[3.x] Add a project setting to control the minimum ReflectionProbe roughness

[Calinou]

This can be used as a form of antialiasing with very little performance cost.

The default value removes almost all aliasing present in ReflectionProbes while still keeping reflections fairly sharp for real world use cases.

I could only get it working in GLES3, so the feature is limited to GLES3. The default value for the minimum roughness is 0.05 and can be changed at run-time.

This closes #49789.

Preview

Reflective materials have Roughness = 0, Metallic = 1.

Before (Min Roughness = 0.0)

After (Min Roughness = 0.05)

[clayjohn]

How does this compare to just setting the material's roughness to 0.05?

Also, I'm a little confused about why this works, for the top level mipmap, the shader uses "USE_DIRECT_WRITE" and just copies the cubemap without blurring based on roughness

godot/drivers/gles3/shaders/cubemap_filter.glsl

Lines 258 to 281 in 1673e3a

	#ifdef USE_DIRECT_WRITE
	#ifdef USE_SOURCE_PANORAMA
	frag_color = vec4(texturePanorama(N, source_panorama, 0.0).rgb, 1.0);
	#endif
	#ifdef USE_SOURCE_DUAL_PARABOLOID_ARRAY
	frag_color = vec4(textureDualParaboloidArray(N).rgb, 1.0);
	#endif
	#ifdef USE_SOURCE_DUAL_PARABOLOID
	frag_color = vec4(textureDualParaboloid(N).rgb, 1.0);
	#endif
	#if !defined(USE_SOURCE_DUAL_PARABOLOID_ARRAY) && !defined(USE_SOURCE_PANORAMA) && !defined(USE_SOURCE_DUAL_PARABOLOID)
	N.y = -N.y;
	frag_color = vec4(texture(N, source_cube).rgb, 1.0);
	#endif
	#else // USE_DIRECT_WRITE

For the higher levels, roughness should already be greater than 0.05.

[Calinou]

How does this compare to just setting the material's roughness to 0.05?

You don't need to edit any existing materials, and the rest of roughness calculations (such as light energy conservation) is not affected. While this is physically incorrect, it results in better usability for people who generally just set roughness to 0 on materials they expect to be fully reflective.

Also, I'm a little confused about why this works, for the top level mipmap, the shader uses "USE_DIRECT_WRITE" and just copies the cubemap without blurring based on roughness

I'm also not sure how it's working as intended.