Modifier mapping in X11

[Adrian Robert]

Hi,

After wondering for a while why emacs-like keybindings were defined in 
my DefaultKeyBindings.dict but not showing up in any apps, I realized 
that GNUstep was apparently not picking up my keymap modifications 
set either with xmodmap or in the XFree86 config file.  E.g., I map my 
caps-lock key to another left-control, but GNUstep apps don't pick up 
control commands, instead inserting characters into the text, as in 
"

".

I traced this to X11/XGServerEvent.m in 'back'.  It checks modifier 
status by first converting the defaults like "GSFirstControlKey" into 
single X KeyCodes on init, then comparing KeyCodes received from the X 
server with these.  The problem is that X conceptually maps modifiers 
to KeySyms, not KeyCodes.  A KeySym is something like "Control_L" and 
is what you specify in 'GSFirstControlKey', etc..  A KeyCode is a 
number corresponding to a physical key, and more than one of these can 
map to the same KeySym.  GNUstep should compare the KeySym rather than 
the KeyCode to determine if a modifier is pressed.  (See, e.g., 
XGetModifierMapping(); also, I'm not sure how the XKeysymToKeycode() 
function currently used in XGServerEvent picks the code to return for 
a sym with more than one.)

Is there any reason not to make this change?  Will it interact badly 
with any locale / input method code?  If not and no one else wants to 
do it I can take a stab at this and send out a patch for people to 
try..

Adrian