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

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

     #include <math.h>

     static GLint cubeArray[][3] = {
         {0, 0, 0}, {0, 1, 0}, {1, 1, 0}, {1, 0, 0},
         {0, 0, 1}, {1, 0, 1}, {1, 1, 1}, {0, 1, 1},
         {0, 0, 0}, {1, 0, 0}, {1, 0, 1}, {0, 0, 1},
         {0, 1, 0}, {0, 1, 1}, {1, 1, 1}, {1, 1, 0},
         {0, 1, 0}, {0, 0, 0}, {0, 0, 1}, {0, 1, 1},
         {1, 0, 0}, {1, 1, 0}, {1, 1, 1}, {1, 0, 1}
     };

     static GLint cubeTextureArray[][2] = {
         {0, 0}, {1, 0}, {1, 1}, {0, 1},
         {0, 0}, {0, 1}, {1, 1}, {1, 0},
         {0, 0}, {1, 0}, {1, 1}, {0, 1},
         {1, 0}, {0, 0}, {0, 1}, {1, 1},
         {0, 0}, {1, 0}, {1, 1}, {0, 1},
         {1, 0}, {0, 0}, {0, 1}, {1, 1}
     };

     static GLint faceArray[][2] = {
         {1, -1}, {1, 1}, {-1, 1}, {-1, -1}
     };

     static GLubyte colorArray[][4] = {
         {170, 202, 0, 255},
         {120, 143, 0, 255},
         {83, 102, 0, 255},
         {120, 143, 0, 255}
     };

     GLWidget::GLWidget(QWidget *parent)
       : QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
     {
         // create the pbuffer
         pbuffer = new QGLPixelBuffer(QSize(512, 512), format(), this);
         timerId = startTimer(20);
         setWindowTitle(tr("OpenGL pbuffers"));
     }

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

     void GLWidget::initializeGL()
     {
         glMatrixMode(GL_MODELVIEW);

         glEnable(GL_CULL_FACE);
         initCommon();
         initPbuffer();

         for (int i = 0; i < 3; ++i) {
             yOffs[i] = 0.0f;
             xInc[i] = 0.005f;
             rot[i] = 0.0f;
         }
         xOffs[0]= 0.0f;
         xOffs[1]= 0.5f;
         xOffs[2]= 1.0f;

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

     void GLWidget::resizeGL(int w, int h)
     {
         glViewport(0, 0, w, h);
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         float aspect = w/(float)(h ? h : 1);
         glFrustum(-aspect, aspect, -1, 1, 10, 100);
         glTranslatef(-0.5f, -0.5f, -0.5f);
         glTranslatef(0.0f, 0.0f, -15.0f);
     }

     void GLWidget::paintGL()
     {
         // draw a spinning cube into the pbuffer..
         pbuffer->makeCurrent();
         glBindTexture(GL_TEXTURE_2D, cubeTexture);
         glCallList(pbufferList);
         glFlush();

         // rendering directly to a texture is not supported on X11 and
         // some Windows implementations, unfortunately
         if (!hasDynamicTextureUpdate)
             pbuffer->updateDynamicTexture(dynamicTexture);

         // ..and use the pbuffer contents as a texture when rendering the
         // background and the bouncing cubes
         makeCurrent();
         glBindTexture(GL_TEXTURE_2D, dynamicTexture);
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

         // draw the background
         glMatrixMode(GL_MODELVIEW);
         glPushMatrix();
         glLoadIdentity();
         glMatrixMode(GL_PROJECTION);
         glPushMatrix();
         glLoadIdentity();

         glVertexPointer(2, GL_INT, 0, faceArray);
         glTranslatef(-1.2f, -0.8f, 0.0f);
         glScalef(0.2f, 0.2f, 0.2f);
         for (int y = 0; y < 5; ++y) {
             for (int x = 0; x < 5; ++x) {
                 glTranslatef(2.0f, 0, 0);
                 glColor4f(0.5, 0.5, 0.5, 1.0);
                 glDrawArrays(GL_QUADS, 0, 4);
             }
             glTranslatef(-10.0f, 2.0f, 0);
         }
         glVertexPointer(3, GL_INT, 0, cubeArray);

         glPopMatrix();
         glMatrixMode(GL_MODELVIEW);
         glPopMatrix();

