From be8879718e24e417d299eb298b8a9d4d2ca324ee Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Sybren=20A=2E=20St=C3=BCvel?= Date: Tue, 11 Feb 2020 10:52:37 +0100 Subject: [PATCH] Documentation: add note on altering data from frame change handlers Blender can crash while rendering, when scene data is changed from within a `frame_change_pre` or `frame_change_post` callback function. This results in bug reports like T60094, T67627, and T73530. Until this is properly resolved, this limitation should be documented. No functional changes. --- doc/python_api/examples/bpy.app.handlers.2.py | 23 +++++++++++++++++++ 1 file changed, 23 insertions(+) create mode 100644 doc/python_api/examples/bpy.app.handlers.2.py diff --git a/doc/python_api/examples/bpy.app.handlers.2.py b/doc/python_api/examples/bpy.app.handlers.2.py new file mode 100644 index 00000000000..aaaedeabecb --- /dev/null +++ b/doc/python_api/examples/bpy.app.handlers.2.py @@ -0,0 +1,23 @@ +""" +Note on Altering Data ++++++++++++++++++++++ + +Altering data from handlers should be done carefully. While rendering the +``frame_change_pre`` and ``frame_change_post`` handlers are called from one +thread and the viewport updates from a different thread. If the handler changes +data that is accessed by the viewport, this can cause a crash of Blender. In +such cases, lock the interface (Render → Lock Interface or +:data:`bpy.types.RenderSettings.use_lock_interface`) before starting a render. + +Below is an example of a mesh that is altered from a handler: +""" + +def frame_change_pre(scene): + # A triangle that shifts in the z direction + zshift = scene.frame_current * 0.1 + vertices = [(-1, -1, zshift), (1, -1, zshift), (0, 1, zshift)] + triangles = [(0, 1, 2)] + + object = bpy.data.objects["The Object"] + object.data.clear_geometry() + object.data.from_pydata(vertices, [], triangles)