I have a QGLWidget that renders fine when using paintGL and also when using paintEvent() however I can't seem to get any painter.draw* commands to work with the paintEvent. I don't understand why this program won't allow me to draw with QPainter. I have mimicked the Overpainting example the best I could, however I am not clear what belongs in paintEvent (I think I know) and what belongs in initializeGL. The code I am posting shows both versions of the code I am trying to execute. All the code that is commented out is mostly the opengl calls used without overriding paintEvent, with the exception of the painter code at the bottom of the paintEvent which is the exact code from the overpainting exampe. I am simply trying to draw a line from the top corner of the widget to the bottom and still not able to get it to render properly.

Qt Code: 
  1. #include "glwidget.h"
  2. #include "../../shared/math3d.h"
  3. #include "../../shared/gltools.h"
  4.  
  5. #include <QPainter>
  6. #include <QPaintEvent>
  7.  
  8. #include <GL/glu.h>
  9.  
  10. #include <math.h>
  11.  
  12. GLWidget::GLWidget(QWidget *parent)
  13.     : QGLWidget(QGLFormat(QGL::SampleBuffers), parent)
  14. {
  15.     animationTimer.setSingleShot(false);
  16.     animationTimer.setInterval(33);
  17.     connect(&animationTimer, SIGNAL(timeout()), this, SLOT(update()));
  18.     animationTimer.start();
  19.  
  20.     qDebug() << pixmap.load("../Transformgl/graphicsview-pixmapitem.png");
  21.     qDebug() << pixmap.width();
  22.     qDebug() << pixmap.height();
  23.  
  24.     setAutoFillBackground(false);
  25.     setMinimumSize(800, 600);
  26.     setWindowTitle("Transformgl with PaintEvent");
  27. }
  28.  
  29. QSize GLWidget::sizeHint() const
  30. {
  31.     return QSize(800, 600);
  32. }
  33.  
  34. void GLWidget::initializeGL()
  35. {
  36.     // Bluish background
  37.     glClearColor(0.0f, 0.0f, .50f, 1.0f );
  38.  
  39.     // Draw everything as wire frame
  40.     glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
  41. }
  42.  
  43. void GLWidget::resizeGL(int w, int h)
  44. {
  45. //    GLfloat fAspect;
  46.  
  47. //    // Prevent a divide by zero, when window is too short
  48. //    // (you cant make a window of zero width).
  49. //    if(h == 0)
  50. //        h = 1;
  51.  
  52. //    glViewport(0, 0, w, h);
  53.  
  54. //    fAspect = (GLfloat)w / (GLfloat)h;
  55.  
  56. //    // Reset the coordinate system before modifying
  57. //    glMatrixMode(GL_PROJECTION);
  58. //    glLoadIdentity();
  59.  
  60. //    // Set the clipping volume
  61. //    gluPerspective(35.0f, fAspect, 1.0f, 50.0f);
  62.  
  63. //    glMatrixMode(GL_MODELVIEW);
  64. //    glLoadIdentity();
  65.  
  66.     setupViewport(w, h);
  67. }
  68.  
  69. //void GLWidget::paintGL()
  70. //{
  71. //    M3DMatrix44f rotationMatrix, translationMatrix, transformationMatrix;
  72.  
  73. //    static GLfloat yRot = 0.0f;         // Rotation angle for animation
  74. //    yRot += 0.5f;
  75.  
  76. //    // Clear the window with current clearing color
  77. //    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  78.  
  79. //    // Build a rotation matrix
  80. //    m3dRotationMatrix44(transformationMatrix, m3dDegToRad(yRot), 0.0f, 1.0f, 0.0f);
  81. //    transformationMatrix[12] = 0.0f;
  82. //    transformationMatrix[13] = 0.0f;
  83. //    transformationMatrix[14] = -2.5f;
  84.  
  85. //    glLoadMatrixf(transformationMatrix);
  86.  
  87. //    gltDrawTorus(0.35f, 0.15f, 40, 20);
  88.  
  89. //    // Do the buffer Swap
  90. //    swapBuffers();
  91. //}
  92.  
  93. void GLWidget::paintEvent(QPaintEvent *event)
  94. {
  95.     makeCurrent();
  96.  
  97.     glMatrixMode(GL_MODELVIEW);
  98.     glPushMatrix();
  99.  
  100.         // Bluish background
  101.         glClearColor(0.0f, 0.0f, .50f, 1.0f );
  102.  
  103.         // Draw everything as wire frame
  104.         glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
  105.  
  106.         M3DMatrix44f rotationMatrix, translationMatrix, transformationMatrix;
  107.  
  108.         static GLfloat yRot = 0.0f;         // Rotation angle for animation
  109.         yRot += 0.5f;
  110.  
  111.         setupViewport(width(), height());
  112.  
  113.         // Clear the window with current clearing color
  114.         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  115.         glLoadIdentity();
  116.  
  117.         // Build a rotation matrix
  118.         m3dRotationMatrix44(transformationMatrix, m3dDegToRad(yRot), 0.0f, 1.0f, 0.0f);
  119.         transformationMatrix[12] = 0.0f;
  120.         transformationMatrix[13] = 0.0f;
  121.         transformationMatrix[14] = -2.5f;
  122.  
  123.         glLoadMatrixf(transformationMatrix);
  124.  
  125.         gltDrawTorus(0.35f, 0.15f, 40, 20);
  126.  
  127.         glMatrixMode(GL_MODELVIEW);
  128.     glPopMatrix();
  129.  
  130.     QPainter painter(this);
  131.     painter.setBrush(Qt::cyan);
  132.     painter.drawLine(0, 0, width(), height());
  133. //    QString text = tr("Click and drag with the left mouse button "
  134. //                           "to rotate the Qt logo.");
  135. //    QFontMetrics metrics = QFontMetrics(font());
  136. //    int border = qMax(4, metrics.leading());
  137.  
  138. //    QRect rect = metrics.boundingRect(0, 0, width() - 2*border, int(height()*0.125),
  139. //                                   Qt::AlignCenter | Qt::TextWordWrap, text);
  140. //    painter.setRenderHint(QPainter::TextAntialiasing);
  141. //    painter.fillRect(QRect(0, 0, width(), rect.height() + 2*border),
  142. //                  QColor(0, 0, 0, 127));
  143. //    painter.setPen(Qt::white);
  144. //    painter.fillRect(QRect(0, 0, width(), rect.height() + 2*border),
  145. //                   QColor(0, 0, 0, 127));
  146. //    painter.drawText((width() - rect.width())/2, border,
  147. //                   rect.width(), rect.height(),
  148. //                   Qt::AlignCenter | Qt::TextWordWrap, text);
  149.     painter.end();
  150. }
  151.  
  152. void GLWidget::setupViewport(int w, int h)
  153. {
  154.     GLfloat fAspect;
  155.  
  156.     // Prevent a divide by zero, when window is too short
  157.     // (you cant make a window of zero width).
  158.     if(h == 0)
  159.         h = 1;
  160.  
  161.     glViewport(0, 0, w, h);
  162.  
  163.     fAspect = (GLfloat)w / (GLfloat)h;
  164.  
  165.     // Reset the coordinate system before modifying
  166.     glMatrixMode(GL_PROJECTION);
  167.     glLoadIdentity();
  168.  
  169.     // Set the clipping volume
  170.     gluPerspective(35.0f, fAspect, 1.0f, 50.0f);
  171.  
  172.     glMatrixMode(GL_MODELVIEW);
  173.     glLoadIdentity();
  174. }
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