Image Composition Example¶
Shows how composition modes work in QPainter
imagecomposer.cpp Example File¶
imagecomposer.h Example File¶
main.cpp Example File¶
imagecomposition.pro Example File¶
imagecomposition.qrc Example File¶
background.png Image File¶
blackrectangle.png Image File¶
butterfly.png Image File¶
checker.png Image File¶
Shows how composition modes work in QPainter.
The Image Composition example lets the user combine images together using any composition mode supported by QPainter, described in detail in Composition Modes.
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:
<Code snippet "/home/mariana/development/Qt/5.13.1/Src/qtbase/painting/imagecomposition/imagecomposition.qrc" not found>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()
, andrecalculateResult()
.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()
, andimagePos()
, 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 toresultSize
. TheoperatorComboBox
is instantiated and then populated using theaddOp()
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 toresultSize
as well. The QLabelsequalLabel
andresultLabel
are created andresultLabel
‘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 tochooseSource()
,
operatorComboBox
’s activated() signal is connected torecalculateResult()
, and
destinationButton
’s clicked() signal is connected tochooseDestination()
.connect(sourceButton, &QAbstractButton::clicked, this, &ImageComposer::chooseSource); connect(operatorComboBox, QOverload<int>::of(&QComboBox::activated), this, &ImageComposer::recalculateResult); connect(destinationButton, &QAbstractButton::clicked, this, &ImageComposer::chooseDestination);A QGridLayout,
mainLayout
, is used to place all the widgets. Note thatmainLayout
‘s sizeConstraint property is set to QLayout::SetFixedSize, which means thatImageComposer
‘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 invokeloadImage()
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()
andchooseDestination()
functions are convenience functions that invokechooseImage()
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 thetitle
,image
, andbutton
.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 theoperatorComboBox
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 thesourceImage
anddestinationImage
are painted, before displaying it onresultLabel
.void ImageComposer::addOp(QPainter::CompositionMode mode, const QString &name) { operatorComboBox->addItem(name, mode); }The
loadImage()
function paints a transparent background using fillRect() and drawsimage
in a centralized position using drawImage(). Thisimage
is then set as thebutton
‘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 inoperatorComboBox
.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
anddestinationButton
, 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 andImageComposer
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(); }