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# The interface example

Adding a graphical user interface around a `QGLViewer`.

Qt's `designer` has been used to create a very simple interface example, described by a `.ui` user interface description file.

Install the QGLViewer designer plugin so that the QGLViewer appears in the designer's widgets tabs. You can then connect signals and slots to and from the viewer. The viewer is fully functional and can be manipulated when you test your interface in `designer`.

The plugin code is in the `designerPlugin` directory. Start from there to create plugins for the classes you will derive from QGLViewer. Select your architecture in the download page for details on the plugin compilation and installation.

Here we use three slots and three signals (axis, grid and fps) to connect to and from the interface and the viewer.

## interface.h

    #include <QGLViewer/qglviewer.h>

    class Viewer : public QGLViewer {
    public:
      Viewer(QWidget *parent);

    protected:
      virtual void draw();
      virtual QString helpString() const;
    };

## interface.cpp

    #include "interface.h"
    #include <math.h>

    // Constructor must call the base class constructor.
    Viewer::Viewer(QWidget *parent) : QGLViewer(parent) {
      restoreStateFromFile();
      help();
    }

    void Viewer::draw() {
      // Draws a spiral
      const float nbSteps = 200.0;
      glBegin(GL_QUAD_STRIP);
      for (float i = 0; i < nbSteps; ++i) {
        float ratio = i / nbSteps;
        float angle = 21.0 * ratio;
        float c = cos(angle);
        float s = sin(angle);
        float r1 = 1.0 - 0.8 * ratio;
        float r2 = 0.8 - 0.8 * ratio;
        float alt = ratio - 0.5;
        const float nor = .5;
        const float up = sqrt(1.0 - nor * nor);
        glColor3f(1.0 - ratio, 0.2f, ratio);
        glNormal3f(nor * c, up, nor * s);
        glVertex3f(r1 * c, alt, r1 * s);
        glVertex3f(r2 * c, alt + 0.05, r2 * s);
      }
      glEnd();
    }

    QString Viewer::helpString() const {
      QString text("<h2>I n t e r f a c e</h2>");
      text += "A GUI can be added to a QGLViewer widget using Qt's "
              "<i>Designer</i>. Signals and slots ";
      text += "can then be connected to and from the viewer.<br><br>";
      text += "You can install the QGLViewer designer plugin to make the QGLViewer "
              "appear as a ";
      text += "standard Qt widget in the Designer's widget tabs. See installation "
              "pages for details.";
      return text;
    }

## main.cpp

    #include <qapplication.h>

    #include "ui_viewerInterface.h"

    class ViewerInterface : public QDialog, public Ui::Dialog {
    public:
      ViewerInterface() { setupUi(this); }
    };

    int main(int argc, char **argv) {
      QApplication application(argc, argv);

      ViewerInterface vi;

      vi.setWindowTitle("interface");

      vi.show();

      return application.exec();
    }

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