Expansion rules for a blank widget

[dohzer]

At the moment I've got a program setup with a main QHBoxLayout containing two widgets.
The right widget is a QTableView, and the left widget is a "blank" widget what I'm using to draw shapes is (basically a paint window). The only dimensional data I've given the "paint" widget is a recommended height and width using the sizeHint() function.
When I expand the whole MainWindow, the paint widget's width remains fixed, while the table widget expands to fill the new area.

A couple of questions:

1. What is the easiest way to make both widgets' widths increase evenly as the main window expands?
2. Is there a way I can add some sort of "drag bar" in between the widgets to enable resizing of both widgets while leaving the overall window size unchanged (i.e. increase one widget's width as the other decreases?
3. Is it easy to add scroll bars to blank widgets? I want to be able to paint objects on a large area with dynamic size (i.e. often increasing or decreasing in size), but I'm not sure how I would go about doing this Are there any useful examples someone can point me to? Would it simply be a matter of adding scroll bars and setting the maximum width/height according to the furthest point I currently have painted to?

[grabalon]

I suggest you take a look a QGraphicsView as a replacement for your "Paint" widget. It should have comparable sizing to your table, and you can put a QGraphicsScene of arbitrary size in it. It automatically supports dragging the scene around, and if you subclass the View, you can add an event listener for the mouse wheel to drive zooming (you'll like the QGraphicsView::scale() function for that). As for the "drag bar" check out QSplitter. I have only used it from the GUI designer, not from code, so you'll have to check the docs on that one for usage.

[dohzer]

Wow... QSplitter was exactly what I was after for controlling the size of the child widgets.
I'm about to try out QGraphicsView, and I suspect it will be exactly what I'm after!
Thanks for the help.

[dohzer]

... if you subclass the View, you can add an event listener for the mouse wheel to drive zooming (you'll like the QGraphicsView::scale() function for that).

Would the below be a logical way to setup my QGraphicsView andQGraphicsScene objects for my program?

I have created a new class, "graphicsEditorWidget" for displaying in my main window as the "CentralWidget", and in the constructor I've basically created a new QGraphicsScene, a QGraphicsView, and an ellipse item to test that it's displaying correctly (which it appears to be). Then I've created a layout for the class to display. Is there anything you would recommend me doing differently?

graphicsEditorWidget::graphicsEditorWidget(graphicsData *data, QWidget *parent)
    : QWidget(parent)
{  
    QGraphicsScene *graphScene = new QGraphicsScene(this);
    graphScene->setSceneRect( -100.0, -100.0, 200.0, 200.0 );
 
    QGraphicsEllipseItem *item = new QGraphicsEllipseItem(0,graphScene);
    item->setRect( -50.0, -50.0, 1000.0, 1000.0 );
    item->setFlag(QGraphicsItem::ItemIsMovable);
 
    QGraphicsView *graphView = new QGraphicsView(graphScene);
    graphView->setRenderHints( QPainter::Antialiasing );
 
    QVBoxLayout *graphLayout = new QVBoxLayout;
    graphLayout ->addWidget(graphView);
    setLayout(graphLayout);
}

graphicsEditorWidget::graphicsEditorWidget(graphicsData *data, QWidget *parent)
    : QWidget(parent)
{  
    QGraphicsScene *graphScene = new QGraphicsScene(this);
    graphScene->setSceneRect( -100.0, -100.0, 200.0, 200.0 );

    QGraphicsEllipseItem *item = new QGraphicsEllipseItem(0,graphScene);
    item->setRect( -50.0, -50.0, 1000.0, 1000.0 );
    item->setFlag(QGraphicsItem::ItemIsMovable);

    QGraphicsView *graphView = new QGraphicsView(graphScene);
    graphView->setRenderHints( QPainter::Antialiasing );
    
    QVBoxLayout *graphLayout = new QVBoxLayout;
    graphLayout ->addWidget(graphView);
    setLayout(graphLayout);
}

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How exactly do I go about "subclassing the View" (C++ noob question, no doubt)? Should I be making graphicsEditorWidget a subclass of "QGraphicsView" instead of "QWidget"?

[grabalon]

Nice work so far. The graphicsEditorWidget is good to keep for ui interface purposes. You can use it to connect mouse and keyboard events to appropriate slots within both your View and Scene. To sub-class you'll need an entirely new class (I'll call it MyGraphicsView for lack of a better name). Declare it as follows:

class MyGraphicsView : public QGraphicsView
{
  Q_OBJECT
public:
  MyGraphicsView(QGraphicsScene*, QWidget* parent = 0);
protected slots: //Use this if you want the zoom features
  void wheelEvent(QWheelEvent* event);
}

class MyGraphicsView : public QGraphicsView
{
  Q_OBJECT
public:
  MyGraphicsView(QGraphicsScene*, QWidget* parent = 0);
protected slots: //Use this if you want the zoom features
  void wheelEvent(QWheelEvent* event);
}

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The constructor is fairly straightforward:

MyGraphicsView::MyGraphicsView(QGraphicsScene* s, QWidget* parent) : QGraphicsView(s, parent) { }

MyGraphicsView::MyGraphicsView(QGraphicsScene* s, QWidget* parent) : QGraphicsView(s, parent) { }

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I'll let you fill in other class features as you see fit, but I suggest the wheel event function looks something like:

void MyGraphicsView::wheelEvent(QWheelEvent *event)
{
    if(event->delta() > 0)
        scale(1.1111,1.1111);
    else
        scale(0.9,0.9);
}

void MyGraphicsView::wheelEvent(QWheelEvent *event)
{
    if(event->delta() > 0)
        scale(1.1111,1.1111);
    else
        scale(0.9,0.9);
}

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Finally, to actually use the View, change line 11 in your code above to:

MyGraphicsView* graphView = new MyGraphicsView(graphScene);

MyGraphicsView* graphView = new MyGraphicsView(graphScene);

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See if that get's you going on how this all works.