[gstreamer-bugs] [Bug 617045] New: [caps] New method for intersecting caps while retaining order

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=617045
  GStreamer | gstreamer (core) | git

           Summary: [caps] New method for intersecting caps while
                    retaining order
    Classification: Desktop
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: Normal
         Component: gstreamer (core)
        AssignedTo: gstreamer-bugs at lists.sourceforge.net
        ReportedBy: bilboed at gmail.com
         QAContact: gstreamer-bugs at lists.sourceforge.net
      GNOME target: ---
     GNOME version: ---


Right now gst_caps_intersect() intersects the caps by zig-zagging through the
structures of each caps. While this tries to keep a homogenous ordering for the
output, there are some cases where we want to intersect two caps but keep the
exact same ordering as one of the caps.

This is essential in two cases so far:
* default caps fixation in GstBaseSrc : we want to fixate to the first
intersecting caps from downstream.
* caps filtering in GstBaseTransform : we want to keep the ordering of caps
that the element gave to us.

c1 = Gst.Caps("A;B;C;D") # our sorted caps
c2 = Gst.Caps("D;A;B;C") # the unsorted caps 

Example with gst_caps_intersect:
gst_caps_intersect(c1, c2) => "B;A;D;C"
gst_caps_intersect(c2, c1) => "A;B;D;C"

Example with gst_caps_sorted:
gst_caps_intersect_sorted(c1, c2) => "A;B;C;D"
gst_caps_intersect_sorted(c2, c1) => "D;A;B;C"

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