pixman-renderer: formalize renderbuffers a bit
This implements the first (pixman) part of @daniels' suggestions in !1106 (comment 1718649).
Add a struct pixman_renderer_interface
and hang it off of struct weston_renderer
. For starters, this interface is used to access pixman renderer output state creation/removal and to create/destroy struct weston_renderbuffer
s, which for now just wrap a pixman_image_t with an added damage region for damage tracking. The current renderbuffer is passed as a new parameter to repaint_output
instead of setting it with a custom function.