QCustomPlot 之平滑曲线（项目笔记）

末蓝、 2023-01-02 03:23 444阅读 0赞

先看下效果显示

![在这里插入图片描述][2021041821405644.gif_pic_center]

今天用采集一个一个正旋函数 发现没有平滑真的 放大后真的好丑，严重失真了。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70]  
百度了一下，发现qcustomplot没有做平滑函数这个功能，

百度上基本上是  
/\* 2020-6-6日更新修复当数据中有NaN的数据时平滑曲线的显示问题  
来源：公孙二狗 ，在这里感谢狗哥  
\*/的方法，  
不过你把代码带入进去发现真的用不了。 又百度了 不过发现百度上的都是一字不漏的拷贝狗哥的文章的，没办法 又返回来折腾狗哥给的方法 ， 不过狗哥给的代码大部分都可以用的，只是一些细节 我们自己要改一下

class SmoothCurveGenerator  // 这段代码是根据狗哥的代码 修改来的 已经验证了 
    { 
    protected:
        static QPainterPath generateSmoothCurveImp(const QVector<QPointF> &points) { 
            QPainterPath path;
            int len = points.size();
    
            if (len < 2) { 
                return path;
            }
    
            QVector<QPointF> firstControlPoints;
            QVector<QPointF> secondControlPoints;
            calculateControlPoints(points, &firstControlPoints, &secondControlPoints);
    
            path.moveTo(points[0].x(), points[0].y());
    
            // Using bezier curve to generate a smooth curve.
            for (int i = 0; i < len - 1; ++i) { 
                path.cubicTo(firstControlPoints[i], secondControlPoints[i], points[i+1]);
            }
    
            return path;
        }
    public:
        static QPainterPath generateSmoothCurve(const QVector<QPointF> &points) { 
            QPainterPath result;
    
            int segmentStart = 0;
            int i = 0;
            int pointSize = points.size();
            while (i < pointSize) { 
                if (qIsNaN(points.at(i).y()) || qIsNaN(points.at(i).x()) || qIsInf(points.at(i).y())) { 
                  // QVector<QPointF> lineData(QVector<QPointF>(points.constBegin() + segmentStart, points.constBegin() + i - segmentStart));
                   QVector<QPointF> lineData(i - segmentStart); std::copy(points.constBegin() + segmentStart, points.constBegin() + i - segmentStart, lineData.begin()); // 报错的地方 修改成上面的代码 。
                    result.addPath(generateSmoothCurveImp(lineData));
                    segmentStart = i + 1;
                }
                ++i;
            }
       // QVector<QPointF> lineData(QVector<QPointF>(points.constBegin() + segmentStart, points.constEnd()));
        QVector<QPointF> lineData(i - segmentStart); std::copy(points.constBegin() + segmentStart, points.constBegin() + i - segmentStart, lineData.begin());
            result.addPath(generateSmoothCurveImp(lineData));
            return result;
        }
    
        static QPainterPath generateSmoothCurve(const QPainterPath &basePath, const QVector<QPointF> &points) { 
            if (points.isEmpty()) return basePath;
    
            QPainterPath path = basePath;
            int len = points.size();
            if (len == 1) { 
                path.lineTo(points.at(0));
                return path;
            }
    
            QVector<QPointF> firstControlPoints;
            QVector<QPointF> secondControlPoints;
            calculateControlPoints(points, &firstControlPoints, &secondControlPoints);
    
            path.lineTo(points.at(0));
            for (int i = 0; i < len - 1; ++i)
                path.cubicTo(firstControlPoints[i], secondControlPoints[i], points[i+1]);
    
            return path;
        }
    
        static void calculateFirstControlPoints(double *&result, const double *rhs, int n) { 
            result = new double[n];
            double *tmp = new double[n];
            double b = 2.0;
            result[0] = rhs[0] / b;
    
            // Decomposition and forward substitution.
            for (int i = 1; i < n; i++) { 
                tmp[i] = 1 / b;
                b = (i < n - 1 ? 4.0 : 3.5) - tmp[i];
                result[i] = (rhs[i] - result[i - 1]) / b;
            }
    
            for (int i = 1; i < n; i++) { 
                result[n - i - 1] -= tmp[n - i] * result[n - i]; // Backsubstitution.
            }
    
            delete[] tmp;
        }
    
        static void calculateControlPoints(const QVector<QPointF> &knots,
                                                           QVector<QPointF> *firstControlPoints,
                                                           QVector<QPointF> *secondControlPoints) { 
            int n = knots.size() - 1;
    
            firstControlPoints->reserve(n);
            secondControlPoints->reserve(n);
    
            for (int i = 0; i < n; ++i) { 
                firstControlPoints->append(QPointF());
                secondControlPoints->append(QPointF());
            }
    
            if (n == 1) { 
                // Special case: Bezier curve should be a straight line.
                // P1 = (2P0 + P3) / 3
                (*firstControlPoints)[0].rx() = (2 * knots[0].x() + knots[1].x()) / 3;
                (*firstControlPoints)[0].ry() = (2 * knots[0].y() + knots[1].y()) / 3;
    
