Android Paint之PathEffect详解

Posted 2020-08-07 数据结构和算法

尊重原创，转载请标明出处    http://blog.csdn.net/abcdef314159

在之前讲 Android Paint的使用详解的时候，其中有一个方法setPathEffect(PathEffect effect)没有详细介绍，这篇就结合代码来介绍一下，在之前说过PathEffect共有6个子类ComposePathEffect，CornerPathEffect，DashPathEffect，DiscretePathEffect，PathDashPathEffect，SumPathEffect，这些类代码量都很少，这里先一个个介绍

CornerPathEffect将Path的线段之间的夹角变成圆角。构造函数，其中radius为圆角的半径

    /**
     * Transforms geometries that are drawn (either STROKE or FILL styles) by
     * replacing any sharp angles between line segments into rounded angles of
     * the specified radius.
     * @param radius Amount to round sharp angles between line segments.
     */
    public CornerPathEffect(float radius) {
        native_instance = nativeCreate(radius);
    }

看一下代码

public class PathEffectView extends View {
	private Paint mPaint;
	private int marging = 82;
	private CornerPathEffect mCornerPathEffect[];
	private Path mPath[];

	public PathEffectView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setColor(Color.BLACK);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mCornerPathEffect = new CornerPathEffect[8];
		mPath = new Path[8];
		for (int i = 0; i < mPath.length; i++) {
			Path path = new Path();
			path.moveTo(i * marging, marging);
			path.lineTo(300 + i * marging, 180);
			path.lineTo(400 + i * marging, 600);
			path.lineTo(200 + i * marging, 1000);
			path.lineTo(110 + i * marging, 1200);
			mPath[i] = path;
			mCornerPathEffect[i] = new CornerPathEffect(i * 10);
		}
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.drawColor(Color.WHITE);
		for (int i = 0; i < mPath.length; i++) {
			mPaint.setPathEffect(mCornerPathEffect[i]);
			canvas.drawPath(mPath[i], mPaint);
		}
	}
}

运行结果为

DashPathEffect主要用于画虚线。构造函数，看注释，intervals必须大于大于2，phase是偏移量

    /**
     * The intervals array must contain an even number of entries (>=2), with
     * the even indices specifying the "on" intervals, and the odd indices
     * specifying the "off" intervals. phase is an offset into the intervals
     * array (mod the sum of all of the intervals). The intervals array
     * controls the length of the dashes. The paint's strokeWidth controls the
     * thickness of the dashes.
     * Note: this patheffect only affects drawing with the paint's style is set
     * to STROKE or FILL_AND_STROKE. It is ignored if the drawing is done with
     * style == FILL.
     * @param intervals array of ON and OFF distances
     * @param phase offset into the intervals array
     */
    public DashPathEffect(float intervals[], float phase) {
        if (intervals.length < 2) {
            throw new ArrayIndexOutOfBoundsException();
        }
        native_instance = nativeCreate(intervals, phase);
    }

看一下代码

public class PathEffectView extends View {
	private Paint mPaint;
	private int marging = 82;
	private DashPathEffect mCornerPathEffect[];
	private Path mPath[];

	public PathEffectView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setColor(Color.BLACK);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mCornerPathEffect = new DashPathEffect[8];
		mPath = new Path[8];
		for (int i = 0; i < mPath.length; i++) {
			Path path = new Path();
			path.moveTo(i * marging, marging);
			path.lineTo(300 + i * marging, 180);
			path.lineTo(400 + i * marging, 600);
			path.lineTo(200 + i * marging, 1000);
			path.lineTo(110 + i * marging, 1200);
			mPath[i] = path;
			mCornerPathEffect[i] = new DashPathEffect(
					new float[] { 1, 2, 4, 8 }, 1);
		}
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.drawColor(Color.WHITE);
		for (int i = 0; i < mPath.length; i++) {
			mPaint.setPathEffect(mCornerPathEffect[i]);
			canvas.drawPath(mPath[i], mPaint);
		}
	}
}

