Provide a guide how to get the original vertex data from boolean operations

[fire]

Hi!

I was trying to get the original vertex data from boolean operations.

https://github.com/V-Sekai/godot/blob/csg-manifold-04/modules/csg/csg.cpp#L298-L419

Having trouble getting the original mesh id and its triangle index so I can check the property.

[elalish]

GetMeshRelation gives you the mesh id and triangles indices, as well as barycentric coordinates. GetMeshIDs gets the mesh ids. For any newly-constructed manifold this vector will length 1 (since it's a new meshID). If you can give some specifics of the trouble you're having, I'll be happy to help more.

[elalish]

These test functions might also give you some idea of how it's used: https://github.com/elalish/manifold/blob/master/test/mesh_test.cpp#L36-L79

[fire]

Can you do an example of getting the triangle from mesh_b when you boolean intersect a and b? Or boolean add if it's too hard.

[elalish]

Is this what you're after?

Mesh a_mesh = ImportMesh('something.glb');
Manifold a(a_mesh);
Manifold b = Manifold.Cube();
Mesh b_mesh = b.GetMesh();
const int aID = a.GetMeshIDs()[0];
const int bID = b.GetMeshIDs()[0];

Manifold c = a ^ b;
MeshRelation rel = c.GetMeshRelation();
Mesh c_mesh = c.GetMesh();
std::vector<int> meshID2Original = Manifold::MeshID2Original();

int c_tri = 0; // referring to c_mesh.triVerts[c_tri]
int triVert = 2; // 0, 1, or 2
BaryRef ref = rel.triBary[c_tri];
Mesh& inMesh = meshID2Original[ref.meshID] == aID ? a_mesh : b_mesh;
glm::ivec3 inTri = inMesh.triVerts[ref.tri];
glm::vec3 uvw = rel.UVW(c_tri, triVert); 

glm::vec3 inProp = {inMesh.vertProp[inMesh.triVerts[inTri][0]],
                            inMesh.vertProp[inMesh.triVerts[inTri][1]],
                            inMesh.vertProp[inMesh.triVerts[inTri][2]]};
float prop = glm::dot(inProp, uvw);

// Or check if(ref.vertBary[triVert] < 0) then this refers to c_mesh.vertPos[ref.vertBary[triVert] + 3]. 
// Otherwise it's a new vertex that will have different properties for each side of the intersection.

This same system works even after many consecutive boolean operations, since it will point each triangle back to whichever original mesh it came from, not just the most recent inputs.

[fire]

Thanks. Maybe we can add to the documentation or a test, but I was able to use this.