place and scale mesh object based on face.

SOLUTION:

I modified some code I found here.

def make_matrix(center, v1, v2, v3):
    a = v2-v1
    b = v3-v1

    c = a.cross(b)
    if c.magnitude>0:
        c = c.normalized()
    else:
        raise BaseException("A B C are colinear")

    b2 = c.cross(a).normalized()
    a2 = a.normalized()
    m = Matrix([a2, b2, c]).transposed()
    s = a.magnitude
    m = Matrix.Translation(center) * Matrix.Scale(1,4) * m.to_4x4()

    return m

that function will give you the transformation matrix needed to properly place meshes or objects in the correct position on a given face.

“center”: the center position of the face. this is basically the new (0,0,0) point of the object being placed.
“v1, v2, v3”: three vertices that are part of the face that you want said object attached too.

then if m = trans_matrix:
bmesh.ops.transform(bm, matrix= trans_matrix, verts= bm.verts[-8:])

I used “bm.verts[-8:]” because the last eight verts that were created are the ones I needed moved. bm = bmesh.from_edit_mesh(bpy.context.object.data). this works on a mesh that is in edit mode.


I have a script that will attach polyhedrons to each other. I need a way to modify the x,y,z coordinates of the vertices of a mesh shape so that it is placed on a given face of another mesh object. I want to do this as I generate the vertices of the new object to be attached to the old. here is an example:

the only thing I can think of, is to get the face normal of the face that will have a new shape attached to it, and use that information somehow to position the new verts accordingly. how might I do this?

EDIT: yes, I know about duplifaces. unless there is something I don’t know about duplifaces, it won’t work for what I am doing.

EDIT: I found a wolframe alpha page that explains face normal vectors. hopefully I can understand it enough to make use of it

is it only for icospheres, or will this be extended to other object types?

Tetrahedrons, pyramids, prisms, cubes, dodecahedrons, hexagonal prisms, and icosahedrons. maybe more, but probably nothing with more faces than an icosahedron.

Sorry for my poor english usage :slight_smile: , i mean, maybe you can find some hints-ideas in its source code …

I’m not sure my python skills are up to such a task. I think it would be easier and more fun to find the equations and implement them myself.