QPainter on a QGLWidget using VBOs

jrevans

I have a QGLWidget that I wish to overpaint onto with a QPainter. I have followed the various examples out there to do this, but I still cannot seem to get it to work properly when I am using VBOs. I have the source code available "here":https://dl.dropboxusercontent.com/u/36712950/QtGlText.tgz

The most relevant sections of code are as follows:

@
void
GlWidget::
paintEvent( QPaintEvent* event )
{
if ( !updatesEnabled() )
{
// do not update this widget
return;
}

if ( !isValid() )
{
// no valid render context
return;
}

// make sure this render context is the active one
makeCurrent();

QPainter painter;
painter.begin( this );
painter.setRenderHint( QPainter::Antialiasing );

#ifndef NO_2D_3D_MIX
// begin OpenGL calls
painter.beginNativePainting();
#endif

// Save the current OpenGL state (extra paranoid)
glPushAttrib( GL_ALL_ATTRIB_BITS );
glMatrixMode( GL_PROJECTION );
glPushMatrix();
glMatrixMode( GL_MODELVIEW );
glPushMatrix();

// setup the viewport
resizeGL( width(), height() );

// pre-render callback
preRender();

// begin rendering
emit rendering();

// 3D render
paintGL();

// Restore OpenGL state
glMatrixMode( GL_MODELVIEW );
glPopMatrix();
glMatrixMode( GL_PROJECTION );
glPopMatrix();
glPopAttrib();

// make sure there are no loaded shader programs
glUseProgram( 0 );
glBindBuffer( GL_ARRAY_BUFFER, 0 );

#ifndef NO_2D_3D_MIX
// end OpenGL calls
painter.endNativePainting();

// 2D render
render2d( &painter );
#endif

// post-render callback
postRender();

// end painting and swap the buffers
painter.end();
}
@

and

@
void
TestWidget::
render3d()
{
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

// This works
glBegin( GL_TRIANGLES );
glColor3ub( 255, 15, 125 );
glVertex3f( -0.85, -0.90, 0.8 ); // triangle #1
glVertex3f( 0.90, -0.90, 0.8 );
glVertex3f( 0.90, 0.85, 0.8 );

glVertex3f( -0.90, -0.85, 0.8 ); // triangle #2
glVertex3f( 0.85, 0.90, 0.8 );
glVertex3f( -0.90, 0.90, 0.8 );
glEnd();

// Bind the shader program
m_shader.bind();

// Bind the vertex buffers
m_vertexBuffer.bind();

// draw them
glDrawArrays( GL_TRIANGLES, 0, NUM_VERTS );
}
@

A couple of things to note are that the fixed-function OpenGL calls (glBegin, glVertex, glEnd) work properly and draw. The vertex buffer items only draw when I define 'NO_2D_3D_MIX'. I feel like I must be missing something simple here, but I cannot figure out what.

Due to other constraints I am using Qt v4.8.5, Mesa-9.2.1 GL headers with the nVidia 304.43 run-time drivers on a 64-bit RedHat Linux machine.

Thanks in advance for any possible help.

8Observer8

This is a very old question but I think it will not be bad if I answer here.

You should draw with QPainter in paintGL()
Place all GL stuff between painter.beginNativePainting(); and painter.endNativePainting();:
Unbind VBO's: m_vertPosBufferForLines.release();
Draw using QPainter after painter.endNativePainting();