Mesh.md

Mesh

There are two ways to create Mesh data.

• One relies on first defining all vertices / edges / faces in lists and then sending them to a function called .from_pydata().
• The other grows the mesh in place by adding vertex coordinates and edge / face indices sequentially.

Both methods have strengths and weaknesses, picking which to use depends largely on what you're doing.

• Are you create a mesh from scratch?
• Are you updating and existing mesh (possibly with new additional geometry)
• Are you purely updating vertex locations of an existing mesh.
• ..etc,..

from_pydata

snippet 1 (creating: Verts and Edges)

---

Date: October 2015

This method expects the Mesh object to be empty (more about that below).

# be in object mode with nothing selected.

import bpy

# create 4 verts, string them together to make 4 edges.
coord1 = (-1.0, 1.0, 0.0)
coord2 = (-1.0, -1.0, 0.0)
coord3 = (1.0, -1.0, 0.0)
coord4 = (1.0, 1.0, 0.0)

Verts = [coord1, coord2, coord3, coord4]
Edges = [[0,1],[1,2],[2,3],[3,0]]

mesh = bpy.data.meshes.new("Base_Data")
mesh.from_pydata(Verts, Edges, [])
mesh.update()

obj = bpy.data.objects.new("Base_Object", mesh)

scene = bpy.context.scene
scene.objects.link(obj)
obj.select = True

This snippet

• adds a new empty mesh called 'Base_Data' to the bpy.data collection.
• pushes Verts, Edges, and an empty list onto the new empty Mesh

  • The empty list [] is because from_pydata expects 3 arguments, none are optional

  • You can choose to pass just verts, or just verts + edges or just verts + faces like:

    mesh.from_pydata(Verts, [], [])
    mesh.from_pydata(Verts, Edges, [])
    mesh.from_pydata(Verts, [], Faces)

  • In the event you want to add some faces and some edges you can of course do mesh.from_pydata(Verts, Edges, Faces)

snippet 2 (creating: Verts and Quad Faces)

---

Date: October 2015

This method expects the Mesh object to be empty (more about that below).

import bpy

verts = [
    (1.0, 1.0, -1.0),
    (1.0, -1.0, -1.0),
    (-1.0, -1.0, -1.0),
    (-1.0, 1.0, -1.0),
    (1.0, 1.0, 1.0),
    (1.0, -1.0, 1.0),
    (-1.0, -1.0, 1.0),
    (-1.0, 1.0, 1.0)
]

faces = [
    (0, 1, 2, 3),
    (4, 7, 6, 5),
    (0, 4, 5, 1),
    (1, 5, 6, 2),
    (2, 6, 7, 3),
    (4, 0, 3, 7)
]

mesh = bpy.data.meshes.new("cube_mesh_data")
mesh.from_pydata(verts, [], faces)
mesh.update()

cube_object = bpy.data.objects.new("Cube_Object", mesh)

scene = bpy.context.scene  
scene.objects.link(cube_object)  
cube_object.select = True  

This should make sense, and the way to make Triangles is to simply pass in sub-lists that index 3 vertices instead of 4.

You are permitted to mix Triangles and Quads in the Faces list.

sequentially adding vertices/edges/faces

In some scenarios you might want to add geometry to existing geometry, use BMesh for this.

Not an empty Mesh?

You will need to get rid of all geometry in the Mesh before you can use .from_pydata on it. This is one way to do it without using bpy.ops. Effectively using Bmesh to overwrite the Mesh data.

import bpy
import bmesh

p = bpy.data.objects['Obj2']

def clear_mesh(mesh):
    bm = bmesh.new()
    bm.to_mesh(mesh)
    bm.free()

clear_mesh(p.data)
p.data.update()

update using foreach_set

flat_list_of_verts = [x1, y1, z1, x2, y2, z1, x3, y3, z3....xn, yn, zn]
mesh.vertices.foreach_set('co', flat_list_of_verts)
mesh.update()

often you can use something like itertools to flatten a nested list of coordinates

flat_list_of_verts = list(itertools.chain.from_iterable(verts))

foreach_set will always expect a flat list.