This is a texture file that, when loaded on an object in a compatible renderer, reveals which mipmapping level the render engine thinks is appropriate for the given render resolution, camera distance, filtering settings, normal angle, etc.
You can use it to debug mipmapping issues with your render engine, but an interesting side effect is that you can also use it to find the ideal texture resolution required to render your object. Handy when doing UV layouts, painting textures, planning UDIM, etc.
For example, set your render resolution to the final output resolution, and use the IPR to check which resolution is shown when the camera is the closest to the object it's likely to get. Whatever resolution is show is the maximum resolution you'll need.
This only works in render engines that support pre-cached mipmaps. If you have trouble getting the texture to display, same issues would occur with any other cached mipmap texture, like those generated with the maketx or img2tiledexr tools. That's something to bring up with the developers of your render engine. Also, keep in mind that different render engines slightly different ways to calculate this, resulting in some differences between engines.
Confirmed compatible with:
- Renderman (Use the .tex file)
- Corona (With VRayHDRI loader)
Confirmed incompatible with:
This idea is based on a very similar texture that I stumbled upon long ago. Unfortunately, that creators site has since gone offline and disappeared without trace, and was unable to track it down, so I decided to create my own version from scratch.