Photoshop混合模式到不带着色器的OpenGL ES [英] Photoshop blending mode to OpenGL ES without shaders
问题描述
我需要在OpenGL ES 1.1代码(无着色器)中模仿Photoshop混合模式(乘"，屏幕"等).
I need to imitate Photoshop blending modes ("multiply", "screen" etc.) in my OpenGL ES 1.1 code (without shaders).
有一些有关如何使用 HLSL进行此操作的文档:
There are some docs on how to do this with HLSL:
- http://www.nathanm. com/photoshop-blending-math/(存档)
- http://mouaif.wordpress.com /2009/01/05/photoshop-math-with-glsl-shaders/
- http://www.nathanm.com/photoshop-blending-math/ (archive)
- http://mouaif.wordpress.com/2009/01/05/photoshop-math-with-glsl-shaders/
我至少需要工作在屏幕模式下.
I need at least working Screen mode.
我可以看一下固定管道上的任何实现吗?
Are there any implementations on fixed pipeline I may look at?
推荐答案
大多数photoshop混合模式都基于Porter-Duff混合模式.
Most photoshop blend-modes are based upon the Porter-Duff blendmodes.
这些要求您所有的图像(纹理，渲染缓冲区)都在预乘的色彩空间中.通常通过将所有像素值乘以alpha值，然后再将它们存储在纹理中来完成此操作.例如.在非预乘颜色空间中，一个全透明像素将看起来像黑色.如果您不熟悉此颜色空间，请花一两个小时在网络上阅读一下.这是一个很好的概念，是类似Photoshop的构图所必需的.
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.
无论如何-拥有该格式的图像后，您可以使用以下命令启用SCREEN:
Anyway - once you have your images in that format you can enable SCREEN using:
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_COLOR)
使用OpenGL | ES管道无法使用完整的MULTIPLY模式.如果您仅使用全不透明像素，则可以使用以下方法进行伪造:
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)
纹理和帧缓冲区中透明像素的结果将是错误的.
The results for transparent pixels either in your texture and your framebuffer will be wrong though.
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