         // draw the bouncing cubes
         drawCube(0, 0.0f, 1.5f, 2.5f, 1.5f);
         drawCube(1, 1.0f, 2.0f, 2.5f, 2.0f);
         drawCube(2, 2.0f, 3.5f, 2.5f, 2.5f);
     }

     void GLWidget::drawCube(int i, GLfloat z, GLfloat rotation, GLfloat jmp, GLfloat amp)
     {
         glMatrixMode(GL_MODELVIEW);
         glLoadIdentity();
         glTranslatef(xOffs[i], yOffs[i], z);
         glTranslatef(0.5f, 0.5f, 0.5f);
         GLfloat scale = 0.75 + i*(0.25f/2);
         glScalef(scale, scale, scale);
         glRotatef(rot[i], 1.0f, 1.0f, 1.0f);
         glTranslatef(-0.5f, -0.5f, -0.5f);

         glColor4f(1.0f, 1.0f, 1.0f, 0.8f);
         glDrawArrays(GL_QUADS, 0, 24);

         if (xOffs[i] > 1.0f || xOffs[i] < -1.0f) {
             xInc[i] = -xInc[i];
             xOffs[i] = xOffs[i] > 1.0f ? 1.0f : -1.0f;
         }
         xOffs[i] += xInc[i];
         yOffs[i] = qAbs(cos((-3.141592f * jmp) * xOffs[i]) * amp) - 1;
         rot[i] += rotation;
     }

     void GLWidget::initCommon()
     {
         glEnableClientState(GL_VERTEX_ARRAY);
         glEnableClientState(GL_TEXTURE_COORD_ARRAY);
         glVertexPointer(3, GL_INT, 0, cubeArray);
         glTexCoordPointer(2, GL_INT, 0, cubeTextureArray);
         glColorPointer(4, GL_UNSIGNED_BYTE, 0, colorArray);

         glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
         glEnable(GL_BLEND);
         glEnable(GL_TEXTURE_2D);
         glEnable(GL_DEPTH_TEST);

         glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
     }

     void GLWidget::initPbuffer()
     {
         // set up the pbuffer context
         pbuffer->makeCurrent();
         initCommon();

         glViewport(0, 0, pbuffer->size().width(), pbuffer->size().height());
         glMatrixMode(GL_PROJECTION);
         glLoadIdentity();
         glOrtho(-1, 1, -1, 1, -99, 99);
         glTranslatef(-0.5f, -0.5f, 0.0f);
         glMatrixMode(GL_MODELVIEW);
         glLoadIdentity();

         pbufferList = glGenLists(1);
         glNewList(pbufferList, GL_COMPILE);
         {
             glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

             // draw cube background
             glPushMatrix();
             glLoadIdentity();
             glTranslatef(0.5f, 0.5f, -2.0f);
             glDisable(GL_TEXTURE_2D);
             glEnableClientState(GL_COLOR_ARRAY);
             glVertexPointer(2, GL_INT, 0, faceArray);
             glDrawArrays(GL_QUADS, 0, 4);
             glVertexPointer(3, GL_INT, 0, cubeArray);
             glDisableClientState(GL_COLOR_ARRAY);
             glEnable(GL_TEXTURE_2D);
             glPopMatrix();

             // draw cube
             glTranslatef(0.5f, 0.5f, 0.5f);
             glRotatef(3.0f, 1.0f, 1.0f, 1.0f);
             glTranslatef(-0.5f, -0.5f, -0.5f);
             glColor4f(0.9f, 0.9f, 0.9f, 1.0f);
             glDrawArrays(GL_QUADS, 0, 24);
         }
         glEndList();
         // 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();
     }