1 files changed, 59 insertions, 6 deletions
diff --git a/src/tiling.rs b/src/tiling.rs
index 9319a94..f2a9b02 100644
--- a/src/tiling.rs
+++ b/src/tiling.rs
@@ -103,13 +103,66 @@ impl TileGrid {
         self.ysize
     }
 
-    pub fn clear_fog_of_war(&mut self, center: &(usize, usize), radius: usize) {
-        let startx: usize = 0.max(center.0 as isize - radius as isize) as usize;
-        let starty: usize = 0.max(center.1 as isize - radius as isize) as usize;
-        for x in startx..self.xsize.min(center.0 + radius) {
-            for y in starty..self.ysize.min(center.1 + radius) {
-                self.grid[y][x].visibility(true)
+    /// Clears all blocks in a single line of sight ray; stop when encountering a wall
+    /// This uses the bresenham algorithm, see:
+    ///     https://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm
+    fn clear_los(&mut self, start: &(usize, usize), end: &(usize, usize)) {
+        let dx = (end.0 as isize - start.0 as isize).abs();
+        let sx: isize = if start.0 < end.0 { 1 } else { -1 };
+        let dy = -(end.1 as isize - start.1 as isize).abs();
+        let sy: isize = if start.1 < end.1 { 1 } else { -1 };
+        let mut err = dx + dy;
+
+        let mut x = start.0;
+        let mut y = start.1;
+
+        loop {
+            if x == end.0 && y == end.1 {
+                break;
+            }
+            if let TileType::Wall = self.grid[y][x].get_type() {
+                break;
+            }
+
+            let err2 = 2 * err;
+            if err2 >= dy {
+                err += dy;
+                x = (x as isize + sx).max(0) as usize;
+            }
+            if err2 <= dx {
+                err += dx;
+                y = (y as isize + sy).max(0) as usize;
             }
+            self.grid[y][x].visibility(true);
+        }
+    }
+
+    /// Walk around the perimeter of the line of sight and ray-trace to clear tiles
+    /// up to the nearest obstacle.
+    pub fn clear_fog_of_war(&mut self, center: &(usize, usize), radius: usize) {
+        let a = (
+            center.0.saturating_sub(radius),
+            center.1.saturating_sub(radius),
+        );
+        let b = (center.0 + radius, center.1.saturating_sub(radius));
+        let c = (center.0 + radius, center.1 + radius);
+        let d = (center.0.saturating_sub(radius), center.1 + radius);
+
+        // From a to b
+        for x in a.0..b.0 {
+            self.clear_los(center, &(x, a.1));
+        }
+        // From b to c
+        for y in b.1..c.1 {
+            self.clear_los(center, &(b.0, y));
+        }
+        // From c to d
+        for x in d.0..c.0 {
+            self.clear_los(center, &(x, c.1));
+        }
+        // From d to a
+        for y in a.1..d.1 {
+            self.clear_los(center, &(d.0, y));
         }
     }
 }