PathMeasure

概念：路径测量，一个用来测量Path，计算Path的工具类

常用api

/**
 * @param path 路径
 * @param forceClosed 路径是否闭合
 */
public void setPath(Path path, boolean forceClosed)

/**
 * 是否闭合
 */
public boolean isClosed()

/**
 * 获取path的长度
 */
public float getLength()

/**
 * 跳转到下一个路径
 */
public boolean nextContour()


/**
 * 截取片段
 * @param startD 开始长度位置
 * @param stopD 结束长度位置
 * @param dst   目标路径
 * @param startWithMoveTo 是否从开始位置进行，如果false，则从0，0位置开始
 * @return
 */
public boolean getSegment(float startD, float stopD, Path dst, boolean startWithMoveTo)

/**
 *  获取指定长度位置坐标及该点切线值
 * @param distance 开始位置的长度，下笔点是从pain所画的形状开始，根据paint的方向来确定
 * @param pos 指定长度终点那个点  是个x，y的数组点值
 * @param tan 切线值
 */
public boolean getPosTan(float distance, float pos[], float tan[])

/**
 *  获取指定长度位置矩阵
 * @param distance 指定长度
 * @param matrix 矩阵
 * @param flags 指定应该在矩阵中返回哪些方面 正切，点的坐标
 *  public static final int POSITION_MATRIX_FLAG = 0x01;    // must match flags in SkPathMeasure.h
 *  public static final int TANGENT_MATRIX_FLAG  = 0x02;
 */
public boolean getMatrix(float distance, Matrix matrix, int flags)

• setPath 设置路径

image.png

private void forceClosed(Canvas canvas) {
        Path path = new Path();
        path.lineTo(0, 200);
        path.lineTo(200, 200);
        path.lineTo(200, 0);

        canvas.drawPath(path, defaultPatin);

        //如果路径进行闭合，则measure.getLength获得是最后点到起点闭合的长度
        //没闭合，则是已画路径的长度
        PathMeasure measure = new PathMeasure();
        measure.setPath(path, false);
        Log.e(TAG, "forceClosed  false:" + measure.getLength());
        Log.e(TAG, "path isClosed:" + measure.isClosed());
        measure.setPath(path, true);
        Log.e(TAG, "forceClosed  true:" + measure.getLength());
        Log.e(TAG, "path isClosed:" + measure.isClosed());
    }

2019-11-04 11:36:55.585 9252-9252/com.wx.paint E/PathMeasureView: forceClosed false:600.0
2019-11-04 11:36:55.585 9252-9252/com.wx.paint E/PathMeasureView: path isClosed:false
2019-11-04 11:36:55.585 9252-9252/com.wx.paint E/PathMeasureView: forceClosed true:800.0
2019-11-04 11:36:55.585 9252-9252/com.wx.paint E/PathMeasureView: path isClosed:true

image.png

Path path = new Path();
Path path1 = new Path();
Path path2 = new Path();

//Path.Direction.CW 顺时针方向
//画一个小矩形
path1.addRect(-100, -100, 100, 100, Path.Direction.CW);
PathMeasure measure1 = new PathMeasure(path1, false);
Log.e(TAG, "path1 length: " + measure1.getLength());

//画一个大矩形
path2.addRect(-200, -200, 200, 200, Path.Direction.CW);
PathMeasure measure2 = new PathMeasure(path2, false);
Log.e(TAG, "path2 length: " + measure2.getLength());

/**
 * 对2个path进行op  path1 path2 XOR保留不共同的部分
 */

path.op(path1, path2, Path.Op.XOR);
canvas.drawPath(path, defaultPatin);
PathMeasure measure = new PathMeasure(path, false);

Log.e(TAG, "path length: " + measure.getLength());
// 跳转到下一条路径
measure.nextContour();   // 注释 1
Log.e(TAG, "path length: " + measure.getLength());

float[] pos = new float[2];
float[] tan = new float[2];

/**
 * distance 开始位置的长度，下笔点是从pain所画的形状开始，根据paint的方向来确定
 * 如果进行了op，则下笔点会改变
 */
measure2.getPosTan(50, pos, tan); // 注释 3
Log.e(TAG, "pos[0]: " + pos[0] + " pos[1]: " + pos[1]);
Log.e(TAG, "tan[0]: " + tan[0] + " tan[1]: " + tan[1]);
canvas.drawLine(pos[0], pos[1], tan[0], tan[1], defaultPatin);

measure.nextContour();  // 注释 2
Log.e(TAG, "path length: " + measure.getLength());

1、nextContour方法会让当前path 获取它里面的下一个path，上段代码中path是由path1，path2进行取不共同部分获得，所获的长度是path2的1600，当执行了注释1，则将路径转化成了800那个path1，再进行注释2的下一个路径，由于没有别的路径了，就转换成0
2、getPosTan方法 开始位置的长度，下笔点是从pain所画的形状开始，根据paint的方向来确定，参数是2个空数组，当执行完成后就会有值

2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: path1 length: 800.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: path2 length: 1600.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: path length: 1600.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: path length: 800.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: pos[0]: -150.0 pos[1]: -200.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: tan[0]: 1.0 tan[1]: 0.0
2019-11-04 12:10:19.199 10016-10016/com.wx.paint E/PathMeasureView: path length: 0.0

• getSegment

Path path = new Path();
path.addRect(-200, -200, 200, 200, Path.Direction.CW);
PathMeasure measure = new PathMeasure(path, false);
Path dst = new Path();
measure.getSegment(100,600,dst,true); //注释1
canvas.drawPath(path,paint);
canvas.drawPath(dst,defaultPatin);

注释1处 截取长度，第4个参数，如果是true，则开始位置第一个参数起作用，也就是从下笔点开始，到目标距离的点，如图1。如果是false，则从0，0位置开始，到截取长度那个点，如图2。
或者说true 保留下笔点的起点位置，false不保留起点位置

image.png

图1

image.png

图2