grabWidget problem

Hello all,

This is supposed to grab a section of the parent widget when this widget is moved and display the grab. It isn't working.
Any insights will be greatly appreciated!!!

TIA,

gonzoboy!

void ZoomWindow::moveFrame()
{
move(mp.x(), mp.y());

QWidget w(this->parentWidget());
w.show();
// grab a 40x40 chunk of parent widget
pm = QPixmap::grabWidget(&w, 0, 0, 39, 39);
}

void ZoomWindow::paintEvent(QPaintEvent* pe)
{
QPainter painter(this);
QRect r(0, 0, 199, 199);
QPen pen(Qt::black);

// paint the pixmap from parent zoomed 5x in ZoomWindow
painter.drawPixmap(r, pm);
painter.drawRect(r);

}

try this

Code:

---

...
pm = QPixmap::grabWidget(parentWidget(), 0, 0, 39, 39);
...

---

Thanks, that actually gave me the same strange result that grabWindow returns. Any other notions?

Hi,

When does your moveFrame() method is called?

Be careful that if it is in response of a mouseMove event,
then moving your widget inside will trigger another mouseMove, since it is moved relatively to the mouse!!

Hard to get rid of this and get expected behaviour. Think well your design.

The mouse event is in the parent. This triggers the grab in the child.

I wonder if the widget your are creating in moveFrame has the time to be painted before go out the method. The event is queued, no?

That is why spirit told you to use direclty the parent instead of creating a temporary widget.

But what about moving a simple colored QPixmap?

Scascio,

It isn't queued. How would one go about doing that?

g

Here is the trigger (in main.cpp):
QObject::connect(&w, SIGNAL(mouseMoved()), &zw, SLOT(moveFrame()));

Yes, I think you've nailed the problem. When I do the grab from the child constructor for a fixed part of the parent, it grabs fine. SO, how do I "slow it down" enough to do an updated grab after a mouseMove without really slowing the app down?


pm = QPixmap::grabWidget(parentWidget(), 0, 0, 50, 50);

In tried to solve your zoom window need and I encountered several problems

• A factor 5 seems a lot.
• You need to set a size for the ZoomWindow to have it painted correctly
• You dont need to get through SIGNAL/SLOT since mouseMoveEvent in parent widget is a virtual method.

I think your main problem is that when you grab the widget in the child window, you will grab all the parent, so with the child(the zoom) in it!! so you need to make it invisible and restore it after.

And ones I didnt solve :

• the zoom is painted under the layout in background (=>maybe a window flag?),
• the mouseMoveEvent is not trigger on child widget of the layout (=>use eventFilter?)

Here is the parent widget :

Code:

---

#ifndef MYMAINWIDGET_H
#define MYMAINWIDGET_H
 
#include <QtGui/QDialog>
#include "ui_MyMainWidget.h"
 
#include <QMouseEvent>
 
#include "ZoomWindow.h"
 
class MyMainWidget : public QDialog {
 
	Q_OBJECT
 
	public:
 
		MyMainWidget(QWidget *parent = 0)
	    : QDialog(parent), m_zoomWindow(this) {
			ui.setupUi(this);
			setMouseTracking(true);
		}
 
		virtual ~MyMainWidget()  {
		}
 
	protected:
 
		void mouseMoveEvent(QMouseEvent * event){
			QWidget::mouseMoveEvent(event);
			m_zoomWindow.update(event->pos());
		}
 
	private:
 
		Ui::MyMainWidgetClass ui;
 
		ZoomWindow m_zoomWindow;
};
 
#endif // MYMAINWIDGET_H

---

And here is the Zoom Window

Code:

---

#ifndef ZOOMWINDOW_H
#define ZOOMWINDOW_H
 
#include <QtGui/QWidget>
 
#include <QPixmap>
#include <QPainter>
 
class ZoomWindow : public QWidget {
 
	Q_OBJECT
 
	public:
 
		ZoomWindow(QWidget *parent = 0, int factor=2)
			:QWidget(parent), m_factor(factor) {
			resize(200, 200);
		}
 
		virtual ~ZoomWindow() {
		}
 
		void update(const QPoint& point) {
			setVisible(false);
			m_pixmap = QPixmap::grabWidget(parentWidget(), QRect(point, size()/m_factor));
			setVisible(true);
			move(point);
			QWidget::update();
		}
 
	protected:
 
		virtual void paintEvent(QPaintEvent * /*event*/) {
			QRect r(rect());
			QPainter painter(this);
			painter.setPen(Qt::black);
			painter.drawPixmap(r, m_pixmap);
			painter.drawRect(r);
		}
 
	private:
 
		int m_factor;
    	QPixmap m_pixmap;
};
 
#endif // ZOOMWINDOW_H

---

Scoscio,

Thanks so much. I will try what you have suggested. I am working on an assignment and it specified zoom factor 5. I like the update overload approach. Stay tuned...

gonzoboy!