engine: redraw when the picture changes, not when the state might have

Every key copied the whole Im and Search rune by rune, compared them
after the transition, and combined the answer with 'eaten', a commit
count that is always zero, and a force flag for caret and owner changes,
while redraw() kept a separate 'visible' bit to know when to send an
empty popup. redraw() now compares the snapshot with the last one sent
and treats two empty popups as equal, so imhandlekey just ends in
redraw(). keystroke() was only a test entry point and moves there.

tests/engine_test.c

@@ -10,6 +10,17 @@ Str shownpre(Im*);
 static int typekeys(struct ct*, char*, Str*);
 static int draindraw(Drawcmd*);
 
+/* One key from the owner, as imhandlekey drives the engine. */
+static int
+keystroke(u32int ks, u32int mod, Str *com)
+{
+	int eaten;
+
+	eaten = transition(ks, mod, com);
+	redraw();
+	return eaten;
+}
+
 void
 testengineinit(int lang)
 {
@@ -675,7 +686,7 @@ struct Searchfix
 	Lang	*dictlang;
 	Trie	*dict;
 	int	activecap;
-	int	visible;
+	Drawcmd	lastdraw;
 	int	candidatechosen;
 };
 
@@ -893,7 +904,7 @@ searchsave(Searchfix *f, int lang)
 	f->dictlang = getlang(lang);
 	f->dict = f->dictlang->dict;
 	f->activecap = activecap;
-	f->visible = visible;
+	f->lastdraw = lastdraw;
 	f->candidatechosen = candidatechosen;
 	draindraw(nil);
 }
@@ -936,7 +947,7 @@ searchend(Searchfix *f)
 	im = f->im;
 	search = f->search;
 	activecap = f->activecap;
-	visible = f->visible;
+	lastdraw = f->lastdraw;
 	candidatechosen = f->candidatechosen;
 }