Workbench transparency rendering issue: "jump" to alpha 1.0 from .999 #66586

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Casey Connor · 2019-07-09T00:55:02+02:00

Casey Connor commented

2019-07-09 00:55:02 +02:00

Not sure if this is a bug: adjusting alpha of object causes it to "snap" in to alpha mode at e.g 0.999 alpha. This would apparently make it impossible to smoothly animate from 0 alpha to 1, due to the "jump" as it goes to 1.

This is apparently only regarding an object's internal geometry: e.g. with the default cube at .999 alpha, its obscured rear edges are clearly visible, which seems wrong. A second cube placed behind it is ~invisible with the front cube at .999 alpha, as expected.

Also, values where 1 > alpha >= ~.8 are almost indistinguishable from each other.

Operating system: Kubuntu 18.10, 4.18.0-25-generic #26-Ubuntu SMP Mon Jun 24 09:32:08 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Graphics card: NVIDIA Corporation GP106 [GeForce GTX 1060 6GB] (rev a1)
Broken: 2.80, a4bc6aca0e

start blender with new profile directory
in Properties, go to render settings, change to Workbench renderer
change viewport render settings to "render"
go to Material tab for cube
in Viewport Display, click color swatch and change alpha with mouse drags left/right
observe the "jump" as it snaps out of 1.0, and observe that values from .8 to .999 appear to have little/no difference.

Not sure if this is a bug: adjusting alpha of object causes it to "snap" in to alpha mode at e.g 0.999 alpha. This would apparently make it impossible to smoothly animate from 0 alpha to 1, due to the "jump" as it goes to 1. This is apparently only regarding an object's internal geometry: e.g. with the default cube at .999 alpha, its obscured rear edges are clearly visible, which seems wrong. A second cube placed behind it is ~invisible with the front cube at .999 alpha, as expected. Also, values where 1 > alpha >= ~.8 are almost indistinguishable from each other. Operating system: Kubuntu 18.10, 4.18.0-25-generic #26-Ubuntu SMP Mon Jun 24 09:32:08 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux Graphics card: NVIDIA Corporation GP106 [GeForce GTX 1060 6GB] (rev a1) Broken: 2.80, a4bc6aca0ef9 * start blender with new profile directory * in Properties, go to render settings, change to Workbench renderer * change viewport render settings to "render" * go to Material tab for cube * in Viewport Display, click color swatch and change alpha with mouse drags left/right * observe the "jump" as it snaps out of 1.0, and observe that values from .8 to .999 appear to have little/no difference.

Casey Connor commented

2019-07-09 00:55:02 +02:00

Added subscriber: @clepsydrae

Jeroen Bakker commented

2019-07-09 09:03:37 +02:00

Added subscriber: @Jeroen-Bakker

Jeroen Bakker commented

2019-07-09 09:03:37 +02:00

Changed status from 'Open' to: 'Archived'

Jeroen Bakker closed this issue

2019-07-09 09:03:37 +02:00

Jeroen Bakker self-assigned this 2019-07-09 09:03:37 +02:00

Jeroen Bakker commented

2019-07-09 09:03:37 +02:00

Hi @clepsydrae,

this is not a bug, but how the system was designed. We ensured that:

Fastest rendering in workbench when no transparency is needed. (the workbench goes from a forward shading render model (0.999) to a deferred shading render model (1.000)
The rendering of the Alpha is done using an order independent transparency. The slider influences the curve of this model. The curve has been optimized to give a good visible range for simple and complex scenes.

Due to this users experience a hard cut when the render model switches and some dis-connectivity with the alpha value. These are trade-offs that have been made to ensure it works for most cases.

Hi @clepsydrae, this is not a bug, but how the system was designed. We ensured that: - Fastest rendering in workbench when no transparency is needed. (the workbench goes from a forward shading render model (0.999) to a deferred shading render model (1.000) - The rendering of the Alpha is done using an `order independent transparency`. The slider influences the curve of this model. The curve has been optimized to give a good visible range for simple and complex scenes. Due to this users experience a hard cut when the render model switches and some dis-connectivity with the alpha value. These are trade-offs that have been made to ensure it works for most cases.

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Workbench transparency rendering issue: "jump" to alpha 1.0 from .999 #66586