内容

• 设置资源文件
• ImageComposer 类定义
• ImageComposer 类实现
• The main() 函数

图像合成范例

Shows how composition modes work in QPainter .

设置资源文件

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>
					

有关资源文件的更多信息，见 Qt 资源系统 .

ImageComposer 类定义

The ImageComposer 类是子类化的 QWidget that implements three private slots, chooseSource() , chooseDestination() ，和 recalculateResult() .

class ImageComposer : public QWidget
{
    Q_OBJECT
public:
    ImageComposer();
private slots:
    void chooseSource();
    void chooseDestination();
    void recalculateResult();
					

此外， ImageComposer consists of five private functions, addOp() , chooseImage() , loadImage() , currentMode() ，和 imagePos() , as well as private instances of QToolButton , QComboBox , QLabel ，和 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 类实现

We declare a QSize 对象， 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 对象， sourceButton and set its iconSize 特性到 resultSize 。 operatorComboBox is instantiated and then populated using the addOp() function. This function accepts a QPainter::CompositionMode , mode ，和 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 QLabel s equalLabel and resultLabel are created and resultLabel 's minimumWidth 有设置。

    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() ，和
• destinationButton 's clicked() signal is connected to chooseDestination() .

    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);
					

创建 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 ，和 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 使用 QComboBox 's addItem function. This function accepts a QPainter::CompositionMode , mode ，和 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() 。此 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();
}
					

使用 imagePos() function to ensure that images loaded onto the QToolButton 对象， 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() 函数

The main() function instantiates QApplication and ImageComposer and invokes its show() 函数。

int main(int argc, char *argv[])
{
    Q_INIT_RESOURCE(imagecomposition);
    QApplication app(argc, argv);
    ImageComposer composer;
    composer.show();
    return app.exec();
}
					

文件：

• painting/imagecomposition/imagecomposer.cpp
• painting/imagecomposition/imagecomposer.h
• painting/imagecomposition/imagecomposition.pro
• painting/imagecomposition/imagecomposition.qrc
• painting/imagecomposition/main.cpp

图像：

• painting/imagecomposition/images/background.png
• painting/imagecomposition/images/blackrectangle.png
• painting/imagecomposition/images/butterfly.png
• painting/imagecomposition/images/checker.png