place and scale mesh object based on face.

Coding Python Support
#1

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:

http://i.imgur.com/jXbZ6sb.gif
jXbZ6sb.gif600×600

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

#2

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

#3

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

#4

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

#5

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.