Setting up and accessing multiple textures in openGL - ios

Question

I am doing some heavy computation with openGLES on IOS. Currently, I am trying to implement lookup tables using textures and texelFetch(), and succeeded in making one, but only one at a time. How to make multiple sampler2d available in the glsl? I tried the following code but it gives weird results.
[Update: After reading the official tutorial #13, I tried reformat the code but it still does not work. It seems both sampler2d refers to the first-set one, even though I checked that the data pointers point to different content.]
In OjbC, I tried something like this
int lookupTabSize = 2000;
GLuint tab0Handle;
glGenTextures(1, &tab0Handle);
glBindTexture(GL_TEXTURE_2D, tab0Handle);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, lookupTabSize,1, 0, GL_RED, GL_FLOAT,[self getConstant:0]); // Pointer checked
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
GLuint tab0ID = glGetUniformLocation(program, "lookupTab0");
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tab0Handle);
glUniform1f(tab0ID,1);
GLuint tab1Handle;
glGenTextures(1, &tab1Handle);
glBindTexture(GL_TEXTURE_2D, tab1Handle);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, lookupTabSize,1, 0, GL_RED, GL_FLOAT,[self getConstant:1]); // Pointer checked
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
GLuint tab1ID = glGetUniformLocation(program, "lookupTab1");
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, tab1Handle);
glUniform1f(tab1ID,0);
In glsl, I just output the look-up content, but it seems both tables refer to the same data source, though they shouldn't as I double-checked the reference! Any ideas about how should I do it correctly? Some sample codes would be much appreciated.
#version 300 es
uniform sampler2D lookupTab0;
uniform sampler2D lookupTab1;
in int InV0;
out float OutV0;
float f(int ptIn){
float valueSum = 0.0f;
ivec2 pos = ivec2(ptIn, 0);
valueSum = valueSum + texelFetch(lookupTab0,pos,0).r;
valueSum = valueSum + texelFetch(lookupTab1,pos,0).r;
return valueSum;
}
void main(){
OutV0 = f(InV0);
}

Answer 1

You need to use glUniform1i() to set sampler uniforms. So these two calls:
glUniform1f(tab0ID,1);
...
glUniform1f(tab1ID,0);
will not work.
Also, the values appear to be swapped, since you're binding lookup table 0 to texture unit GL_TEXTURE0, and lookup table 1 to GL_TEXTURE1. So the correct calls are:
glUniform1i(tab0ID, 0);
...
glUniform1i(tab1ID, 1);
This is based on the following found on page 66, in the section "2.12.6 Uniform Values", of the ES 3.0 spec:
Only the Uniform1i{v}commands can be used to load sampler values