                // P2 = 2P1 – P0
                (*secondControlPoints)[0].rx() = 2 * (*firstControlPoints)[0].x() - knots[0].x();
                (*secondControlPoints)[0].ry() = 2 * (*firstControlPoints)[0].y() - knots[0].y();
    
                return;
            }
    
            // Calculate first Bezier control points
            double *xs = nullptr;
            double *ys = nullptr;
            double *rhsx = new double[n]; // Right hand side vector
            double *rhsy = new double[n]; // Right hand side vector
    
            // Set right hand side values
            for (int i = 1; i < n - 1; ++i) { 
                rhsx[i] = 4 * knots[i].x() + 2 * knots[i + 1].x();
                rhsy[i] = 4 * knots[i].y() + 2 * knots[i + 1].y();
            }
            rhsx[0] = knots[0].x() + 2 * knots[1].x();
            rhsx[n - 1] = (8 * knots[n - 1].x() + knots[n].x()) / 2.0;
            rhsy[0] = knots[0].y() + 2 * knots[1].y();
            rhsy[n - 1] = (8 * knots[n - 1].y() + knots[n].y()) / 2.0;
    
            // Calculate first control points coordinates
            calculateFirstControlPoints(xs, rhsx, n);
            calculateFirstControlPoints(ys, rhsy, n);
    
            // Fill output control points.
            for (int i = 0; i < n; ++i) { 
                (*firstControlPoints)[i].rx() = xs[i];
                (*firstControlPoints)[i].ry() = ys[i];
    
                if (i < n - 1) { 
                    (*secondControlPoints)[i].rx() = 2 * knots[i + 1].x() - xs[i + 1];
                    (*secondControlPoints)[i].ry() = 2 * knots[i + 1].y() - ys[i + 1];
                } else { 
                    (*secondControlPoints)[i].rx() = (knots[n].x() + xs[n - 1]) / 2;
                    (*secondControlPoints)[i].ry() = (knots[n].y() + ys[n - 1]) / 2;
                }
            }
    
            delete xs;
            delete ys;
            delete[] rhsx;
            delete[] rhsy;
        }
    };

二，drawLinePlot函数的修改  
mSmooth为我们添加的一个bool型的类成员变量，并且我们限制了QCPGraph的线样式mLineStyle为lsLine的时候才会真正的倾斜平滑曲线

void QCPGraph::drawLinePlot(QCPPainter *painter, const QVector<QPointF> &lines) const
    { 
        if (painter->pen().style() != Qt::NoPen && painter->pen().color().alpha() != 0) { 
            applyDefaultAntialiasingHint(painter);
            if (mSmooth && mLineStyle == lsLine) painter->drawPath(SmoothCurveGenerator::generateSmoothCurve(lines));
            else drawPolyline(painter, lines);
        }
    }

2，自己在设置一个 setSmooth函数

class QCP_LIB_DECL QCPGraph : public QCPAbstractPlottable1D<QCPGraphData>
    { 
    public: 
        void setSmooth(bool smooth);             // 新增内容
    protected:
        bool mSmooth;                            // 新增内容
    }

// QCPGraph.cpp源文件
    void QCPGraph::setSmooth(bool smooth) 
    { 
        mSmooth = smooth;
    }

3 这下就可以使用了，  
要用的时候 自己添加下面代码就好了  
ui->customPlot->graph(0)->setSmooth(true); // 开启平滑曲线  
（ 头文件 Qpainterpath 自己添加吧 很常用的）  
如下截图是我自己的： ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70 1]  
效果图 ：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70 2]  
跟第一张图对比 效果好很多了吧

[2021041821405644.gif_pic_center]: /images/20221120/a0c0c9d52e8b4eb6b74d1748a521483a.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70]: /images/20221120/9a116300ccf940f1980acab98bd909c9.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70 1]: /images/20221120/ed530f7c8c8c48c58ba6a086bde9b65e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl8zOTMyODQwNg_size_16_color_FFFFFF_t_70 2]: /images/20221120/765e511bfaa5447cae3bd8a5978d583c.png