What is the difference between textureLodOffset and texelFetchOffset with respect to their expected offsets?

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I know that texelFetch performs a lookup using texture coordinates with range [0, textureSize], and textureLod with range [0,1] both with explicit level of detail. But I have noticed that textureLodOffset requires an offset as ivec2, int and so on. This seems to be the case for texelFetchOffset as well. I can see why this makes sense for texelFetch, but I am not sure how it relates to textureLod.

I am used to computing the offset coordinate manually in the shader with something like coord.xy + 1/textureSize() for textureLod. I don't think this is causing any issues with performance etc, but I would like to know how we can use textureLodOffset with integer coordinates as specified in the documentation what makes their use different from texelFetchOffset.

glsl shader opengl
1 Answers

The difference between textureLodOffset and texelFetchOffset are the texture coordinates.
The texture coordinates of textureLodOffset are in rage [0, 1]. But the unit of the texture coordinates of texelFetchOffset are texels and the range of the coordinates depends on the size of the texture. In compare to the *Fetch* functions, textureLodOffset respects texture filtering and sampling.
The *Fetch* functions performs a lookup of a single texel from an unambiguous texture coordinate. See OpenGL 4.6 API Compatibility Profile Specification - 11.1.3.2 Texel Fetches

In both cases, the offset argument is integral because it is meant to access neighboring texels. See further OpenGL Shading Language 4.60 Specification - 8.9.1. Texture Query Functions.

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