[9front] [PATCH] allow kbdfs to rewrite altgr combinations from drawterm

[Jacob Moody <moody@mail.posixcafe.org>]

Currently most drawterm guis simply map right alt to to left alt. This is fine, but we do have support
for making use of altgr so why not send that? Once we are sending altgr, this tweaks how kbdfs ingests
those 'R/r' messages and allows it to switch over in to the altgr page on matching runes. This only
effects the processing for /dev/kbd messages _in to_ kbdfs which is seemingly only used by drawterm.

This also captures when the algr combination may have been precomposed by the host
running drawterm, and sets k.b correctly.

diff 59d978eeb6d9f987d2c2b17d2799f3c15655284f uncommitted
--- a/sys/src/cmd/aux/kbdfs/kbdfs.c
+++ b/sys/src/cmd/aux/kbdfs/kbdfs.c
@@ -514,12 +514,14 @@
 		k.b = 0;
 		k.down = (p[0] == 'r');
 		for(i=0; i<Nscan; i++){
-			if(kbtab[i] == k.r || kbtabshift[i] == k.r || (i >= 16 && kbtabctl[i] == k.r)){
+			if(kbtab[i] == k.r || kbtabshift[i] == k.r || (i >= 16 && kbtabctl[i] == k.r) || kbtabaltgr[i] == k.r){
 				/* assign button from kbtab */
 				k.b = kbtab[i];
 				/* handle ^X forms */
 				if(k.r == kbtab[i] && kbtabctl[i] && !a->shift && !a->altgr && a->ctl)
 					k.r = kbtabctl[i];
+				else if(k.r == kbtab[i] && kbtabaltgr[i] && !a->shift && a->altgr && !a->ctl)
+					k.r = kbtabaltgr[i];
 				break;
 			}
 		}