运行结果为

这里phase的偏移量是指偏移指定长度的位置开始画，但总长度还是不变，我们改一下再看看

			mCornerPathEffect[i] = new DashPathEffect(new float[] { 10, 20, 40,
					80 }, i * 10);

运行结果

先画长度为10的实线，再画长度为20的虚线，接着画长度为40的实线，最后画长度为80的虚线，看一下起始位置，每次的最开始都不一样，因为每次偏移的都不一样，但总长度是不变的，因为上面的线只是左右平移，长度并没有减少，看到上面的线是越来越短，其实这是一种巧合，因为后面到虚线了，看不到了。通俗一点来说就是，线的开始位置和终止位置都没有改变，线就像一个无限长的绳，偏移量就相当于绳往下（后）拽的距离。我们打印看一下长度就知道了，修改一下

		for (int i = 0; i < mPath.length; i++) {
			mPaint.setPathEffect(mCornerPathEffect[i]);
			canvas.drawPath(mPath[i], mPaint);
			PathMeasure measure = new PathMeasure(mPath[i], false);
			Log.d("wld_________", measure.getLength() + "");
		}

看一下log，长度都一样，没有变。

DiscretePathEffect切断线段，segmentLength是指定切断的长度，deviation为切断之后线段的偏移量，随机的，小于等于deviation。

    /**
     * Chop the path into lines of segmentLength, randomly deviating from the
     * original path by deviation.
     */
    public DiscretePathEffect(float segmentLength, float deviation) {
        native_instance = nativeCreate(segmentLength, deviation);
    }

看一下代码

public class PathEffectView extends View {
	private Paint mPaint;
	private int marging = 82;
	private DiscretePathEffect mPathEffect[];
	private Path mPath[];

	public PathEffectView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setColor(Color.BLACK);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mPathEffect = new DiscretePathEffect[8];
		mPath = new Path[8];
		for (int i = 0; i < mPath.length; i++) {
			Path path = new Path();
			path.moveTo(i * marging, marging);
			path.lineTo(300 + i * marging, 180);
			path.lineTo(400 + i * marging, 600);
			path.lineTo(200 + i * marging, 1000);
			path.lineTo(110 + i * marging, 1200);
			mPath[i] = path;
			mPathEffect[i] = new DiscretePathEffect(10, 3 * i);
		}
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.drawColor(Color.WHITE);
		for (int i = 0; i < mPath.length; i++) {
			mPaint.setPathEffect(mPathEffect[i]);
			canvas.drawPath(mPath[i], mPaint);
		}
	}
}

运行结果

第一条线偏移量为0，所以看不出来有什么变化。下面再来修改一下，每隔长度为1就中断一次，3*i是偏移的最大长度，

			mPathEffect[i] = new DiscretePathEffect(1, 3 * i);

感觉有点像磁铁一样，我们来测量一下他的长度

for (int i = 0; i < mPath.length; i++) {
			mPaint.setPathEffect(mPathEffect[i]);
			canvas.drawPath(mPath[i], mPaint);
			PathMeasure measure = new PathMeasure(mPath[i], false);
			Log.d("wld__________", measure.getLength() + "");
		}

不可思议，每个长度都一样，还和之前测的一样，一点都没变。

PathDashPathEffect和DashPathEffect差不多，不同的是PathDashPathEffect可以通过自定义图形来绘制path，先看一下他的代码

    public enum Style {
        TRANSLATE(0),   //!< translate the shape to each position
        ROTATE(1),      //!< rotate the shape about its center
        MORPH(2);       //!< transform each point, and turn lines into curves
        
        Style(int value) {
            native_style = value;
        }
        int native_style;
    }

