How to draw a rectangle or line on an image

[Shubham]

I have loaded the image using QLabel but i dont know how to draw on it......
This works fine as far as opening of images is concerned please guide how to draw rectangle,line etc. on the image


#include <QtGui>

#include "mainwindow.h"

ImageViewer::ImageViewer()
{
imageLabel = new QLabel;
imageLabel->setBackgroundRole(QPalette::Base);
imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
imageLabel->setScaledContents(true);

scrollArea = new QScrollArea;
scrollArea->setBackgroundRole(QPalette::Dark);
scrollArea->setWidget(imageLabel);
setCentralWidget(scrollArea);

createActions();
createMenus();

setWindowTitle(tr("Image Viewer"));
resize(500, 400);
}



void ImageViewer::open()
{
QString fileName = QFileDialog::getOpenFileName(this,
tr("Open File"), QDir::currentPath());
if (!fileName.isEmpty()) {
QImage image(fileName);
if (image.isNull()) {
QMessageBox::information(this, tr("Image Viewer"),
tr("Cannot load %1.").arg(fileName));
return;
}
imageLabel->setPixmap(QPixmap::fromImage(image));
scaleFactor = 1.0;


fitToWindowAct->setEnabled(true);
updateActions();

if (!fitToWindowAct->isChecked())
imageLabel->adjustSize();
}
}



void ImageViewer::zoomIn()
{
scaleImage(1.25);
}

void ImageViewer::zoomOut()
{
scaleImage(0.8);
}

void ImageViewer::normalSize()
{
imageLabel->adjustSize();
scaleFactor = 1.0;
}

void ImageViewer::fitToWindow()
{
bool fitToWindow = fitToWindowAct->isChecked();
scrollArea->setWidgetResizable(fitToWindow);
if (!fitToWindow) {
normalSize();
}
updateActions();
}



void ImageViewer::createActions()
{
openAct = new QAction(tr("&Open..."), this);
openAct->setShortcut(tr("Ctrl+O"));
connect(openAct, SIGNAL(triggered()), this, SLOT(open()));



exitAct = new QAction(tr("E&xit"), this);
exitAct->setShortcut(tr("Ctrl+Q"));
connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

zoomInAct = new QAction(tr("Zoom &In (25%)"), this);
zoomInAct->setShortcut(tr("Ctrl++"));
zoomInAct->setEnabled(false);
connect(zoomInAct, SIGNAL(triggered()), this, SLOT(zoomIn()));

zoomOutAct = new QAction(tr("Zoom &Out (25%)"), this);
zoomOutAct->setShortcut(tr("Ctrl+-"));
zoomOutAct->setEnabled(false);
connect(zoomOutAct, SIGNAL(triggered()), this, SLOT(zoomOut()));

normalSizeAct = new QAction(tr("&Normal Size"), this);
normalSizeAct->setShortcut(tr("Ctrl+S"));
normalSizeAct->setEnabled(false);
connect(normalSizeAct, SIGNAL(triggered()), this, SLOT(normalSize()));

fitToWindowAct = new QAction(tr("&Fit to Window"), this);
fitToWindowAct->setEnabled(false);
fitToWindowAct->setCheckable(true);
fitToWindowAct->setShortcut(tr("Ctrl+F"));
connect(fitToWindowAct, SIGNAL(triggered()), this, SLOT(fitToWindow()));


}

void ImageViewer::createMenus()
{
fileMenu = new QMenu(tr("&File"), this);
fileMenu->addAction(openAct);

fileMenu->addSeparator();
fileMenu->addAction(exitAct);

viewMenu = new QMenu(tr("&View"), this);
viewMenu->addAction(zoomInAct);
viewMenu->addAction(zoomOutAct);
viewMenu->addAction(normalSizeAct);
viewMenu->addSeparator();
viewMenu->addAction(fitToWindowAct);



menuBar()->addMenu(fileMenu);
menuBar()->addMenu(viewMenu);

}

void ImageViewer::updateActions()
{
zoomInAct->setEnabled(!fitToWindowAct->isChecked());
zoomOutAct->setEnabled(!fitToWindowAct->isChecked());
normalSizeAct->setEnabled(!fitToWindowAct->isChecked());
}

void ImageViewer::scaleImage(double factor)
{
Q_ASSERT(imageLabel->pixmap());
scaleFactor *= factor;
imageLabel->resize(scaleFactor * imageLabel->pixmap()->size());

adjustScrollBar(scrollArea->horizontalScrollBar(), factor);
adjustScrollBar(scrollArea->verticalScrollBar(), factor);

zoomInAct->setEnabled(scaleFactor < 3.0);
zoomOutAct->setEnabled(scaleFactor > 0.333);
}

void ImageViewer::adjustScrollBar(QScrollBar *scrollBar, double factor)
{
scrollBar->setValue(int(factor * scrollBar->value()
+ ((factor - 1) * scrollBar->pageStep()/2)));
}






Thanks in advance

[anda_skoa]

You use QPainter for painting.

Where you paint onto depends on what you want to do. QPainter works on any class that is a QPaintDevice:
You can paint onto the QImage, onto the QPixmap created from the image, on a separate Image/Pixmap that you combine with the oroginal, or derive from QLabel and paint into the label after it has painted the image.

Cheers,
_

[Shubham]

I tried this
QPainter painter(&image);
painter.drawRect(0,0,100,100);


but this doesn't work.since i am a total newbie in Qt, i am finding it difficult to get it done.
It would be great if you could provide me with the source code or just edit my code.

Thanks..

[stampede]

Can you show us full code where you are trying to draw on image and display it after drawing ?

