bpy.ops.render.render('INVOKE_DEFAULT') returns 'CANCELLED' during UI interaction #52258

New Issue

Robert Guetzkow · 2017-08-03T20:27:30+02:00

Robert Guetzkow commented

2017-08-03 20:27:30 +02:00

System Information
Windows 10 (64-Bit), GeForce GTX 1080 Ti

Blender Version
Broken: 2.78c e92f235283, 2.80.0 3ededb1

Short description of error
Using a modal operator to call bpy.ops.render.render('INVOKE_DEFAULT') multiple times, results in 'CANCELLED' return value as soon as the user interacts with the UI. This happens without modifying the scene in the python script and with each call to render being made after the previous render is finished.

The intention behind such a script (in an actual project) is to create multiple renders with motion blur, which have no temporal connection to each other.
An example would be soccer player kicking a ball, at many different positions on the field.
MWE_bug.blend
Exact steps for others to reproduce the error
Open the attached .blend file. The script is based on the one provided by Bastien Montagne (mont29) https://developer.blender.org/T32076

Press the "Run Script"-Button
Open the tool shelf in 3D view by pressing 'T'
Go to the 'Misc.' tab and press 'Crashing Render'
Click around in the UI, e.g. switching between render tab and material tab.
Alternatively you can also minimize and maximize the window.

**System Information** Windows 10 (64-Bit), GeForce GTX 1080 Ti **Blender Version** Broken: 2.78c e92f235283, 2.80.0 3ededb1 **Short description of error** Using a modal operator to call bpy.ops.render.render('INVOKE_DEFAULT') multiple times, results in 'CANCELLED' return value as soon as the user interacts with the UI. This happens without modifying the scene in the python script and with each call to render being made after the previous render is finished. The intention behind such a script (in an actual project) is to create multiple renders with motion blur, which have no temporal connection to each other. An example would be soccer player kicking a ball, at many different positions on the field. [MWE_bug.blend](https://archive.blender.org/developer/F691842/MWE_bug.blend) **Exact steps for others to reproduce the error** Open the attached .blend file. The script is based on the one provided by Bastien Montagne (mont29) https://developer.blender.org/T32076 - Press the "Run Script"-Button - Open the tool shelf in 3D view by pressing 'T' - Go to the 'Misc.' tab and press 'Crashing Render' - Click around in the UI, e.g. switching between render tab and material tab. Alternatively you can also minimize and maximize the window.

Robert Guetzkow commented

2017-08-03 20:27:30 +02:00

Changed status to: 'Open'

Robert Guetzkow commented

2017-08-03 20:27:30 +02:00

Added subscriber: @rjg

Robert Guetzkow commented

2017-08-04 08:52:29 +02:00

This behavior can be reproduced on Linux (Ubuntu 64-Bit).

Robert Guetzkow commented

2017-08-06 19:44:11 +02:00

Can somebody verify whether this is intended behavior or actually a bug? I would greatly appreciate a workaround.

Sergey Sharybin commented

2017-08-08 16:00:31 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2017-08-08 16:00:31 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2017-08-08 16:00:31 +02:00

Sergey Sharybin self-assigned this 2017-08-08 16:00:31 +02:00

Sergey Sharybin commented

2017-08-08 16:00:31 +02:00

You are invoking one modal operator from another one.. This is a straight way to have all sort of weird and wonderful issues. This is not recommended to run operator from another one.

In any case, root of this particular issue is that render happens from a job (separate thread), and we don't allow two render jobs to be existing at the same time. However, since render works from a job, we call render_finished callback from that thread (this is the only place we can call it..). This might be seen by your script logic that system is ready for the next render, while it is not true since it might take some time to free remaining parts of render data and close job completely.

I'm not sure about reliable way of solving this problem, usually such tasks are done from a command line render script. You might try adding some delay after render_finish or re-try render later if 'CANCEL' is returned.

In any case, you're just stressing system to something it's not designed for.

