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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] = {
     {102, 176, 54, 255},
     {81, 141, 41, 255},
     {62, 108, 32, 255},
     {45, 79, 23, 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(0.8, 0.8, 0.8, 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();
 }