前言：用path画折线，2条线相交处导圆角

简介：为开发者提供工具类，方便对使用path画折线设置圆角。使用path画多边形，如三角形、矩形、平行四边形等，同时设置圆角。另外提供计算直线上某点坐标。

实现原理

三个点，2条直线相交，给中间点连接处导圆角。设圆角半径为radius,  三个点分别为p2, p3,p1,  如下图所示：给p3点处导圆角。先求出导圆角处连接的2点p4、p5坐标，再用path连接p2和p4，然后通过p4、p3、p5绘制贝塞尔曲线连接p4、p5两个点，最后连接p5、p1两个点。
总结：计算圆角的起始和结束点，使用贝塞尔曲线绘制圆角。

API使用：
 

三角形导圆效果如下：

 导圆角之后

 调用api如下

        int r = 22;//圆角尺寸Path path = SimplePath.buildle().moveTo(50, 50, r, r)//起始点.lineTo(200, 50, r, r).lineTo(200, 250, r, r).close()//结束，完成三角形.build();

矩形导圆角

Path path = SimplePath.buildle().addRect(50, 50, 200, 250, r).build();

其它API使用：

获取线上点坐标   public static float[] getOnLinePointLocationEnd(float lenght, float x1, float y1, float x2, float y2)

示例：上述实现原理中，计算圆角起始坐标点p4. 
float[] p2f = SimplePath.getOnLinePointLocationEnd(r,x1,y1,x2,y2);
Point p2 = new Point(p2f[0], p2f[1]);
其中r在这里是圆角半径，表示圆角起始点p4与中间点p2之间的距离。​​​​​​​画线并添加圆角 （绘制的线是起始点到圆角结束点的路径，并不包含到第三点路径）  public static void lineToAndCorner(Path path, float startRadius, float endRadius, float x1, float y1, float x2, float y2, float x3, float y3) 

示例：上述实现原理中，如果给p3点导圆角r.

path先要自行设置起始点p2,  然后

SimplePath.lineToAndCorner(path, r, r, p2.x, p2.y, p3.x, p3.y, p1.x,p1y);

绘制的线是 p2到p4，再到p5的路径， 不包含，p5到p1的路径。目标点是中间点p3.

