Warning
This section contains snippets that were automatically translated from C++ to Python and may contain errors.
Image Composition Example#
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 "/data/qt5-full-670/6.7.0/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()
, and recalculateResult()
.
class ImageComposer(QWidget): Q_OBJECT # public ImageComposer() # private slots def chooseSource(): def chooseDestination(): def 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 def addOp(mode, name): def chooseImage(title, image, button): def loadImage(fileName, image, button): QPainter.CompositionMode currentMode() imagePos = QPoint(QImage image) sourceButton = QToolButton() destinationButton = QToolButton() operatorComboBox = QComboBox() equalLabel = QLabel() resultLabel = QLabel() sourceImage = QImage() destinationImage = QImage() resultImage = QImage()
ImageComposer Class Implementation#
We declare a QSize object, resultSize
, as a static constant with width and height equal to 200.
resultSize = QSize(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.
def __init__(self): sourceButton = QToolButton() sourceButton.setIconSize(resultSize) operatorComboBox = 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 QLabel
s equalLabel
and resultLabel
are created and resultLabel
's minimumWidth
is set.
destinationButton = QToolButton() destinationButton.setIconSize(resultSize) equalLabel = QLabel(tr("=")) resultLabel = QLabel() resultLabel.setMinimumWidth(resultSize.width())
We connect the following signals to their corresponding slots:
sourceButton
'sclicked()
signal is connected tochooseSource()
,
operatorComboBox
'sactivated()
signal is connected torecalculateResult()
, and
destinationButton
'sclicked()
signal is connected tochooseDestination()
.sourceButton.clicked.connect( self.chooseSource) operatorComboBox.activated.connect( self.recalculateResult) destinationButton.clicked.connect( self.chooseDestination)
A QGridLayout
, mainLayout
, is used to place all the widgets. Note that mainLayout
's sizeConstraint
property is set to SetFixedSize
, which means that ImageComposer
's size cannot be resized at all.
mainLayout = 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.
def chooseSource(self): chooseImage(tr("Choose Source Image"), sourceImage, sourceButton) def chooseDestination(self): 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
.
def chooseImage(self, title, image,): QToolButton button) fileName = QFileDialog.getOpenFileName(self, title) if not 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.
def recalculateResult(self): QPainter.CompositionMode mode = currentMode() painter = QPainter(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
.
def addOp(self, mode, 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.
def loadImage(self, fileName, image,): QToolButton button) image.load(fileName) # Scale the image to given size image = image.scaled(resultSize, Qt.KeepAspectRatio) fixedImage = QImage(resultSize, QImage.Format_ARGB32_Premultiplied) painter = QPainter(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() 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.
def imagePos(self, QImage image): 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.
if __name__ == "__main__": app = QApplication([]) composer = ImageComposer() composer.show() sys.exit(app.exec())