You are invoking one modal operator from another one.. This is a straight way to have all sort of weird and wonderful issues. This is not recommended to run operator from another one. In any case, root of this particular issue is that render happens from a job (separate thread), and we don't allow two render jobs to be existing at the same time. However, since render works from a job, we call render_finished callback from that thread (this is the only place we can call it..). This might be seen by your script logic that system is ready for the next render, while it is not true since it might take some time to free remaining parts of render data and close job completely. I'm not sure about reliable way of solving this problem, usually such tasks are done from a command line render script. You might try adding some delay after render_finish or re-try render later if 'CANCEL' is returned. In any case, you're just stressing system to something it's not designed for.

Robert Guetzkow commented

2017-08-08 18:35:52 +02:00

Added subscriber: @mont29

Robert Guetzkow commented

2017-08-08 18:35:52 +02:00

What you described as root issue was pretty much what I imagined. Unfortunately the re-try idea doesn't work well, once it has returned 'CANCELLED' it's pretty much guaranteed to fail at subsequent attempts.

I haven't looked at the source at such a detailed level, but is there a particular reason why the callback isn't called after the (render) thread is joined?
Not sure if I missed something, but does the UI-button for rendering behave differently? Though it is unlikely that the user is clicking the button just as the render has finished, it should be causing the same problem.

The command line render script would be another option, but wouldn't give any benefit over calling bpy.ops.render.render() instead of bpy.ops.render.render('INVOKE_DEFAULT'). That was actually the main
reason that had me wondering if this is a bug, bpy.ops.render.render() works perfectly (though UI is not responsive). However that is due to not using a background thread. What is the correct way to call bpy.ops.render.render() (with whatever parameters)? The modal version was based on the code from @mont29, but apparently that is discouraged? If I'm not entirely mistaken every addon will (directly or indirectly) call it through another operator, since all buttons are operators.

What you described as root issue was pretty much what I imagined. Unfortunately the re-try idea doesn't work well, once it has returned 'CANCELLED' it's pretty much guaranteed to fail at subsequent attempts. I haven't looked at the source at such a detailed level, but is there a particular reason why the callback isn't called after the (render) thread is joined? Not sure if I missed something, but does the UI-button for rendering behave differently? Though it is unlikely that the user is clicking the button just as the render has finished, it should be causing the same problem. The command line render script would be another option, but wouldn't give any benefit over calling bpy.ops.render.render() instead of bpy.ops.render.render('INVOKE_DEFAULT'). That was actually the main reason that had me wondering if this is a bug, bpy.ops.render.render() works perfectly (though UI is not responsive). However that is due to not using a background thread. What is the correct way to call bpy.ops.render.render() (with whatever parameters)? The modal version was based on the code from @mont29, but apparently that is discouraged? If I'm not entirely mistaken every addon will (directly or indirectly) call it through another operator, since all buttons are operators.

Bastien Montagne commented

2017-08-08 19:14:07 +02:00

Just do not use 'INVOKE_DEFAULT', which will launch it in modal mode, but rather 'EXEC_DEFAULT', that way operation will be regular blocking one and will only return once render is actually finished.

Just do not use `'INVOKE_DEFAULT'`, which will launch it in modal mode, but rather `'EXEC_DEFAULT'`, that way operation will be regular blocking one and will only return once render is actually finished.

Robert Guetzkow commented

2017-08-08 19:43:44 +02:00

Yes that is what I was doing already. ‘EXEC_DEFAULT’ is used when no arguments are given. So the solution is to have no responsive/interactive UI and no preview.
I will take a look at the code. Perhaps this can be changed in future versions. It is very counter intuitive that the callback claims everything is done, but it isn't.

Yes that is what I was doing already. ‘EXEC_DEFAULT’ is used when no arguments are given. So the solution is to have no responsive/interactive UI and no preview. I will take a look at the code. Perhaps this can be changed in future versions. It is very counter intuitive that the callback claims everything is done, but it isn't.

Sergey Sharybin commented

2017-08-08 20:11:05 +02:00

Callback says that rendering is done, as in there is final render and saved. It doesn't mean that render thread is destroyed (because callback is called from render thread). We do not have API to query whether particular thread is active is not.

Robert Guetzkow commented

2017-08-09 16:47:13 +02:00

I understood that. An API to check thread status would still be very useful.

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

bpy.ops.render.render('INVOKE_DEFAULT') returns 'CANCELLED' during UI interaction #52258