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QT下过多点的曲线绘制

作者:互联网

绘制过多点的曲线意义重大。但通过试验,QT的PainterPath不是很如意。当多段曲线围成一个区域时,PainterPath内并不包含该区域的所有面积,只包含曲线和其弦构成的面积。

为了解决这一问题,采用如下方法:

1. 生成自己的bezier曲线点集

2. 将多个bezier曲线头尾相联,形成整个polygon的点集

3. 将这个polygon放入一个PainterPath,然后绘制;

4. 这个PainterPath返回留待下次使用。

下面是代码:

1. 头文件graphic.h

#ifndef GRAPHIC_H
#define GRAPHIC_H
#include <QPainter>
#include <QPoint>
#include <QColor>
#include <QVector>
//step是步长,即t每次的递增量,traceSet返回本曲线的所有生成点
void getBezier3(const QPointF& startPos, const QPointF& controlPos1, const QPointF& controlPos2, const QPointF& endPos,
                const double step, QVector<QPointF>& traceSet);
//画一个多边形的外接曲线,points是多边形的顶点集合,方向是CCW或CW;k_c是连接处的尖锐度,越大越光滑,通常选0.6;path是返回量,它是一个包含了外接曲线所有点的多边形区域,可用于
//测试一个点是否在这个区域内,或两个区域是否相交等,还可以完成path的绘制。
void drawEncloseCurve(QPainter& painter, const QVector<QPoint>& points, float k_c, const QColor& color, int strokWidth, QPainterPath& path);
#endif // GRAPHIC_H

2. 绘制实现graphic.cpp

#include "graphic.h"
//求两点距离
double distance(const QPoint& p1, const QPoint& p2)
{
        return sqrt(((p1.x() - p2.x()) * (p1.x() - p2.x()) + (p1.y() - p2.y()) * (p1.y() - p2.y())));
}
//根据比例调整点的位置
QPoint ratioPointConvert(const QPoint& p1, const QPoint& p2, const double ratio)
{
        QPoint p;
        p.setX((int) (ratio * (p1.x() - p2.x()) + p2.x()));
        p.setY((int) (ratio * (p1.y() - p2.y()) + p2.y()));
        return p;
}

void getBezier3(const QPointF& startPos, const QPointF& controlPos1, const QPointF& controlPos2, const QPointF& endPos,
                const double step, QVector<QPointF>& traceSet)
{
    double t = 0.0;
    double x_t, y_t;
    while (t <= 1.0) {
        x_t = startPos.x() * (1 - t) * (1 - t) * (1 - t) + 3 * controlPos1.x() * t * (1 - t) * (1 - t) + 3 * controlPos2.x() * t * t * (1 - t) + endPos.x() * t * t * t;
        y_t = startPos.y() * (1 - t) * (1 - t) * (1 - t) + 3 * controlPos1.y() * t * (1 - t) * (1 - t) + 3 * controlPos2.y() * t * t * (1 - t) + endPos.y() * t * t * t;
        traceSet.push_back(QPointF(x_t, y_t));
        t += step;
    }
}

void drawEncloseCurve(QPainter& painter, const QVector<QPoint>& points, float k_c, const QColor& color, int strokWidth, QPainterPath& path)
{
    //path.clear();
    int size = points.size();
    QVector<QPoint> midpoints;
    // 计算中点
    for(int i = 0; i < size; i++)
    {
        int j = (i + 1) % size;
        midpoints.push_back(QPoint((points[i].x() + points[j].x()) / 2, (points[i].y() + points[j].y()) / 2));
    }
    // 计算比例点
    QVector<QPoint> ratioPoints;
    for(int i = 0; i < size; i++)
    {
        int j = (i + 1) % size;
        int m = (i + 2) % size;
        double l1 = distance(points[i], points[j]);
        double l2 = distance(points[j], points[m]);
        double ratio = l1 / (l1 + l2);
        ratioPoints.push_back(ratioPointConvert(midpoints[i], midpoints[j], ratio));
    }

    // 移动线段,计算控制点
    QVector<QPoint> controlPoints;
    for (int i = 0; i < size; i++)
    {
        QPoint ratioPoint = ratioPoints[i];
        QPoint verPoint = points[(i + 1) % size];
        int dx = ratioPoint.x() - verPoint.x();
        int dy = ratioPoint.y() - verPoint.y();
        QPoint controlPoint1 = QPoint(midpoints[i].x() - dx, midpoints[i].y() - dy);
        QPoint controlPoint2 = QPoint(midpoints[(i + 1) % size].x() - dx, midpoints[(i + 1) % size].y() - dy);
        controlPoints.push_back(ratioPointConvert(controlPoint1, verPoint, k_c));
        controlPoints.push_back(ratioPointConvert(controlPoint2, verPoint, k_c));
    }

    // 用三阶贝塞尔曲线连接顶点
    //QPainterPath path;
    QVector<QPointF> polypoints;
    QPen pen;
    pen.setColor(color);
    pen.setWidth(strokWidth);
    pen.setCapStyle(Qt::RoundCap);
    pen.setJoinStyle(Qt::RoundJoin);
    painter.setPen(pen);

    for (int i = 0; i < size; i++)
    {
        QPoint startPoint = points[i];
        QPoint endPoint = points[(i + 1) % size];
        QPoint controlPoint1 = controlPoints[(i * 2 + controlPoints.size() - 1) % controlPoints.size()];
        QPoint controlPoint2 = controlPoints[(i * 2) % controlPoints.size()];
//        path.moveTo(startPoint.x(), startPoint.y());
//        path.cubicTo(controlPoint1.x(), controlPoint1.y(), controlPoint2.x(), controlPoint2.y(), endPoint.x(), endPoint.y());
        QVector<QPointF> bezier;
        getBezier3(startPoint, controlPoint1, controlPoint2, endPoint, 0.01, bezier);
        bezier.removeLast();
        polypoints += bezier;
    }
    QPolygonF poly(polypoints);
    path.addPolygon(poly);
    painter.drawPath(path);
}

3. 测试(mainwindow.cpp)

测试时发现了问题:当Qdebug()<< 输入中文时,调试直接跳走,无法继续步进,但如果改成英文,则没有问题。

void MainWindow::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    //绘制封闭的外接曲线
    painter.setRenderHint(QPainter::Antialiasing, true);
    QVector<QPoint> points;
    points.push_back(QPoint(200, 200));
    points.push_back(QPoint(400, 100));
    points.push_back(QPoint(600, 200));
    points.push_back(QPoint(400, 400));
    drawEncloseCurve(painter, points, 0.6, QColor(Qt::black), 2, npath);

    painter.save();
    painter.translate(400, 0);
    painter.fillPath(npath, QBrush(Qt::green));
    painter.restore();


测试鼠标是否在这个区域中
void MainWindow::mousePressEvent(QMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        QPointF p = event->pos();
        if(npath.contains(p))
            qDebug() << ("you hit it path");
        //通过试验,有时用npath测试无效,但poly总是有效
        QPolygonF poly = npath.toFillPolygon();

        if(poly.containsPoint(p, Qt::WindingFill))
        {
            qDebug() << ("you hit it poly");
            startDrawing = false;
        }
        else
        {
            startDrawing = true;
            startPos = event->pos();
        }
    }
}

4.结果:
通过四个点的封闭曲线,并通过了鼠标选取测试

 

 

 

标签:const,QT,int,QPoint,points,多点,下过,painter,size
来源: https://www.cnblogs.com/myboat/p/11535760.html