Android 补间动画原理
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这段时间项目中用到了动画,所以趁热打铁,看看动画原理
补间动画
使用举例
TranslateAnimation translateAnim = new TranslateAnimation(0, 100, 0, 100); translateAnim.setDuration(1000); translateAnim.setFillAfter(true); testBut.startAnimation(translateAnim)
源码分析
public void startAnimation(Animation animation) { animation.setStartTime(Animation.START_ON_FIRST_FRAME); setAnimation(animation); invalidateParentCaches(); invalidate(true); }protected void invalidateParentCaches() { if (mParent instanceof View) { ((View) mParent).mPrivateFlags |= PFLAG_INVALIDATED; } }invalidate(true);
invalidateParentCaches();
方法中可以看到为当前该view的parent,就是所在的viewgroup的标志为设置了PFLAG_INVALIDATED。所以viewgroup发生了重绘,这里为什么会这样值得深入研究进一步分析?
invalidateParentCaches();
invalidate(true);//这样很明显只是导致了该view的重绘
为什么这样导致了view所在viewgroup的重绘
首先调用
public void draw(Canvas canvas) { // Step 1, draw the background, if needed drawBackground(canvas); // Step 3, draw the content onDraw(canvas); // Step 4, draw the children dispatchDraw(canvas); // Step 6, draw decorations (foreground, scrollbars) onDrawForeground(canvas);}所以可以得出结论,如果对viewgroup下的任何一个view执行动画,那么都会导致view执行整个绘制流程,不相信的话,可以自定义一个viewgroup然后重写
draw(canvas),onDraw(canvas),dispatchDraw(canvas)方法在里面打印log
这里关键的是步骤4,dispatchDraw(canvas);会去绘制子view
ViewGroup类中的方法
protected void dispatchDraw(Canvas canvas) { ........ for (int i = 0; i < childrenCount; i++) { while (transientIndex >= 0 && mTransientIndices.get(transientIndex) == i) { final View transientChild = mTransientViews.get(transientIndex); if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE || transientChild.getAnimation() != null) { more |= drawChild(canvas, transientChild, drawingTime); } transientIndex++; if (transientIndex >= transientCount) { transientIndex = -1; } } int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get(childIndex); if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { more |= drawChild(canvas, child, drawingTime); } } .......}只要子view可见或者子view设置了动画,那么就会对该子view调用drawChild(canvas, child, drawingTime)
protected boolean drawChild(Canvas canvas, View child, long drawingTime) { return child.draw(canvas, this, drawingTime); }回到View中的draw带三个参数的重载方法,注意区别于draw(canvas)重载方法
boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) { .......... Transformation transformToApply = null; boolean concatMatrix = false; final boolean scalingRequired = mAttachInfo != null && mAttachInfo.mScalingRequired; final Animation a = getAnimation();//首先获取当前view的动画 if (a != null) { more = applyLegacyAnimation(parent, drawingTime, a, scalingRequired); concatMatrix = a.willChangeTransformationMatrix(); if (concatMatrix) { mPrivateFlags3 |= PFLAG3_VIEW_IS_ANIMATING_TRANSFORM; } transformToApply = parent.getChildTransformation();//获取的Transformation对象,包含动画矩阵 }..........if (!drawingWithRenderNode || transformToApply != null) { restoreTo = canvas.save();//保存该canvas }..........if (transformToApply != null) { .......... if (concatMatrix) { if (drawingWithRenderNode) { renderNode.setAnimationMatrix(transformToApply.getMatrix()); } else { // Undo the scroll translation, apply the transformation matrix, // then redo the scroll translate to get the correct result. canvas.translate(-transX, -transY); canvas.concat(transformToApply.getMatrix());//为该canvas画布应用了该动画矩阵 