GLSL Texture Size

Question

I have a problem with my fragment shader. I want to get the size of a texture (which is loaded from an image).

I know that it is possible to use textureSize(sampler) to get an ivec2 which contains the texture size. But i don't know why this isn't working (it doesn't compile):

#version 120

uniform sampler2D tex;

float textureSize;
float texelSize;


void main()
{
    textureSize = textureSize(tex).x;//first line
    //textureSize = 512.0;//if i set the above line as comment and use this one the shader compiles.
    texelSize = 1.0 / textureSize;

    vec4 color = texture2D(tex,gl_TexCoord[0].st);
    gl_FragColor = color * gl_Color;
}

Sivan

it doesn't compile - what error are you getting? Come on. – Shultz

after compiling glGetShader(handle, GL_COMPILE_STATUS) == GL_FALSE returns true. Is there anyway to get more specific info about the error? – Sivan

It would be rather hard if there wasn't, won't you agree? The function was called ShaderInfoLog or something like that, and if you have a fairly modern (4.x) system, you should have some version of debug_output extension (which should be preferred, as it's much nicer to use, configurable and gives overall better information). – Shultz

The error is: ERROR: 0:11: 'textureSize' : no matching overloaded function found (using implicit conversion) In which version was textureSize() implemented? – Sivan

This shows that it was implemented in Version 130: opengl.org/sdk/docs/man/html/textureSize.xhtml But if i change the version it still doesn't work. – Sivan

Because the error states that there's no overload, not that there's no function. In this case, you apparently can't ask for a size of sampler2D. – Shultz

Answer 1

Th problem was that my GLSL version was to low (implemented in 1.30) and that i was missing a parameter.

Here the working version:

#version 130

uniform sampler2D tex;

float textureSize;
float texelSize;


void main()
{
    ivec2 textureSize2d = textureSize(tex,0);
    textureSize = float(textureSize2d.x);
    texelSize = 1.0 / textureSize;

    vec4 color = texture2D(tex,gl_TexCoord[0].st);
    gl_FragColor = color * gl_Color;
}

Sivan