[Webkit-unassigned] [Bug 173050] New: [GTK][WPE][GSTREAMER_GL] Change the colorspace used by the video frames provided by GStreamer

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=173050

            Bug ID: 173050
           Summary: [GTK][WPE][GSTREAMER_GL] Change the colorspace used by
                    the video frames provided by GStreamer
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebKit Gtk
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: magomez at igalia.com
                CC: bugs-noreply at webkitgtk.org

Currently, when using gstreamer-gl, the colorspace used by gstreamer to provide the video frames in RGBA. While this is convenient to paint the frames to the TextureMapper (which uses RGBA as well), it's a problem when the video frames need to be rendered with the CPU, for example when rendering to a non accelerated canvas or to webgl through glTexSubImage2D (yes, this is not accelerated!!). The problem comes because when the video frames are downloaded to the CPU, RGBA gets turned into ABGR (with the endianness change), and cairo expects ARGB, which means that the R and B components are swapped.

We could fix this by manually swapping the R and B components, but it's a waste of resources. What we need to do instead is changing the format used by gstreamer to BGRA, so when downloaded to the CPU it will automatically be the ARGB expected by cairo, and perform a colorspace conversion from BGRA to RGBA on with the shader when drawing the frames to the TextureMapper, so we don't waste CPU on byte swapping.

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