[Bug 668483] video: add support for global-alpha multiplicator for overlay rectangles

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=668483
  GStreamer | gst-plugins-base | git

--- Comment #18 from Holger Kaelberer <hk at getslash.de> 2012-03-21 19:41:14 UTC ---
Created an attachment (id=210277)
 View: https://bugzilla.gnome.org/attachment.cgi?id=210277
 Review: https://bugzilla.gnome.org/review?bug=668483&attachment=210277

Unit tests for global alpha

Managed to write up some test-cases, too ;-) (Recompiling liborc from git fixed
my problems).

I was complete in iterating over all combinations of
premultiplied/unpremultiplied vs. scaled/not-scaled vs. global alpha
applied/not applied, and also tested the more theoretical combinations. Just
throw away whatever you think is not necessary.

Also note, that the tests take account of the fact that you end up with
rounding errors, when you apply global-alpha to premultiplied pixel-data. Think
this is a reasonable tradeoff you pay for performance.

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