From 2d5773d11a0698f1cf421d7fc7c7d823be601124 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sybren=20A=2E=20St=C3=BCvel?= <sybren@blender.org>
Date: Fri, 6 Mar 2020 14:28:54 +0100
Subject: Documentation: added bpy.msgbus description and examples

The `bpy.msgbus` namespace was not included in the documentation generation.
I've added it, and ported Campbell's examples from P563.
---
 doc/python_api/examples/bpy.msgbus.1.py | 44 +++++++++++++++++++++++++++++++++
 doc/python_api/examples/bpy.msgbus.2.py |  6 +++++
 doc/python_api/examples/bpy.msgbus.3.py |  5 ++++
 3 files changed, 55 insertions(+)
 create mode 100644 doc/python_api/examples/bpy.msgbus.1.py
 create mode 100644 doc/python_api/examples/bpy.msgbus.2.py
 create mode 100644 doc/python_api/examples/bpy.msgbus.3.py

(limited to 'doc/python_api/examples')

diff --git a/doc/python_api/examples/bpy.msgbus.1.py b/doc/python_api/examples/bpy.msgbus.1.py
new file mode 100644
index 00000000000..21198471ffa
--- /dev/null
+++ b/doc/python_api/examples/bpy.msgbus.1.py
@@ -0,0 +1,44 @@
+"""
+The message bus system can be used to receive notifications when properties of
+Blender datablocks are changed via the data API.
+
+
+Limitations
+-----------
+
+The message bus system is triggered by updates via the RNA system. This means
+that the following updates will result in a notification on the message bus:
+
+- Changes via the Python API, for example ``some_object.location.x += 3``.
+- Changes via the sliders, fields, and buttons in the user interface.
+
+The following updates do **not** trigger message bus notifications:
+
+- Moving objects in the 3D Viewport.
+- Changes performed by the animation system.
+
+
+Example Use
+-----------
+
+Below is an example of subscription to changes in the active object's location.
+"""
+
+import bpy
+
+# Any Python object can act as the subscription's owner.
+owner = object()
+
+subscribe_to = bpy.context.object.location
+
+def msgbus_callback(*args):
+    # This will print:
+    # Something changed! (1, 2, 3)
+    print("Something changed!", args)
+
+bpy.msgbus.subscribe_rna(
+    key=subscribe_to,
+    owner=owner,
+    args=(1, 2, 3),
+    notify=msgbus_callback,
+)
diff --git a/doc/python_api/examples/bpy.msgbus.2.py b/doc/python_api/examples/bpy.msgbus.2.py
new file mode 100644
index 00000000000..5ac2187f7f9
--- /dev/null
+++ b/doc/python_api/examples/bpy.msgbus.2.py
@@ -0,0 +1,6 @@
+"""
+Some properties are converted to Python objects when you retrieve them. This
+needs to be avoided in order to create the subscription, by using
+``datablock.path_resolve("property_name", False)``:
+"""
+subscribe_to = bpy.context.object.path_resolve("name", False)
diff --git a/doc/python_api/examples/bpy.msgbus.3.py b/doc/python_api/examples/bpy.msgbus.3.py
new file mode 100644
index 00000000000..3af5660eff6
--- /dev/null
+++ b/doc/python_api/examples/bpy.msgbus.3.py
@@ -0,0 +1,5 @@
+"""
+It is also possible to create subscriptions on a property of all instances of a
+certain type:
+"""
+subscribe_to = (bpy.types.Object, "location")
-- 
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