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000 SoText2 won't show with drawstyle == hidden line. Bug reported by
    Jean Davy. Reproduce with this minimal, stand-alone example:

    ----8<--- [snip] ---------8<--- [snip] ---------8<--- [snip] ---
    #include <Inventor/Qt/SoQt.h>
    #include <Inventor/Qt/viewers/SoQtExaminerViewer.h>
    #include <Inventor/nodes/SoCone.h>
    #include <Inventor/nodes/SoSeparator.h>
    #include <Inventor/nodes/SoText2.h>
    
    int
    main(int argc, char* argv[])
    {
      QWidget * mainwin = SoQt::init(argv[0]);
      SoSeparator * root = new SoSeparator;
    
      root->addChild(new SoCone);
      SoText2 * text2d = new SoText2;
      root->addChild(text2d);
      text2d->string = "tjo-bing";
    
      SoQtExaminerViewer * viewer = new SoQtExaminerViewer(mainwin);
      viewer->setSceneGraph(root);
      viewer->setDrawStyle(SoQtExaminerViewer::STILL,
                           SoQtExaminerViewer::VIEW_HIDDEN_LINE);
    
      SoQt::show(mainwin);
      SoQt::mainLoop();
    
      return 0;
    }
    ----8<--- [snip] ---------8<--- [snip] ---------8<--- [snip] ---

    This is the cause of the bug, according to <pederb@sim.no>:

      We use GL polygon offset to do hidden line rendering, and this
      caused problems since the SoText2 characters are rendered twice
      (for the first pass we just draw everything black, with an
      z-buffer offset). SoText2 characters are drawn as bitmaps, which
      are not affected by polygon offset.

    <mortene@sim.no> 20020521.

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