GL_R32I TexImage2D not uploading correctly

Question

I'm trying to create a tonemap fragment shader, to map values from [0, someint] to RGB values, but when I try to use GLints, the texture that gets rendered is all 0s.

Here's the relevant texture creation and binding code:

std::array<GLint , 25 > pixels;
int i=0;
float di = 255.0f / 25;
std::generate(pixels.begin(), pixels.end(), [&]{return di * i++;});

glTexImage2D(GL_TEXTURE_2D, 0, GL_R32I, 5,5 ,0, 
GL_RED_INTEGER, GL_INT, pixels.data());

and a fragment shader of:

#version 330

in vec2 Texcoord;
out vec4 outColor;
uniform isampler2D tex;

void main()
{
    ivec4 val = texture(tex, Texcoord);
    float ret = 0;
    if(val.r == 0)
    {
        ret = 1;
    }
    outColor = vec4(ret,0,0, 1.0);
}

Which is applied to a basic 2 triangles UV textured from [0,1] The expected result would be one red corner and the rest black, but the entire square is red, signifying the entire texture is 0.

When I try the experiment with glTexImage2D(GL_TEXTURE_2D, 0, GL_RED, 5, 5 ,0, GL_RED, GL_FLOAT, pixels.data()); and a sampler2D, the shader behaves as expected, but my values are clamped to [0,1]. Are the enums mismatched? glGetError returns no error, but it might be silently failing in some other way?

I'm using GLFW and OpenGL 3.3 on Ubuntu, not sure if GL_R32I is supported with that version?

Answer 1

Are you setting GL_TEXTURE_MIN_FILTER to be anything but GL_*_MIPMAP_*? The initial value is GL_NEAREST_MIPMAP_LINEAR.

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

If not then the texture won't work because you only have a single mipmap level defined. Thus the texture being incomplete.

By default the highest defined mipmap level is 1000. You can set it to 0 and that would equally work.

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0)

The max level is a zero-based index.