public void setPadding(Rect padding) {
        if (padding == null) {
            mState.mPadding = null;
        } else {
            if (mState.mPadding == null) {
                mState.mPadding = new Rect();
            }
            mState.mPadding.set(padding);
        }
        invalidateSelf();
    }
Sets padding for this shape, defined by a Rect object. Define the padding
in the Rect object as: left, top, right, bottom.
caprice/ui/src/main/java/net/qiujuer/genius/ui/drawable/TouchEffectDrawable.java