engine: a mode switch shows the mode it switched to

Ctrl+S, Ctrl+N and the rest changed the mode with nothing to see; the
next key was the only way to tell.  The popup now shows A, 한, あ, ア, or
ă until a key is typed, beside the ☺ and 漢 a search already shows.

strans.c

@@ -7,6 +7,7 @@ static void *lostowner;	/* the context the engine was taken from */
 static Str lost;
 static int clientpre;	/* the owner draws its own preedit */
 static Caret caret;
+static Rune modemark;	/* the mode the last key switched to */
 static Drawcmd lastdraw;
 static Emit transjp(Im*, Rune);
 static void backjp(Im*);
@@ -197,6 +198,8 @@ snapshot(Drawcmd *dc)
 		dc->pre = pre;
 	if(search.lang && pre.n == 0)	/* a search just begun shows itself */
 		sputr(&dc->pre, search.lang == LangEMOJI ? L'☺' : L'漢');
+	else if(modemark != 0 && pre.n == 0 && im.nkouho == 0)
+		sputr(&dc->pre, modemark);
 	first = pagefirst();
 	n = im.nkouho - first;
 	if(n > Maxdisp) n = Maxdisp;
@@ -336,6 +339,19 @@ katakouho(void)
 		addkouho(&k);
 }
 
+/* What the popup shows for a moment when the mode changes. */
+static Rune
+langmark(int lang)
+{
+	switch(lang){
+	case LangJP:	return L'あ';
+	case LangJPK:	return L'ア';
+	case LangKO:	return L'한';
+	case LangVI:	return L'ă';
+	}
+	return L'A';
+}
+
 static int
 setlang(int c)
 {
@@ -344,6 +360,8 @@ setlang(int c)
 	l = getlang(c);
 	if(l == nil)
 		return 0;
+	if(l != im.l)
+		modemark = langmark(l->lang);
 	im.l = l;
 	return 1;
 }
@@ -783,6 +801,7 @@ transition(u32int ks, u32int mod, Str *com)
 	int n;
 	Rune c;
 
+	modemark = 0;	/* any key after the switch takes its mark away */
 	if(im.l->lang == LangKO)
 		ks = kokey(ks, mod);
 	else if(isjp(&im))
@@ -897,6 +916,7 @@ init(void)
 	im.sel = -1;
 	memset(&search, 0, sizeof search);
 	memset(&caret, 0, sizeof caret);
+	modemark = 0;
 	activeowner = nil;
 	lostowner = nil;
 	clientpre = 0;