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# 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(512, 512);
         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/qt4-logo.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());
         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));
             }
         }
     }