Slower frame-change with many objects in the scenes collection #104798

New Issue

Campbell Barton · 2023-02-16T01:25:43+01:00

Campbell Barton commented

2023-02-16 01:25:43 +01:00

Update: since 4.0 there is significantly less change in performance described in this report no matter the value of USE_SCENE_COLLECTION when the script runs. However the PR to resolve this (!104801) speeds up both cases.

When objects are in the scenes collection (instead of a sub-collection), changing frames using left/right keys is slower.

There is also a slowdown when animation playback restarts.

This occurs in 3.5x ab63fe9eab8fd01d4a763199442987191d105c55 and 3.4x release.

To reproduce the problem:

With a new file paste the script inlined at the bottom of the report into a text editor and run it.
Press Spacebar in the 3D viewport to play back animation.
Note the FPS (~13.1 FPS here).
Start again, doing the previous steps with USE_SCENE_COLLECTION = True in the script.
Note the FPS is much lower (~3.46 FPS here).

Explanation

This is an issue I ran into when investigating why objects in collections were being re-populated during animation playback in some files, see !104553.
The cause of the problem is the scene is tagged by the depsgraph (see: ANIMPLAY_FLAG_JUMPED). (note: the jumped flag is set when changing frame via arrow keys & when the animation restarts).
When ANIMPLAY_FLAG_JUMPED is set scene is tagged with ID_RECALC_FRAME_CHANGE.
This causes the scene to be copied (see blender::deg::deg_update_copy_on_write_datablock).
The scene->master_collection is copied (non recursively).
- When scene->master_collection contains many objects, copying has a noticeable performance penalty.
- When it only contains some collections, the problem isn't noticeable.

Other Notes

This is mainly noticeable when loading files pre 2.8x which load objects directly into scene->master_collection.
This report mentions animation playback speed because it's easily measurable, however many other operations trigger this (left/right arrow keys to change frames, every update when dragging scene number buttons "Sampling" (Render or Viewport) for e.g.).
In the test script the start and end frames are the same to so the playback is continually restarting to accentuate the problem and match the slowdown from changing frames via arrow keys.

This script adds many objects to the factory settings file, hides them, adds some keyframes to the Light and sets the 3D viewport full-screen, ready for animation playback.

import bpy

USE_SCENE_COLLECTION = False
OBJECT_NUMBER = 20_000

def objects_create(object_num):
    objects = []
    new = bpy.data.objects.new
    for i in range(object_num):
        objects.append(new(hex(i), None))
    return objects


def objects_collection_link(collection, objects):
    link = collection.objects.link
    for ob in objects:
        link(ob)


def main():
    from bpy import context

    bpy.ops.wm.read_homefile(use_factory_startup=True)

    if USE_SCENE_COLLECTION:
        collection = context.scene.collection
    else:
        collection = context.collection

    # Keyframe the lamps location, this is important as without this
    # the scene is not considered "animated".
    ob_lamp = bpy.data.objects["Light"]
    ob_lamp.keyframe_insert("location", frame=1)

    # The short frame range shows the problem most,
    # as this tags the scene to be tagged to update on frame-change.
    context.scene.frame_start = 1
    context.scene.frame_end = 1
    
    # Attempt max FPS.
    context.scene.render.fps = 1000

    objects = objects_create(OBJECT_NUMBER)
    objects_collection_link(collection, objects)
    
    # Hide everything, except the lamp.
    bpy.ops.object.select_all(action='SELECT')
    window = bpy.data.window_managers[0].windows[0]
    area = next(area for area in window.screen.areas if area.type == 'VIEW_3D')
    
    # Hide needs an 3D viewport (but select doesn't, hrm..).
    with context.temp_override(window=window, area=area):
        bpy.ops.object.hide_view_set(unselected=False)
    ob_lamp.hide_set(False)
    
    # Fullscreen 3D view (rule out slowdown from drawing other areas).
    with context.temp_override(window=window, area=area):
        bpy.ops.screen.screen_full_area()
    

if __name__ == "__main__":
    main()

