Rotation problem

Hi all,

I am new to Qt, currently I am using Qt 4 on Linux. I am writing a application similar to the "draggableicons" sample. All I need is icons should rotate say 40 degrees when we right click on it. Can some body explain how to do it? Here is the code I have modified
in the draggableicons sample, but it doesnt work :(

Code:

---

void DragWidget::mousePressEvent(QMouseEvent *event)
{
       .
       .
       .
   QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    //rotate abt 60 degrees
    painter.rotate(60);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();
    .
    .
    .
 
}

---

Thanks in advance,
Prasanna Bhat

Do not try to paint outside of the paint event.

have a Variable containing the current rotation which you use in the paint event to redraw the screen. When you register a click, update the variable and request an update.

boss_bha, the problem is that you copy a pixmap as it is, then create and rotate the painter, and fill a rotated rectangle over the copied pixmap. So the pixmap is not rotated anywhere in that code.

Quote:

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Originally Posted by camel

Do not try to paint outside of the paint event.

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This applies only to QWidgets and he seems to be painting on a QPixmap.

Here's something to get you going. This might be a bit slow (due to QPixmap->QImage->QPixmap conversions), but close to a working solution:

Code:

---

QImage tempImage = pixmap.toImage();
//rotate abt 60 degrees
QMatrix matrix;
matrix.rotate(60);
tempImage = tempImage.transformed(matrix);
QPainter painter;
painter.begin(&tempImage);
painter.fillRect(tempImage.rect(), QColor(127, 127, 127, 127));
painter.end();
 
child->setPixmap(QPixmap::fromImage(tempImage));

---

What does it miss is some proper scaling. A rotated image takes naturally more space to get drawn entirely.
Another way is not to copy the pixmap, but draw it after the painter has been rotated.

Hi JP-N,

Sorry to bug you again,
I tried your code but it's not working, Am I wrong here?? I am pasting the entire code of mousePressEvent()

Code:

---

void DragWidget::mousePressEvent(QMouseEvent *event)
{
    QLabel *child = static_cast<QLabel*>(childAt(event->pos()));
    if (!child)
        return;
 
    QPixmap pixmap = *child->pixmap();
 
    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << pixmap << QPoint(event->pos() - child->pos());
 
    QMimeData *mimeData = new QMimeData;
    mimeData->setData("application/x-dnditemdata", itemData);
 
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(pixmap);
    drag->setHotSpot(event->pos() - child->pos());
 
 
if (event->button()==Qt::RightButton){
   QImage tempImage = pixmap.toImage();
   //rotate abt 60 degrees
   QMatrix matrix;
   matrix.rotate(60);
   tempImage = tempImage.transformed(matrix);
   QPainter painter;
   painter.begin(&tempImage);
   painter.fillRect(tempImage.rect(),
   QColor(127, 127, 127, 127));
   painter.end();
   child->setPixmap(QPixmap::fromImage(tempImage));
   }
else
{
    QPixmap tempPixmap = pixmap;
    QPainter painter;
    painter.begin(&tempPixmap);
    painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127));
    painter.end();
    child->setPixmap(tempPixmap);
 
}
    if (drag->start(Qt::CopyAction | Qt::MoveAction) == Qt::MoveAction)
        child->close();
    else {
        child->show();
        child->setPixmap(pixmap);
    }
}

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Thanks in advance,
Prasanna Bhat

Could you elaborate what you intend to do? If you plan to rotate the same image multiple times in a row, I'd suggest you to use some another approach. Like for example keeping the original image around..