Allow children of gui_container be resized anytime

So far, their position inside the container was determined when
initializing the interface. However, if a child were resized
afterwards, the container would not adjust its elements accordingly.
Moreover, the implementation for gui_container relied on hacking the
children's X/Y coordinates, which could only be done once.

Now, two additional members have been added to gui_common so that
specific X/Y offset can be determined by the parent, additionally to the
traditional rules followed by gui_coords. Despite the extra memory
footprint, it now allows containers to set specific X/Y offsets for
their children on every game cycle.

src/gui/inc/gui.h

@@ -21,7 +21,7 @@ struct gui_common
         void (*get_dim)(const struct gui_common *, short *w, short *h);
     } *cb;
 
-    short x, y;
+    short x, y, xoff, yoff;
     bool hcentered, vcentered;
     struct gui_common *parent, *child, *sibling;
 };

src/gui/src/container.c

@@ -1,5 +1,7 @@
 #include <gui/container.h>
 #include <gui.h>
+#include <camera.h>
+#include <peripheral.h>
 
 static void add_child(struct gui_common *const parent,
     struct gui_common *const child)
@@ -18,7 +20,7 @@ static void add_child(struct gui_common *const parent,
             if (c->w)
                 c->w += c->spacing;
 
-            child->x += c->w;
+            child->xoff = c->w;
             c->w += w;
 
             if (h > c->h)
@@ -30,7 +32,7 @@ static void add_child(struct gui_common *const parent,
             if (c->h)
                 c->h += c->spacing;
 
-            child->y += c->h;
+            child->yoff = c->h;
             c->h += h;
 
             if (w > c->w)
@@ -49,12 +51,31 @@ static void get_dim(const struct gui_common *const g,
     *h = c->h;
 }
 
+static int update(struct gui_common *const g,
+    const union peripheral *const p, const struct camera *const cam)
+{
+    struct gui_container *const c = (struct gui_container *)g;
+
+    c->w = c->h = 0;
+
+    struct gui_common *const child = c->common.child;
+
+    if (child->cb->get_dim)
+        add_child(&c->common, child);
+
+    for (struct gui_common *s = child->sibling; s; s = s->sibling)
+        add_child(&c->common, s);
+
+    return 0;
+}
+
 void gui_container_init(struct gui_container *const c)
 {
     static const struct gui_common_cb cb =
     {
         .add_child = add_child,
-        .get_dim = get_dim
+        .get_dim = get_dim,
+        .update = update
     };
 
     *c = (const struct gui_container)

src/gui/src/gui.c

@@ -31,14 +31,14 @@ static void get_centered(const struct gui_common *const g,
 void gui_coords(const struct gui_common *const g, short *const x,
     short *const y)
 {
-    *x = g->x;
-    *y = g->y;
+    *x = g->x + g->xoff;
+    *y = g->y + g->yoff;
 
     const struct gui_common *p = g->parent;
 
     if (p)
     {
-        short px = p->x, py = p->y;
+        short px = p->x + p->xoff, py = p->y + p->yoff;
 
         if (p->hcentered || p->vcentered)
             gui_coords(p, &px, &py);

src/menu/src/gamecfg_menu.c

@@ -20,8 +20,11 @@ static int update(struct menu_common *const c, void *const arg)
     struct gamecfg_menu *const m = arg;
 
     m->bcnt.common.y = screen_h - 40;
+    m->r.w = screen_w / 2;
+    m->r.h = screen_h / 2;
 
-    if (gui_update(&m->bcnt.common, &c->p, &c->cam))
+    if (gui_update(&m->cnt.common, &c->p, &c->cam)
+        || gui_update(&m->bcnt.common, &c->p, &c->cam))
         return -1;
 
     return 0;
@@ -48,8 +51,6 @@ int menu_gamecfg(struct menu_common *const c)
     m.cnt.common.vcentered = true;
 
     gui_rounded_rect_init(&m.r);
-    m.r.w = screen_w / 2;
-    m.r.h = screen_h / 2;
     gui_add_child(&m.cnt.common, &m.r.common);
 
     gui_container_init(&m.bcnt);