Surface world: grass in daylight, forests, cliffs with cave mouths; free-game and editor option

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/map.rs

@@ -350,6 +350,8 @@ pub struct Map {
     pub explored: Vec<bool>, // fog of war: tiles the dungeon knows (empty: no fog)
     #[serde(skip)]
     pub visible: Vec<bool>, // fog of war: tiles in sight right now
+    #[serde(default, with = "crate::fog::bits")]
+    pub sky: Vec<bool>, // tiles above ground (daylight, grass); empty: all underground
 }
 
 fn default_size() -> usize {
@@ -367,6 +369,21 @@ impl Map {
         }
     }
 
+    // tile i lies above ground
+    pub fn sky(&self, i: usize) -> bool {
+        self.sky.get(i).copied().unwrap_or(false)
+    }
+
+    pub fn set_sky(&mut self, i: usize, on: bool) {
+        if self.sky.len() != self.t.len() {
+            if !on {
+                return;
+            }
+            self.sky = vec![false; self.t.len()];
+        }
+        self.sky[i] = on;
+    }
+
     pub fn get(&self, x: i32, y: i32) -> Option<&Tile> {
         if inb(x, y) {
             Some(&self.t[idx(x, y)])
@@ -587,7 +604,7 @@ impl Map {
                 tl.hp = 6.0;
             }
         }
-        Map { w, h, t, core, portals, legacy_portal: None, gate, treasures, explored: Vec::new(), visible: Vec::new() }
+        Map { w, h, t, core, portals, legacy_portal: None, gate, treasures, explored: Vec::new(), visible: Vec::new(), sky: Vec::new() }
     }
 
     // Carves a meandering river; the player's area, the core and portals stay dry.