I've been writing GLSL shaders, and using an integer texture (GL_RED) to store values in the shader. When I attempt to divide a value taken from the usampler2D texture, it stays the same. The following is the minimal reproducible shader.
#version 440
in vec2 uv;
out vec3 color;
layout (binding = 1) uniform usampler2D tm_data;
void main(){
float index = texture(tm_data, uv).r;
float divisor = 16.0f
color = vec3(index / divisor, 0, 0);
}
The rendered red value is always 1.0 regardless of a way i try to divide or mutate the index value.
When the sampler is changed to a normalized one (sampler2D) the color manipulation works as expected
#version 440
in vec2 uv;
out vec3 color;
layout (binding = 1) uniform sampler2D tm_data; //Loads as normalized from [0,255] to [0,1]
void main(){
float index = texture(tm_data, uv).r * 255.0f; //Convert back to integer approximation
float divisor = 4.0f
color = vec3(index / divisor, 0, 0); //Shade of red now appears considerably darker
}
Does anyone know why this unexpected behaviour happens?
The tm_data texture is loaded as GL_RED -> GL_RED The OpenGL version used is 4.4 There is no framework being used (no sneaky additions), everything is loaded using gl function calls.
For the use of usampler2D, the internal format has to be a unsigned integral format (e.g. GL_R8UI). See Sampler types.
If the internal format is the basic format GL_RED, then the sampler type has to be sampler2D.
Note, sampler* is for the use of floating point formats, isampler* for signed integral formats and usampler* for unsigned integral formats.
See OpenGL Shading Language 4.60 Specification - 4.1.7. Opaque Types and OpenGL Shading Language 4.60 Specification - 8.9. Texture Functions