glwidget.cpp Example File
opengl/framebufferobject/glwidget.cpp

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 #include <QtGui/QImage>
 #include "glwidget.h"

 #include <math.h>

 #ifndef GL_MULTISAMPLE
 #define GL_MULTISAMPLE  0x809D
 #endif

 GLWidget::GLWidget(QWidget *parent)
     : QGLWidget(QGLFormat(QGL::SampleBuffers|QGL::AlphaChannel), parent)
 {
     setWindowTitle(tr("OpenGL framebuffer objects"));
     makeCurrent();
     fbo = new QGLFramebufferObject(1024, 1024);
     rot_x = rot_y = rot_z = 0.0f;
     scale = 0.1f;
     anim = new QTimeLine(750, this);
     anim->setUpdateInterval(20);
     connect(anim, SIGNAL(valueChanged(qreal)), SLOT(animate(qreal)));
     connect(anim, SIGNAL(finished()), SLOT(animFinished()));

     svg_renderer = new QSvgRenderer(QLatin1String(":/res/bubbles.svg"), this);
     connect(svg_renderer, SIGNAL(repaintNeeded()), this, SLOT(draw()));

     logo = QImage(":/res/designer.png");
     logo = logo.convertToFormat(QImage::Format_ARGB32);

     tile_list = glGenLists(1);
     glNewList(tile_list, GL_COMPILE);
     glBegin(GL_QUADS);
     {
         glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
         glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
         glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
         glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);

         glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
         glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
         glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
         glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);

         glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
         glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
         glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
         glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);

         glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
         glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
         glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);
         glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);

         glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
         glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f,  1.0f, -1.0f);
         glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f,  1.0f,  1.0f);
         glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f,  1.0f);

         glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
         glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f,  1.0f);
         glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f,  1.0f,  1.0f);
         glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f,  1.0f, -1.0f);
     }
     glEnd();
     glEndList();

     wave = new GLfloat[logo.width()*logo.height()];
     memset(wave, 0, logo.width()*logo.height());
     startTimer(30); // wave timer
 }

 GLWidget::~GLWidget()
 {
     delete[] wave;
     glDeleteLists(tile_list, 1);
     delete fbo;
 }

 void GLWidget::paintEvent(QPaintEvent *)
 {
     draw();
 }

 void GLWidget::draw()
 {
     QPainter p(this); // used for text overlay

     // save the GL state set for QPainter
     saveGLState();

     // render the 'bubbles.svg' file into our framebuffer object
     QPainter fbo_painter(fbo);
     svg_renderer->render(&fbo_painter);
     fbo_painter.end();

     // draw into the GL widget
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
     glFrustum(-1, 1, -1, 1, 10, 100);
     glTranslatef(0.0f, 0.0f, -15.0f);
     glMatrixMode(GL_MODELVIEW);
     glLoadIdentity();
     glViewport(0, 0, width(), height());
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

     glBindTexture(GL_TEXTURE_2D, fbo->texture());
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
     glEnable(GL_TEXTURE_2D);
     glEnable(GL_MULTISAMPLE);
     glEnable(GL_CULL_FACE);

     // draw background
     glPushMatrix();
     glScalef(1.7f, 1.7f, 1.7f);
     glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
     glCallList(tile_list);
     glPopMatrix();

     const int w = logo.width();
     const int h = logo.height();

     glRotatef(rot_x, 1.0f, 0.0f, 0.0f);
     glRotatef(rot_y, 0.0f, 1.0f, 0.0f);
     glRotatef(rot_z, 0.0f, 0.0f, 1.0f);
     glScalef(scale/w, scale/w, scale/w);

     glDepthFunc(GL_LESS);
     glEnable(GL_DEPTH_TEST);
     // draw the Qt icon
     glTranslatef(-w+1, -h+1, 0.0f);
     for (int y=h-1; y>=0; --y) {
         uint *p = (uint*) logo.scanLine(y);
         uint *end = p + w;
         int  x = 0;
         while (p < end) {
             glColor4ub(qRed(*p), qGreen(*p), qBlue(*p), uchar(qAlpha(*p)*.9));
             glTranslatef(0.0f, 0.0f, wave[y*w+x]);
             if (qAlpha(*p) > 128)
                 glCallList(tile_list);
             glTranslatef(0.0f, 0.0f, -wave[y*w+x]);
             glTranslatef(2.0f, 0.0f, 0.0f);
             ++x;
             ++p;
         }
         glTranslatef(-w*2.0f, 2.0f, 0.0f);
     }

