VSE: Clips with Alpha Over against a transparent background fail to reflect opacity changes #38557
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Reference: blender/blender#38557
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System Information
Observed on Mac OS X 10.6 and 10.8
Blender Version
Broken: 2.69.0 r60991 Also confirmed on latest unofficial build 2.69b53f310
Worked: never, as far as I know
Short description of error
In the Video Sequence Editor a clip with its blend mode set to Alpha Over cannot have its Opacity adjusted when over a transparent background. I observed this with PNG image sequences, but it may occur with other file types as well.
If a solid background image is added to a channel beneath the transparent clip the problem disappears.
This leads me to suspect that Alpha Over was coded only to account for transparency over solid - not transparency over tranparency.
This bug prevents image sequences with transparency from being composited correctly and in that regard is a workflow-stopper.
For example if a client wanted an animated logo fading in over a transparent background this bug would stop you from being able to produce it.
Exact steps for others to reproduce the error
Refreshing the Sequencer doesn't help. Neither does reloading the .blend.
A PNG with transparency for testing:
An example .blend (uses above .png file)
vse-alpha-over-opacity-bug.blend
Changed status to: 'Open'
Added subscriber: @quantumanomaly
This issue was referenced by blender/blender-addons-contrib@23fe23f951
This issue was referenced by
23fe23f951
Changed status from 'Open' to: 'Resolved'
Closed by commit
23fe23f951
.Thank you for the prompt fix, sergey! You're awesome!