remove display lists and qt3d-ize overpainting/hellogl example

On the way to making opengl examples portable, remove display lists
and go to triangles only. Use QMatrix4x4. While on the job use Qt/3D
stylee to make the QtLogo as an example of 3D programming more Qt-like.

Reviewed-by: Rhys Weatherley

2 files changed, 75 insertions, 21 deletions

diff --git a/doc/src/examples/hellogl.qdoc b/doc/src/examples/hellogl.qdoc
index 6dc9e26..77deefe 100644
--- a/doc/src/examples/hellogl.qdoc
+++ b/doc/src/examples/hellogl.qdoc
@@ -65,7 +65,8 @@
     \snippet examples/opengl/hellogl/glwidget.h 0
 
     We use a destructor to ensure that any OpenGL-specific data structures
-    are deleted when the widget is no longer needed.
+    are deleted when the widget is no longer needed (although in this case nothing
+    needs cleaning up).
 
     \snippet examples/opengl/hellogl/glwidget.h 1
 
@@ -84,8 +85,8 @@
 
     The rest of the class contains utility functions and variables that are
     used to construct and hold orientation information for the scene. The
-    \c object variable will be used to hold an identifier for an OpenGL
-    display list.
+    \c logo variable will be used to hold a pointer to the QtLogo object which
+    contains all the geometry.
 
     \section1 GLWidget Class Implementation
 
@@ -95,8 +96,9 @@
 
     \section2 Widget Construction and Sizing
 
-    The constructor provides default rotation angles for the scene, initializes
-    the variable used for the display list, and sets up some colors for later use.
+    The constructor provides default rotation angles for the scene, sets
+    the pointer to the QtLogo object to null, and sets up some colors for
+    later use.
 
     \snippet examples/opengl/hellogl/glwidget.cpp 0
 
@@ -105,7 +107,7 @@
 
     \snippet examples/opengl/hellogl/glwidget.cpp 1
 
-    The destructor ensures that the display list is deleted properly.
+    In this case nothing requires cleaning up.
 
     We provide size hint functions to ensure that the widget is shown at a
     reasonable size:
@@ -139,9 +141,9 @@
     \snippet examples/opengl/hellogl/glwidget.cpp 6
 
     In this example, we reimplement the function to set the background color,
-    create a display list containing information about the object we want to
+    create a QtLogo object instance which will contain all the geometry to
     display, and set up the rendering process to use a particular shading model
-    and rendering flags:
+    and rendering flags.
 
     \section2 Resizing the Viewport
 
@@ -172,8 +174,8 @@
 
     In this example, we clear the widget using the background color that
     we defined in the \l{QGLWidget::initializeGL()}{initializeGL()} function,
-    set up the frame of reference for the object we want to display, and call
-    the display list containing the rendering commands for the object.
+    set up the frame of reference for the geometry we want to display, and
+    call the draw method of the QtLogo object to render the scene.
 
     \section2 Mouse Handling
 
@@ -196,12 +198,57 @@
     cursor to rotate the object, the cursor's position is updated every time
     a move event is received.
 
-    \section2 Utility Functions
+    \section1 QtLogo Class
 
-    We have omitted the utility functions, \c makeObject(), \c quad(),
-    \c extrude(), and \c normalizeAngle() from our discussion. These can be
-    viewed in the quoted source for \c glwidget.cpp via the link at the
-    start of this document.
+    This class encapsulates the OpenGL geometry data which will be rendered
+    in the basic 3D scene.
+
+    \snippet examples/opengl/hellogl/qtlogo.h 0
+
+    The geometry is divided into a list of parts which may be rendered in
+    different ways.  The data itself is contained in a Geometry structure that
+    includes the vertices, their lighting normals and index values which
+    point into the vertices, grouping them into faces.
+
+    \snippet examples/opengl/hellogl/qtlogo.cpp 0
+
+    The data in the Geometry class is stored in QVector<QVector3D> members
+    which are convenient for use with OpenGL because they expose raw
+    contiguous floating point values via the constData() method.  Methods
+    are included for adding new vertex data, either with smooth normals, or
+    facetted normals; and for enabling the geometry ready for rendering.
+
+    \snippet examples/opengl/hellogl/qtlogo.cpp 1
+
+    The higher level Patch class has methods for accumulating the geometry
+    one face at a time, and treating collections of faces or "patches" with
+    transformations, applying different colors or smoothing.  Although faces
+    may be added as triangles or quads, at the OpenGL level all data is
+    treated as triangles for compatibility with OpenGL/ES.
+
+    \snippet examples/opengl/hellogl/qtlogo.cpp 2
+
+    Drawing a Patch is simply acheived by applying any transformation,
+    and material effect, then drawing the data using the index range for
+    the patch.  The model-view matrix is saved and then restored so that
+    any transformation does not affect other parts of the scene.
+
+    \snippet examples/opengl/hellogl/qtlogo.cpp 3
+
+    The geometry is built once on construction of the QtLogo, and it is
+    paramaterized on a number of divisions - which controls how "chunky" the
+    curved section of the logo looks - and on a scale, so larger and smaller
+    QtLogo objects can be created without having to use OpenGL scaling
+    (which would force normal recalculation).
+
+    The building process is done by helper classes (read the source for full
+    details) which only exist during the build phase, to assemble the parts
+    of the scene.
+
+    \snippet examples/opengl/hellogl/qtlogo.cpp 4
+
+    Finally the complete QtLogo scene is simply drawn by enabling the data arrays
+    and then iterating over the parts, calling draw() on each one.
 
