Android Paint 之 PathEffect 详解
zhangwenyinlove
8年前
<p>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</p> <p>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</p> <pre> <code class="language-java">/** * 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); }</code></pre> <p>看一下代码</p> <pre> <code class="language-java">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); } } }</code></pre> <p>运行结果为</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/f352af115a25c990c3f851f5b5dac163.png"></p> <p>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</p> <pre> <code class="language-java">/** * 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); }</code></pre> <p>看一下代码</p> <pre> <code class="language-java">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); } } }</code></pre> <p>运行结果为</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/9f34aad1c0f77d0782d7a8d376931061.png"></p> <p>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</p> <pre> <code class="language-java">mCornerPathEffect[i] = new DashPathEffect(new float[] { 10, 20, 40, 80 }, i * 10);</code></pre> <p>运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/61d6eb6a7babc0dcfa85469faa0d0e06.png"></p> <p>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</p> <pre> <code class="language-java">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() + ""); }</code></pre> <p>看一下log，长度都一样，没有变。</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/788b3bbe2090b9c324401eb0479ae36e.png"></p> <p>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。</p> <pre> <code class="language-java">/** * 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); }</code></pre> <p>看一下代码</p> <pre> <code class="language-java">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); } } }</code></pre> <p>运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/6303919b4a2074d5c89bc4498fa91142.png"></p> <p>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，</p> <pre> <code class="language-java">mPathEffect[i] = new DiscretePathEffect(1, 3 * i);</code></pre> <p style="text-align:center"><img src="https://simg.open-open.com/show/a274d7383acd33cd87767624b3f1d63b.png"></p> <p>感觉有点像磁铁一样，我们来测量一下他的长度</p> <pre> <code class="language-java">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() + ""); }</code></pre> <p>不可思议，每个长度都一样，还和之前测的一样，一点都没变。</p> <p><img src="https://simg.open-open.com/show/ef413e275838582e5446ce8c717064e9.png"></p> <p>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</p> <pre> <code class="language-java">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);</code></pre> <p>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</p> <pre> <code class="language-java">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); } }</code></pre> <p>看一下运行效果，</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/ec90aefe515fab97f747d3494d7c32e8.png"></p> <p>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</p> <pre> <code class="language-java">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);</code></pre> <p>看一下运行的结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/9e1fb215f0e66a10c5657fefe318cbed.png"></p> <p>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</p> <pre> <code class="language-java">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); }</code></pre> <p>看一下运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/8de3ec11e3c9ca43042ca317d976a0d3.png"></p> <p>我们看到是没有偏移的，在修改一下代码</p> <pre> <code class="language-java">mPathEffect1 = new PathDashPathEffect(p, 128, 129, android.graphics.PathDashPathEffect.Style.MORPH);</code></pre> <p>看一下结果，</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/a4a82a9aef989fed9240f467cdfb43ed.png"></p> <p>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</p> <pre> <code class="language-java">mPathEffect1 = new PathDashPathEffect(p, 28, 1, android.graphics.PathDashPathEffect.Style.MORPH);</code></pre> <p>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</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/3fa237fe9b2ca91b239b6dfc12a7944a.png"></p> <p>当把代码在改一下的时候</p> <pre> <code class="language-java">mPathEffect1 = new PathDashPathEffect(p, 28, 28, android.graphics.PathDashPathEffect.Style.MORPH);</code></pre> <p>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 <a href="/misc/goto?guid=4959723257084780336" rel="nofollow,noindex">PathDashPathEffect视频</a></p> <p>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</p> <pre> <code class="language-java">/** * 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);</code></pre> <p>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</p> <pre> <code class="language-java">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); } } }</code></pre> <p>在看一下运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/a58f4ef264b1917244f50ca133097015.png"></p> <p>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，</p> <pre> <code class="language-java">mEffects[2] = new ComposePathEffect(mEffects[0], mEffects[1]);</code></pre> <p>看一下运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/fddb6cb2ab84678d9617b2a5703ecfac.png"></p> <p>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</p> <pre> <code class="language-java">mEffects[1] = new DashPathEffect(new float[] { 200, 10, 5, 10 }, 0);</code></pre> <p>在看一下运行结果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/adf0a4e6c9383d96f04b135a66045423.png"></p> <p>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</p> <pre> <code class="language-java">mEffects[1] = new DashPathEffect(new float[] { 20, 10, 5, 10 }, 0); mEffects[2] = new SumPathEffect(mEffects[1], mEffects[0]);</code></pre> <p>来看一下运行效果</p> <p style="text-align:center"><img src="https://simg.open-open.com/show/592986b3b58dd4fabbc3d946ccd91a82.png"></p> <p>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。</p> <p> </p> <p>来自：http://www.androidchina.net/5545.html</p> <p> </p>