So, consider a button with text. In the shm file are:
    * three button states: normal, pressed and hovered pointer,
    * the rendered text.
A total of 4 bitmaps.

How best to organize the rendering of the button?
    1. To use the "subsurfaces" for the text and for the button, changing its 3 state when needed.
    2. To draw directly in "shellsurface". The text and the button state is stored in memory, but each time the update button will be copied into a separate memory area "wl_buffer" for "shellsurface".

At the end of the article concludes that the surface is better not to use when building widgets. http://ppaalanen.blogspot.ru/2013/11/sub-surfaces-now.html

It turns out that you need to use method #2, but then each time you hover the cursor, the client will copy the button state and text. You can make a crutch: cutting text bitmap from the bitmaps of the button states, then when you hover the cursor would to copy _only_ the button state. But still not effective..

Stop, handling the pointer-hover is possible because only in the presence of the surface.. of a button.