canvas.translate(transX, transY); } parent.mGroupFlags |= ViewGroup.FLAG_CLEAR_TRANSFORMATION; } float transformAlpha = transformToApply.getAlpha(); if (transformAlpha < 1) { alpha *= transformAlpha; parent.mGroupFlags |= ViewGroup.FLAG_CLEAR_TRANSFORMATION; } }.......... }.......... if (restoreTo >= 0) { canvas.restoreToCount(restoreTo);//恢复到之前状态的canvas,所以并不会影响到其它子view的绘制,即使他们使用的都是viewgroup传递下来的画布 }}Transformation对象中包含一个矩阵和 alpha 值,矩阵是用来做平移、旋转和缩放动画的。
1. 视图层的绘制都是共用一个画布canvas,其实都是在最底层的decorview在viewrootimpl中创建的。
viewgroup中的子view对canvas进行操作,并不会影响到其它子view还有该viewgroup,因为可以在draw(Canvas canvas, ViewGroup parent, long drawingTime)看到
每绘制一个子view,都会先对画布状态进行保存save(),然后绘制完该子view之后。又会恢复restore(),所以如果在任何一个子view的onDraw(canvas)对canvas进行操作都不会
影响到所在的viewgroup和同级的其他子view,但是如果该view是viewgroup,会影响到其所有的子view的绘制,见第二点分析
2. 如果重写viewgroup的onDraw(canvas)方法,然后对该画布进行translate,concat等操作,就会影响到整个子view的绘制。
// Step 3, draw the content
onDraw(canvas);
// Step 4, draw the children
dispatchDraw(canvas);
可以看到绘制该viewgroup过程中,是先调用onDraw(canvas)绘制其内容,然后绘制子view,而默认的onDraw(canvas)又是一个空实现,没有进canvas进行保存还原的操作,
所以导致viewgroup的onDraw(canvas)方法,然后对该画布进行translate,concat等操作,就会影响到整个子view的绘制
回到动画上的分析来,关键调用了applyLegacyAnimation(parent, drawingTime, a, scalingRequired);
/** * Utility function, called by draw(canvas, parent, drawingTime) to handle the less common * case of an active Animation being run on the view. */ private boolean applyLegacyAnimation(ViewGroup parent, long drawingTime, Animation a, boolean scalingRequired) { Transformation invalidationTransform; final int flags = parent.mGroupFlags; final boolean initialized = a.isInitialized(); if (!initialized) { a.initialize(mRight - mLeft, mBottom - mTop, parent.getWidth(), parent.getHeight()); a.initializeInvalidateRegion(0, 0, mRight - mLeft, mBottom - mTop); if (mAttachInfo != null) a.setListenerHandler(mAttachInfo.mHandler); onAnimationStart(); } final Transformation t = parent.getChildTransformation(); boolean more = a.getTransformation(drawingTime, t, 1f); if (scalingRequired && mAttachInfo.mApplicationScale != 1f) { if (parent.mInvalidationTransformation == null) { parent.mInvalidationTransformation = new Transformation(); } invalidationTransform = parent.mInvalidationTransformation; a.getTransformation(drawingTime, invalidationTransform, 1f); } else { invalidationTransform = t; }.............}final Transformation t = parent.getChildTransformation();
boolean more = a.getTransformation(drawingTime, t, 1f);//操作Transformation对象t
这两行是关键
所以进入Animation的getTransformation方法
public boolean getTransformation(long currentTime, Transformation outTransformation) { if (mStartTime == -1) { mStartTime = currentTime; } final long startOffset = getStartOffset(); final long duration = mDuration; float normalizedTime; if (duration != 0) { normalizedTime = ((float) (currentTime - (mStartTime + startOffset))) / (float) duration; } else { // time is a step-change with a zero duration normalizedTime = currentTime < mStartTime ? 