I am having problems getting a blending equation to work inside a QGLWidget. This works fine for me on a system where I use 8-bit color indexing mode but now I am on a system that can use 24-bit colors. I am trying to draw a box based on the user's mouse clicking and dragging. Here is what my code looks like:

Qt Code: 
  1. if( mDrawBoxZoom == true )
  2. {
  3.    setAutoBufferSwap( false );
  4.    qglColor( mPlotBoxZoomColor );
  5.    glDrawBuffer( GL_FRONT );
  6.    glLogicOp( GL_XOR );
  7.    glEnable( GL_COLOR_LOGIC_OP );
  8.    glEnable( GL_BLEND );
  9.    glBlendEquationEXT( GL_COLOR_LOGIC_OP );
  10.    glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
  11.    glLineWidth( 2.0 );
  12.    // Draw back over the previously drawn box
  13.    glBegin( GL_LINE_LOOP );
  14.       glVertex3d( mBeginDrawBox[0], mBeginDrawBox[1], 0.0 );
  15.       glVertex3d( mBeginDrawBox[0], mOldEndDrawBox[1], 0.0 );
  16.       glVertex3d( mOldEndDrawBox[0], mOldEndDrawBox[1], 0.0 );
  17.       glVertex3d( mOldEndDrawBox[0], mBeginDrawBox[1], 0.0 );
  18.    glEnd( );
  19.    // Draw the new box with the current mouse position
  20.    glBegin( GL_LINE_LOOP );
  21.       glVertex3d( mBeginDrawBox[0], mBeginDrawBox[1], 0.0 );
  22.       glVertex3d( mBeginDrawBox[0], mEndDrawBox[1], 0.0 );
  23.       glVertex3d( mEndDrawBox[0], mEndDrawBox[1], 0.0 );
  24.       glVertex3d( mEndDrawBox[0], mBeginDrawBox[1], 0.0 );
  25.    glEnd( );
  26.    glFlush( );
  27.    glLineWidth( 1.0 );
  28.    glDisable( GL_COLOR_LOGIC_OP );
  29.    glDisable( GL_BLEND );
  30.    glDrawBuffer( GL_BACK );
  31.    setAutoBufferSwapping( true );
  32. }
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mDrawBoxZoom is set to true when the mouse button is clicked and set to false when the mouse button is released. I do other painting code when the box is not being drawn but this is the part that is not working. Like I said earlier it works fine when I am in 8-bit color indexing mode but not when I am in 24-bit color. The qglColor( ) call is similar to making a glColor*( ) call. My problem is I am capturing all my mouse coordinates correctly which I store in my 3 2-member arrays mBeginDrawBox, mOldEndDrawBox, and mEndDrawBox. These values are correct but I cannot see any box being drawn. I can see some flicker when I move my mouse so I know it's drawing to the front buffer but for some reason I cannot see the box being drawn. Thanks for your help in helping me to try and figure out why I cannot see my mouse.