[3.x] Use Bullet's convex hull computer in place of QuickHull when available.

[mortarroad]

Fixes #45946, maybe more.

[pouleyKetchoupp]

This is a good idea and it seems to work well!

There are just two things I would like to address before approving:

• This change adds a dependency to VHACD module in Godot Physics, so given that the old QuickHull code is very small, I'd like to keep it as an alternative in case the engine is compiled with VHACD disabled (see my review comment).
• Another PR needs to be opened on master to keep the codebase in sync. The usual process is to open a PR on master first, and then the changes can be cherry-picked on 3.x when possible. In this case the file names have changed on master, so it makes sense to keep this separate 3.x PR.

[mortarroad]

Superseded by #47332

Another PR needs to be opened on master to keep the codebase in sync. The usual process is to open a PR on master first, and then the changes can be cherry-picked on 3.x when possible. In this case the file names have changed on master, so it makes sense to keep this separate 3.x PR.

I tend to make patches against 3.x, since that's what I use and where I encounter bugs that I want to fix.
With master, I can't test them as easily.

[pouleyKetchoupp]

This PR can stay open, since it would still be nice to have this fixed on 3.4 as well and the file names have changed.
Sorry for the confusion, in my previous comment I just meant that it would need an extra PR on master.

[lawnjelly]

And just to note I'm using quick hull in several modules (and I presume others are too) and also in the rooms / portals PR. So keeping the old version available would be very useful (any replacement would have to be a drop in replacement, and always available).

[mortarroad]

And just to note I'm using quick hull in several modules (and I presume others are too) and also in the rooms / portals PR. So keeping the old version available would be very useful (any replacement would have to be a drop in replacement, and always available).

That's the plan. QuickHull will remain available.
And it should be possible to simply replace any call to QuickHull::build with Geometry::build_convex_hull.
Take a look at the PR against master for reference.

[jitspoe]

Does this VHACD have the same issue that the Mesh::convex_decompose() did? If I recall correctly, that also used the VHACD algorithm, and when "convcolonly" for mesh imports was updated to use that instead of quickhull, it would result in incorrect collision (ex: a simple box would have the verts slightly off).

Edit: Actually, looking closer, it seems the VHACD algorithm uses btConvexHullComputer, and you included the VHACD version, so you could just skip the VHACD:: in front of that and use the bullet one directly.

[mortarroad]

@jitspoe I have not done much testing, but I assume that this algorithm is precise.
As you mentioned, this does not actually use VHACD; it simply uses what's provided by Bullet, which happens to be included in that module.
The reason is to allow compilation with Bullet disabled, as mentioned here: #41522 (comment)

[pouleyKetchoupp]

@jitspoe From what I've tested with basic primitives, the Bullet convex hull algorithm itself doesn't introduce the problem you mentioned (#29971).

[akien-mga]

Superseded by #48533.