Drawable newDrawable = getResources().getDrawable(mImageIds[newState])
.mutate();
Drawable oldDrawable = getResources().getDrawable(mImageIds[oldState])
.mutate();
Bitmap bitmap = null;
bitmap = Bitmap.createBitmap(width, bitmapHeight,
Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
newDrawable.setBounds(0, 0, newDrawable.getIntrinsicWidth(),
newDrawable.getIntrinsicHeight());
oldDrawable.setBounds(0, oldBitmapOffset,
oldDrawable.getIntrinsicWidth(),
oldDrawable.getIntrinsicHeight() + oldBitmapOffset);
//canvas.rotate(orientation+180, width / 2, width / 2);
//canvas.translate(-oldBitmapOffset, 0);
newDrawable.draw(canvas);
oldDrawable.draw(canvas);
canvas看作画布,Drawable看作图画,bitmap看作能显示这幅画的画框大小
canvas旋转平移后,坐标原点也会随之改变。