[AD] 4.3 display update methods

["Peter Hull" <peterhull90@xxxxxxxxxx>]

I know we may be going over old ground here but:

Looking at the update method flags for the display, I see that they
are 'implementations' – i.e. double buffer, triple buffer etc.

I think it would be desirable, and in the spirit of things we
discussed earlier, if they were instead a representation of what the
user wants to achieve.

I imagine that the user might want to specify a 'retained' mode, where
anything drawn is maintained by Allegro, and a 'non-retained' mode, if
the user is able to respond to a system request to redraw the display
(this would be handled via events). There might also be a
'never-retained' mode which could give better performance if the user
knows that the display is _always_ going to be redrawn every frame.
There might also be a direct access mode where the user can get a
pointer to video memory (or a simulation of it), which would be useful
for emulators.

Allegro would then decide how to achieve this – for example retained
mode might be a window backed by a memory bitmap.

Would this be possible? Are there other modes that would be necessary?

Pete