Code review comment for lp:~kdub/mir/display-groups

> I don't feel I understand the relationship between graphics::DisplayBuffer and
> graphics::DisplayGroup.

DisplayGroups are DisplayBuffers that share a common post() function. The DisplayBuffer becomes an abstraction for the content of the buffer, and the DisplayGroup becomes the abstraction for how that content is flipped to the frontbuffer. In lp:mir right now, DisplayBuffer is the abstraction for the content, and the posting.

> My gut says there's a composite pattern hidden in there somewhere, but that
> the interfaces are not quite right.

For android, I was intending to split the inheritance in the next round of updates. For mesa, I was intending on leaving it, but since having to look at it, the code does become more clean if I switch mgm::DisplayBuffer from inheritance to to composition. I am working on disentangling this too, will propose mesa and android in subsequent MP's, as they're both about 1k lines each.