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# glwidget.cpp Example File
opengl/pbuffers/glwidget.cpp

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     #include "glwidget.h"
     #include <math.h>

     #include "cube.h"

     #include <QGLPixelBuffer>

     #ifndef GL_MULTISAMPLE
     #define GL_MULTISAMPLE  0x809D
     #endif

     static GLfloat colorArray[][4] = {
         {0.243f, 0.423f, 0.125f, 1.0f},
         {0.176f, 0.31f, 0.09f, 1.0f},
         {0.4f, 0.69f, 0.212f, 1.0f},
         {0.317f, 0.553f, 0.161f, 1.0f}
     };

     GLWidget::GLWidget(QWidget *parent)
         : QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
         , geom(0)
         , cube(0)
     {
         // create the pbuffer
         pbuffer = new QGLPixelBuffer(QSize(512, 512), format(), this);
         setWindowTitle(tr("OpenGL pbuffers"));
         initializeGeometry();
     }

     GLWidget::~GLWidget()
     {
         pbuffer->releaseFromDynamicTexture();
         glDeleteTextures(1, &dynamicTexture);
         delete pbuffer;

         qDeleteAll(cubes);
         qDeleteAll(tiles);
         delete cube;
     }

     void GLWidget::initializeGL()
     {
         initCommon();
         glShadeModel(GL_SMOOTH);
         glEnable(GL_LIGHTING);
         glEnable(GL_LIGHT0);
         static GLfloat lightPosition[4] = { 0.5, 5.0, 7.0, 1.0 };
         glLightfv(GL_LIGHT0, GL_POSITION, lightPosition);
         initPbuffer();
         cube->startAnimation();
         connect(cube, SIGNAL(changed()), this, SLOT(update()));
         for (int i = 0; i < 3; ++i)
         {
             cubes[i]->startAnimation();
             connect(cubes[i], SIGNAL(changed()), this, SLOT(update()));
         }
     }

     void GLWidget::paintGL()
     {
         pbuffer->makeCurrent();
         drawPbuffer();
         // On direct render platforms, drawing onto the pbuffer context above
         // automatically updates the dynamic texture.  For cases where rendering
         // directly to a texture is not supported, explicitly copy.
         if (!hasDynamicTextureUpdate)
             pbuffer->updateDynamicTexture(dynamicTexture);
         makeCurrent();

         // Use the pbuffer as a texture to render the scene
         glBindTexture(GL_TEXTURE_2D, dynamicTexture);

         // set up to render the scene
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
         glLoadIdentity();
         glTranslatef(0.0f, 0.0f, -10.0f);

         // draw the background
         glPushMatrix();
         glScalef(aspect, 1.0f, 1.0f);
         for (int i = 0; i < tiles.count(); ++i)
             tiles[i]->draw();
         glPopMatrix();

         // draw the bouncing cubes
         for (int i = 0; i < cubes.count(); ++i)
             cubes[i]->draw();
     }

     void GLWidget::initializeGeometry()
     {
         geom = new Geometry();
         CubeBuilder cBuilder(geom, 0.5);
         cBuilder.setColor(QColor(255, 255, 255, 212));
         // build the 3 bouncing, spinning cubes
         for (int i = 0; i < 3; ++i)
             cubes.append(cBuilder.newCube(QVector3D((float)(i-1), -1.5f, 5 - i)));

         // build the spinning cube which goes in the dynamic texture
         cube = cBuilder.newCube();
         cube->removeBounce();

         // build the background tiles
         TileBuilder tBuilder(geom);
         tBuilder.setColor(QColor(Qt::white));
         for (int c = -2; c <= +2; ++c)
             for (int r = -2; r <= +2; ++r)
                 tiles.append(tBuilder.newTile(QVector3D(c, r, 0)));

         // graded backdrop for the pbuffer scene
         TileBuilder bBuilder(geom, 0.0f, 2.0f);
         bBuilder.setColor(QColor(102, 176, 54, 210));
         backdrop = bBuilder.newTile(QVector3D(0.0f, 0.0f, -1.5f));
         backdrop->setColors(colorArray);
     }

     void GLWidget::initCommon()
     {
         qglClearColor(QColor(Qt::darkGray));

         glEnable(GL_DEPTH_TEST);
         glEnable(GL_CULL_FACE);
         glEnable(GL_MULTISAMPLE);

         glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
         glEnable(GL_BLEND);

         glEnable(GL_TEXTURE_2D);

         geom->loadArrays();
     }

     void GLWidget::perspectiveProjection()
     {
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
     #ifdef QT_OPENGL_ES
         glFrustumf(-aspect, +aspect, -1.0, +1.0, 4.0, 15.0);
     #else
         glFrustum(-aspect, +aspect, -1.0, +1.0, 4.0, 15.0);
     #endif
         glMatrixMode(GL_MODELVIEW);
     }

     void GLWidget::orthographicProjection()
     {
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
     #ifdef QT_OPENGL_ES
         glOrthof(-1.0, +1.0, -1.0, +1.0, -90.0, +90.0);
     #else
         glOrtho(-1.0, +1.0, -1.0, +1.0, -90.0, +90.0);
     #endif
         glMatrixMode(GL_MODELVIEW);
     }

     void GLWidget::resizeGL(int width, int height)
     {
         glViewport(0, 0, width, height);
         aspect = (qreal)width / (qreal)(height ? height : 1);
         perspectiveProjection();
     }

     void GLWidget::drawPbuffer()
     {
         orthographicProjection();

         glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         glDisable(GL_TEXTURE_2D);
         backdrop->draw();
         glEnable(GL_TEXTURE_2D);

         glBindTexture(GL_TEXTURE_2D, cubeTexture);
         glDisable(GL_CULL_FACE);
         cube->draw();
         glEnable(GL_CULL_FACE);

         glFlush();
     }

     void GLWidget::initPbuffer()
     {
         pbuffer->makeCurrent();

         cubeTexture = bindTexture(QImage(":res/cubelogo.png"));

         initCommon();

         // generate a texture that has the same size/format as the pbuffer
         dynamicTexture = pbuffer->generateDynamicTexture();

         // bind the dynamic texture to the pbuffer - this is a no-op under X11
         hasDynamicTextureUpdate = pbuffer->bindToDynamicTexture(dynamicTexture);
         makeCurrent();
     }

     void GLWidget::setAnimationPaused(bool enable)
     {
         cube->setAnimationPaused(enable);
         for (int i = 0; i < 3; ++i)
             cubes[i]->setAnimationPaused(enable);
     }