Compiler would complain about include directory that didn't
exist because QPA_INCLUDE_PATH gets subst-ed regardless
(and if it didn't we'd have just an empty -I argument).
https://bugzilla.gnome.org/show_bug.cgi?id=767553
We don't directly link to GL in the element, though we use GL headers.
For this reason we need to include the proper GL headers path. This
prevent this element from using a different GL header then libgstgl.
Very much in the same spirit as the Gtk GL sink
Two things are provided
1. A QQuickItem subclass that renders out RGBA filled GstGLMemory
buffers that is instantiated from qml.
2. A sink element that will push buffers into (1)
To use
1. Declare the GstGLVideoItem in qml with an appropriate
objectName property set.
2. Get the aforementioned GstGLVideoItem from qml using something like
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
QObject *rootObject = engine.rootObjects().first();
QQuickItem *videoItem = rootObject->findChild<QQuickItem *> ("videoItem");
3. Set the videoItem on the sink
https://bugzilla.gnome.org/show_bug.cgi?id=752185
