Archived:Rotate picture in Qt

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Qt Quick should be used for all UI development on mobile devices. The approach described in this article (using C++ for the Qt app UI) is deprecated.

Article Metadata

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Tested with

Devices(s): Nokia 5800 XpressMusic, Nokia N900

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Compatibility

Platform(s): Qt

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Article

Keywords: QPixmap, QPainter

Created: tepaa (20 Oct 2009)

Last edited: hamishwillee (11 Oct 2012)

Overview

This example shows how to rotate a QPixmap picture using the QPainter class.

Preconditions

• Qt is installed on your platform.
  • Download Qt release from here: [1]
  • Qt on Maemo can be found here: Qt4 Maemo port

Header

private:
    // Original pixmap that will be rotated
    QPixmap pixmap;

Source

// Create new rotatedPixmap that size is same as original
QPixmap rotatedPixmap(pixmap.size());
 
// Create a QPainter for it
QPainter p(&rotatedPixmap); 
 
// Set rotation origo into pixmap center
QSize size = pixmap.size();
p.translate(size.height()/2,size.height()/2);
 
// Rotate the painter 90 degrees
p.rotate(90);
 
// Set origo back to upper left corner 
p.translate(-size.height()/2,-size.height()/2);
 
// Draw your original pixmap on it
p.drawPixmap(0, 0, pixmap);
p.end();
 
// Change original pixmap reference into new rotated pixmap
pixmap = rotatedPixmap;

Postconditions

The picture is rotated 90 degrees.

See also

• QPainter