Doc: Add docs for Multi Viewport QML example

- Add a brief (needed by Qt Creator)
- Add an image (needed by Qt Creator)
- Add a standard include file about building and running
  examples
- Copy instructions from the rendering overview (as applicable)

Change-Id: I5342a7ad644acf97ecd247d47725d5978e5c6fb4
Reviewed-by: Topi Reiniö <topi.reinio@theqtcompany.com>

2 files changed, 41 insertions, 0 deletions

diff --git a/examples/qt3d/multiviewport/doc/images/multiviewport-qml-example.png b/examples/qt3d/multiviewport/doc/images/multiviewport-qml-example.png
new file mode 100644
index 000000000..75c13ffcd
--- /dev/null
+++ b/examples/qt3d/multiviewport/doc/images/multiviewport-qml-example.png
diff --git a/examples/qt3d/multiviewport/doc/src/multiviewport.qdoc b/examples/qt3d/multiviewport/doc/src/multiviewport.qdoc
index 42eb836b2..86212c4c6 100644
--- a/examples/qt3d/multiviewport/doc/src/multiviewport.qdoc
+++ b/examples/qt3d/multiviewport/doc/src/multiviewport.qdoc
@@ -29,4 +29,45 @@
     \example multiviewport
     \title Qt 3D: Multi Viewport QML Example
     \ingroup qt3d-examples-qml
+    \brief A QML example that demonstrates rendering a Scenegraph from multiple
+    viewports.
+
+    \image multiviewport-qml-example.png
+
+    \e {Multi Viewport} renders a Scenegraph from the point of view of four
+    virtual cameras into the four quadrants of a window. This is a common
+    configuration for 3D CAD or modelling tools or could be adjusted to help
+    with rendering a rear-view mirror in a car racing game or a CCTV camera
+    display.
+
+    For more information, see \l{A Multi Viewport FrameGraph}.
+
+    \include examples-run.qdocinc
+
+    \section1 Creating Multiple RenderViews
+
+    Using the rules defined in \l {Framegraph Rules}, we construct five
+    RenderView objects from the FrameGraph:
+
+    \quotefromfile multiviewport/QuadViewportFrameGraph.qml
+    \skipto Viewport {
+    \printuntil /^\}/
+
+    The \e {order is important}. If the ClearBuffers node were to be the last
+    instead of the first, this would result in a black screen for the simple
+    reason that everything would be cleared right after having been so carefully
+    rendered. For a similar reason, it could not be used as the root of the
+    FrameGraph as that would result in a call to clear the whole screen for each
+    of our viewports.
+
+    Although the declaration order of the FrameGraph is important, Qt 3D is able
+    to process each RenderView in parallel as each RenderView is independent of
+    the others for the purposes of generating a set of RenderCommands to be
+    submitted whilst the RenderView's state is in effect.
+
+    Qt 3D uses a task-based approach to parallelism which naturally scales up
+    with the number of available cores. The RenderCommands for the RenderViews
+    can be generated in parallel across many cores, and as long as we take care
+    to submit the RenderViews in the correct order on the dedicated OpenGL
+    submission thread, the resulting scene will be rendered correctly.
 */