基础知识

主要的三个类
- QPainter
  - QWidget
  - QPixmap
  - QPicture
  - QPrinter
  - QOpenGLPaintDevice
- QPainterDevice
- QPainterEngine

三者关系图

QPainter

QPainEngine

QPaintDevice

基本绘制和填充

绘图系统由QPainter完成具体的绘制操作，QPainter可以绘制一切想要的图形，QPainter可以在继承自QPainterDevice类的任何对象上进行绘制操作

Qt 之图形（QPainter 的基本绘图）看这里

绘制文字

可参考Qt 之图形（绘制文本）

代码

QPainter painter(this);
    QRectF rect(10.0, 10.0, 380.0, 280.0);
    painter.setPen(Qt::red);
    painter.drawRect(rect);
    painter.setPen(Qt::blue);
    painter.setPen(Qt::blue);
    painter.drawText(rect, Qt::AlignHCenter, QStringLiteral("你好"));
    painter.drawText(rect, Qt::AlignLeft, QStringLiteral("左对齐"));
    painter.drawText(rect, Qt::AlignRight, QStringLiteral("右对齐"));
    painter.drawText(rect, Qt::AlignVCenter, QStringLiteral("中间左侧对齐"));
    painter.drawText(rect, Qt::AlignBottom, QStringLiteral("底部对齐"));
    painter.drawText(rect, Qt::AlignCenter, QStringLiteral("中间对齐"));
    painter.drawText(rect, Qt::AlignBottom | Qt::AlignRight, QStringLiteral("底部 | 右侧对齐"));

效果

在这里插入图片描述

绘制路径

详细看这里Qt 之图形（QPainterPath）

代码

QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(Qt::red);
    QPainterPath path;
    path.moveTo(50, 250);
    path.lineTo(50, 230);
    path.cubicTo(QPointF(105, 40), QPointF(115, 80), QPointF(120, 60));
    path.lineTo(130, 130);
    path.addEllipse(QPoint(130, 130), 30, 30);
    painter.setBrush(Qt::red);
    painter.drawPath(path);
    path.translate(200, 0);
    painter.setPen(Qt::darkBlue);
    painter.drawPath(path);

效果

在这里插入图片描述

绘制图像

四种常见的绘制图像的方法

在这里插入图片描述

代码

QPainter painter;
    //绘制image
    QImage image(100, 100, QImage::Format_ARGB32);
    painter.begin(&image);
    painter.setPen(QPen(Qt::green, 3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10, 10, 60, 60);
    painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QImage"));
    painter.setBrush(QColor(0, 0, 0, 100));
    painter.drawRect(50, 50, 40, 40);
    painter.end();
    //绘制pixmap
    QPixmap pix(100, 100);
    painter.begin(&pix);
    painter.setPen(QPen(Qt::green, 3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10, 10, 60, 60);
    painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QPixmap"));
    painter.setBrush(QColor(0, 0, 0, 100));
    painter.drawRect(50, 50, 40, 40);
    painter.end();
    //绘制bitmap
    QBitmap bit(100, 100);
    painter.begin(&bit);
    painter.setPen(QPen(Qt::green, 3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10, 10, 60, 60);
    painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QBitmap"));
    painter.setBrush(QColor(0, 0, 0, 100));
    painter.drawRect(50, 50, 40, 40);
    painter.end();
    //绘制picture
    QPicture picture;
    painter.begin(&picture);
    painter.setPen(QPen(Qt::green, 3));
    painter.setBrush(Qt::yellow);
    painter.drawRect(10, 10, 60, 60);
    painter.drawText(10, 10, 60, 60, Qt::AlignCenter, QStringLiteral("QPicture"));
    painter.setBrush(QColor(0, 0, 0, 100));
    painter.drawRect(50, 50, 40, 40);
    painter.end();
    painter.begin(this);
    painter.drawImage(50, 20, image);
    painter.drawPixmap(200, 20, pix);
    painter.drawPixmap(50, 170, bit);
    painter.drawPicture(200, 170, picture);

效果

在这里插入图片描述

双缓冲绘图

在这里插入图片描述 ### 代码
在头文件加入

private:
    QPixmap pix;
    QPixmap tempPix;
    QPoint startPoint;
    QPoint endPoint;
    //是否正在绘图的标志
    bool isDrawing;
protected:
    void mousePressEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    void paintEvent(QPaintEvent *event);

在cpp文件加入

void ch10_4_1::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        startPoint = event->pos();
        isDrawing = true;
    }
}
void ch10_4_1::mouseMoveEvent(QMouseEvent *event)
{
    if (event->button() & Qt::LeftButton){
        endPoint = event->pos();
        tempPix = pix;
        update();
    }
}
void ch10_4_1::mouseReleaseEvent(QMouseEvent *event)
{
    if (event->button() == Qt::LeftButton){
        endPoint = event->pos();
        isDrawing = false;
        update();
    }
}
void ch10_4_1::paintEvent(QPaintEvent *event)
{
    int x = startPoint.x();
    int y = startPoint.y();
    int width = endPoint.x() - x;
    int height = endPoint.y() - y;
    QPainter painter;
    painter.begin(&tempPix);
    painter.drawRect(x, y, width, height);
    painter.end();
    painter.begin(this);
    painter.drawPixmap(0, 0, tempPix);
    if (! isDrawing)
    {
        pix = tempPix;
    }
}