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Viewing value passes in render view displays the value as alpha
Closed, ResolvedPublicBUG

Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 3080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 460.79

Blender Version
Broken: version: 2.92.0 Release Candidate, branch: master, commit date: 2021-02-19 06:58, hash: rB241273d36261
Worked: (newest version of Blender that worked as expected)

Short description of error
When you render a pass that is a single value (eg. Mist, Z, value AOV...) when you switch to in in the passes dropdown, the value is interpreted as alpha in the viewer.
The display channels dropdown updates to colour only but does not properly update the viewer. Re-selecting the option fixes it.

Exact steps for others to reproduce the error
In the default scene, enable the Mist pass.
Render the image and change the viewer to the mist pass and the cube will show as transparent.

Event Timeline

James Horsley (mmdanggg2) renamed this task from Viewing float passes in render view displays the value as alpha to Viewing value passes in render view displays the value as alpha.Mon, Feb 22, 6:52 PM
James Horsley (mmdanggg2) created this task.
Philipp Oeser (lichtwerk) changed the subtype of this task from "Report" to "Bug".Tue, Feb 23, 11:44 AM

There was a similar report prior to the introduction of the Image Engine, see T74586.
This was fixed by rB6a5bd812b569 at that time, but got lost in the refactor it seems.

Above commit introduced the ED_space_image_get_display_channel_mask function that will determine
the valid bitflags for the display channel of a given ImBuf.

But since the refactor, this is not called anymore (draw_image_main is not called anymore)
Now it seems we can safely reuse that said function ED_space_image_get_display_channel_mask also for the Image Engine.