Update: since 4.0 there is significantly less change in performance described in this report no matter the value of `USE_SCENE_COLLECTION` when the script runs. However the PR to resolve this (!104801) speeds up both cases. ---- When objects are in the scenes collection (instead of a sub-collection), changing frames using left/right keys is slower. There is also a slowdown when animation playback restarts. This occurs in 3.5x `ab63fe9eab8fd01d4a763199442987191d105c55` and 3.4x release. To reproduce the problem: - With a new file paste the script inlined at the bottom of the report into a text editor and run it. - Press Spacebar in the 3D viewport to play back animation. - Note the FPS (~13.1 FPS here). - Start again, doing the previous steps with `USE_SCENE_COLLECTION = True` in the script. - Note the FPS is much lower (~3.46 FPS here). --- #### Explanation - This is an issue I ran into when investigating why objects in collections were being re-populated during animation playback in some files, see !104553. - The cause of the problem is the scene is tagged by the depsgraph (see: `ANIMPLAY_FLAG_JUMPED`). _(note: the jumped flag is set when changing frame via arrow keys & when the animation restarts)._ - When `ANIMPLAY_FLAG_JUMPED` is set `scene` is tagged with `ID_RECALC_FRAME_CHANGE`. - This causes the scene to be copied (see `blender::deg::deg_update_copy_on_write_datablock`). - The `scene->master_collection` is copied (non recursively). - When `scene->master_collection` contains many objects, copying has a noticeable performance penalty. - When it only contains some collections, the problem isn't noticeable. #### Other Notes - This is mainly noticeable when loading files pre 2.8x which load objects directly into `scene->master_collection`. - This report mentions animation playback speed because it's easily measurable, however many other operations trigger this (left/right arrow keys to change frames, every update when dragging scene number buttons "Sampling" (Render or Viewport) for e.g.). - In the test script the start and end frames are the same to so the playback is continually restarting to accentuate the problem and match the slowdown from changing frames via arrow keys. --- This script adds many objects to the factory settings file, hides them, adds some keyframes to the Light and sets the 3D viewport full-screen, ready for animation playback. ```python import bpy USE_SCENE_COLLECTION = False OBJECT_NUMBER = 20_000 def objects_create(object_num): objects = [] new = bpy.data.objects.new for i in range(object_num): objects.append(new(hex(i), None)) return objects def objects_collection_link(collection, objects): link = collection.objects.link for ob in objects: link(ob) def main(): from bpy import context bpy.ops.wm.read_homefile(use_factory_startup=True) if USE_SCENE_COLLECTION: collection = context.scene.collection else: collection = context.collection # Keyframe the lamps location, this is important as without this # the scene is not considered "animated". ob_lamp = bpy.data.objects["Light"] ob_lamp.keyframe_insert("location", frame=1) # The short frame range shows the problem most, # as this tags the scene to be tagged to update on frame-change. context.scene.frame_start = 1 context.scene.frame_end = 1 # Attempt max FPS. context.scene.render.fps = 1000 objects = objects_create(OBJECT_NUMBER) objects_collection_link(collection, objects) # Hide everything, except the lamp. bpy.ops.object.select_all(action='SELECT') window = bpy.data.window_managers[0].windows[0] area = next(area for area in window.screen.areas if area.type == 'VIEW_3D') # Hide needs an 3D viewport (but select doesn't, hrm..). with context.temp_override(window=window, area=area): bpy.ops.object.hide_view_set(unselected=False) ob_lamp.hide_set(False) # Fullscreen 3D view (rule out slowdown from drawing other areas). with context.temp_override(window=window, area=area): bpy.ops.screen.screen_full_area() if __name__ == "__main__": main() ```

👍 1

Campbell Barton added the

labels 2023-02-16 01:25:43 +01:00

Campbell Barton changed title from ~~Slower frame-change with objects are in the scenes collection~~ to Slower frame-change with many objects in the scenes collection

2023-02-16 01:28:58 +01:00

Campbell Barton referenced a pull request that will close this issue

2023-02-16 02:08:48 +01:00

Fix #104798: Slow frame-change & scrubbing with many objects #104801

Richard Antalik added

and removed

labels 2023-02-16 03:51:03 +01:00

Richard Antalik added the