    /**
     * Dash the drawn path by stamping it with the specified shape. This only
     * applies to drawings when the paint's style is STROKE or STROKE_AND_FILL.
     * If the paint's style is FILL, then this effect is ignored. The paint's
     * strokeWidth does not affect the results.
     * @param shape The path to stamp along
     * @param advance spacing between each stamp of shape
     * @param phase amount to offset before the first shape is stamped
     * @param style how to transform the shape at each position as it is stamped
     */
    public PathDashPathEffect(Path shape, float advance, float phase,
                              Style style) {
        native_instance = nativeCreate(shape.ni(), advance, phase,
                                       style.native_style);
    }
    
    private static native long nativeCreate(long native_path, float advance,
                                           float phase, int native_style);

shape是填充的图形，这个图形可以自己绘制，advance是图形之间的间距，phase是path的偏移量，其中有3种style，TRANSLATE是指图形以平移的方式填充path，ROTATE会根据path的旋转而旋转，MORPH和ROTATE差不多，不过有一点就是MORPH会在转角的连接处以平滑的方式连接，下面看一下代码

public class PathEffectView extends View {
	private Paint mPaint;
	private int marging = 82;
	private PathEffect mPathEffect1;
	private PathEffect mPathEffect2;
	private PathEffect mPathEffect3;
	private Path mPath;

	public PathEffectView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mPaint.setColor(Color.RED);
		mPath = new Path();
		mPath.moveTo(0, marging);
		mPath.lineTo(300, 180);
		mPath.lineTo(400, 600);
		mPath.lineTo(200, 1000);
		mPath.lineTo(800, 1200);
		Path p = new Path();
		p.addRect(0, 0, 64, 12, Path.Direction.CCW);
		mPathEffect1 = new PathDashPathEffect(p, 128, 0,
				android.graphics.PathDashPathEffect.Style.MORPH);
		mPathEffect2 = new PathDashPathEffect(p, 128, 0,
				android.graphics.PathDashPathEffect.Style.ROTATE);
		mPathEffect3 = new PathDashPathEffect(p, 128, 0,
				android.graphics.PathDashPathEffect.Style.TRANSLATE);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.drawColor(Color.WHITE);
		mPaint.setPathEffect(mPathEffect1);
		canvas.drawPath(mPath, mPaint);
		canvas.translate(200, 0);
		mPaint.setPathEffect(mPathEffect2);
		canvas.drawPath(mPath, mPaint);
		canvas.translate(200, 0);
		mPaint.setPathEffect(mPathEffect3);
		canvas.drawPath(mPath, mPaint);
	}
}

看一下运行效果，

自定义了一个矩形，前两个矩形的方向会随着path的方向而改变，且第一个在连接处会以平滑的方式过渡。下面着重说一下PathDashPathEffect的几个参数，第一个是自定义的图形，这个就不在多说，主要分析一下第二个和第三个参数，第二个参数是图形的间距，这个间距是指第一个图形和第二个图形起始位置的间距，修改一下代码，全部用MORPH模式来测试

		mPathEffect1 = new PathDashPathEffect(p, 0, 0,
				android.graphics.PathDashPathEffect.Style.MORPH);
		mPathEffect2 = new PathDashPathEffect(p, 64, 0,
				android.graphics.PathDashPathEffect.Style.MORPH);
		mPathEffect3 = new PathDashPathEffect(p, 228, 0,
				android.graphics.PathDashPathEffect.Style.MORPH);

看一下运行的结果

第一个是没有间距的，第二个间距等于矩形的宽度，所以正好相当于矩形首尾相连中间没有间隙，最后一个有间隙。再看第三个参数，就是偏移量，这个和第二个参数有关，在1到advance中间时，偏移的距离在逐渐减少，当偏移量等于advance的倍数的时候，偏移的距离为0，当偏移量大于advance的时候，会对他求余。我们看一下代码

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mPaint.setColor(Color.RED);
		mPath = new Path();
		mPath.moveTo(0, marging);
		mPath.lineTo(300, 180);
		mPath.lineTo(400, 600);
		mPath.lineTo(200, 1000);
		mPath.lineTo(800, 1200);
		Path p = new Path();
		p.addRect(0, 0, 64, 12, Path.Direction.CCW);
		mPathEffect1 = new PathDashPathEffect(p, 128, 128,
				android.graphics.PathDashPathEffect.Style.MORPH);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		canvas.drawColor(Color.WHITE);
		mPaint.setPathEffect(mPathEffect1);
		canvas.drawPath(mPath, mPaint);
	}

