mode is not possible with the OpenGL|ES pipeline. If you only work with full opaque pixels you can fake it using: 

glBlendFunc(GL_ZERO, GL_SRC_COLOR)

The results for transparent pixels either in your texture and your framebuffer will be wrong though.

Nils Pipenbrinck
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you should try this:

glBlendFunc(GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA)

This looks like multiplying to me on the iPhone / OpenGL ES

Vlad Lego
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    Thank you for great answer, looks exactly like multiply in photoshop (: – Yetispapa Oct 05 '14 at 13:44
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    This only works if the image is a solid color (opaque). If you have an image with transparency you simply need to put it in front of a white background and then try this. – Peter Apr 18 '16 at 21:00
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I have found that using this:

glDepthFun( GL_LEQUAL);

was all need to get a screen effect, at least it worked well on my project.

I am not sure why this works, but if someone knows please share.

h221baker
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Your best place to start is to pick up a copy of the Red Book and read through the chapters on on materials and blending modes. It has a very comprehensive and clear explanation of how the 'classic' OpenGL blending functions work.

Cruachan
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