select QPixmap area with mouse

[tommy]

Hi. I have a code (please see below) that displays a user-provided bitmap image (image_ori.bmp) when a pushbutton is clicked. I want the user to be able to select two coordinates on the image using mouse (one left click and one right click) and by doing it, crop the picture. Then I want the cropped picture to be displayed instead of the original picture. When the pushbutton is clicked, the original picture (uncropped) is displayed again.
I can get this to sort of work. But the coordinates are off and selection is offset. I think this is because I use global coordinates but I need local to that QLabel widget. How do you get local coordinates with mouse? Do you need to subclass mouse event for that (in the same subclass with the QLabel that displays the picture?)?
Also, what's the best way of avoiding having to save an load files every time you crop the picture like I rather unprofessionally do it?
I know you say that the QLabel approach is not the best for cropping and displaying but I kind of need to stick to this weird appraoch because a program that I write this code for requires this approach. Thanks a lot guys!

////////////////////////main.cpp//////////////////////////////
#include <QApplication>
#include <QtGui>
#include "tom.h"
 
int right_x, right_y, left_x, left_y;
 
MyWidget::MyWidget(QWidget* parent): QWidget(parent)
{
    m_pixmapLabel = new QLabel;
    m_drawButton = new QPushButton("&Load Original Image");
    connect(m_drawButton, SIGNAL(clicked()), this, SLOT(refresh()));
    QVBoxLayout* mainLayout = new QVBoxLayout;
    mainLayout->addWidget(m_pixmapLabel);
    mainLayout->addWidget(m_drawButton);
    setLayout(mainLayout);
}
 
void MyWidget::refresh()
{
QPixmap pm3;
pm3.load("image_ori.bmp");
pm3.save("image.bmp", 0, -1);
testDraw();
}
 
void MyWidget::testDraw()
{   
    right_x=-1;
    right_y=-1;
    left_x=9999;
    left_y=9999;
    QPixmap pm;
    pm.load("image.bmp");
    m_pixmapLabel->setPixmap(pm);
}
 
void MyWidget::mousePressEvent(QMouseEvent *event)
{
if (event->button() == Qt::RightButton)
   {
   right_x=event->x();
   right_y=event->y();
   }
if 
   (event->button() == Qt::LeftButton)
   {
   left_x=event->x();
   left_y=event->y();
   }
 
  if ( (right_x - left_x) >=0 && (right_y - left_y >=0) && (left_x !=9999) && (right_x !=-1))
  {
   QPixmap pm2;
   pm2.load("image.bmp");
   pm2 = pm2.copy(left_x,left_y,right_x,right_y);
   pm2.save("image.bmp", 0, -1);
   m_pixmapLabel->setPixmap(pm2);
  }
 
else QWidget::mousePressEvent(event);
}
 
 
int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
    MyWidget window;
    window.show();
    return application.exec();
}

////////////////////////main.cpp//////////////////////////////
#include <QApplication>
#include <QtGui>
#include "tom.h"

int right_x, right_y, left_x, left_y;

MyWidget::MyWidget(QWidget* parent): QWidget(parent)
{
    m_pixmapLabel = new QLabel;
    m_drawButton = new QPushButton("&Load Original Image");
    connect(m_drawButton, SIGNAL(clicked()), this, SLOT(refresh()));
    QVBoxLayout* mainLayout = new QVBoxLayout;
    mainLayout->addWidget(m_pixmapLabel);
    mainLayout->addWidget(m_drawButton);
    setLayout(mainLayout);
}

void MyWidget::refresh()
{
QPixmap pm3;
pm3.load("image_ori.bmp");
pm3.save("image.bmp", 0, -1);
testDraw();
}

void MyWidget::testDraw()
{   
    right_x=-1;
    right_y=-1;
    left_x=9999;
    left_y=9999;
    QPixmap pm;
    pm.load("image.bmp");
    m_pixmapLabel->setPixmap(pm);
}

void MyWidget::mousePressEvent(QMouseEvent *event)
{
if (event->button() == Qt::RightButton)
   {
   right_x=event->x();
   right_y=event->y();
   }
if 
   (event->button() == Qt::LeftButton)
   {
   left_x=event->x();
   left_y=event->y();
   }
  
  if ( (right_x - left_x) >=0 && (right_y - left_y >=0) && (left_x !=9999) && (right_x !=-1))
  {
   QPixmap pm2;
   pm2.load("image.bmp");
   pm2 = pm2.copy(left_x,left_y,right_x,right_y);
   pm2.save("image.bmp", 0, -1);
   m_pixmapLabel->setPixmap(pm2);
  }

else QWidget::mousePressEvent(event);
}


int main(int argc, char *argv[])
{
    QApplication application(argc, argv);
    MyWidget window;
    window.show();
    return application.exec();
}

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////////////////////////////////////tom.h///////////////////////////////////////
#ifndef TOM_H
#define TOM_H
 
#include <QtGui>
class MyWidget : public QWidget
{
    Q_OBJECT
    public:
        MyWidget (QWidget* parent = 0);
    protected:
        void mousePressEvent(QMouseEvent *event);
 
    public slots:
        void testDraw();
        void refresh();
    private:
        QLabel* m_pixmapLabel;
        QPushButton* m_drawButton;
};
 
#endif

////////////////////////////////////tom.h///////////////////////////////////////
#ifndef TOM_H
#define TOM_H

#include <QtGui>
class MyWidget : public QWidget
{
    Q_OBJECT
    public:
        MyWidget (QWidget* parent = 0);
    protected:
        void mousePressEvent(QMouseEvent *event);

    public slots:
        void testDraw();
        void refresh();
    private:
        QLabel* m_pixmapLabel;
        QPushButton* m_drawButton;
};

#endif

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