Hero movement affects water bubble direction

src/mkmaze.c

@@ -1489,6 +1489,9 @@ fumaroles(void)
 #define gbxmax (gx.xmax - 1)
 #define gbymax (gy.ymax - 1)
 
+/* the bubble hero is in */
+static struct bubble *hero_bubble = NULL;
+
 staticfn void set_wportal(void);
 staticfn void mk_bubble(coordxy, coordxy, int);
 staticfn void mv_bubble(struct bubble *, coordxy, coordxy, boolean);
@@ -1513,6 +1516,8 @@ movebubbles(void)
 
     vision_recalc(2);
 
+    hero_bubble = NULL;
+
     if (Is_waterlevel(&u.uz)) {
         /* keep attached ball&chain separate from bubble objects */
         if (Punished)
@@ -1583,6 +1588,7 @@ movebubbles(void)
 
                             cons->next = b->cons;
                             b->cons = cons;
+                            hero_bubble = b;
                         }
                         if ((btrap = t_at(x, y)) != 0) {
                             cons = (struct container *) alloc(sizeof *cons);
@@ -1875,6 +1881,22 @@ mk_bubble(coordxy x, coordxy y, int n)
     mv_bubble(b, 0, 0, TRUE);
 }
 
+/* maybe change the movement direction of the bubble hero is in */
+void
+maybe_adjust_hero_bubble(void)
+{
+    if (!Is_waterlevel(&u.uz))
+        return;
+
+    if (!u.dx && !u.dy)
+        return;
+
+    if (hero_bubble && !rn2(2)) {
+        hero_bubble->dx = u.dx;
+        hero_bubble->dy = u.dy;
+    }
+}
+
 /*
  * The player, the portal and all other objects and monsters
  * float along with their associated bubbles.  Bubbles may overlap