0.0f : 1.0f; } final boolean expired = normalizedTime >= 1.0f; mMore = !expired; if (!mFillEnabled) normalizedTime = Math.max(Math.min(normalizedTime, 1.0f), 0.0f); if ((normalizedTime >= 0.0f || mFillBefore) && (normalizedTime <= 1.0f || mFillAfter)) { if (!mStarted) { fireAnimationStart(); mStarted = true; if (USE_CLOSEGUARD) { guard.open("cancel or detach or getTransformation"); } } if (mFillEnabled) normalizedTime = Math.max(Math.min(normalizedTime, 1.0f), 0.0f); if (mCycleFlip) { normalizedTime = 1.0f - normalizedTime; } final float interpolatedTime = mInterpolator.getInterpolation(normalizedTime);//获取一个0-1的值 applyTransformation(interpolatedTime, outTransformation); } ......... return mMore; }final float interpolatedTime = mInterpolator.getInterpolation(normalizedTime);//插值器最终返回一个0-1的值
applyTransformation(interpolatedTime, outTransformation);//然后用这个0-1的值,应用到Transformation对象上去
TranslateAnimation动画调用Transformation对象的setTranslate,RotateAnimation调用Transformation对象的setRotate。。。。
public Animation() { ensureInterpolator(); }protected void ensureInterpolator() { if (mInterpolator == null) { mInterpolator = new AccelerateDecelerateInterpolator(); } }public void setInterpolator(Interpolator i) { mInterpolator = i; }所以,默认情况下是AccelerateDecelerateInterpolator加速减速插值器
Animation中applyTransformation默认是一个空实现,interpolatedTime是一个0-1的值
protected void applyTransformation(float interpolatedTime, Transformation t) { } //TranslateAnimation中实现@Override protected void applyTransformation(float interpolatedTime, Transformation t) { float dx = mFromXDelta; float dy = mFromYDelta; if (mFromXDelta != mToXDelta) { dx = mFromXDelta + ((mToXDelta - mFromXDelta) * interpolatedTime); } if (mFromYDelta != mToYDelta) { dy = mFromYDelta + ((mToYDelta - mFromYDelta) * interpolatedTime); } t.getMatrix().setTranslate(dx, dy); } //RotateAnimation中实现 @Override protected void applyTransformation(float interpolatedTime, Transformation t) { float degrees = mFromDegrees + ((mToDegrees - mFromDegrees) * interpolatedTime); float scale = getScaleFactor(); if (mPivotX == 0.0f && mPivotY == 0.0f) { t.getMatrix().setRotate(degrees); } else { t.getMatrix().setRotate(degrees, mPivotX * scale, mPivotY * scale); } }其实最终目的都是操作Transformation t对象,其实这个对象就是上文中的,transformToApply对象。
在绘制子view过程中canvas.concat(transformToApply.getMatrix());
自定义补间动画
public class Rotate3dAnimation extends Animation { private final float mFromDegrees; private final float mToDegrees; private final float mCenterX; private final float mCenterY; private final float mDepthZ; private final boolean mReverse; private Camera mCamera; /** * Creates a new 3D rotation on the Y axis. The rotation is defined by its * start angle and its end angle. Both angles are in degrees. The rotation * is performed around a center point on the 2D space, definied by a pair * of X and Y coordinates, called centerX and centerY. When the animation * starts, a translation on the Z axis (depth) is performed. The length * of the translation can be specified, as well as whether the translation * should be reversed in time. * * @param fromDegrees the start angle of the 3D rotation * @param toDegrees the end angle of the 3D rotation * @param centerX the X center of the 3D rotation * @param centerY the Y center of the 3D rotation * @param reverse true if the translation should be reversed, false otherwise */ public Rotate3dAnimation(float fromDegrees, float toDegrees, float centerX, float centerY, float depthZ, boolean