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Maniphest T69410

Shadow catcher receive shadows even if there is no light in the scene
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Description

System Information
Operating system: Windows
Graphics card: GeForce GTX 1080 Ti

system-info.txt27 KBDownload

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: f6cb5f54494e, type: build date: 2019-07-29, 09:44 AM
Worked: -

Short description of error
See my attached .blend file for an example and the screenshot for additional infos.

If you set the light object power to "0", then the shadow catcher object receives shadows. But there is no light in the scene.
I've set the world light to "0" too. This should not happen.

Exact steps for others to reproduce the error

  • Open my blend file.
  • Set one of the top views to "Rendered". Use the Cycles renderer.
  • Set the light power to "0" now.
  • The shadow catcher on the ground receives shadows then, but there is no light in the scene anymore. This isn't what I expect. Actually there shouldn't be any shadows around the box.

Do I misunderstand something when using the shadows catcher or is this an error?

shadowcatcher_problem01.blend650 KBDownload

Related Objects

Event Timeline

Christoph Werner (Taros) created this task.Sep 2 2019, 3:04 PM
Marcin Twarowski (Tvaroog) added a subscriber: Marcin Twarowski (Tvaroog).Sep 2 2019, 3:55 PM
This comment was removed by Marcin Twarowski (Tvaroog).
Christoph Werner (Taros) updated the task description. (Show Details)Sep 2 2019, 4:41 PM
Philipp Oeser (lichtwerk) changed the task status from Needs Triage to Confirmed.Dec 29 2019, 1:31 PM
Philipp Oeser (lichtwerk) added projects: Render & Cycles, Cycles.
Philipp Oeser (lichtwerk) added subscribers: Sergey Sharybin (sergey), Philipp Oeser (lichtwerk).

Although a bit on shaky ground here, but I would kind of confirm this issue.

Relevant commits:
rBd14e39622ae6
rBbd069a89aa3a

For absolutely no light (path_total == 0.0f), rBbd069a89aa3a changed behavior from returning 1.0f to returning L->shadow_transparency (see what is now path_radiance_sum_shadowcatcher).
Since above commit was only intended to fix problems with transparent shadow casters, but also changed the behavior for opaque shadow casters in the case of no light, I would assume this can somehow be fixed and was not intended, @Sergey Sharybin (sergey)?
(to me it would make more snese to actually have no shadow in the case of no light -- so agree with the report, but will leave up to @Sergey Sharybin (sergey) to decide.... confirming for now though...)

Sidenote: there are all sorts of (other) improvements to make, so if this turns out to be a known limitation for now, maybe this can be considered elswhere:
https://devtalk.blender.org/t/lets-finally-fix-the-shadowcatcher/691
T71253: Cycles shadow catcher improvements

Bastien Montagne (mont29) changed the subtype of this task from "Report" to "Bug".Jan 15 2020, 5:45 PM
Christoph Werner (Taros) added a comment.EditedJan 16 2020, 8:30 AM

Exactly. I repeat it for better understanding:

If there is no world light set (environment light strength is set to 0 )
and there is no light object set or all light objects are set to power of 0 then no shadows should be seen on any shadow catchers.

For me this is often a problem, when I work with render passes.

Thank you for the attention
Chris

Brecht Van Lommel (brecht) closed this task as Archived.Nov 5 2021, 10:28 PM
Brecht Van Lommel (brecht) added a subscriber: Brecht Van Lommel (brecht).

The rewritten shadow catcher in Blender 3.0 does not have this problem anymore.