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by: andy.xie ? 转载请注明出处?http://blog.csdn.net/xiexh0921/article/details/7929847
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1，概述：
Launcher桌面由Workspace.java包含Celllayout.java构成，一个celllayout就是一个桌面，默认5个。?Workspace和celllayout都继承于viewgroup。
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2，获得Touch坐标：
Launcher.java为activity，workspace是viewgroup。所以在activity中会注册一个scroller来记录滑动状态，scroller start后workspace中的computeScroll() 会接收到scroller的状态。这里获取到 mTouchX = mScrollX = mScroller.getCurrX();。Launcher会对滑动事件进行管理使得每次都能切屏或返回，而不会出现滑动到一半的状态。
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3，重绘view：
scroller start的时候会不断重绘view直到scroller结束（mScroller.computeScrollOffset()返回false），所以要实现效果只需直接修改dispathDraw函数。dispathDraw和onDraw的区别是一个是画自己一个是画子view，dispathDraw在onDraw之后执行。
这里我们要实现伪3D效果，所以不用opengl，根据上面得到的mTouchX直接用camera和matrix配合就可以实现了。根据上面得到的mTouchX计算出子view需要旋转的角度，隐藏childview后，1）用drawchild画子view；2）直接抓取子view的bitmap（getChildAt(0).buildDrawingCache();Bitmap?bitmap?= getChildAt(0).getDrawingCache();）然后画到workspace的canvas。
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4，实现代码：
上面大概的讲了下原理，下面给出实现代码，其实很简单，只需要修改Launcher2中的workspace.java就可以实现了。
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- @Override??
- ????protected?void?dispatchDraw(Canvas?canvas)?{??
- ????????boolean?restore?=?false;??
- ????????int?restoreCount?=?0;??
- ??
- ????????//?ViewGroup.dispatchDraw()?supports?many?features?we?don't?need:??
- ????????//?clip?to?padding,?layout?animation,?animation?listener,?disappearing??
- ????????//?children,?etc.?The?following?implementation?attempts?to?fast-track??
- ????????//?the?drawing?dispatch?by?drawing?only?what?we?know?needs?to?be?drawn.??
- ??
- ????????boolean?fastDraw?=?mTouchState?!=?TOUCH_STATE_SCROLLING?&&?mNextScreen?==?INVALID_SCREEN;??
- ????????//?If?we?are?not?scrolling?or?flinging,?draw?only?the?current?screen??
- ????????if?(fastDraw)?{??
- ????????????//add?by?andy.xie?20120831??
- ????????????getChildAt(<span?class="s1">mCurrentScreen</span>).setBackgroundResource(android.R.color.transparent);??
- ????????????drawChild(canvas,?getChildAt(mCurrentScreen),?getDrawingTime());??
- ????????}?else?{??
- ????????????final?long?drawingTime?=?getDrawingTime();??
- ????????????final?float?scrollPos?=?(float)?mScrollX?/?getWidth();??
- ????????????final?int?leftScreen?=?(int)?scrollPos;??
- ????????????final?int?rightScreen?=?leftScreen?+?1;??
- ?????????//edit?by?andy.xie?20120831??
- //????????????if?(leftScreen?>=?0)?{??
- //????????????????drawChild(canvas,?getChildAt(leftScreen),?drawingTime);??
- //????????????}??
- //????????????if?(scrollPos?!=?leftScreen?&&?rightScreen?<?getChildCount())?{??
- //????????????????drawChild(canvas,?getChildAt(rightScreen),?drawingTime);??
- //????????????}??
- ????????????//add?by?andy.xie?20120831??
- ????????????Camera?camera?=?new?Camera();??
- ????????????????Matrix?matrix?=?new?Matrix();??
- ????????????????int?width?=?getWidth();??
- ????????????????int?height?=?getHeight();??
- ??
- ????????????????float?rotateY?=?((float)(mTouchX?%?width)?/?width)?*?90;??
- ????????????????if(rotateY?<?0)?rotateY?=?0;??
- ????????????????if(rotateY?>?90)?rotateY?=?90;??
- if(rotateY?>?90)?rotateY?=?90;??
- ??
- ????????????????//??
- ????????????????Log.d("xxh",?"x="?+?mTouchX?+?"?rotateY="?+?rotateY?+?"?scrollPos="?+?scrollPos);??
- ??
- ????????????if?(leftScreen?>=?0)?{??
- ????????????????????????//??
- ????????????????????????canvas.save();??
- ????????????????????????camera.save();??
- ????????????????????????//camera.translate(0,?0,?mWidth/2);??
- ????????????????????????camera.rotateY(-rotateY);??
- ????????????????????????camera.getMatrix(matrix);??
- ????????????????????????camera.restore();??
- ????????????????????????matrix.preTranslate(-width?*?((int)scrollPos?+?1),?-height/2);??
- ????????????????????????matrix.postTranslate(width?*?((int)scrollPos?+?1),?height/2);??
- ????????????????????????//??
- ????????????????????????canvas.concat(matrix);??
- ????????????????getChildAt(leftScreen).setBackgroundResource(android.R.drawable.screen_background_dark_transparent);??
- ????????????????????????drawChild(canvas,?getChildAt(leftScreen),?drawingTime);??
- getChildAt(leftScreen).setBackgroundResource(android.R.drawable.screen_background_dark_transparent);??
- ????????????????????????drawChild(canvas,?getChildAt(leftScreen),?drawingTime);??
- ????????????????????????canvas.restore();??
- ????????????}??
- ??
- ??
- ????????????if?(scrollPos?!=?leftScreen?&&?rightScreen?<?getChildCount())?{??
- ????????????????Matrix?matrix2?=?new?Matrix();??
- ????????????????canvas.save();??
- ????????????????????????camera.save();??
- ????????????????????????//camera.translate(0,?0,?mWidth/2);??
- ????????????????????????camera.rotateY(90-rotateY);??
- ????????????????????????camera.getMatrix(matrix2);??
- ????????????????????????camera.restore();??
- ????????????????????????matrix2.preTranslate(-width?*?((int)scrollPos?+?1),?-height/2);??
- ????????????????????????matrix2.postTranslate(width?*?((int)scrollPos?+?1),?height/2);??
- ????????????????????????//??
- ????????????????????????canvas.concat(matrix2);??
- ????????????????getChildAt(rightScreen).setBackgroundResource(android.R.drawable.screen_background_dark_transparent);??
- canvas.concat(matrix2);??
- ????????????????getChildAt(rightScreen).setBackgroundResource(android.R.drawable.screen_background_dark_transparent);??
- ????????????????drawChild(canvas,?getChildAt(rightScreen),?drawingTime);??
- ????????????????canvas.restore();??
- ????????????}??
- ????????}??
- ??
- ????????if?(restore)?{??
- ????????????canvas.restoreToCount(restoreCount);??
- ????????}??
- ????}??