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);
 }