qt C++使用QPainterPath 实现鼠标白板画线-QT开发中文网

以下是一个使用QPainterPath实现鼠标白板画线的示例代码：

#include <QtWidgets>

class Whiteboard : public QWidget {
public:
    Whiteboard(QWidget *parent = nullptr) : QWidget(parent) {
        setAttribute(Qt::WA_StaticContents);
    }

protected:
    void paintEvent(QPaintEvent *event) override {
        QPainter painter(this);
        painter.drawPixmap(0, 0, pixmap);
    }

    void resizeEvent(QResizeEvent *event) override {
        if (width() > pixmap.width() || height() > pixmap.height()) {
            int newWidth = qMax(width() + 128, pixmap.width());
            int newHeight = qMax(height() + 128, pixmap.height());
            resizeImage(&pixmap, QSize(newWidth, newHeight));
            update();
        }
        QWidget::resizeEvent(event);
    }

    void mousePressEvent(QMouseEvent *event) override {
        if (event->button() == Qt::LeftButton) {
            path.moveTo(event->pos());
            drawing = true;
        }
    }

    void mouseMoveEvent(QMouseEvent *event) override {
        if ((event->buttons() & Qt::LeftButton) && drawing)
            path.lineTo(event->pos());

        update();
    }

    void mouseReleaseEvent(QMouseEvent *event) override {
        if (event->button() == Qt::LeftButton && drawing) {
            path.lineTo(event->pos());
            
            QPainter painter(&pixmap);
            painter.setRenderHint(QPainter::Antialiasing, true);
            painter.setPen(Qt::black);
            painter.drawPath(path);

            path = QPainterPath();
            
           // 更新绘图区域
           update();

           drawing = false;
       }
   }

private:
   void resizeImage(QPixmap *image, const QSize &newSize) {
       if (image->size() == newSize)
           return;

       QPixmap newImage(newSize);
       newImage.fill(Qt::white);
       QPainter painter(&newImage);
       painter.drawPixmap(QPoint(0, 0), *image);
       *image = newImage;
   }

private:
   bool drawing = false;
   QPainterPath path;
   QPixmap pixmap{800, 600};
};

int main(int argc, char *argv[]) {
   QApplication app(argc, argv);

   Whiteboard whiteboard;
   whiteboard.show();

   return app.exec();
}

这个示例代码创建了一个Whiteboard类继承自QWidget，用于显示和绘制白板。通过重写相关事件函数，可以实现鼠标按下、移动、释放时绘制线条的功能。使用QPainterPath来记录画笔路径，并在鼠标释放时将路径绘制到pixmap上。然后在paintEvent中将pixmap绘制到窗口上，从而实现画线的效果。

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