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Does anybody know how to do switch case syntax in the fragment shader on the Samsung Galaxy S2? I get the compilation error: Expected literal or '(', got 'switch'.
My syntax is as follows:
switch(i){
case 0: x = alphas[0]; break;
case 1: //...etc.
}
This works fine on the Nexus 7, but on the Galaxy S2 I get the above error. Are switch case instructions simply impossible on the Galaxy S2? The reason why I want to use them is they appear to give a performance improvement over if else on the Nexus 7. If they are impossible on the Galaxy S2, is there a way to query the device and use switch case if available, and if else otherwise?
347
The OpenGL Shading Language (GLSL) is the principal shading language for OpenGL.
A Fragment Shader is the Shader stage that will process a Fragment generated by the Rasterization into a set of colors and a single depth value. The fragment shader is the OpenGL pipeline stage after a primitive is rasterized. For each sample of the pixels covered by a primitive, a "fragment" is generated.
OpenGL Shading Language (GLSL) is a high-level shading language with a syntax based on the C programming language.
In this case, your fragment shader runs once for every fragment within that quad. For this program, that means 100 * 100 = 10000 times, once for every pixel on your screen. However, not every fragment rendered in the shader has to be displayed on the screen.
switch statement is not supported in OpenGL ES 2.0.
From the OpenGL ES Shading Language 1.0.17 spec 3.7:
The following are the keywords reserved for future use. Using them will result in an error:
asm class union enum typedef template this packed goto switch default ...
64
GLSL ES is based on version 1.10 of the desktop GLSL, but 'switch case' statements were added in vesrion 1.30, so you cannot assume device will support it.
Also I would recommend avoiding branching in fragment shader as it hits perfomanace badly.
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