how to write QT openGL code in two classes

[tbscope]

I suggest a good C++ book.

Are you using Qt3 or Qt4?
The hellogl example uses QGLWidget like you are. But it shows you how to use the QGLWidget constructor. It doesn't matter if you split your program in different parts.

C++ contains several ways to exchange information between different objects or different classes.

[tbscope]

By the way, I think you handle this a bit in the wrong way.

You should only have one GL Widget.
Then you can create different classes that do different things. Like a Building class or a Car class which each can serialise data and create the GL code. Then you can paint that GL code on the widget. There are several techniques and programming patterns you can use for this.

[qtUse]

Ohhhh .....I verified, HelloGL's using QGLWidget only as you said
I tried according to it and it's finely taking GL contexts from calling function

Thanks for your prompt help, tbscope

@second post:
But in order to draw, say car, I need to paint different sides in car drawing class only (to avoid passing all its vertices to single QGLWidget), so GL context must be available to my BuildingPainter class. So I am using multiple OGLWidgets

[tbscope]

I would probably go with the Model and View pattern. The view being the QGLWidget and the model a tree of objects.

Example:

+------------------+
| MyGlModel        |
|                  |
| Rootitem         |      +-------------+
|  |               |      | MyGlView    |
|  +- Item         |      |             |
|  |		   |----->| setModel()  |
|  +- Item         |      |             |
|      |           |      |             |
|      + Item      |      +-------------+
|                  |
+------------------+
 
 
 
 
 
+------------------+      +-------------------+
| MyGlView         |      | MyGlItem          |
|                  |      |                   |
| paintGl()        |      | drawItem(context) |
|  |               |----->|                   |
|  +- iterate      |      |                   |
|     over model   |      +-------------------+
|                  |
+------------------+
 
 
 
void MyGlView::drawGl()
{
    // recursive call each item in the model tree
 
    // For each item:
    item->drawItem(context(), /*maybe other stuff*/);
}
 
void MyGlItem::drawItem(QGLContext *context, /*maybe other things*/)
{
    // Do the GL Painting for this item based on the context.
}

+------------------+
| MyGlModel        |
|                  |
| Rootitem         |      +-------------+
|  |               |      | MyGlView    |
|  +- Item         |      |             |
|  |		   |----->| setModel()  |
|  +- Item         |      |             |
|      |           |      |             |
|      + Item      |      +-------------+
|                  |
+------------------+





+------------------+      +-------------------+
| MyGlView         |      | MyGlItem          |
|                  |      |                   |
| paintGl()        |      | drawItem(context) |
|  |               |----->|                   |
|  +- iterate      |      |                   |
|     over model   |      +-------------------+
|                  |
+------------------+



void MyGlView::drawGl()
{
    // recursive call each item in the model tree

    // For each item:
    item->drawItem(context(), /*maybe other stuff*/);
}

void MyGlItem::drawItem(QGLContext *context, /*maybe other things*/)
{
    // Do the GL Painting for this item based on the context.
}

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