WPF折线/坐标点绘制LargestTriangleThreeBuckets算法

  public static List Get(List data, int threshold)
            {
                int dataLength = data.Count;
                if (threshold >= dataLength || threshold == 0)
                    return data; // Nothing to do

                List sampled = new List (threshold);

                // 点集大小，排除首尾点，阈值减2， 
                double every = (double)(dataLength - 2) / (threshold - 2);

                int a = 0;
                Point maxAreaPoint = new Point();
                int nextA = 0;

                sampled.Add(data[a]); //默认添加首点

                for (int i = 0; i 2; i++)
                {
                    // 假设第三个点是此前区间的平均值，大概率不存在，凭空捏造一个????
                    double avgX = 0;
                    double avgY = 0;
                    int avgRangeStart = (int)(((i + 1) * every) + 1);
                    int avgRangeEnd = (int)(((i + 2) * every) + 1);
                    avgRangeEnd = avgRangeEnd  avgRangeEnd : dataLength;

                    int avgRangeLength = avgRangeEnd - avgRangeStart;

                    for (; avgRangeStart )
                    {
                        avgX += data[avgRangeStart].X; // * 1 enforces Number (value may be Date)
                        avgY += data[avgRangeStart].Y;
                    }
                    avgX /= avgRangeLength;

                    avgY /= avgRangeLength;

                    // +1是为了排除当前点
                    int rangeOffs = (int)(Math.Floor((i + 0) * every) + 1);
                    int rangeTo = (int)(Math.Floor((i + 1) * every) + 1);

                    // Point a
                    double pointAx = data[a].X; // enforce Number (value may be Date)
                    double pointAy = data[a].Y;

                    double maxArea = -1;

                    for (; rangeOffs )
                    {
                        //计算面积 点1  点集2  虚拟的点3~~
                        double area = Math.Abs((pointAx - avgX) * (data[rangeOffs].Y - pointAy) -
                                               (pointAx - data[rangeOffs].X) * (avgY - pointAy)
                                          ) * 0.5;
                        if (area > maxArea)
                        {
                            maxArea = area;
                            maxAreaPoint = data[rangeOffs];
                            nextA = rangeOffs; //设置下一个点
                        }
                    }

                    sampled.Add(maxAreaPoint);  
                    a = nextA; // 进入下一次循环
                }

                sampled.Add(data[dataLength - 1]);  //默认添加尾点

                return sampled;
            }