improved algorithm for mapping/unmapping

In previous versions, all the previous current visible menus are
unmapped and the new currently visible menus are mapped when the
current visible menu changed. Now, using an algorithm that finds
the lowest common ancestor between current and current_new menus,
only the necessary menus are remapped on the display.

xmenu.c

@@ -9,6 +9,7 @@
 /* macros */
 #define LEN(x) (sizeof (x) / sizeof (x[0]))
 #define MAX(x,y) ((x)>(y)?(x):(y))
+#define MIN(x,y) ((x)<(y)?(x):(y))
 
 /* color enum */
 enum {ColorFG, ColorBG, ColorLast};
@@ -42,25 +43,25 @@ struct ScreenGeometry {
 
 /* menu item structure */
 struct Item {
-	char *label;
-	char *output;
-	int y;
-	int h;
-	size_t labellen;
-	struct Item *next;
-	struct Menu *submenu;
+	char *label;            /* string to be drawed on menu */
+	char *output;           /* string to be outputed when item is clicked */
+	int y;                  /* item y position relative to menu */
+	int h;                  /* item height */
+	size_t labellen;        /* strlen(label) */
+	struct Item *next;      /* next item */
+	struct Menu *submenu;   /* submenu spawned by clicking on item */
 };
 
 /* menu structure */
 struct Menu {
-	struct Menu *parent;
-	struct Item *caller;
-	struct Item *list;
-	struct Item *selected;
-	int x, y, w, h;
-	unsigned level;
-	Drawable pixmap;
-	Window win;
+	struct Menu *parent;    /* parent menu */
+	struct Item *caller;    /* item that spawned the menu */
+	struct Item *list;      /* list of items contained by the menu */
+	struct Item *selected;  /* item currently selected in the menu */
+	int x, y, w, h;         /* menu geometry */
+	unsigned level;         /* menu level relative to root */
+	Drawable pixmap;        /* pixmap to draw the menu on */
+	Window win;             /* menu window to map on the screen */
 };
 
 /* function declarations */
@@ -138,6 +139,10 @@ main(int argc, char *argv[])
 	calcscreengeom();
 	calcmenu(rootmenu);
 
+	/* map root menu */
+	currmenu = rootmenu;
+	XMapWindow(dpy, rootmenu->win);
+
 	/* run event loop */
 	run();
 
@@ -454,20 +459,45 @@ done:
 static void
 setcurrmenu(struct Menu *currmenu_new)
 {
-	struct Menu *menu;
+	struct Menu *menu, *menu_;
 	struct Item *item;
+	struct Menu *lcamenu;   /* lowest common ancestor menu */
+	unsigned minlevel;      /* level of the closest to root menu */
+	unsigned maxlevel;      /* level of the closest to root menu */
 
 	if (currmenu_new == currmenu)
 		return;
 
-	for (menu = currmenu; menu != NULL; menu = menu->parent) {
+	/* find lowest common ancestor menu */
+	lcamenu = rootmenu;
+	if (currmenu != NULL) {
+		minlevel = MIN(currmenu_new->level, currmenu->level);
+		maxlevel = MAX(currmenu_new->level, currmenu->level);
+		if (currmenu_new->level == maxlevel) {
+			menu = currmenu_new;
+			menu_ = currmenu;
+		} else {
+			menu = currmenu;
+			menu_ = currmenu_new;
+		}
+		while (menu->level > minlevel)
+			menu = menu->parent;
+
+		while (menu != menu_) {
+			menu = menu->parent;
+			menu_ = menu_->parent;
+		}
+		lcamenu = menu;
+	}
+
+	for (menu = currmenu; menu != lcamenu; menu = menu->parent) {
 		XUnmapWindow(dpy, menu->win);
 	}
 
 	currmenu = currmenu_new;
 
 	item = NULL;
-	for (menu = currmenu; menu != NULL; menu = menu->parent) {
+	for (menu = currmenu; menu != lcamenu; menu = menu->parent) {
 		XMapWindow(dpy, menu->win);
 		if (item != NULL)
 			menu->selected = item;