Crash during OpenGL context creation

[PaladinOfKaos]

I'm having an interesting problem with OpenGL contexts in Qt 4.3.3 (Kubuntu 8.04).

When I try to customize the format, liks so:

MainWindow::MainWindow(QWidget *parent)
  : KXmlGuiWindow(parent)
{
  QGLFormat format;
  QGLContext *context;
 
  qDebug("Setting up GL format...");
  format.setAccum(false);
  format.setAlpha(true);
  format.setAlphaBufferSize(8);
  format.setBlueBufferSize(8);
  format.setDepth(true);
  format.setDepthBufferSize(24);
  format.setDirectRendering(true);
  format.setDoubleBuffer(true);
  format.setGreenBufferSize(8);
  format.setOverlay(false);
  format.setPlane(0);
  format.setRedBufferSize(8);
  format.setRgba(true);
  format.setSampleBuffers(true);
  format.setSamples(4);
  format.setStencil(true);
  format.setStencilBufferSize(8);
  format.setStereo(false);
  format.setSwapInterval(0);
 
  qDebug("Creating Context...");
  context = new QGLContext(format);
  if(!context->create()) {
    qWarning("Failed to create context...");
    qDebug("Disabling multisampling...");
    format.setSampleBuffers(false);
    context->setFormat(format);
    if(!context->create()) {
      qFatal("Still can't create a context...");
      exit(0);
    }
  }
 
  qDebug("Creating preview widget...");
  preview = new MaterialPreview(context);
 
  setCentralWidget(preview);
  setupGUI();
}

MainWindow::MainWindow(QWidget *parent)
  : KXmlGuiWindow(parent)
{
  QGLFormat format;
  QGLContext *context;

  qDebug("Setting up GL format...");
  format.setAccum(false);
  format.setAlpha(true);
  format.setAlphaBufferSize(8);
  format.setBlueBufferSize(8);
  format.setDepth(true);
  format.setDepthBufferSize(24);
  format.setDirectRendering(true);
  format.setDoubleBuffer(true);
  format.setGreenBufferSize(8);
  format.setOverlay(false);
  format.setPlane(0);
  format.setRedBufferSize(8);
  format.setRgba(true);
  format.setSampleBuffers(true);
  format.setSamples(4);
  format.setStencil(true);
  format.setStencilBufferSize(8);
  format.setStereo(false);
  format.setSwapInterval(0);

  qDebug("Creating Context...");
  context = new QGLContext(format);
  if(!context->create()) {
    qWarning("Failed to create context...");
    qDebug("Disabling multisampling...");
    format.setSampleBuffers(false);
    context->setFormat(format);
    if(!context->create()) {
      qFatal("Still can't create a context...");
      exit(0);
    }
  }

  qDebug("Creating preview widget...");
  preview = new MaterialPreview(context);

  setCentralWidget(preview);
  setupGUI();
}

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I get a crash during the first call to context->create().

When I don't setup a custom format and context, and just create a QGLWidget, I don't have the crash.

In case you're curious, the odd bit with multisampling is just a test to see if I can actually setup a multisampled rendering context on my machine.

EDIT:
Here's the backtrace:

#0 0xb755dc35 in QX11Info::screen () from /usr/lib/libQtGui.so.4
#1 0xb6d31671 in QGLContext::tryVisual () from /usr/lib/libQtOpenGL.so.4
#2 0xb6d30529 in QGLContext::chooseVisual () from /usr/lib/libQtOpenGL.so.4
#3 0xb6d30984 in QGLContext::chooseContext () from /usr/lib/libQtOpenGL.so.4
#4 0xb6d062a4 in QGLContext::create () from /usr/lib/libQtOpenGL.so.4
#5 0x0804ca79 in MainWindow (this=0x80fdf80, parent=0x0) at mainwindow.cpp:39
#6 0x0804c778 in main (argc=1, argv=0xbfc0c574) at main.cpp:25

#0 0xb755dc35 in QX11Info::screen () from /usr/lib/libQtGui.so.4
#1 0xb6d31671 in QGLContext::tryVisual () from /usr/lib/libQtOpenGL.so.4
#2 0xb6d30529 in QGLContext::chooseVisual () from /usr/lib/libQtOpenGL.so.4
#3 0xb6d30984 in QGLContext::chooseContext () from /usr/lib/libQtOpenGL.so.4
#4 0xb6d062a4 in QGLContext::create () from /usr/lib/libQtOpenGL.so.4
#5 0x0804ca79 in MainWindow (this=0x80fdf80, parent=0x0) at mainwindow.cpp:39
#6 0x0804c778 in main (argc=1, argv=0xbfc0c574) at main.cpp:25

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*Yes, I know this is a KDE program, but the problem appears to be in Qt

[rbp]

hello,

I know this was a long time ago, but did you ever figure out the context problem?

On my system (Windows XP, Qt 4.5.1) I found setting the context manually does not work and the only way to enable multisampling was through the constructor:

MyWidget:: MyWidget(QWidget *parent):QGLWidget(QGLFormat(QGL::SampleBuffers), parent)

MyWidget:: MyWidget(QWidget *parent):QGLWidget(QGLFormat(QGL::SampleBuffers), parent)

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I got the hint from this article that setContext() has problems: http://doc.trolltech.com/qq/qq06-glimpsing.html

hope that helps someone,
Richard