Image Composition Example▲
Setting Up The Resource File▲
The Image Composition example requires two source images, butterfly.png and checker.png that are embedded within imagecomposition.qrc. The file contains the following code:
<!DOCTYPE RCC><RCC version="1.0">
<qresource>
<file>images/butterfly.png</file>
<file>images/checker.png</file>
</qresource>
</RCC>For more information on resource files, see The Qt Resource System.
ImageComposer Class Definition▲
The ImageComposer class is a subclass of QWidget that implements three private slots, chooseSource(), chooseDestination(), and recalculateResult().
class ImageComposer : public QWidget
{
Q_OBJECT
public:
ImageComposer();
private slots:
void chooseSource();
void chooseDestination();
void recalculateResult();In addition, ImageComposer consists of five private functions, addOp(), chooseImage(), loadImage(), currentMode(), and imagePos(), as well as private instances of QToolButton, QComboBox, QLabel, and QImage.
private:
void addOp(QPainter::CompositionMode mode, const QString &name);
void chooseImage(const QString &title, QImage *image, QToolButton *button);
void loadImage(const QString &fileName, QImage *image, QToolButton *button);
QPainter::CompositionMode currentMode() const;
QPoint imagePos(const QImage &image) const;
QToolButton *sourceButton;
QToolButton *destinationButton;
QComboBox *operatorComboBox;
QLabel *equalLabel;
QLabel *resultLabel;
QImage sourceImage;
QImage destinationImage;
QImage resultImage;
};ImageComposer Class Implementation▲
We declare a QSize object, resultSize, as a static constant with width and height equal to 200.
static const QSize resultSize(200, 200);Within the constructor, we instantiate a QToolButton object, sourceButton and set its iconSize property to resultSize. The operatorComboBox is instantiated and then populated using the addOp() function. This function accepts a QPainter::CompositionMode, mode, and a QString, name, representing the name of the composition mode.
ImageComposer::ImageComposer()
{
sourceButton = new QToolButton;
sourceButton->setIconSize(resultSize);
operatorComboBox = new QComboBox;
addOp(QPainter::CompositionMode_SourceOver, tr("SourceOver"));
addOp(QPainter::CompositionMode_DestinationOver, tr("DestinationOver"));
addOp(QPainter::CompositionMode_Clear, tr("Clear"));
addOp(QPainter::CompositionMode_Source, tr("Source"));
addOp(QPainter::CompositionMode_Destination, tr("Destination"));
addOp(QPainter::CompositionMode_SourceIn, tr("SourceIn"));
addOp(QPainter::CompositionMode_DestinationIn, tr("DestinationIn"));
addOp(QPainter::CompositionMode_SourceOut, tr("SourceOut"));
addOp(QPainter::CompositionMode_DestinationOut, tr("DestinationOut"));
addOp(QPainter::CompositionMode_SourceAtop, tr("SourceAtop"));
addOp(QPainter::CompositionMode_DestinationAtop, tr("DestinationAtop"));
addOp(QPainter::CompositionMode_Xor, tr("Xor"));
addOp(QPainter::CompositionMode_Plus, tr("Plus"));
addOp(QPainter::CompositionMode_Multiply, tr("Multiply"));
addOp(QPainter::CompositionMode_Screen, tr("Screen"));
addOp(QPainter::CompositionMode_Overlay, tr("Overlay"));
addOp(QPainter::CompositionMode_Darken, tr("Darken"));
addOp(QPainter::CompositionMode_Lighten, tr("Lighten"));
addOp(QPainter::CompositionMode_ColorDodge, tr("ColorDodge"));
addOp(QPainter::CompositionMode_ColorBurn, tr("ColorBurn"));
addOp(QPainter::CompositionMode_HardLight, tr("HardLight"));
addOp(QPainter::CompositionMode_SoftLight, tr("SoftLight"));
addOp(QPainter::CompositionMode_Difference, tr("Difference"));
addOp(QPainter::CompositionMode_Exclusion, tr("Exclusion"));The destinationButton is instantiated and its iconSize property is set to resultSize as well. The QLabels equalLabel and resultLabel are created and resultLabel's minimumWidth is set.
destinationButton = new QToolButton;
destinationButton->setIconSize(resultSize);
equalLabel = new QLabel(tr("="));
resultLabel = new QLabel;
resultLabel->setMinimumWidth(resultSize.width());We connect the following signals to their corresponding slots:
-
sourceButton's clicked() signal is connected to chooseSource(),
-
operatorComboBox's activated() signal is connected to recalculateResult(), and
-
destinationButton's clicked() signal is connected to chooseDestination().
connect(sourceButton, &QAbstractButton::clicked,
this, &ImageComposer::chooseSource);
connect(operatorComboBox, &QComboBox::activated,
this, &ImageComposer::recalculateResult);
connect(destinationButton, &QAbstractButton::clicked,
this, &ImageComposer::chooseDestination);A QGridLayout, mainLayout, is used to place all the widgets. Note that mainLayout's sizeConstraint property is set to QLayout::SetFixedSize, which means that ImageComposer's size cannot be resized at all.
