Vulkan: Directional LightmapGI does not look correct with emissive surface light

[atirut-w]

Godot version

v4.0.alpha14.official [106b680]

System information

N/A

Issue description

When using lightmap GI, specular lobes and reflections looks broken for lights from emissive objects. May be related to #63016

Cornell box model from McGuire CG Archive

2022-08-20_10-19-10.mp4

Steps to reproduce

1. Set up a static scene with everything having their UV2 unwrapped, and preferably with only lighting from emissive objects.
2. Add LightmapGI, enable directional mode and bake.

Minimal reproduction project

No response

[Calinou]

LightmapGI directional mode only provides rough reflections – it's not designed to provide sharp reflections like ReflectionProbe. This is done for performance reasons, as LightmapGI is something you'll most likely be using when targeting mobile.

If you need more precise reflections while using lightmaps, nothing prevents you from using VoxelGI, SDFGI or ReflectionProbe at the same time as LightmapGI. For VoxelGI and SDFGI, this will be faster than using VoxelGI/SDFGI alone as they won't affect surfaces that already receive baked lighting.

[Calinou]

Closing in favor of #81556, which shows cases where directional lightmap rendering is actually broken and has a MRP available.

Regarding the lack of specular lobes for direct light, see #63016.