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When rendering in viewport mode the draw engines do not pass correct Alpha values.
Confirmed, NormalPublicTO DO

Description

During testing D4638: Camera Background Images we came across the issues that holdouts and DoF rendering were having render artifacts might be solveable. Investigating into it lead to that the alpha values were all set to 1, so we couldn't do the right compositing of the background images afterwards.

Holdout in combination with transparent film doesn't seem to work. When scene as Film Transparent enabled and I create a viewlayer that is set to holdout, the Cycles viewport rendering shows the transparent area created by the holdout as grey world background, but not the Background images. You can try this file:

Just hit shift+z to go to rendered viewport to see the issue.
It does work fine in 2.79 (using mask layer in renderlayers)

Event Timeline

Jeroen Bakker (jbakker) lowered the priority of this task from 90 to Normal.Jun 21 2019, 10:44 AM
Jeroen Bakker (jbakker) created this task.
Jeroen Bakker (jbakker) edited a custom field.
Jeroen Bakker (jbakker) updated the task description. (Show Details)
Jeroen Bakker (jbakker) renamed this task from When rendering in viewport mode the draw manager do not pass correct Alpha values. to When rendering in viewport mode the draw engines do not pass correct Alpha values..Jun 21 2019, 10:50 AM
Jeroen Bakker (jbakker) claimed this task.

Looks like it was fixed beetween 2.81 (sub 13), branch: master, commit date: 2019-10-02 21:39, hash: rB93e8c962fcc1 and 2.81 (sub 14), branch: master, commit date: 2019-10-06 14:05, hash: rB54a9649e2636

Patch is ready, but needs a lot of testing. As this is not a high prio, postponing this to b2.82

This is marked with the 2.82 milestone. If no fix is planned for that release, please move it to 2.83 or untag it from a specific milestone.