• Full Blender Python notes

Doing research to make a panel to control Baking Texture assignments.

• https://www.youtube.com/watch?v=Mjy-zGG3Wk4 (Blender 2.8 Updating Addon Python Scripts)
• https://docs.blender.org/api/blender_python_api_2_65_5/info_quickstart.html#info-quickstart (Blender/Python API quickstart)
• https://docs.blender.org/api/3.0/

list(bpy.data.objects)
   # -> Lists objects array
type(bpy.data.objects)
<class 'bpy_prop_collection'>
   # -> Get the Python type
dir(bpy.data.objects)
   # -> Get the variables and methods on this class

The menu item: Help → Operator Cheat Sheet” gives a list of all operators and their default values in Python syntax, along with the generated docs. This is a good way to get an overview of all blender’s operators.

Operators don’t have return values as you might expect, instead they return a set() which is made up of: {'RUNNING_MODAL', 'CANCELLED', 'FINISHED', 'PASS_THROUGH'}. Common return values are {'FINISHED'} and {'CANCELLED'}.

https://docs.blender.org/api/blender_python_api_2_65_5/info_tutorial_addon.html#operator-property

Example:

# moved assignment from execute() to the body of the class...
total = bpy.props.IntProperty(name="Steps", default=2, min=1, max=100)
 
# and this is accessed on the class
# instance within the execute() function as...
self.total

from https://youtu.be/mljWBuj0Gho (Curtis Holt)

This is how to do it without using BMesh.

so = bpy.context.active_object
verts = so.data.vertices
edges = so.data.edges
faces = so.data.polygons

# coordinates:
# verts[i].co
for v in verts:
   print(v.co)

# edges[i].vertices[j]
for e in edges:
  # v is an index, 0 - N
  for v in e.vertices:
    print(v)

import bpy
 
verts = []
edges = []
faces = []
 
verts.append([ #index 0
  0.0, #x
  1.0, #y
  0.0 #z
])
verts.append([ #index 1
  1.0, #x
  0.0, #y
  0.0 #z
])
verts.append([ #index 2
  0.0, #x
  0.0, #y
  1.0 #z
])
verts.append([ #index 3
  -1.0, #x
  0.0, #y
  0.0 #z
])
 
# values are indexes
edges.append([0,1]) # but this isn't needed, because edges are added automatically
 
# values are index of vertexes
faces.append([0,1,2])
faces.append([2,0,3])

# The following works as long as there is a Collection called "Objects"
 
name = "New Object"
mesh = bpy.data.meshes.new(name)
obj = bpy.data.objects.new(name, mesh) # Object contains meta data, not just the mesh
col = bpy.data.collections.get("Objects")
col.objects.link(obj) # This will make the object actually display
bpy.context.view_layer.objects.active = obj # makes the object active (isn't working for me)
mesh.from_pydata(verts, edges, faces) # actually makes the mesh

To register a Python class, so that it can be used within Blender, this function needs to run when the Python file is loaded. This means it is at the same level as the class defintion, that is, not indented.

def register():
    bpy.utils.register_class(LayoutDemoPanel)

To unregister a Python class, so that it disappears from the menuing, you typically use something like this:

def unregister():
    bpy.utils.unregister_class(LayoutDemoPanel)

but when run from the Blender Python text editor, the class doesn't have any name space, so you have to find it first.

Note that “Panel” needs to be the type that this class is, one of Panel, UIList, Menu, Header, Operator, KeyingSetInfo, RenderEngine.

def unregister():
    myPanelClass = bpy.types.Panel.bl_rna_get_subclass_py("SCENE_PT_layout")
    bpy.utils.unregister_class(myPanelClass )

So we include this at the end of a Python script so that when running inside of Blender, it registers this class. Otherwise it doesn't need to, because the Script runner takes care of this. 2/15/2022

if __name__ == "__main__":
    register()