子类化QWidget

源码：

iconeditor.h

#ifndef ICONEDITOR_H
#define ICONEDITOR_H

#include <QColor>
#include <QImage>
#include <QWidget>

class IconEditor : public QWidget
{
    Q_OBJECT

　　//Q_PROPERTY()宏来设置属性
    Q_PROPERTY(QColor penColor READ penColor WRITE setPenColor)
    Q_PROPERTY(QImage iconImage READ iconImage WRITE setIconImage)
    Q_PROPERTY(int zoomFactor READ zoomFactor WRITE setZoomFactor)

public:
    IconEditor(QWidget *parent = 0);

    void setPenColor(const QColor &newColor);
    QColor penColor() const { return curColor; }
    void setZoomFactor(int newZoom);
    int zoomFactor() const { return zoom; }
    void setIconImage(const QImage &newImage);
    QImage iconImage() const { return image; }
    QSize sizeHint() const;

protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void paintEvent(QPaintEvent *event);

private:
    void setImagePixel(const QPoint &pos, bool opaque);
    QRect pixelRect(int i, int j) const;

    QColor curColor;
    QImage image;
    int zoom;
};

#endif

 iconeditor.cpp

#include <QtGui>

#include "iconeditor.h"

IconEditor::IconEditor(QWidget *parent)
    : QWidget(parent)
{
    setAttribute(Qt::WA_StaticContents);
    setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);

    curColor = Qt::black;
    zoom = 8;  //缩放因子
    image = QImage(16, 16, QImage::Format_ARGB32);   //16*16的像素大小和32位的ARGB
    image.fill(qRgba(0, 0, 0, 0));
}

void IconEditor::setPenColor(const QColor &newColor)
{
    curColor = newColor;
}

void IconEditor::setZoomFactor(int newZoom)
{
    if (newZoom < 1)
        newZoom = 1;

    if (newZoom != zoom) {
        zoom = newZoom;
        update();
        updateGeometry();
    }
}

void IconEditor::setIconImage(const QImage &newImage)
{
    if (newImage != image) {
        image = newImage.convertToFormat(QImage::Format_ARGB32);
        update();
        updateGeometry();
    }
}

QSize IconEditor::sizeHint() const
{
    QSize size = zoom * image.size();
    if (zoom >= 3)
        size += QSize(1, 1);
    return size;
}

void IconEditor::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton) {
        setImagePixel(event->pos(), true);
    } else if (event->button() == Qt::RightButton) {
        setImagePixel(event->pos(), false);
    }
}

void IconEditor::mouseMoveEvent(QMouseEvent *event)
{
    if (event->buttons() & Qt::LeftButton) {
        setImagePixel(event->pos(), true);
    } else if (event->buttons() & Qt::RightButton) {
        setImagePixel(event->pos(), false);
    }
}

void IconEditor::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);

    if (zoom >= 3) {
        painter.setPen(palette().foreground().color());
        for (int i = 0; i <= image.width(); ++i)
            painter.drawLine(zoom * i, 0,
                             zoom * i, zoom * image.height());
        for (int j = 0; j <= image.height(); ++j)
            painter.drawLine(0, zoom * j,
                             zoom * image.width(), zoom * j);
    }

    for (int i = 0; i < image.width(); ++i) {
        for (int j = 0; j < image.height(); ++j) {
            QRect rect = pixelRect(i, j);
            if (!event->region().intersect(rect).isEmpty()) {
                QColor color = QColor::fromRgba(image.pixel(i, j));
                if (color.alpha() < 255)
                    painter.fillRect(rect, Qt::white);
                painter.fillRect(rect, color);
            }
        }
    }
}

void IconEditor::setImagePixel(const QPoint &pos, bool opaque)
{
    int i = pos.x() / zoom;
    int j = pos.y() / zoom;

    if (image.rect().contains(i, j)) {
        if (opaque) {
            image.setPixel(i, j, penColor().rgba());
        } else {
            image.setPixel(i, j, qRgba(0, 0, 0, 0));
        }

        update(pixelRect(i, j));
    }
}

QRect IconEditor::pixelRect(int i, int j) const
{
    if (zoom >= 3) {
        return QRect(zoom * i + 1, zoom * j + 1, zoom - 1, zoom - 1);
    } else {
        return QRect(zoom * i, zoom * j, zoom, zoom);
    }
}

main.c

#include <QApplication>

#include "iconeditor.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    IconEditor iconEditor;
    iconEditor.setWindowTitle(QObject::tr("Icon Editor"));
    iconEditor.setIconImage(QImage(":/images/mouse.png"));
    iconEditor.show();
    return app.exec();
}

 

附加小知识：

1：一个具有32位色深的图像分别对每一个像素各使用8位来存储它的红绿蓝分量，剩余的8位存储这个像素的alpha分量(即不透明度)

  如： QRgb red = qRgba(255, 0,0,255);  或 QRgb red = 0xFFFF0000;

2：Qt提供来俩种存储颜色的类型：QRgb和QColor

3：QPainter::drawLine() 例：painter.drawLine(x1,y1,x2,y2);

4：每一个窗口部件都会配备一个调色板，由它来确定做什么事应该使用什么颜色

5：QWidget::palette()函数可用返回窗口部件的调色板，它是一个QPalette型对象

6：QRect(x ,y , width, height);