The mention of lock/unlock leaves me wishing for an additional API
something like...
cairo_surface_t *
cairo_surface_get_image(cairo_surface_t *surface,
int x_offset,
int y_offset,
int width,
int height);
Which would flush the given surface, and return an image surface
which you could use cairo_image_surface_get_data() etc. directly
on.
For image surfaces, this would generally just create another image
surface offset into the same buffer as the "parent". For other
types of surface, this might actually blit/draw to a temporary
buffer and create a temporary image surface from that.
When you finish the "child" surface, it would either mark_dirty the
parent surface (in the case of a parent image surface), or blit
back to the parent.
Drawing operations on the parent surface would be disallowed until
the child surface was finished.
Rough idea, anyway. I don't know how this should relate to e.g.
some of the group stuff.
-mental