Re: [9fans] new versions of graphics programs?

[Elliott Hughes <elliott.hughes@genedata.com>]

"Russ Cox" <rsc@plan9.bell-labs.com> wrote in message
news:20000915020412.AA23219A01@mail...
> I admit to not understanding the
> appeal of double-buffering, especially
> the claim that it is more efficient.

it's not really an efficiency thing, but it does help make your program look
more snappy. the usefulness of double-buffering is that you don't get caught
with your pants down: the user will never see a half-finished display. as
you say, there's more work to be done, but the point is that you're making
the deadline easier to meet. you don't have to synchronize yourself with the
screen refresh and you don't have to get your drawing done before the next
refresh.

the interesting question is where to do the double-buffering, at what
granularity. if you have a container, is it worth double-buffering each of
its sub-components separately if they're only going to be 'drawn' into the
double-buffered parent? is it worth working out whether you need
double-buffering on a particular repaint? do you end up deciding you may as
well have one buffer per top-level window and do all your drawing into that?

last time i looked at GTK+, which i admit was a while ago, it wasn't using
double-buffering, and it looked terrible. particularly with a window manager
supporting opaque reshaping (i.e. the window changes all the time, rather
than making you guess from a rubber-band outline whether it would now look
the way you want, were you to stop rubber-banding). i haven't seen such
flicker in a long time. it doesn't matter how efficient your repainting is,
you're almost certain to look spastic if you don't double-buffer.

> To me, it
> seems like a software solution to a
> hardware problem.

you can say that about anything. this trade-off is ever-present. but until
all hardware is able to remove the need for double-buffering,
double-buffering is very useful indeed.

double-buffering may seem a waste of time, but speaking as a pragmatist, i
know i wouldn't want to live without it. (nor even do it myself; i'd rather
have it done for me, as it is in Java.)

 - Elliott