====== Blender Python Addon Notes ======
  * [[..start|Full Blender Python notes]]
  * [[https://b3d.interplanety.org/en/working-with-uv-maps-through-the-blender-api/|Info about UV Meshes]]

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/

===== Quick Tips =====

<code python>
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
</code>

===== Operators =====

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'}.

==== Operator Property ====

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

**Example:**

<code python>
# 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
</code>

===== How to Make Meshes with Python in Blender =====

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

This is how to do it without using BMesh.

<code python>
so = bpy.context.active_object
verts = so.data.vertices
edges = so.data.edges
faces = so.data.polygons
</code>

<code python>
# coordinates:
# verts[i].co
for v in verts:
   print(v.co)
</code>

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

==== Creating a mesh ====

<code python>
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])

</code>

<code python>
# 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
</code>

===== Blender member variables =====

^BL Variable^Example^Description^
|bl_context|uv|The context in which the panel belongs to|
|bl_idname|VIEW3D_PT_test_1|Name of the object. Unique identifier for buttons and menu items to reference.. If this is set, the panel gets a custom ID, otherwise it takes the name of the class used to define the panel. For example, if the class name is “OBJECT_PT_hello”, and bl_idname is not set by the script, then bl_idname = “OBJECT_PT_hello”|
|bl_label|Panel One|Display name in the interface. Name of the object, shows up in a menu. The panel label, shows up in the panel header at the right of the triangle used to collapse the panel|
|bl_space_type|VIEW_3D|The space the panel will be used in. enum in [‘EMPTY’, ‘VIEW_3D’, ‘IMAGE_EDITOR’, ‘NODE_EDITOR’, ‘SEQUENCE_EDITOR’, ‘CLIP_EDITOR’, ‘DOPESHEET_EDITOR’, ‘GRAPH_EDITOR’, ‘NLA_EDITOR’, ‘TEXT_EDITOR’, ‘CONSOLE’, ‘INFO’, ‘TOPBAR’, ‘STATUSBAR’, ‘OUTLINER’, ‘PROPERTIES’, ‘FILE_BROWSER’, ‘SPREADSHEET’, ‘PREFERENCES’], default ‘EMPTY’|
|bl_region_type|UI|The region where the panel is going to be used in. enum in [‘WINDOW’, ‘HEADER’, ‘CHANNELS’, ‘TEMPORARY’, ‘UI’, ‘TOOLS’, ‘TOOL_PROPS’, ‘PREVIEW’, ‘HUD’, ‘NAVIGATION_BAR’, ‘EXECUTE’, ‘FOOTER’, ‘TOOL_HEADER’, ‘XR’], default ‘WINDOW’|
|bl_category|Tool|The category (tab) in which the panel will be displayed, when applicable. Leave blank if panel doesn't have tabs.|
|bl_options|DEFAULT_CLOSED|One of DEFAULT_CLOSED, HIDE_HEADER, INSTANCED, HEADER_LAYOUT_EXPAND - Formatting for this panel, set to <nowiki>{'REGISTER', 'UNDO'}</nowiki> to enable undo|
|bl_region_type|WINDOW|enum in [‘WINDOW’, ‘HEADER’, ‘CHANNELS’, ‘TEMPORARY’, ‘UI’, ‘TOOLS’, ‘TOOL_PROPS’, ‘PREVIEW’, ‘HUD’, ‘NAVIGATION_BAR’, ‘EXECUTE’, ‘FOOTER’, ‘TOOL_HEADER’, ‘XR’], default ‘WINDOW’|


===== register, unregister =====

**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.

<code python>
def register():
    bpy.utils.register_class(LayoutDemoPanel)
</code>

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

<code python>
def unregister():
    bpy.utils.unregister_class(LayoutDemoPanel)
</code>

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.

<code python>
def unregister():
    myPanelClass = bpy.types.Panel.bl_rna_get_subclass_py("SCENE_PT_layout")
    bpy.utils.unregister_class(myPanelClass )
</code>

===== Python's automatic script variables =====

^Variable^Description^
|<nowiki>__name__</nowiki>|Contains "<nowiki>__main__</nowiki>" if run from the Blender text editor, otherwise, it contains the Python class which calls this|

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

<code python>
if __name__ == "__main__":
    register()
</code>