[Shubham]

Qt Code

#include <QtGui>

#include "mainwindow.h"

ImageViewer::ImageViewer()
{
imageLabel = new QLabel;
imageLabel->setBackgroundRole(QPalette::Base);
imageLabel->setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
imageLabel->setScaledContents(true);

scrollArea = new QScrollArea;
scrollArea->setBackgroundRole(QPalette::Dark);
scrollArea->setWidget(imageLabel);
setCentralWidget(scrollArea);

createActions();
createMenus();

setWindowTitle(tr("Image Viewer"));
resize(500, 400);
}



void ImageViewer::open()
{
QString fileName = QFileDialog::getOpenFileName(this,
tr("Open File"), QDir::currentPath());
if (!fileName.isEmpty()) {
QImage image(fileName);
if (image.isNull()) {
QMessageBox::information(this, tr("Image Viewer"),
tr("Cannot load %1.").arg(fileName));
return;
}
imageLabel->setPixmap(QPixmap::fromImage(image));
scaleFactor = 1.0;


fitToWindowAct->setEnabled(true);
updateActions();

if (!fitToWindowAct->isChecked())
imageLabel->adjustSize();
}
}



void ImageViewer::zoomIn()
{
scaleImage(1.25);
}

void ImageViewer::zoomOut()
{
scaleImage(0.8);
}

void ImageViewer::normalSize()
{
imageLabel->adjustSize();
scaleFactor = 1.0;
}

void ImageViewer::fitToWindow()
{
bool fitToWindow = fitToWindowAct->isChecked();
scrollArea->setWidgetResizable(fitToWindow);
if (!fitToWindow) {
normalSize();
}
updateActions();
}



void ImageViewer::createActions()
{
openAct = new QAction(tr("&Open..."), this);
openAct->setShortcut(tr("Ctrl+O"));
connect(openAct, SIGNAL(triggered()), this, SLOT(open()));



exitAct = new QAction(tr("E&xit"), this);
exitAct->setShortcut(tr("Ctrl+Q"));
connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

zoomInAct = new QAction(tr("Zoom &In (25%)"), this);
zoomInAct->setShortcut(tr("Ctrl++"));
zoomInAct->setEnabled(false);
connect(zoomInAct, SIGNAL(triggered()), this, SLOT(zoomIn()));

zoomOutAct = new QAction(tr("Zoom &Out (25%)"), this);
zoomOutAct->setShortcut(tr("Ctrl+-"));
zoomOutAct->setEnabled(false);
connect(zoomOutAct, SIGNAL(triggered()), this, SLOT(zoomOut()));

normalSizeAct = new QAction(tr("&Normal Size"), this);
normalSizeAct->setShortcut(tr("Ctrl+S"));
normalSizeAct->setEnabled(false);
connect(normalSizeAct, SIGNAL(triggered()), this, SLOT(normalSize()));

fitToWindowAct = new QAction(tr("&Fit to Window"), this);
fitToWindowAct->setEnabled(false);
fitToWindowAct->setCheckable(true);
fitToWindowAct->setShortcut(tr("Ctrl+F"));
connect(fitToWindowAct, SIGNAL(triggered()), this, SLOT(fitToWindow()));


}

void ImageViewer::createMenus()
{
fileMenu = new QMenu(tr("&File"), this);
fileMenu->addAction(openAct);

fileMenu->addSeparator();
fileMenu->addAction(exitAct);

viewMenu = new QMenu(tr("&View"), this);
viewMenu->addAction(zoomInAct);
viewMenu->addAction(zoomOutAct);
viewMenu->addAction(normalSizeAct);
viewMenu->addSeparator();
viewMenu->addAction(fitToWindowAct);



menuBar()->addMenu(fileMenu);
menuBar()->addMenu(viewMenu);

}

void ImageViewer::updateActions()
{
zoomInAct->setEnabled(!fitToWindowAct->isChecked());
zoomOutAct->setEnabled(!fitToWindowAct->isChecked());
normalSizeAct->setEnabled(!fitToWindowAct->isChecked());
}

void ImageViewer::scaleImage(double factor)
{
Q_ASSERT(imageLabel->pixmap());
scaleFactor *= factor;
imageLabel->resize(scaleFactor * imageLabel->pixmap()->size());

adjustScrollBar(scrollArea->horizontalScrollBar(), factor);
adjustScrollBar(scrollArea->verticalScrollBar(), factor);

zoomInAct->setEnabled(scaleFactor < 3.0);
zoomOutAct->setEnabled(scaleFactor > 0.333);
}

void ImageViewer::adjustScrollBar(QScrollBar *scrollBar, double factor)
{
scrollBar->setValue(int(factor * scrollBar->value()
+ ((factor - 1) * scrollBar->pageStep()/2)));
}

void ImageViewer::mousePressEvent(QMouseEvent *e)
{
p1.setX(e->x());
p1.setY(e->y());
}

void ImageViewer::mouseReleaseEvent(QMouseEvent *e)
{
p2.setX(e->x());
p2.setY(e->y());
draw();
}

void ImageViewer::draw()
{
QPainter painter(&imageLabel);
painter.drawRect(p1.x(),p1.y(),p2.x()-p1.x(),p2.y()-p1.y());
}

[stampede]

Please use CODE tags, this is very hard to read.


void ImageViewer::draw()
{
QPainter painter(&imageLabel);
painter.drawRect(p1.x(),p1.y(),p2.x()-p1.x(),p2.y()-p1.y());
}

Is imageLabel an instance of QLabel ?
Think about it, you want to draw on a label or image ?

[Susannamoore]

Hello, is it possible to highlight a portion of an image by drawing (http://www.rasteredge.com/how-to/vb-net-imaging/image-drawing/) a red line on the image?