Why can't we use buffergeometry directly when converting to geometry

[zh-pan]

`var positions=item.geometry.attributes.position.array;
var i,triangles=[];
for(i=0;i<positions.length;i+=3){
triangles.push( new THREE.Vector3().fromArray( positions, i ) );
}

                        if (!triangles.length) return false;
                        for ( i = 0; i < triangles.length; i++ ) {
                            triangle = triangles[i];

                            vec3_1.setX(triangle.x);
                            vec3_1.setY(triangle.y);
                            vec3_1.setZ(triangle.z);
                            vec3_2.setX(triangle.x);
                            vec3_2.setY(triangle.y);
                            vec3_2.setZ(triangle.z);
                            vec3_3.setX(triangle.x);
                            vec3_3.setY(triangle.y);
                            vec3_3.setZ(triangle.z);

                            triangle_mesh.addTriangle(vec3_1, vec3_2, vec3_3, true);
                        }

                        var meshShape = new Ammo.btBvhTriangleMeshShape(triangle_mesh, true, true);`

[InfiniteLee]

btBvhTriangleMeshShape requires a btStridingMeshInterface for its constructor. btTriangleMesh is the only class implemented in Ammo.js of that type but has no constructor or method for creating a btTriangleMesh from an array of vertices. It only has the addTriangle method, which requires you to specify each vertex of a triangle, like in your example.

There are other classes that implement btStridingMeshInterface like btTriangleIndexVertexArray whose constructor takes a pointer (so you could pass a pointer to the start of an array of vertices), but you would need to figure out how to define it in ammo.idl and how to use it, as it is currently not implemented in Ammo.js.

[suddenly4]

If you want concave shape, as an option, atfirst make some triangles form buffergeometry for example - btConvexTriangleMeshShape by set .addTriangle(Ammo.btVector3) then you can build different shape by using btConvexTriangleMeshShape, if dinamic shape - btCompoundShape. if static
btBvhTriangleMeshShape