One QGLWidget that manage QGLWidget childs

[polch]

Hi.

I would like to know if the following use case is supported by QT.

I have one “Parent” QGLWidget :

class ParentGLWidget : public QGLWidget 
    {
    ...
        ParentGLWidget(QGLContext * context, QWidget *parent = 0) : QGLWidget(context, parent) {... }
    ...
        void initializeGL()
        {
        qglClearColor(qtPurple.dark());
        glEnable(GL_CULL_FACE);
        ...
        }
 
        void paintGL()
        {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        }
 
        void resizeGL(int width, int height)
        {
        glViewport((width - side) / 2, (height - side) / 2, side, side);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrthof(-0.5, +0.5, -0.5, +0.5, 4.0, 15.0);
        glMatrixMode(GL_MODELVIEW);
        }
    }

class ParentGLWidget : public QGLWidget 
    {
    ...
        ParentGLWidget(QGLContext * context, QWidget *parent = 0) : QGLWidget(context, parent) {... }
    ...
        void initializeGL()
        {
        qglClearColor(qtPurple.dark());
        glEnable(GL_CULL_FACE);
        ...
        }
     
        void paintGL()
        {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        }
     
        void resizeGL(int width, int height)
        {
        glViewport((width - side) / 2, (height - side) / 2, side, side);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrthof(-0.5, +0.5, -0.5, +0.5, 4.0, 15.0);
        glMatrixMode(GL_MODELVIEW);
        }
    }

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There are other “childs" GLWidget that should be drawn "inside" the parent widget context :

class ChildGLWidget : public QGLWidget 
    {
    ...
        ChildGLWidget(QGLContext * context, QWidget *parent = 0) : QGLWidget(context, parent) {... }
    ...
        void initializeGL()
        {
         // optional
         // at least, should not overwrite what have been done in the top level widget
        }
 
        void paintGL()
        {
        glLoadIdentity();
        glTranslatef(0.0, 0.0, -10.0);
        glRotatef(xRot, 1.0, 0.0, 0.0);
        // draw some object in the gl world
        }
 
        void resizeGL(int width, int height)
        {
         // optional
         // at least, should not overwrite what have been done in the top level widget
        }
    }

class ChildGLWidget : public QGLWidget 
    {
    ...
        ChildGLWidget(QGLContext * context, QWidget *parent = 0) : QGLWidget(context, parent) {... }
    ...
        void initializeGL()
        {
         // optional
         // at least, should not overwrite what have been done in the top level widget
        }
     
        void paintGL()
        {
        glLoadIdentity();
        glTranslatef(0.0, 0.0, -10.0);
        glRotatef(xRot, 1.0, 0.0, 0.0);
        // draw some object in the gl world
        }
     
        void resizeGL(int width, int height)
        {
         // optional
         // at least, should not overwrite what have been done in the top level widget
        }
    }

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I would like to use them like this :

QGLContext * context = new QGLContext(QGLFormat(QGL::SampleBuffers));
ParentGLWidget * parent = new ParentGLWidget(context);
ChildGLWidget * child_1 = new ChildGLWidget(context, parent);
ChildGLWidget * child_2 = new ChildGLWidget(context, parent);

QGLContext * context = new QGLContext(QGLFormat(QGL::SampleBuffers));
ParentGLWidget * parent = new ParentGLWidget(context);
ChildGLWidget * child_1 = new ChildGLWidget(context, parent);
ChildGLWidget * child_2 = new ChildGLWidget(context, parent);

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The childs could be managed (drawing, deletion, …) by the parent (like traditional widgets do), and I would be able to have some part of 3D rendering in "modules".

I haven’t been able to run such a use case.

Is there any design flaw in this use case ? Do you think there are others ways to do that ?

Thank for your help.

[wysota]

Traditional widgets are not managed by their parent in any way. Sharing GL contexts makes it possible to share textures and display lists.

[polch]

Thank you for your reply.

I thought that the parent widget recursively triggered the display of its childs... So i thought that i would be possible to call the InitializeGL, paintGL, and resizeGL methods of the childs by a parent.

Actualy i have a class that contains a list of object with GL drawing methods that are called inside the paintGL method of an unique QGLWidget. I wondered if it was a good design.

Regards.

Paul.

[wysota]

I thought that the parent widget recursively triggered the display of its childs...

No. The parent paints itself on a given canvas and then each of its children paints itself on the same (or different) canvas. Then everything is assembled and rendered to the screen.

So i thought that i would be possible to call the InitializeGL, paintGL, and resizeGL methods of the childs by a parent.

I don't think stacking GL widgets onto each other would do you any good.

Actualy i have a class that contains a list of object with GL drawing methods that are called inside the paintGL method of an unique QGLWidget. I wondered if it was a good design.

Seems ok. Just call them from the GL widget's paintGL() implementation and you're done. No need for any extra widgets.

[polch]

Seems ok. Just call them from the GL widget's paintGL() implementation and you're done. No need for any extra widgets.

That what i actually do.

Thank you for the discussion.