[gstreamer-bugs] [Bug 639237] New: textoverlay: patch to use "A OVER B" alpha compositing

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=639237
  GStreamer | gst-plugins-base | git

           Summary: textoverlay: patch to use "A OVER B" alpha compositing
    Classification: Desktop
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: Normal
         Component: gst-plugins-base
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: dirjud at gmail.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


Created an attachment (id=178071)
 View: https://bugzilla.gnome.org/attachment.cgi?id=178071
 Review: https://bugzilla.gnome.org/review?bug=639237&attachment=178071

patch

'A OVER B' compositing is explained at
http://en.wikipedia.org/wiki/Alpha_compositing.

Currently, overlaying text on a transparent background image leaves the text
overlay also transparent (and this invisible). This pipeline shows such an
example:

gst-launch videotestsrc pattern=white ! video/x-raw-yuv,format=\(fourcc\)AYUV !
alpha alpha=0.0 ! textoverlay text=Testing auto-resize=False font-desc=60px !
videomixer ! ffmpegcolorspace ! autovideosink

The attached patch changes the AYUV compositing rules put the text "OVER" the
background image and thus is visible regardless of the alpha of the background
image. The overlay in the above pipeline works after applying this patch.

I personally prefer this approach, but I would like to understand the reasons
and advantages of the current implementation as well. Can someone comment? If
"A OVER B" compositing is deemed better, I can apply it to the ARGB/BGRA
formats as well.

Let me know.

-- 
Configure bugmail: https://bugzilla.gnome.org/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are the QA contact for the bug.
You are the assignee for the bug.