Android 穿过点画平滑曲线

先上效果图

参考了这篇文章 穿过已知点画平滑曲线（3次贝塞尔曲线） 原理什么的我也不说了，有兴趣的看这篇文章好了

直接上代码

public class DrawUtil {

/**
* 绘制穿过多边形顶点的平滑曲线
* 用三阶贝塞尔曲线实现
* @param canvas 画布
* @param points 多边形的顶点
* @param k 控制点系数，系数越小，曲线越锐利
* @param color 线条颜色
* @param strokeWidth 线条宽度
*/
public static void drawCurvesFromPoints(Canvas canvas, List<Point> points, double k, int color, float strokeWidth) {
int size = points.size();
Paint paint = new Paint();

// 计算中点
Point[] midPoints = new Point[size];
for (int i = 0; i < size; i++) {
Point p1 = points.get(i);
Point p2 = points.get((i + 1) % size);
midPoints[i] = new Point((p1.x + p2.x) / 2, (p1.y + p2.y) / 2);
}

// 计算比例点
Point[] ratioPoints = new Point[size];
for (int i = 0; i < size; i++) {
Point p1 = points.get(i);
Point p2 = points.get((i + 1) % size);
Point p3 = points.get((i + 2) % size);
double l1 = distance(p1, p2);
double l2 = distance(p2, p3);
double ratio = l1 / (l1 + l2);
Point mp1 = midPoints[i];
Point mp2 = midPoints[(i + 1) % size];
ratioPoints[i] = ratioPointConvert(mp2, mp1, ratio);
}

// 移动线段，计算控制点
Point[] controlPoints = new Point[size * 2];
for (int i = 0, j = 0; i < size; i++) {
Point ratioPoint = ratioPoints[i];
Point verPoint = points.get((i + 1) % size);
int dx = ratioPoint.x - verPoint.x;
int dy = ratioPoint.y - verPoint.y;
Point controlPoint1 = new Point(midPoints[i].x - dx, midPoints[i].y - dy);
Point controlPoint2 = new Point(midPoints[(i + 1) % size].x - dx, midPoints[(i + 1) % size].y - dy);
controlPoints[j++] = ratioPointConvert(controlPoint1, verPoint, k);
controlPoints[j++] = ratioPointConvert(controlPoint2, verPoint, k);
}

// 用三阶贝塞尔曲线连接顶点
Path path = new Path();
paint.setColor(color);
paint.setStrokeWidth(strokeWidth);
paint.setStyle(Paint.Style.STROKE);
for (int i = 0; i < size; i++) {
Point startPoint = points.get(i);
Point endPoint = points.get((i + 1) % size);
Point controlPoint1 = controlPoints[(i * 2 + controlPoints.length - 1) % controlPoints.length];
Point controlPoint2 = controlPoints[(i * 2) % controlPoints.length];
path.reset();
path.moveTo(startPoint.x, startPoint.y);
path.cubicTo(controlPoint1.x, controlPoint1.y, controlPoint2.x, controlPoint2.y, endPoint.x, endPoint.y);
canvas.drawPath(path, paint);
}
}

/**
* 计算两点之间的距离
*/
private static double distance(Point p1, Point p2) {
return Math.sqrt(((p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y)));
}

/**
* 比例点转换
*/
private static Point ratioPointConvert(Point p1, Point p2, double ratio) {
Point p = new Point();
p.x = (int) (ratio * (p1.x - p2.x) + p2.x);
p.y = (int) (ratio * (p1.y - p2.y) + p2.y);
return p;
}
}

调用

DrawUtil.drawCurvesFromPoints(canvas, points, 0.6, Color.WHITE, 2f)