[cairo] How to clear a surface ?

[minh thu]

Hi,

I'm new to cairo and this list. I've a little question.

I'd like to know how I can clear a surface. The result should not
simply be white, black or pink but fully transparent, just as when the
surface is initially created.

I'd like to do that because I copy the cairo data to an OpenGL texture and want
the resulting textured quad be transparent, and because I animate/update
the texture.

Thank you,
Vo Minh Thu