Depsgraph not updating properly for frame_change_pre handler #77126

New Issue

Christopher Gearhart · 2020-05-28T15:30:32+02:00

2020-05-28 15:30:32 +02:00

System Information
Operating system: Windows 10
Graphics card:

Blender Version
Broken: 2.83
Worked: Never

Short description of error

Depsgraph access in the frame_update_pre handler differs from viewport animation to render animation. It seems the global depsgraph does not update during render animation. I believe a simple solution would be to provide a depsgraph argument in the frame_update_pre handler (similar to the frame_change_post handler).

Exact steps for others to reproduce the error
Based on the default startup:

Animate the default cube's location over the first 10 frames (and set timeline end frame to 10)
Run the following script:

import bpy
from bpy.app.handlers import persistent

@persistent
def get_mw_translation(scene, depsgraph=None):
    text="post:"
    if depsgraph is None:
        depsgraph = bpy.context.evaluated_depsgraph_get()
        text = "pre:"
        print()
    cube = bpy.data.objects["Cube"].evaluated_get(depsgraph)
    print(text, cube.matrix_world.to_translation())
    
bpy.app.handlers.frame_change_pre.append(get_mw_translation)
bpy.app.handlers.frame_change_post.append(get_mw_translation)

Play the animation. Watch the output in the console, and note that the matrix world data updates appropriately for both 'pre' and 'post' handlers.
Simplify your render settings to render quickly (e.g. Cycles at 5 samples)
Render the animation. Watch the output in the console, and note that the 'pre' handler does not update, while the 'post' handler updates appropriately.

**System Information** Operating system: Windows 10 Graphics card:<irrelevant> **Blender Version** Broken: 2.83 Worked: Never **Short description of error** Depsgraph access in the `frame_update_pre` handler differs from viewport animation to render animation. It seems the global depsgraph does not update during render animation. I believe a simple solution would be to provide a depsgraph argument in the `frame_update_pre` handler (similar to the `frame_change_post` handler). **Exact steps for others to reproduce the error** Based on the default startup: 1. Animate the default cube's location over the first 10 frames (and set timeline end frame to 10) 2. Run the following script: ``` import bpy from bpy.app.handlers import persistent @persistent def get_mw_translation(scene, depsgraph=None): text="post:" if depsgraph is None: depsgraph = bpy.context.evaluated_depsgraph_get() text = "pre:" print() cube = bpy.data.objects["Cube"].evaluated_get(depsgraph) print(text, cube.matrix_world.to_translation()) bpy.app.handlers.frame_change_pre.append(get_mw_translation) bpy.app.handlers.frame_change_post.append(get_mw_translation) ``` 3. Play the animation. Watch the output in the console, and note that the matrix world data updates appropriately for both 'pre' and 'post' handlers. 4. Simplify your render settings to render quickly (e.g. Cycles at 5 samples) 5. Render the animation. Watch the output in the console, and note that the 'pre' handler does not update, while the 'post' handler updates appropriately.

Christopher Gearhart commented

2020-05-28 15:30:32 +02:00

Added subscriber: @bblanimation

Germano Cavalcante commented

2020-05-29 15:50:48 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-05-29 15:50:48 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Germano Cavalcante commented

2020-05-29 15:50:48 +02:00

Looks well related to #71908 if not the same problem.

Sybren A. Stüvel commented

2020-06-02 14:35:25 +02:00

Added subscriber: @dr.sybren

Sybren A. Stüvel self-assigned this 2020-06-02 14:35:25 +02:00

Sybren A. Stüvel commented

2020-06-02 14:35:25 +02:00

This is not the same as #71908.

The difference between viewport & render animation is as follows. In the viewport the depsgraph is "active", and thus the updates by the animation system are written back to the original datablocks. For rendering a new depsgraph is made (because all kinds of things have to be evaluated differently), which as a result is not marked as "active", and thus animation updates are not written back to the original datablocks. The problem here is that bpy.context will give you the viewport depsgraph, and not the render depsgraph. It'll thus always return the values as are currently seen in the viewport.

As can be seen in BKE_scene_graph_update_for_newframe() (in scene.c), updating the scene for a new frame happens as follows:

Prior to calling BKE_scene_graph_update_for_newframe(), the scene's current frame is updated to the new frame.
The frame_change_pre() callback is called.
The depsgraph receives the new scene time and is evaluated.
The frame_change_post() callback is called.

If that callback changed any data, the depsgraph is re-evaluated.

As you can see, in the pre-handler the depsgraph hasn't been updated for the new frame yet (hence the 'pre'). This can be used to change things around before the depsgraph is evaluated.

I agree that it is a good idea to explicitly pass the depsgraph here (also see #77086).

This is not the same as #71908. The difference between viewport & render animation is as follows. In the viewport the depsgraph is "active", and thus the updates by the animation system are written back to the original datablocks. For rendering a new depsgraph is made (because all kinds of things have to be evaluated differently), which as a result is not marked as "active", and thus animation updates are not written back to the original datablocks. The problem here is that `bpy.context` will give you the viewport depsgraph, and not the render depsgraph. It'll thus always return the values as are currently seen in the viewport. As can be seen in `BKE_scene_graph_update_for_newframe()` (in `scene.c`), updating the scene for a new frame happens as follows: - Prior to calling `BKE_scene_graph_update_for_newframe()`, the scene's current frame is updated to the new frame. - The `frame_change_pre()` callback is called. - The depsgraph receives the new scene time and is evaluated. - The `frame_change_post()` callback is called. # If that callback changed any data, the depsgraph is re-evaluated. As you can see, in the pre-handler the depsgraph hasn't been updated for the new frame yet (hence the 'pre'). This can be used to change things around before the depsgraph is evaluated. I agree that it is a good idea to explicitly pass the depsgraph here (also see #77086).

Sybren A. Stüvel commented

2020-06-02 15:56:17 +02:00

Added subscriber: @Sergey

Sybren A. Stüvel commented

2020-06-02 15:56:17 +02:00

I agree that it is a good idea to explicitly pass the depsgraph here

Discussed with @Sergey, and this is not possible. The handler is not to be used as a "before the frame changes" handler, but as a "before the depsgraph updates". This means it can be used for adjusting the data & relations for the new frame. The depsgraph itself is intentionally not available, as it's out of date (i.e. it's not in sync with either the previous or the current frame).

I'll see this as a documentation task, as the code is working as intended.

> I agree that it is a good idea to explicitly pass the depsgraph here Discussed with @Sergey, and this is not possible. The handler is not to be used as a "before the frame changes" handler, but as a "before the depsgraph updates". This means it can be used for adjusting the data & relations for the new frame. The depsgraph itself is intentionally not available, as it's out of date (i.e. it's not in sync with either the previous or the current frame). I'll see this as a documentation task, as the code is working as intended.

blender-admin commented

2020-06-02 16:33:35 +02:00

This issue was referenced by cdf0d95a50

This issue was referenced by cdf0d95a50e6ea5592e65242c3c8ffbdfd4629a0

Sybren A. Stüvel commented

2020-06-02 17:33:29 +02:00

Changed status from 'Confirmed' to: 'Resolved'

Sybren A. Stüvel closed this issue

2020-06-02 17:33:29 +02:00

bar commented

2022-06-15 18:50:19 +02:00

Added subscriber: @barakooda

bar commented

2022-06-15 18:50:19 +02:00

This comment was removed by @barakooda

*This comment was removed by @barakooda*

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Depsgraph not updating properly for frame_change_pre handler #77126

If that callback changed any data, the depsgraph is re-evaluated.

Depsgraph not updating properly for `frame_change_pre` handler #77126