     \section1 Window Class Definition
 
diff --git a/doc/src/examples/overpainting.qdoc b/doc/src/examples/overpainting.qdoc
index 52bb160..e00ec91 100644
--- a/doc/src/examples/overpainting.qdoc
+++ b/doc/src/examples/overpainting.qdoc
@@ -53,7 +53,7 @@
     yet also behaves like any other standard Qt widget with support for
     signals and slots, properties, and Qt's action system.
 
-    Usually, QGLWidget is subclassed to display a pure 3D scene; the
+    Usually, QGLWidget is subclassed to display a pure 3D scene.  The
     developer reimplements \l{QGLWidget::initializeGL()}{initializeGL()}
     to initialize any required resources, \l{QGLWidget::resizeGL()}{resizeGL()}
     to set up the projection and viewport, and
@@ -83,7 +83,7 @@
     \snippet examples/opengl/overpainting/glwidget.h 4
 
     As usual, the widget uses \l{QGLWidget::initializeGL()}{initializeGL()}
-    to set up objects for our scene and perform other OpenGL initialization tasks.
+    to set up geometry for our scene and perform OpenGL initialization tasks.
     The \l{QGLWidget::resizeGL()}{resizeGL()} function is used to ensure that
     the 3D graphics in the scene are transformed correctly to the 2D viewport
     displayed in the widget.
@@ -100,7 +100,7 @@
     \c animationTimer to update the widget; the \c createBubbles() function
     initializes the \c bubbles list with instances of a helper class used to
     draw the animation; the \c drawInstructions() function is responsible for
-    a semi-transparent messages that is also overpainted onto the OpenGL scene.
+    a semi-transparent message that is also overpainted onto the OpenGL scene.
 
     \section1 GLWidget Class Implementation
 
@@ -119,8 +119,9 @@
 
     \snippet examples/opengl/overpainting/glwidget.cpp 1
 
-    The \c initializeGL() function is fairly minimal, only setting up the display
-    list used in the scene.
+    The \c initializeGL() function is fairly minimal, only setting up the QtLogo
+    object used in the scene.  See the \l{Hello GL Example}{Hello GL} example
+    for details of the QtLogo class.
 
     \snippet examples/opengl/overpainting/glwidget.cpp 2
 
@@ -159,7 +160,7 @@
 
     \snippet examples/opengl/overpainting/glwidget.cpp 7
 
-    Once the list containing the object has been executed, the GL
+    Once the QtLogo object's draw method has been executed, the GL
     states we changed and the matrix stack needs to be restored to its
     original state at the start of this function before we can begin
     overpainting:
@@ -176,6 +177,12 @@
     When QPainter::end() is called, suitable OpenGL-specific calls are made to
     write the scene, and its additional contents, onto the widget.
 
+    With \l{QGLWidget::paintGL()}{paintGL()} the
+    \l{QGLWidget::swapBuffers()}{swapBuffers()} call is done for us.  But an explicit
+    call to swapBuffers() is still not required because in the
+    \l{QWidget::paintEvent()}{paintEvent()} method the QPainter on the OpenGL
+    widget takes care of this for us.
+
     The implementation of the \l{QGLWidget::resizeGL()}{resizeGL()} function
     sets up the dimensions of the viewport and defines a projection
     transformation: