USD export: fix missing animation frames. #111248

Michael Kowalski · 2023-08-18T04:47:54+02:00

Michael Kowalski commented

2023-08-18 04:47:54 +02:00

This fixes a bug where only the time sample for the first frame
is written to a USD animation.

Replaced the hard-coded USDExporterContext::time_code value with a
USDExporterContext::get_time_code function wrapper which is called
from USDAbstractWriter::get_export_time_code() to query the current
frame when writing an animation.

Steps to Reproduce

Load the attached simple_cube_anim.blend and export the
scene to USDA, making sure the Animation USD export option is enabled.

Examine the exported USDA in a text editor an notice that the Cube xformOp:transform
only has a single time sample. When loading the USDA in USDView or Blender, the
Cube transform doesn't animate.

I've attached bad_cube_anim.usda and good_cube_anim.usda for example output
before and after the fix

Discussion

This appears to be an issue introduced in commit 288fe44d4c

That commit changed USDAbstractWriter::get_export_time_code()
to return usd_export_context_.time_code, rather than querying the
current time code from the hierarchy iterator.

When exporting an animation, a USDAbstractWriter instance is used
to write multiple frames. However, since the value of
usd_export_context_.time_code is set when the writer is constructed,
the time code is never updated and all the frames are written to the same
time sample.

An alternative fix I considered was to make USDExporterContext::time_code
a reference or pointer which could be updated "live" over the frame range,
but this seemed less intuitive. However, I'm open to reconsidering this or
other solutions as well.

This fixes a bug where only the time sample for the first frame is written to a USD animation. Replaced the hard-coded `USDExporterContext::time_code` value with a `USDExporterContext::get_time_code` function wrapper which is called from `USDAbstractWriter::get_export_time_code()` to query the current frame when writing an animation. ### Steps to Reproduce Load the attached `simple_cube_anim.blend` and export the scene to USDA, making sure the `Animation` USD export option is enabled. Examine the exported USDA in a text editor an notice that the Cube xformOp:transform only has a single time sample. When loading the USDA in USDView or Blender, the Cube transform doesn't animate. I've attached `bad_cube_anim.usda` and `good_cube_anim.usda` for example output before and after the fix ### Discussion This appears to be an issue introduced in commit https://projects.blender.org/blender/blender/commit/288fe44d4cd4f5b0ee0358a8e7639ca80984a350 That commit changed `USDAbstractWriter::get_export_time_code()` to return `usd_export_context_.time_code`, rather than querying the current time code from the hierarchy iterator. When exporting an animation, a `USDAbstractWriter` instance is used to write multiple frames. However, since the value of `usd_export_context_.time_code` is set when the writer is constructed, the time code is never updated and all the frames are written to the same time sample. An alternative fix I considered was to make `USDExporterContext::time_code` a reference or pointer which could be updated "live" over the frame range, but this seemed less intuitive. However, I'm open to reconsidering this or other solutions as well.

bad_cube_anim.usda

1.7 KiB

simple_cube_anim.blend

837 KiB

good_cube_anim.usda

4.2 KiB

Michael Kowalski added 1 commit 2023-08-18 04:48:07 +02:00

buildbot/vexp-code-patch-coordinator Build done. Details

b7d3d4e01f USD export: fix missing animation frames.

This fixes a bug where only the time sample for the first frame
is written to a USD animation.

Replaced the hard-coded USDExporterContext::time_code value with a
USDExporterContext::get_time_code function wrapper which is called
from USDAbstractWriter::get_export_time_code() to query the current
frame when writing an animation.

Michael Kowalski commented

2023-08-18 04:49:50 +02:00

@blender-bot build

Michael Kowalski added the

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

USD export: fix missing animation frames. #111248

Steps to Reproduce

Discussion