Mipmap Biasing

[JMS55]

What problem does this solve or what need does it fill?

Temporal filtering techniques like TAA and FSR2 do best with a small negative mipmap bias, e.g. biased slightly towards higher resolution (lower number) mips. This helps counteract some of the blurriness typical of these techniques.

Apparently this can also increase sharpness even without temporal techniques.

What solution would you like?

Add some kind of component, resource, field, etc that would let you give the rendering system a specified mip bias, so that TAA/FSR2 can add a bias appropriate to their technique.

We can copy the value to one of the existing uniforms, and use wgsl's textureSampleBias() function to sample the StandardMaterial texture maps with the bias.

Open questions

• How is this configured? Globally via a resource, per-view via a Camera3d field, per StandardMaterial?
• Does textureSampleBias() with a 0 bias cost performance vs textureSample()?

Additional context

• Section labeled "Texture Blurring" https://www.elopezr.com/temporal-aa-and-the-quest-for-the-holy-trail
• https://github.com/GPUOpen-Effects/FidelityFX-FSR2#mipmap-biasing
• Godot Issue: Use a negative mipmap LOD bias automatically if FXAA and/or TAA are enabled to improve sharpness godotengine/godot-proposals#4657