The surface-to-buffer matrix provides a generic mechanism for mapping
things from the surface-local coordinate space to the buffer coordinate
space. If it changes, we know for sure that the texture coordinates
have to be re-computed.
Sub-surface contribute to the window quads cache. So, we must re-build
it, if any sub-surface has been changed.
Differential Revision: https://phabricator.kde.org/D29131