“流水下滩非有意，白云出岫本无心。”
正文
在上一篇的Android Path的使用详解中分析了Path类的一些常用的方法，下面顺便看一下和他有关联的一个类PathMeasure，顾名思义，就是测量Path的，来先看一下注释
PathMeasure
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/**
* Create an empty PathMeasure object. To uses this to measure the length
* of a path, and/or to find the position and tangent along it, call
* setPath.
*
* Note that once a path is associated with the measure object, it is
* undefined if the path is subsequently modified and the the measure object
* is used. If the path is modified, you must call setPath with the path.
*/
public PathMeasure() {
mPath = null;
native_instance = native_create(0, false);
}
为了测量他的长度或切线需要先调用setPath方法。如果path修改了，需要测量，则必须再次调用setPath方法。再来看一下另外的一个构造方法
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/**
* Create a PathMeasure object associated with the specified path object
* (already created and specified). The measure object can now return the
* path's length, and the position and tangent of any position along the
* path.
*
* Note that once a path is associated with the measure object, it is
* undefined if the path is subsequently modified and the the measure object
* is used. If the path is modified, you must call setPath with the path.
*
* @param path The path that will be measured by this object
* @param forceClosed If true, then the path will be considered as "closed"
* even if its contour was not explicitly closed.
*/
public PathMeasure(Path path, boolean forceClosed) {
// The native implementation does not copy the path, prevent it from being GC'd
mPath = path;
native_instance = native_create(path != null ? path.ni() : 0,
forceClosed);
}
其中forceClosed表示测量的时候是否强制关闭，只是作为一个测量的值，但并不会关闭path，看一下代码
PathView
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package test.view;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
public class PathView extends View {
private Paint mPaint;
private Path mPath;
public PathView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private void init() {
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setColor(Color.RED);
mPaint.setStyle(Style.STROKE);
mPaint.setStrokeWidth(8);
mPath = new Path();
mPath.moveTo(100, 100);
mPath.lineTo(400, 400);
mPath.lineTo(600, 200);
Log.d("wld_____", new PathMeasure(mPath, false).getLength() + "");
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawPath(mPath, mPaint);
}
}
看一下运行结果
再看一下打印log
修改一下
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Log.d("wld_____", new PathMeasure(mPath, true).getLength() + "");
看一下结果
在看一下打印log
可以看到两个图图形虽然没有变，但测量长度变了。
setPath(Path path, boolean forceClosed)方法和上面的构造方法其实差不多。
getLength()返回path当前轮廓的长度。
getPosTan(float distance, float pos[], float tan[])其中的distance(0<=distance<=getLength())，pos是在长度为distance的点的坐标，其中(x==[0], y==[1])，tan是在那个点的切线的值，其中(x==[0], y==[1])，返回true数据会存入 pos 和 tan 中，返回false，pos 和 tan 不会改变
getMatrix(float distance, Matrix matrix, int flags)得到路径上某一长度的位置以及该位置正切值的矩阵，flags有两种类型
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public static final int POSITION_MATRIX_FLAG = 0x01; // must match flags in SkPathMeasure.h
public static final int TANGENT_MATRIX_FLAG = 0x02; // must match flags in SkPathMeasure.h
一个表示位置，一个表示正切。
getSegment(float startD, float stopD, Path dst, boolean startWithMoveTo)根据开始和结束的长度得到path中的一个片段，startWithMoveTo为true表示截取到的位置不会改变，为false表示截取到的会连接在一起，看一下代码。
PathView
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package test.view;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.util.AttributeSet;
import android.view.View;
public class PathView extends View {
private Paint mPaint;;
private Path dst;
public PathView(Context context, AttributeSet attrs) {
super(context, attrs);
init();
}
private void init() {
mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPaint.setStyle(Style.STROKE);
mPaint.setStrokeWidth(12);
mPaint.setColor(Color.RED);
dst = new Path();
Path mPath1 = new Path();
mPath1.addRect(200, 200, 600, 600, Path.Direction.CW);
PathMeasure measure1 = new PathMeasure(mPath1, false);
measure1.getSegment(200, 600, dst, true);
Path mPath2 = new Path();
mPath2.addRect(200, 1000, 600, 1400, Path.Direction.CW);
PathMeasure measure = new PathMeasure(mPath2, false);
measure.getSegment(200, 900, dst, true);
}
@Override
protected void onDraw(Canvas canvas) {
canvas.drawPath(dst, mPaint);
}
}
看一下运行结果
截取的两段是互不干涉的，下面修改一下
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Path mPath1 = new Path();
mPath1.addRect(200, 200, 600, 600, Path.Direction.CW);
PathMeasure measure1 = new PathMeasure(mPath1, false);
measure1.getSegment(200, 600, dst, false);
Path mPath2 = new Path();
mPath2.addRect(200, 1000, 600, 1400, Path.Direction.CW);
PathMeasure measure = new PathMeasure(mPath2, false);
measure.getSegment(200, 900, dst, false);
看一下结果
他会找到上一个截取的来进行连接，第一个没有上一个所以连接的为初始位置（0,0）。 isClosed()返回这个路径是否是关闭的。
nextContour()移动到下一个轮廓，因为path可能会有多个轮廓。
