grouping VSE strips can break translucency #40491

New Issue

Robert Forsman · 2014-06-03T23:33:35+02:00

Robert Forsman commented

2014-06-03 23:33:35 +02:00

System Information
Linux bubastis 3.10.25-gentoo #10 SMP Thu Jan 30 22:17:35 UTC 2014 x86_64 Intel(R) Core(TM) i7-4800MQ CPU @ 2.70GHz GenuineIntel GNU/Linux
01:00.0 VGA compatible controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1) (prog-if 00 [VGA controller])

Blender Version
Broken: git 2c69f1e574 and probably earlier

Short description of error

When grouping a set of VSE strips into a meta strip sometimes the translucency is broken.

Exact steps for others to reproduce the error

When grouping a set of VSE strips into a meta strip sometimes the translucency is broken.

In the VSE
Add a color strip on the bottom (1)
add a strip over that (2: from scene or image sequence).
Add another strip over that (3) from a scene that has transparency (its sky is unchecked in the Render Layers).
Set both strips to blend = Over Drop or Alpha Over
Animate the opacity on the top strip to make it fade out over time (from 75,1 to 90,0
Animate the opacity on the middle strip (2) to make it fade from 60,0 to 90,1 (fading in).

Render images at 60, 67, 75, 82, and 90.

Now group the top strips (2,3) to make a meta strip. Since the meta strip defaults to Replace (which seems like a bad default to me) adjust it to Over Drop or Alpha Over

Render images at 60, 67, 75, 82, and 90.

Become disappointed.

**System Information** Linux bubastis 3.10.25-gentoo #10 SMP Thu Jan 30 22:17:35 UTC 2014 x86_64 Intel(R) Core(TM) i7-4800MQ CPU @ 2.70GHz GenuineIntel GNU/Linux 01:00.0 VGA compatible controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1) (prog-if 00 [VGA controller]) **Blender Version** Broken: git 2c69f1e574587c2364e9a94b45d0b363ffeebf61 and probably earlier **Short description of error** When grouping a set of VSE strips into a meta strip sometimes the translucency is broken. **Exact steps for others to reproduce the error** When grouping a set of VSE strips into a meta strip sometimes the translucency is broken. In the VSE Add a color strip on the bottom (1) add a strip over that (2: from scene or image sequence). Add another strip over that (3) from a scene that has transparency (its sky is unchecked in the Render Layers). Set both strips to blend = Over Drop or Alpha Over Animate the opacity on the top strip to make it fade out over time (from 75,1 to 90,0 Animate the opacity on the middle strip (2) to make it fade from 60,0 to 90,1 (fading in). Render images at 60, 67, 75, 82, and 90. Now group the top strips (2,3) to make a meta strip. Since the meta strip defaults to Replace (which seems like a bad default to me) adjust it to Over Drop or Alpha Over Render images at 60, 67, 75, 82, and 90. Become disappointed.

Robert Forsman commented

2014-06-03 23:33:35 +02:00

Changed status to: 'Open'

Robert Forsman commented

2014-06-03 23:33:35 +02:00

Added subscriber: @mutantbob

Robert Forsman commented

2014-06-03 23:35:32 +02:00

This is a .blend file I constructed to reproduce the problem I was having.

Bastien Montagne commented

2014-06-04 12:08:22 +02:00

Added subscriber: @mont29

Sergey Sharybin was assigned by Bastien Montagne

2014-06-04 12:11:17 +02:00

Bastien Montagne commented

2014-06-04 12:11:17 +02:00

Added subscriber: @Sergey

Bastien Montagne commented

2014-06-04 12:11:17 +02:00

So, can confirm the problem, here is a quick hack to “fix” it: add a dummy strip below all other ones in the meta, e.g. a color one, with an alpha of zero.

@Sergey: Don’t know whether this is a bug or an internal limitation? Your call. :)

So, can confirm the problem, here is a quick hack to “fix” it: add a dummy strip below all other ones in the meta, e.g. a color one, with an alpha of zero. @Sergey: Don’t know whether this is a bug or an internal limitation? Your call. :)

Robert Forsman commented

2014-06-04 17:03:53 +02:00

Ideally the meta strip would have the same effect grouped as ungrouped, if only to keep the math of the system beautiful.

I'm assuming that the meta strips don't have an alpha layer when they are composing their internal bits. This problem is NOT evident when there is only one strip in effect (probably because it does not require any composition).

It will take someone familiar with that code to come up with a fix, and it will not be a high priority.

Ideally the meta strip would have the same effect grouped as ungrouped, if only to keep the math of the system beautiful. I'm assuming that the meta strips don't have an alpha layer when they are composing their internal bits. This problem is NOT evident when there is only one strip in effect (probably because it does not require any composition). It will take someone familiar with that code to come up with a fix, and it will not be a high priority.

Sergey Sharybin commented

2014-06-04 18:34:38 +02:00

Changed status from 'Open' to: 'Resolved'

Sergey Sharybin closed this issue

2014-06-04 18:34:38 +02:00

Sergey Sharybin commented

2014-06-04 18:34:38 +02:00

I've committed some changes to ec97cb8 which tries to make it so adding an invisible strip at the bottom of the meta doesn't change final render. This needs to be stress-tested tho..

As for meta strip blend type -- it's rather tricky to choose right one automatically, so i would just consider this a TODO for the future.

Thanks for the report and let us know if you've got more issues!

I've committed some changes to ec97cb8 which tries to make it so adding an invisible strip at the bottom of the meta doesn't change final render. This needs to be stress-tested tho.. As for meta strip blend type -- it's rather tricky to choose right one automatically, so i would just consider this a TODO for the future. Thanks for the report and let us know if you've got more issues!

Robert Forsman commented

2014-06-05 21:23:48 +02:00

I was able to fetch the latest tree and it seems 8355955058 composites strips how I want. Hopefully there are no regressions and this fix will work well for everyone.

I was able to fetch the latest tree and it seems 835595505858fcfcc106ce721c2f270923ead2b7 composites strips how I want. Hopefully there are no regressions and this fix will work well for everyone.

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grouping VSE strips can break translucency #40491