reverse) { mFromDegrees = fromDegrees; mToDegrees = toDegrees; mCenterX = centerX; mCenterY = centerY; mDepthZ = depthZ; mReverse = reverse; } @Override public void initialize(int width, int height, int parentWidth, int parentHeight) { super.initialize(width, height, parentWidth, parentHeight); mCamera = new Camera(); } @Override protected void applyTransformation(float interpolatedTime, Transformation t) { final float fromDegrees = mFromDegrees; float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime); final float centerX = mCenterX; final float centerY = mCenterY; final Camera camera = mCamera; final Matrix matrix = t.getMatrix(); camera.save(); if (mReverse) { camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime); } else { camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime)); } camera.rotateY(degrees); camera.getMatrix(matrix); camera.restore(); matrix.preTranslate(-centerX, -centerY); matrix.postTranslate(centerX, centerY); }}重写applyTransformation 函数,interpolatedTime 就是 getTransformation 函 数传下来的差值点,在这里做了一个线性插值算法来生成中间角度:float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime); Camera 类是用来实现绕 Y 轴旋转后透视投影的,我们只需要其返回的 Matrix 值 , 这个值会赋给 Transformation 中的矩阵成员,当 ParentView 去为 ChildView 设置画布时,就会用它来设置坐标系,这样 ChildView 画出来的效果就是一个绕 Y 轴旋转同时带有透视投影的效果。利用这个动画便可以作出像立体翻页等比较酷的效果。
简单的使用
Rotate3dAnimation rotate = new Rotate3dAnimation(0f, 180f, startAnim.getMeasuredWidth() / 2, startAnim.getMeasuredHeight() / 2, 0f, true); rotate.setFillAfter(true); rotate.setDuration(2000); startAnim.startAnimation(rotate);startAnim这个View就能中心点绕着Z轴旋转了
触摸事件处理
触摸事件首先传递到ViewGroup中
ViewGroup的dispatchTouchEvent中有
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled;…… if (child == null) { handled = super.dispatchTouchEvent(transformedEvent); } else { final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; transformedEvent.offsetLocation(offsetX, offsetY); if (! child.hasIdentityMatrix()) { transformedEvent.transform(child.getInverseMatrix()); } handled = child.dispatchTouchEvent(transformedEvent); } // Done. transformedEvent.recycle(); return handled; }
可以看到offsetX,offsetY只对mScrollX,child.mLeft进行了取值。。。
transformedEvent.transform(child.getInverseMatrix());不是前面设置的补间动画,而应该是属性动画。。
如果设置的是属性动画,所以能在动画结束的位置获取到触摸事件,但是补间动画就不行了。。
public final Matrix getInverseMatrix() { ensureTransformationInfo(); if (mTransformationInfo.mInverseMatrix == null) { mTransformationInfo.mInverseMatrix = new Matrix(); } final Matrix matrix = mTransformationInfo.mInverseMatrix; mRenderNode.getInverseMatrix(matrix); return matrix; }此时返回的Matrix对象跟mRenderNode对象有关联。而属性动画会改变属性,比如此时在一个view上设置一个TranslationX的属性动画,那么必然会调用
该view的setTranslationX方法,果然此时操作了mRenderNode对象。。。setRotationX方法也一样
public void setTranslationX(float translationX) { if (translationX != getTranslationX()) { invalidateViewProperty(true, false); mRenderNode.setTranslationX(translationX); invalidateViewProperty(false, true); invalidateParentIfNeededAndWasQuickRejected(); notifySubtreeAccessibilityStateChangedIfNeeded(); } } public void setRotationX(float rotationX) { if (rotationX != getRotationX()) { invalidateViewProperty(true, false); mRenderNode.setRotationX(rotationX); invalidateViewProperty(false, true); invalidateParentIfNeededAndWasQuickRejected(); notifySubtreeAccessibilityStateChangedIfNeeded(); } }
