qt C++使用贝塞尔算法实现鼠标白板画线-QT开发中文网

以下是使用贝塞尔算法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.setRenderHint(QPainter::Antialiasing, true);
        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) {
            lastPoint = event->pos();
            drawing = true;
        }
    }

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

        update();
    }

    void mouseReleaseEvent(QMouseEvent *event) override {
        if (event->button() == Qt::LeftButton && drawing) {
            drawLineTo(event->pos());

            QPainter painter(&pixmap);
            painter.setRenderHint(QPainter::Antialiasing, true);
            painter.setPen(Qt::black);

            // 使用贝塞尔曲线绘制平滑路径
            for (int i = 1; i < linePath.size(); i++) {
                painter.drawLine(linePath[i - 1], linePath[i]);
            }

            linePath.clear();

            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;
    }

    void drawLineTo(const QPoint &endPoint) {
        // 计算中间点作为贝塞尔曲线的控制点
        QPoint controlPoint = (lastPoint + endPoint) / 2;
        
        // 将起始点、终止点和控制点加入路径
        linePath.append(lastPoint);
        linePath.append(controlPoint);
        linePath.append(endPoint);

        lastPoint = endPoint;
    }

private:
    bool drawing = false;
    QPoint lastPoint;
    QPixmap pixmap{800, 600};
    QVector<QPoint> linePath;
};

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

   Whiteboard whiteboard;
   whiteboard.show();

   return app.exec();
}

在这个示例代码中，我们使用QPainter绘制平滑的线条，实现了通过贝塞尔算法计算控制点来绘制路径。在mousePressEvent中记录下鼠标按下的坐标，并在mouseMoveEvent中根据当前位置和上一个位置之间插值计算出控制点，并将其与起始点和终止点一起加入路径。在mouseReleaseEvent中使用QPainter绘制贝塞尔曲线。通过这种方式，可以实现平滑的鼠标白板画线效果。

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