Fix T74440: Blend Factor in Color Mix strips is broken
AbandonedPublic
Actions

Authored by Richard Antalik (ISS) on Apr 3 2020, 5:21 AM.

Details

Reviewers

Brecht Van Lommel (brecht)

Maniphest Tasks

T74440: Video Sequencer: The Blend Factor in Color Mix strips is broken.

Summary

Blend factor slider modulates alpha to change how much second input contributes in blending.

blend_color_xxxx_floatexpects modulated alpha in first channel*.
blend_color_xxxx_byte expects modulated alpha in second channel.

*Unfortunately this is also not consistent, which I could fix, but I am not sure if
some editor already has hacks in place, and I would break something.
Only float functions seem to be "broken" by having a quick look

Diff Detail

Repository

rB Blender

Branch

T74440 (branched from master)

Build Status

Buildable 7426
Build 7426: arc lint + arc unit

Event Timeline

Richard Antalik (ISS) created this revision.Apr 3 2020, 5:21 AM

Harbormaster completed remote builds in B7426: Diff 23384.Apr 3 2020, 5:21 AM

As far as I know the difference between the byte and float functions is that byte has unpremultiplied alpha while float has premultiplied alpha.

Maybe what you're missing for float is that you need to multiply the 4 rgba channels of the second input by the blend factor, instead of only the alpha channel?

In D7314#176222, @Brecht Van Lommel (brecht) wrote:

As far as I know the difference between the byte and float functions is that byte has unpremultiplied alpha while float has premultiplied alpha.

Maybe what you're missing for float is that you need to multiply the 4 rgba channels of the second input by the blend factor, instead of only the alpha channel?

Thanks, that seems indeed like correct approach. I forgot how to color...
However I did that and results were wildly different still. Since same functions are used by texture paint, I have checked how that works and it produces different results as well. T75844: Blend modes are broken

Richard Antalik (ISS) mentioned this in T75844: Blend modes are broken.Apr 17 2020, 8:12 PM

Philipp Oeser (lichtwerk) mentioned this in T79333: Some Blend mode opacity in VSE (Video Sequence Editor) cannot adjust opacity.Jul 28 2020, 10:56 AM

Closing as this was fixed in rBbdcc25830506