与Scroll的异同
前面有写过一篇《Android Scroll原理分析》
1. 滑动之后还是可以处理触摸事件的,因为触摸事件处理mScrollX,mScrollY,可以在ViewGroup的dispatchTransformedTouchEvent方法中看到
2. 滑动的原理其实也是调整了该view画布canvas的坐标系,所以默认情况下,整个view都会滑动。比如viewgroup.scrollby(-10,10),那么viewgroup的viewgroup在dispatchDraw时绘制该viewgroup,就会把该viewgroup的画布translate10个单位,所以最终结果就是viewgroup在父控件中移动了10个单位一样,如果不是viewgroup,
view.scrollby(-10,10)也是一样。
3. 但是另外一种情况,比如系统自定义的view或者viewgroup,比如linearlayout布局,button,textview控件(可以看到textview中的onDraw方法应用了mScrollX,mScrollY。但为什么控件的位置不变呢? 很奇怪,不知道怎么做到的),滑动的是本身的内容,自身的位置却不变。这是怎么做到的,需要进一步研究,如果自定义view直接继承自view,或者直接继承子viewgroup,那么scrollto,scrollby移动的是整个控件。
viewgroup.scrollby(-10,-10)。那么重绘的时候,会调用viewgroup的viewgroup的draw方法。。。
public void scrollTo(int x, int y) { if (mScrollX != x || mScrollY != y) { int oldX = mScrollX; int oldY = mScrollY; mScrollX = x; mScrollY = y; invalidateParentCaches(); onScrollChanged(mScrollX, mScrollY, oldX, oldY); if (!awakenScrollBars()) { postInvalidateOnAnimation(); } } }invalidateParentCaches();
postInvalidateOnAnimation();
有木有很熟悉,跟上面动画是基本差不多的,都是导致view的parent发生了重绘,进而导致了该view的重绘,但是不会引起viewgroup其它控件的重绘
public void draw(Canvas canvas) { // Step 1, draw the background, if needed drawBackground(canvas); // Step 3, draw the content onDraw(canvas); // Step 4, draw the children dispatchDraw(canvas); // Step 6, draw decorations (foreground, scrollbars) onDrawForeground(canvas);}
dispatchDraw绘制顶层parent的子view,接着调用draw三个参数的重载方法。绘制该viewgroup
boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) { ........... int sx = 0; int sy = 0; if (!drawingWithRenderNode) { computeScroll(); sx = mScrollX; sy = mScrollY; } final boolean drawingWithDrawingCache = cache != null && !drawingWithRenderNode; final boolean offsetForScroll = cache == null && !drawingWithRenderNode; int restoreTo = -1; if (!drawingWithRenderNode || transformToApply != null) { restoreTo = canvas.save(); } if (offsetForScroll) { canvas.translate(mLeft - sx, mTop - sy); } ........... }
此时viewgroup的画布,被右下移动了10个单位。。所以最后viewgroup在parent中整个的被移动了10个单位。。。
另一方面,mybutton是一个Button控件
mybutton.scrollBy(-10, -10);那么最终的结果是button的内容右下平移了10个单位,而控件本身还停留在原来位置,这个比较费解,需要进一步研究。。
linearlayout.scrollBy(-10, -10);
最终结果linearlayout不变,里面的子控件全部右下移动10个单位,很奇怪。。。
见如下:startscroll按钮分别对上下两个viewgroup进行scrollBy(-10, -10);
第一个viewgroup是我自定义的,直接继承子viewgroup,第二个viewgroup使用的系统自定义的linearlayout。。
那么最终结果,自定义的viewgroup,整个的右下移动了10个单位。linearlayout位置并没有移动,只是其中的子view发生了右下10个单位的移动
总结:
1. 相同点都是其实重绘了该view所在的viewgroup,进而重绘view本身,而不是直接重绘view本身(直接调用invalidate就是直接重绘view本身)。。。
2. 动画结束的地方是处理不了触摸事件,但是scrollto,scrollby结束的地方可以处理到。。。
动画总结
1. Animation中主要定义了动画的一些属性比如开始时间、持续时间、是否重复播放等,这个类主要有两个重要的函数:getTransformation 和 applyTransformation,
在 getTransformation 中 Animation 会根据动画的属性来产生一系列的差值点,然后将这些差值点传给 applyTransformation,
这个函数将根据这些点来生成不同的 Transformation,Transformation 中包含一个矩阵和 alpha 值,矩阵是用来做平移、旋转和缩放动画的,
而 alpha 值是用来做 alpha 动画的(简单理解的话,alpha 动画相当于不断变换透明度或颜色来实现动画),以上面的平移矩阵为例子,
当调用 dispatchDraw 时会调用 getTransformation 来得到当前的 Transformation
2. Android动画就是通过ParentView来不断调整ChildView的画布canvas坐标系来实现的。发生动画的其实是ParentView而不是该view
3. 补间动画其实只是调整了子view画布canvas的坐标系,其实并没有修改任何属性,所以只能在原位置才能处理触摸事件。。。
参考:
1.Android 动画原理
2.Android动画原理分析
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