QGridLayout *mainLayout = new QGridLayout;
mainLayout->addWidget(sourceButton, 0, 0, 3, 1);
mainLayout->addWidget(operatorComboBox, 1, 1);
mainLayout->addWidget(destinationButton, 0, 2, 3, 1);
mainLayout->addWidget(equalLabel, 1, 3);
mainLayout->addWidget(resultLabel, 0, 4, 3, 1);
mainLayout->setSizeConstraint(QLayout::SetFixedSize);
setLayout(mainLayout);We create a QImage, resultImage, and we invoke loadImage() twice to load both the image files in our imagecomposition.qrc file. Then, we set the windowTitle property to "Image Composition".
resultImage = QImage(resultSize, QImage::Format_ARGB32_Premultiplied);
loadImage(":/images/butterfly.png", &sourceImage, sourceButton);
loadImage(":/images/checker.png", &destinationImage, destinationButton);
setWindowTitle(tr("Image Composition"));
}The chooseSource() and chooseDestination() functions are convenience functions that invoke chooseImage() with specific parameters.
void ImageComposer::chooseSource()
{
chooseImage(tr("Choose Source Image"), &sourceImage, sourceButton);
}
void ImageComposer::chooseDestination()
{
chooseImage(tr("Choose Destination Image"), &destinationImage, destinationButton);
}The chooseImage() function loads an image of the user's choice, depending on the title, image, and button.
void ImageComposer::chooseImage(const QString &title, QImage *image,
QToolButton *button)
{
QString fileName = QFileDialog::getOpenFileName(this, title);
if (!fileName.isEmpty())
loadImage(fileName, image, button);
}The recalculateResult() function is used to calculate amd display the result of combining the two images together with the user's choice of composition mode.
void ImageComposer::recalculateResult()
{
QPainter::CompositionMode mode = currentMode();
QPainter painter(&resultImage);
painter.setCompositionMode(QPainter::CompositionMode_Source);
painter.fillRect(resultImage.rect(), Qt::transparent);
painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
painter.drawImage(0, 0, destinationImage);
painter.setCompositionMode(mode);
painter.drawImage(0, 0, sourceImage);
painter.setCompositionMode(QPainter::CompositionMode_DestinationOver);
painter.fillRect(resultImage.rect(), Qt::white);
painter.end();
resultLabel->setPixmap(QPixmap::fromImage(resultImage));
}The addOp() function adds an item to the operatorComboBox using QComboBox's addItem function. This function accepts a QPainter::CompositionMode, mode, and a QString, name. The rectangle is filled with Qt::Transparent and both the sourceImage and destinationImage are painted, before displaying it on resultLabel.
void ImageComposer::addOp(QPainter::CompositionMode mode, const QString &name)
{
operatorComboBox->addItem(name, mode);
}The loadImage() function paints a transparent background using fillRect() and draws image in a centralized position using drawImage(). This image is then set as the button's icon.
void ImageComposer::loadImage(const QString &fileName, QImage *image,
QToolButton *button)
{
image->load(fileName);
// Scale the image to given size
*image = image->scaled(resultSize, Qt::KeepAspectRatio);
QImage fixedImage(resultSize, QImage::Format_ARGB32_Premultiplied);
QPainter painter(&fixedImage);
painter.setCompositionMode(QPainter::CompositionMode_Source);
painter.fillRect(fixedImage.rect(), Qt::transparent);
painter.setCompositionMode(QPainter::CompositionMode_SourceOver);
painter.drawImage(imagePos(*image), *image);
painter.end();
button->setIcon(QPixmap::fromImage(fixedImage));
*image = fixedImage;
recalculateResult();
}The currentMode() function returns the composition mode currently selected in operatorComboBox.
QPainter::CompositionMode ImageComposer::currentMode() const
{
return (QPainter::CompositionMode)
operatorComboBox->itemData(operatorComboBox->currentIndex()).toInt();
}We use the imagePos() function to ensure that images loaded onto the QToolButton objects, sourceButton and destinationButton, are centralized.
QPoint ImageComposer::imagePos(const QImage &image) const
{
return QPoint((resultSize.width() - image.width()) / 2,
(resultSize.height() - image.height()) / 2);
}The main() Function▲
The main() function instantiates QApplication and ImageComposer and invokes its show() function.
int main(int argc, char *argv[])
{
Q_INIT_RESOURCE(imagecomposition);
QApplication app(argc, argv);
ImageComposer composer;
composer.show();
return app.exec();
}