     // restore the GL state that QPainter expects
     restoreGLState();

     // draw the overlayed text using QPainter
     p.setPen(QColor(197, 197, 197, 157));
     p.setBrush(QColor(197, 197, 197, 127));
     p.drawRect(QRect(0, 0, width(), 50));
     p.setPen(Qt::black);
     p.setBrush(Qt::NoBrush);
     const QString str1(tr("A simple OpenGL framebuffer object example."));
     const QString str2(tr("Use the mouse wheel to zoom, press buttons and move mouse to rotate, double-click to flip."));
     QFontMetrics fm(p.font());
     p.drawText(width()/2 - fm.width(str1)/2, 20, str1);
     p.drawText(width()/2 - fm.width(str2)/2, 20 + fm.lineSpacing(), str2);
 }

 void GLWidget::mousePressEvent(QMouseEvent *e)
 {
     anchor = e->pos();
 }

 void GLWidget::mouseMoveEvent(QMouseEvent *e)
 {
     QPoint diff = e->pos() - anchor;
     if (e->buttons() & Qt::LeftButton) {
         rot_x += diff.y()/5.0f;
         rot_y += diff.x()/5.0f;
     } else if (e->buttons() & Qt::RightButton) {
         rot_z += diff.x()/5.0f;
     }

     anchor = e->pos();
     draw();
 }

 void GLWidget::wheelEvent(QWheelEvent *e)
 {
     e->delta() > 0 ? scale += scale*0.1f : scale -= scale*0.1f;
     draw();
 }

 void GLWidget::mouseDoubleClickEvent(QMouseEvent *)
 {
     anim->start();
 }

 void GLWidget::animate(qreal val)
 {
     rot_y = val * 180;
     draw();
 }

 void GLWidget::animFinished()
 {
     if (anim->direction() == QTimeLine::Forward)
         anim->setDirection(QTimeLine::Backward);
     else
         anim->setDirection(QTimeLine::Forward);
 }

 void GLWidget::saveGLState()
 {
     glPushAttrib(GL_ALL_ATTRIB_BITS);
     glMatrixMode(GL_PROJECTION);
     glPushMatrix();
     glMatrixMode(GL_MODELVIEW);
     glPushMatrix();
 }

 void GLWidget::restoreGLState()
 {
     glMatrixMode(GL_PROJECTION);
     glPopMatrix();
     glMatrixMode(GL_MODELVIEW);
     glPopMatrix();
     glPopAttrib();
 }

 #define PI 3.14159

 void GLWidget::timerEvent(QTimerEvent *)
 {
     if (QApplication::mouseButtons() != 0)
         return;

     static bool scale_in = true;

     if (scale_in && scale > 35.0f)
         scale_in = false;
     else if (!scale_in && scale < .5f)
         scale_in = true;

     scale = scale_in ? scale + scale*0.01f : scale-scale*0.01f;
     rot_z += 0.3f;
     rot_x += 0.1f;

     int dx, dy; // disturbance point
     float s, v, W, t;
     int i, j;
     static float wt[128][128];
     const int width = logo.width();
     const int AMP = 5;

     dx = dy = width >> 1;

     W = .3f;
     v = -4; // wave speed

     for (i = 0; i < width; ++i) {
         for ( j = 0; j < width; ++j) {
             s = sqrt((double) ((j - dx) * (j - dx) + (i - dy) * (i - dy)));
             wt[i][j] += 0.1f;
             t = s / v;
             if (s != 0)
                 wave[i*width + j] = AMP * sin(2 * PI * W * (wt[i][j] + t)) / (0.2*(s + 2));
             else
                 wave[i*width + j] = AMP * sin(2 * PI * W * (wt[i][j] + t));
         }
     }
 }