Eli Zaretskii skrev 2010-07-15 08.55:
. Canvas seems to need GTK+. What does this mean for platforms where
GTK+ is unavailable or not maintained? What about supporting the
TTY? Do these issues mean we will need to keep the existing
display engine in parallel with the Canvas-based one?
Gtk+ is required, you would have to have a parallel display engine for all
non-Gtk+ cases.
. The Canvas redisplay runs from the GTK+ idle handlers. In Emacs,
the idle loop, in addition to triggering redisplay, also checks for
input from the keyboard and from subprocesses. Does this mean that
part of the input handling will need to be run by GTK+?
Yes. Now we run the Gtk+ event loop (or actually not the loop, just a step)
only when we know there is events pending. Again, parallel implementation for
non-Gtk+. But normal redisplay for Gtk+ also happens in idle handlers. We are
in the Gtk+ event loop often enough for this to happen often enough. Sometimes
though (scroll bars mainly) we force redisplay in Gtk+. I assume you can do
that for the Canvas also.
. Canvas redisplay is caused by requests from the application to
update some "canvas item" when the underlying application's objects
are modified; these requests are then served when GTK+ idle
handlers are run. Emacs display engine works differently: changes
that require redisplay are not considered until redisplay is
entered; the "requests" to update the display are implicitly
recorded in the buffers and in the various related data structures
(text properties and overlays, display strings, etc.), but not
explicitly translated to display terms until redisplay time, and as
an inherent part of redisplay itself. These two very different
models will need to be reconciled in some reasonably efficient way.
The changes that require redisplay would have to notify the Canvas that things
changed. I think this style is more efficient.
But I'm not sure it is the right way to go for Emacs unless Gtk+ can run on
all platforms now. Even if it can, do we want Gtk+ look and feel on W32, OSX,
Nextstep etc.? TTY is still a separate issue though.
Jan D.