As the title says, I can't do vector_array[foo] (assuming foo is in-range and integer) in webgl vertex shaders, correct?
Are textures the best alternative, or is there a workaround or some better way to mimick a lookup table?
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2 Answers
http://www.khronos.org/registry/webgl/specs/latest/#DYNAMIC_INDEXING_OF_ARRAYS "WebGL only allows dynamic indexing with constant expressions, loop indices or a combination. The only exception is for uniform access in vertex shaders, which can be indexed using any expression."
Did you try it? If it didn't work, there are a couple options.
If you have a small number of values, if-else could work ok. AFAIK the uniform values are going to be loaded into registers anyhow, so doing a dozen cycles of math on them isn't going to make your shader much slower.
For a large number of values, textures are your best bet.
1 Comment
Steven Devijver
There is a workaround:
/* given variable i is the index */ for (int x = 0; x < MAX_VALUE_FOR_INDEX; x++) { if (x == i) { /* use variable x as index here */ }}I haven't tested it, but I don't get any compilation error from the following
//index as a float
attribute lowp float vColorIndex;
//the array
uniform vec4 Colors[16];
//type cast the float in an int
int index = int(vColorIndex);
//use index
vec4 col = Colors[index];
1 Comment
jes5199
This fails at runtime.