OpenGL Programming Guide: The Official Guide to Learning OpenGL, Version 4.3, Eighth Edition

Texture Queries in Shaders

The following two built-in GLSL functions don’t actually read from the texture, but return information about the texture or about how it will be processed. The first function, textureQueryLod retrieves mipmap information calculated by the fixed-function texture lookup hardware.

vec2 textureQueryLod(gsampler1D tex, float P);vec2 textureQueryLod(gsampler2D tex, vec2 P);vec2 textureQueryLod(gsampler3D tex, vec3 P);vec2 textureQueryLod(gsamplerCube tex, vec3 P);vec2 textureQueryLod(gsampler1DArray tex, float P);vec2 textureQueryLod(gsampler2DArray tex, vec2 P);vec2 textureQueryLod(gsamplerCubeArray tex, vec3 P);vec2 textureQueryLod(sampler1DShadow tex, float P);vec2 textureQueryLod(sampler2DShadow tex, vec2 P);vec2 textureQueryLod ...