To display image in Qt4 you can use a QLabel and the setPixmap() method. But if you need something more complex that will keep the aspect ratio and can zoom and rotate you will have to create a custom widget. This is how i did it for a Image viewer application that i make it in Qt4 using c++.
#ifndef IMAGEWIDGET_H
#define IMAGEWIDGET_H
#include <QWidget>
class QSize;
class QImage;
class ImageWidget : public QWidget
{
Q_OBJECT
public:
explicit ImageWidget(QWidget *parent = 0);
void setImage(const QImage &image);
QImage *getImage();
float getZoomFactor();
//this is absolute depends only on the size of the image
void setZoomFactor(float zf);
//this is relative with the curent size/zoom
void zoom(float zoomWithThisFactor);
//if set to true the image will be zoomed to fit the widget
void setZoomToFit(bool ztf);
signals:
public slots:
protected:
//custom drawing rutine
void paintEvent(QPaintEvent *);
//custom sizeHint method
QSize sizeHint() const;
private:
QImage *image;
float zoomFactor;
float aspectRatio;
bool zoomToFit;
void computeZoomFactorToFitImage();
void adjustSize();
};
#endif // IMAGEWIDGET_H
I subclased QWidget and reimpemented 2 methods paintEvent() and sizeHint():
void ImageWidget::paintEvent(QPaintEvent *)
{
int x,y,w,h;
//compute the image displaty size by multipling with the zoom factor
w=image->width()*zoomFactor;
h=image->height()*zoomFactor;
//compute the x and y offset
x=(rect().width()-w)/2;
y=(rect().height()-h)/2;
//if from some strange bug we get a negative value,
//probly this must be changed to an assert or thow and error and fix the eventual problem
x=qMax(x,0);
y=qMax(y,0);
QRectF target(x,y,w,h);
QPainter p(this);
p.drawImage(target,*image);
}
QSize ImageWidget::sizeHint() const
{
if(image!=NULL)
{
QSize hint= image->size();
hint=zoomFactor*hint;
return hint;
}else
return this->minimumSize();
}
The zoomToFit method will compute the zoom factor to fit the widget and will zoom the image
void ImageWidget::setZoomToFit(bool ztf)
{
this->zoomToFit=ztf;
if(zoomToFit)
{
computeZoomFactorToFitImage();
}
else
{
zoomFactor=1.0;
}
adjustSize();
this->update();
}
void ImageWidget::computeZoomFactorToFitImage()
{
//compute the aspect ration of the widget
//cast t float to get a float result, if forget (float) you will get
//a int value
float ratio=rect().width()/(float)rect().height();
if(ratio>aspectRatio)
{//the widget width is larger relative of the image wirth
zoomFactor=rect().height()/(float)image->height();
}
else
{
zoomFactor=rect().width()/(float)image->width();
}
}
void ImageWidget::adjustSize()
{
resize(this->sizeHint());
}
You can find all the code on source forge in a Image viewer application, the application is licnsed under GPL v3 , if someone needs the code under other license email me and i can give the rights
UPDATE:
download
svn co https://kisviwer.svn.sourceforge.net/svnroot/kisviwer kisviwer
you must use a svn client or the svn command line application, if in linux install svn and paste that line in the terminal,and a drectory kisviwer will appear with the code,windws guys google it