备注：方法参数详情请查阅源码

源码：

package com.ttkx.deviceinfo.bkchart;import android.graphics.Path;
import android.graphics.Rect;
import android.graphics.RectF;import java.util.ArrayList;
import java.util.List;public class SimplePath {public static Buildle buildle() {return new Buildle();}public static class Buildle {private Path mPath;private class P {public float x;public float y;public float startRadius;public float endRadius;public boolean isStartPoint;//是否是起始点public P(float x, float y) {this.x = x;this.y = y;}public P(float x, float y, float startRadiu, float endRadiu) {this.x = x;this.y = y;this.startRadius = startRadiu;this.endRadius = endRadiu;}}private List<P> mList = new ArrayList<>();public void moveTo(float x, float y) {moveTo(x, y, 0, 0);}public Buildle setPath(Path path) {mPath = path;return this;}public Buildle moveTo(float x, float y, float startRadius, float endRadius) {P p = new P(x, y, startRadius, endRadius);p.isStartPoint = true;mList.add(0, p);return this;}public Buildle addRect(Rect rect, float r) {return addRect(rect.left, rect.top, rect.right, rect.bottom, r);}public Buildle addRect(RectF rect, float r) {return addRect(rect.left, rect.top, rect.right, rect.bottom, r);}public Buildle addRect(float left, float top, float right, float bottom, float r) {moveTo(left, top, r, r);lineTo(right, top, r, r);lineTo(right, bottom, r, r);lineTo(left, bottom, r, r);close();return this;}public Buildle lineTo(float x, float y) {lineTo(x, y, 0, 0);return this;}public Buildle lineTo(float x, float y, float startRadius, float endRadius) {mList.add(new P(x, y, startRadius, endRadius));return this;}public Buildle close() {if (mList.size() >= 1) {mList.add(mList.get(0));}return this;}public Path build() {Path path = mPath;if (path == null) {path = new Path();}for (int i = 0; i < mList.size(); i++) {P p = mList.get(i);float x = p.x;float y = p.y;if (i == 0) {if (p.isStartPoint) {if (hasCorner(p)) {P p1 = mList.get(i + 1);P p2 = p;float[] onePoint = getOnLinePointLocationEnd(p.startRadius, p1.x, p1.y, p2.x, p2.y);path.moveTo(onePoint[0], onePoint[1]);} else {path.moveTo(x, y);}} else {path.lineTo(x, y);}} else if (i == mList.size() - 1) {//最后一个点P p0 = mList.get(0);if (p.x == p0.x && p.y == p0.y && hasCorner(p0)) {P p1 = mList.get(i - 1);P p2 = p0;P p3 = mList.get(1);lineToAndCorner(path, p2.startRadius, p2.endRadius, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y);} else {path.lineTo(p.x, p.y);}} else {if (hasCorner(p)) {P p1 = mList.get(i - 1);P p2 = p;P p3 = mList.get(i + 1);lineToAndCorner(path, p2.startRadius, p2.endRadius, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y);} else {path.lineTo(x, y);}}}return path;}private boolean hasCorner(P p) {return p.endRadius > 0 && p.startRadius > 0;}}/*** 画线并添加圆点 （绘制的线是起始点到圆角结束点的路径，并不包含到p3点路径）** @param path* @param startRadius 起始圆角半径* @param endRadius   结束圆角半径* @param x1          起始点* @param y1* @param x2          中间点* @param y2* @param x3          结束点* @param y3*/public static void lineToAndCorner(Path path, float startRadius, float endRadius, float x1, float y1, float x2, float y2, float x3, float y3) {float[] onePoint = getOnLinePointLocationEnd(startRadius, x1, y1, x2, y2);path.lineTo(onePoint[0], onePoint[1]);float[] twoPoint = getOnLinePointLocationStart(endRadius, x2, y2, x3, y3);//绘制圆角path.cubicTo(onePoint[0], onePoint[1], x2, y2, twoPoint[0], twoPoint[1]);}/*** 获取线上点坐标** @param lenght 线上点距离起始点(x1,y1）长度* @param x1     起始点x坐标* @param y1     起始点y坐标* @param x2     结束点x坐标* @param y2     结束点y坐标* @return*/public static float[] getOnLinePointLocationStart(float lenght, float x1, float y1, float x2, float y2) {double degree = getDegree(x1, y1, x2, y2);double dx = getRightSideFromDegree(degree, lenght);double dy = getLeftSideFromDegree(degree, lenght);double v2 = x1 + dx;double v3 = y1 + dy;return new float[]{(float) v2, (float) v3};}/*** 获取线上点坐标** @param lenght 线上点距离结束点（x2,y2）长度* @param x1     起始点x坐标* @param y1     起始点y坐标* @param x2     结束点x坐标* @param y2     结束点y坐标* @return*/public static float[] getOnLinePointLocationEnd(float lenght, float x1, float y1, float x2, float y2) {double degree = MathHelper.getDegree(x1, y1, x2, y2);double dx = MathHelper.getRightSideFromDegree(degree, lenght);double dy = MathHelper.getLeftSideFromDegree(degree, lenght);double v2 = x2 - dx;double v3 = y2 - dy;return new float[]{(float) v2, (float) v3};}//两点间的角度private static double getDegree(float sx, float sy, float tx, float ty) {float nX = tx - sx;float nY = ty - sy;double angrad = 0d, angel = 0d, tpi = 0d;float tan = 0.0f;if (Float.compare(nX, 0.0f) != 0) {tan = Math.abs(nY / nX);angel = Math.atan(tan);if (Float.compare(nX, 0.0f) == 1) {if (Float.compare(nY, 0.0f) == 1 || Float.compare(nY, 0.0f) == 0) {angrad = angel;} else {angrad = 2 * Math.PI - angel;}} else {if (Float.compare(nY, 0.0f) == 1 || Float.compare(nY, 0.0f) == 0) {angrad = Math.PI - angel;} else {angrad = Math.PI + angel;}}} else {tpi = Math.PI / 2;if (Float.compare(nY, 0.0f) == 1) {angrad = tpi;} else {angrad = -1 * tpi;}}return Math.toDegrees(angrad);}/*** 直角三角形 根据角度和斜边求直角边** @param degree 角度* @param width  斜边* @return 直角边长*/private static double getRightSideFromDegree(double degree, double width) {double cos = Math.cos(Math.toRadians(degree));return width * cos;}private static double getLeftSideFromDegree(double degree, double width) {double sin = Math.sin(Math.toRadians(degree));return width * sin;}
}

实践：绘制带箭头的提示框背景

第一步：先绘制带圆角的三角形。

三角形只有一个角导圆角

        int r = 10;//圆角尺寸int ph = 30;//箭头离左侧距离int arrowsHeight = 35;//箭头高度Point p1 = new Point(ph, arrowsHeight);Point p2 = new Point(ph + arrowsHeight * 2, arrowsHeight);Point p3 = new Point(ph + arrowsHeight, 0);Path path = SimplePath.buildle().setPath(new Path())//设置path （可以设置也可以不设置, 若不设置工具类自己创建一个path对象）.moveTo(p1.x, p1.y)//起始点.lineTo(p2.x, p2.y).lineTo(p3.x, p3.y, r, r).close().build();

效果如下：

 第二步：添加圆角矩形

int rectRadius = 30;
path.addRoundRect(new RectF(0,arrowsHeight, getBounds().right, getBounds().bottom), rectRadius, rectRadius ,Path.Direction.CW);

第三步：创建自定义Drawable， 将path绘制出来，再将drawable设置为textView 背景， 最后给textView设置padding即可。

效果如下：