Maniphest T61103

Mirrored objects render black when using the Bevel Node
Closed, Resolved
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Assigned To
Brecht Van Lommel (brecht)
Authored By
Sebastian Koenig (sebastian_k)
Feb 1 2019, 4:54 PM
Tags
  • BF Blender
  • Cycles
Subscribers
Sebastian Koenig (sebastian_k)
Tim Stullich (tstullich)
Tokens
"Love" token, awarded by sebastian_k.

Description

System Information
Operating system: elementaryOS 0.4.1
Graphics card: GTX1080

Blender Version
Broken: 2.80, 7b05b2564d8

Short description of error
Objects that use the Bevel Node render almost black. Happens to regular objects as well as Collection Instances. But only on F12! The error is not visible in Viewport Rendering.
Here's how it looks in the viewport:

And this is how it looks when rendered (F12):

Happens also in 2.79 (master)
Exact steps for others to reproduce the error
Open this file and compare viewport render and F12:

bevel_mirror.blend99 KBDownload

Revisions and Commits

rC Cycles
rC19db93a06ed1 Fix T61103: Cycles bevel wrong on objects with negative scale.
rB Blender
rB56a633fd2c40 Fix T61103: Cycles bevel wrong on objects with negative scale.

Related Objects

Mentioned Here
T56950: UI Paper Cuts (Parent Task)
rB7b05b2564d8f: Fix T61088: Cycles particle viewport render stuck in loop.

Event Timeline

Sebastian Koenig (sebastian_k) assigned this task to Brecht Van Lommel (brecht).Feb 1 2019, 4:54 PM
Sebastian Koenig (sebastian_k) created this task.
Sebastian Koenig (sebastian_k) added a project: Cycles.
Brecht Van Lommel (brecht) lowered the priority of this task from 90 to 50.Feb 1 2019, 5:03 PM
Tim Stullich (tstullich) added a subscriber: Tim Stullich (tstullich).Mar 5 2019, 12:11 PM
Tim Stullich (tstullich) added a comment.Mar 6 2019, 1:06 AM

Hi, I am interested in trying to fix this issue. I was wondering in which files would I need to look in order to start tracking down the source of the bug?

Brecht Van Lommel (brecht) added a comment.Mar 6 2019, 12:59 PM

The bevel shader code is in intern/cycles/kernel/svm/svm_bevel.h.

Tim Stullich (tstullich) added a comment.Mar 8 2019, 7:00 PM

Ok, so I started taking a look at the shader code but I am having a hard time understanding it all, even with the reference paper in the comments. Is there a way to debug the shader code when it is running?

Brecht Van Lommel (brecht) added a comment.Mar 8 2019, 7:22 PM

You can use a debugger to set a breakpoint on this function and step through the code. Which one depends on your development environment, it's not really a Blender specific thing.

This is not the easiest bug to start with though, if you're just getting start with Blender development you might want to pick an easier bug.

Tim Stullich (tstullich) added a comment.Mar 8 2019, 7:34 PM

Yeah, I am thinking I might be a little in over my head with this bug, although it has been fun reading up on MIS and BSSRDF concepts and getting to know the code base.

Do you have a suggestion for an easier bug to start with? I had asked in the IRC channel for one and this one was suggested to me as a starter.

Sebastian Koenig (sebastian_k) added a comment.Mar 8 2019, 10:02 PM

@Tim Stullich (tstullich) so sorry to have put you on this, I really thought this would be an easy one , especially because it works fine in preview rendering.... I better shut up next time :)

Brecht Van Lommel (brecht) changed the task status from Unknown Status to Resolved by committing rB56a633fd2c40: Fix T61103: Cycles bevel wrong on objects with negative scale..Mar 11 2019, 2:34 PM
Brecht Van Lommel (brecht) added a commit: rB56a633fd2c40: Fix T61103: Cycles bevel wrong on objects with negative scale..
Sebastian Koenig (sebastian_k) awarded a token.Mar 11 2019, 2:37 PM

@Brecht Van Lommel (brecht) thanks so much for fixing! this makes so many things so much easier now! :)

Brecht Van Lommel (brecht) added a comment.Mar 11 2019, 2:42 PM

@Tim Stullich (tstullich), T56950: UI Paper Cuts (Parent Task) and Good First Issue are probably a better place to start.

Brecht Van Lommel (brecht) added a commit: rC19db93a06ed1: Fix T61103: Cycles bevel wrong on objects with negative scale..Aug 22 2019, 5:14 PM