examples: Add OpenGL under Qml example

This is example is based on the Qt's scene graph example
that uses and OpenGL animation inside Qml code.

Fixes: PYSIDE-1034
Change-Id: I012818d81d757571a711fcea68df51fa566ae5f9
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

1 files changed, 21 insertions, 0 deletions

diff --git a/examples/declarative/openglunderqml/doc/openglunderqml.rst b/examples/declarative/openglunderqml/doc/openglunderqml.rst
new file mode 100644
index 000000000..6a89a99d9
--- /dev/null
+++ b/examples/declarative/openglunderqml/doc/openglunderqml.rst
@@ -0,0 +1,21 @@
+OpenGL under QML Squircle
+=========================
+
+The OpenGL under QML example shows how an application can make use of the
+QQuickWindow::beforeRendering() signal to draw custom OpenGL content under a Qt
+Quick scene. This signal is emitted at the start of every frame, before the
+scene graph starts its rendering, thus any OpenGL draw calls that are made as
+a response to this signal, will stack under the Qt Quick items.
+
+As an alternative, applications that wish to render OpenGL content on top of
+the Qt Quick scene, can do so by connecting to the
+QQuickWindow::afterRendering() signal.
+
+In this example, we will also see how it is possible to have values that are
+exposed to QML which affect the OpenGL rendering. We animate the threshold
+value using a NumberAnimation in the QML file and this value is used by the
+OpenGL shader program that draws the squircles.
+
+.. image:: squircle.png
+   :width: 400
+   :alt: Squircle Screenshot