NullPointerException in MikktspaceTangentGenerator

[stephengold]

When a model containing a mesh without indices is passed to MikktspaceTangentGenerator.generate():

SEVERE: Caught unexpected throwable:
java.lang.NullPointerException: Cannot invoke "com.jme3.scene.mesh.IndexBuffer.get(int)" because "index" is null
	at com.jme3.util.mikktspace.MikkTSpaceImpl.getIndex(MikkTSpaceImpl.java:119)
	at com.jme3.util.mikktspace.MikkTSpaceImpl.getPosition(MikkTSpaceImpl.java:68)
	at com.jme3.util.mikktspace.MikktspaceTangentGenerator.getPosition(MikktspaceTangentGenerator.java:719)
	at com.jme3.util.mikktspace.MikktspaceTangentGenerator.generateSharedVerticesIndexList(MikktspaceTangentGenerator.java:279)
	at com.jme3.util.mikktspace.MikktspaceTangentGenerator.genTangSpace(MikktspaceTangentGenerator.java:164)
	at com.jme3.util.mikktspace.MikktspaceTangentGenerator.genTangSpaceDefault(MikktspaceTangentGenerator.java:126)
	at com.jme3.util.mikktspace.MikktspaceTangentGenerator.generate(MikktspaceTangentGenerator.java:118)

[Ali-RS]

When a model containing a mesh without indices

Would a mesh without an index buffer still be rendered? What is the use case? A point mesh?

[zzuegg]

You can render any mesh without indicies. used that before gl3 as instancing replacement

[pspeed42]

An index buffer is only needed when you want to share vertexes. Otherwise it's a waste of space.

[stephengold]

Meshes in JME are incredibly flexible, which makes generalized editing of meshes incredibly difficult. I know there are many other cases that MikktspaceTangentGenerator currently can't handle; this is just the one that happened to bite me first.

From glancing at the code, the next bug that jumps out at me is that MikktspaceTangentGenerator assumes all meshes are in Triangles mode. Meshes in Lines or Points mode should simply be skipped, but perhaps solutions are needed for the TriangleFan and TriangleStrip modes.

[pspeed42]

I half-remember that JME has a utility class to treat Triangles, TriangleFan, and TriangleStrip the same and I believe the original tangent generator might have used it. My memory says that the Mikkspace generator was ported from something else and so probably just cut-pasted code as directly as possible.

It's also possible I have no idea what I'm talking about. Normally I look at the code before making such statements but I'm pressed for time and I didn't want to leave the memory unmentioned.

[stephengold]

I guess you're half-remembering Mesh.getIndicesAsList(), which is what I used in #1910 to solve this issue. You're correct that getIndicesAsList() handles TriangleFan and TriangleStrip modes correctly. However, the tangent generator assumes throughout that the vertices of a triangle appear sequentially in vertex buffers, so I think there's still work to do for those modes---and also for indexed meshes in general(!)

[Ali-RS]

Merging #1910 automatically closed this. Please feel free to reopen it if more action is required.