关于Canvas的旋转和平移

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。