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The Image Composition example lets the user combine images together using any composition mode supported by QPainter, described in detail in Composition Modes.
<!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.
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; };
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"));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:
connect(sourceButton, SIGNAL(clicked()), this, SLOT(chooseSource())); connect(operatorComboBox, SIGNAL(activated(int)), this, SLOT(recalculateResult())); connect(destinationButton, SIGNAL(clicked()), this, SLOT(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); }The chooseImage() function loads an image of the user's choice, depending on the title, image, and button.
void ImageComposer::chooseDestination() { chooseImage(tr("Choose Destination Image"), &destinationImage, destinationButton); }
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); 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); }
int main(int argc, char *argv[]) { Q_INIT_RESOURCE(imagecomposition); QApplication app(argc, argv); ImageComposer composer; composer.show(); return app.exec(); }
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