Sampling unsigned integers from 1D texture using integer texture coordinates

Question

I want to pass a big array of unsigned short tuples (rect geometries) to my Fragment Shader and be able to sample them as-is using integer texture coordinates, to do this I'm trying with a 1D texture as follows, but get just blank (0) values.

Texture creation and initialization:

GLushort data[128][2];
// omitted array initialization

GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_1D, tex);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAX_LEVEL, 0);
glTexImage1D(
    GL_TEXTURE_1D,
    0,
    GL_RG16UI,
    128,
    0,
    GL_RG_INTEGER,
    GL_UNSIGNED_SHORT,
    data
);

Texture passing to shader:

int tex_unit = 0;
glActiveTexture(GL_TEXTURE0 + tex_unit);
glBindTexture(GL_TEXTURE_1D, tex);
glUniform1iv(loc, 1, &tex_unit);

Debug fragment shader:

#version 330 core
out vec4 out_color;

uniform usampler1D tex;

void main()
{
    uvec4 rect = texelFetch(tex, 70, 0);
    uint w = rect.r;
    uint h = rect.g;
    out_color = w > 0u ? vec4(1) : vec4(0);
}

Things that work for sure: non-zero data in data array, texture image unit setup and sampler uniform initialization.

OpenGL 4.1, OSX 10.11.6 "El Capitan"

As an arguable "proof" that the texture is created and sampled, the debug shader renders white colors if the texture image data is populated like this, with everything else untouched: glTexImage1D(GL_TEXTURE_1D, 0, GL_RG, 128, 0, GL_RG, GL_UNSIGNED_SHORT, data); (although this makes little sense to me, because if I understood the documentation well, the internalFormat must match the sampler type, and in this case, the first is float and second is unsigned int) — Ivan Nikolaev

Ivan Nikolaev Ivan Nikolaev · Accepted Answer · 2016-09-19T16:44:56

After some googling and by trial and error, I discovered this post, which states that with integer texture formats (for example, GL_RG16UI internal format) GL_LINEAR filtering cannot be specified and only GL_NEAREST applies, thus, everything worked out with the following texture creation code:

GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_1D, tex);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_BASE_LEVEL, 0);
glTexParameteri(GL_TEXTURE_1D, GL_TEXTURE_MAX_LEVEL, 0);
glTexImage1D(
    GL_TEXTURE_1D,
    0,
    GL_RG16UI,
    128,
    0,
    GL_RG_INTEGER,
    GL_UNSIGNED_BYTE,
    data
);

Sampling unsigned integers from 1D texture using integer texture coordinates

1 Answers