One very handy feature of many modern GUI programs (at least, gnome apps
and mozilla :-) is that they have commands to grow and shrink the base
font-size, usually bound to the nicely mnemonic C-+ and C-- (mozilla and
some other programs also bind C-= to the same thing as C-+, so you don't
have to use the shift key; gnome unfortunately assigns a _different_
meaning to C-=).

I think emacs should also have this feature (and others have said the same
thing), and it seems simple enough in theory.  I've appended a possible
implementation of `increase-default-face-height' and
`decrease-default-face-height' and associated bindings.

However there are a few little wrinkles I'd like to ask the list about:

  (1) In most programs, such commands only affect the current X window, so
      in my implementation I've used (selected-frame) when manipulating the
      default face.  With `emacs -q', this works great.

      However with my .emacs in effect, this doesn't work: the font-size
      increases (causing the X window to grow) -- and then immediately
      reverts to the old font-size (and the X window shrinks again)!

      It seems that there's some state somewhere in the convoluted
      machinery that gets invoked when the default face changes, which is
      overriding the change; I think this is probably a bug (you _ought_ to
      be able to make local changes to the default face!), but I don't know
      where.  If I change my commands to use a frame of `nil' -- meaning
      `every frame' -- it works properly, albeit affecting every frame
      rather than just the current one.

      I'd appreciate any insight people have into this.

  (2) My commands just grow/shrink the :height of the default face by a
      factor of 1.2, which generally works `pretty well', but occasionally
      there isn't an appropriate font available, so growing/shrinking can
      happen without any visible effect.  It would perhaps be nice if there
      was a way to find the next `nice size' for the default face; however
      maybe this idea is hard given today's scalable fonts etc.  Any ideas?

Thanks,

-Miles