Added a custom mesh to the example models/mesh_generation

[Hultan]

This example at raylib.com has a custom mesh, which was missing in the golang example. So I added it...

However, the program panics when unloading the custom model. So I had to create the following function to clear the mesh before calling unload, and now it does not panic.

I don't know if this is something that I don't understand, or if it is because of some underlying problem in the Mesh type, or UnloadModel function? Someone who knows more about the C code than me, might want to take a look at that.

func clearCustomMesh(models []rl.Model) {
	// For some reason the custom model
	// (id = 8) panics when unloading it.
	// So we clear the mesh for it manually
	// here.
	models[8].Meshes.Vertices = nil
	models[8].Meshes.Normals = nil
	models[8].Meshes.Texcoords = nil
}

[gen2brain]

This is probably related to #303, what you are clearing there doesn't look like is doing anything at all.

[Hultan]

Well, try it out yourself. Remove the call to the clearCustomMesh function, and the program will panic in rl.UnloadModel(models[i]).

I don't understand why it works to set these values to nil, but it did on my machine...

[gen2brain]

Did you check the issue?

[Hultan]

I have now skimmed through it, but I still not sure what I am supposed to do differently?
Should I do something like this? This code still crashes:

	rl.UnloadTexture(texture)
	for i := 0; i < numModels; i++ {
		meshes := unsafe.Slice(models[i].Meshes, models[i].MeshCount)
		for m := range meshes {
			rl.UnloadMesh(&meshes[m])
		}
		rl.UnloadModel(models[i])
	}

[gen2brain]

No idea, I was just pointing out that it is probably related as you are using the custom mesh. There is an explanation there and a workaround implemented. Sorry, I don't have time to go through all that now.

[Hultan]

No problem, I will look into it a little bit more, but that might take a couple of days...

[JupiterRider]

Vertices, Normals and Texcoords of your custom mesh are Go slices.
UnloadModel calls UnloadMesh for every mesh and UnloadMesh tries to free your Go slices. The panic happens, because it cannot free Go slices.

free is a C function and it expects to free C memory and not a Go slice.

[Hultan]

Ok, now I understand the problem, but what is the solution then? To just do what I did, and nilthem?

Or to not call UnloadModel/UnloadMesh at all for Custom Models?

[JupiterRider]

Ok, now I understand the problem, but what is the solution then? To just do what I did, and nilthem?

Or to not call UnloadModel/UnloadMesh at all for Custom Models?

Yes. Setting the Go slices to Nil (like you already did) is fine.

[Hultan]

Then I guess this can be merged now, I added your explanation to my clearCustomMesh function as a comment.