看一下运行结果

我们看到是没有偏移的，在修改一下代码

		mPathEffect1 = new PathDashPathEffect(p, 128, 129,
				android.graphics.PathDashPathEffect.Style.MORPH);

看一下结果，

我们看到偏移量已经达到最大，其实129和1的结果是一样的，因为129对128求余所得结果也是1，偏移量从1到128逐渐增大时，偏移的距离逐渐减少，且当偏移量为128时则没有偏移。再来改一下代码

		mPathEffect1 = new PathDashPathEffect(p, 28, 1,
				android.graphics.PathDashPathEffect.Style.MORPH);

前面已经分析过，当advance大于自定义图形的尺寸时才会出现间隙（这里主要是对MORPH这个style，当style为TRANSLATE时，advance必须大于自定义图形的高时才会出现间隙，这个也很好理解），所以这个就会是一条看不到间隙的path，且有偏移，我们看一下

当把代码在改一下的时候

		mPathEffect1 = new PathDashPathEffect(p, 28, 28,
				android.graphics.PathDashPathEffect.Style.MORPH);

会看到没有偏移的，这个截图就不在贴出。如果还是不太明白，也可以看一下下面这个视频 PathDashPathEffect视频

ComposePathEffect是一种组合模式，把两种path所具有的特性组合起来，先看一下源码

    /**
     * Construct a PathEffect whose effect is to apply first the inner effect
     * and the the outer pathEffect (e.g. outer(inner(path))).
     */
    public ComposePathEffect(PathEffect outerpe, PathEffect innerpe) {
        native_instance = nativeCreate(outerpe.native_instance,
                                       innerpe.native_instance);
    }
    
    private static native long nativeCreate(long nativeOuterpe,
                                            long nativeInnerpe);

他会会首先将innerpe的特性表现出来，然后再增加outerpe的效果，我们看一下代码

public class PathEffectView extends View {
	private Paint mPaint;
	private int marging = 82;
	private PathEffect mEffects[];
	private Path mPath;

	public PathEffectView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	private void init() {
		mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
		mPaint.setStyle(Style.STROKE);
		mPaint.setStrokeWidth(6);
		mPaint.setColor(Color.RED);
		mPath = new Path();
		mPath.moveTo(0, marging);
		mPath.lineTo(300, 180);
		mPath.lineTo(400, 600);
		mPath.lineTo(200, 1000);
		mPath.lineTo(800, 1200);
		Path p = new Path();
		p.addRect(0, 0, 64, 12, Path.Direction.CCW);
		mEffects = new PathEffect[3];
		mEffects[0] = new CornerPathEffect(80);
		mEffects[1] = new DashPathEffect(new float[] { 20, 10, 5, 10 }, 0);
		mEffects[2] = new ComposePathEffect(mEffects[1], mEffects[0]);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		for (int i = 0; i < mEffects.length; i++) {
			mPaint.setPathEffect(mEffects[i]);
			canvas.drawPath(mPath, mPaint);
			canvas.translate(200, 0);
		}
	}
}

在看一下运行结果

第一个是圆角的，第二个是虚线的，所以组合的第三个就是圆角到虚线的。在修改一下代码，调换一下组合的位置，

		mEffects[2] = new ComposePathEffect(mEffects[0], mEffects[1]);

看一下运行结果

我们看到组合模式基本上没变，这是因为我们先提取的是第二个图的效果，再提取的是第一个的，所以看不到上面效果，我们在改一下代码

		mEffects[1] = new DashPathEffect(new float[] { 200, 10, 5, 10 }, 0);

在看一下运行结果

OK，我们再来看最后一种SumPathEffect，他相当于把两种效果分别展示然后再组合在一起。还是用上面的代码简单的修改一下

		mEffects[1] = new DashPathEffect(new float[] { 20, 10, 5, 10 }, 0);
		mEffects[2] = new SumPathEffect(mEffects[1], mEffects[0]);

来看一下运行效果

OK，到目前为止，PathEffect的6种效果全部分析完毕。当然，如果想制作动态的效果，可以在onDraw方法中调用invalidate()方法，然后不停的修改偏移量就行了。