Baking LightmapGI with shadowmasks can crash Godot after transparency support was added

[GustJc]

Tested versions

-Reproducible in latest master v4.4.dev.gh [24d7451]

System information

Windows 10 - Godot 4.4dev - Vulkan (Foward+) - Nvidea 1070

Issue description

Trying to bake the LightmapGI with shadowmasks can get stuck and crash Godot in some circunstances.

Using the latest master (v4.4.dev.gh [24d7451]) and trying to bake the lightmapGI using the testproject from (#85653 (comment)) crashes Godot.
With a lot of "Couldn't map PC to fn name" errors.

shadowmap_bug.mp4

Here is the start of the crash:
(On Windows 10, Foward+, Nvidea 1070)

It appears this started happening since adding transparency support to the lightmapGI (#99538)

As found out by #85653 (comment)

@Geometror EDIT: Tested some some PR's and is crashing since #99538 (Transparency PR). Something broke between Dec 12 and Dec 19.

EDIT2: It seems like if I insist and try again it manage to bake, but taking double the time and the computer becomes unresponsive in the process.

Steps to reproduce

I didn't figure out the MRP yet, but you can
use the test project from #85653 (comment)
(Used to work until the transparency to GI was added)
(direct download link)

• Try to bake the LIghtmapGI

Expected: LightmapGI baked
Results: Goes until about 50% then Godot gets stuck and crashes.

Minimal reproduction project (MRP)

Use the test project from #85653 (comment)
(direct download link)

[SpockBauru]

I don’t know if I did the bisect thing right, but compiling one commit before #99538 the test project still works, but not on that PR (build a3525bc). Hope I did it right.

A bit of history about this test project: for more than a year it was used to test several LightmapGI bugs like light probes not working, large lightmaps bug, and I accumulated the tested bugs on each interaction so it tests multiple past issues at once. I’ve recently changed to a simpler test but it seems like this old monstrosity is still needed.

About the current issue, I tried clean all the light probes, addons and reduce the lightmap size but the crash persists on #99538.

Another interesting issue is that it crashes on the first time the project is opened, but if I insist a few times it freezes the PC for a while but complete the baking after several minutes, a way longer than previews commits.

This project has hundreds of trees with transparent materials set to “Alpha Scissor”. Maybe there’s something with this mode.

Edit:
My system info: Godot v4.4.dev (a3525bc01) - Windows 10.0.22631 - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3080 (NVIDIA; 32.0.15.6614) - 12th Gen Intel(R) Core(TM) i7-12700KF (20 threads)

Edit 2: By turning off the transparency on the leaves material (res://DemoScene/Trees/leaves.tres) the terrain bakes normally but the tunnel doesn't receive shadowmasks anymore (It was working normally on the Shasowmasks PR). The the terrain has local UVs, but tunnel have both UV1 and UV2 imported from Blender.