From b1075e661c2ce2f107350b8d4f5f9a92e047b93e Mon Sep 17 00:00:00 2001
From: =?utf8?q?Tomas=20Wenstr=C3=B6m?= <tomas.wenstrom@gmail.com>
Date: Sun, 14 Feb 2021 20:55:16 +0100
Subject: [PATCH] Only collide with walls from the front

---
 src/core/level/mod.rs | 19 ++++++++++++++-----
 src/geometry.rs       |  4 ++++
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/src/core/level/mod.rs b/src/core/level/mod.rs
index 4d828de..bdc6cb0 100644
--- a/src/core/level/mod.rs
+++ b/src/core/level/mod.rs
@@ -135,11 +135,13 @@ impl Level {
 	for c in self.wall_grid.grid_coordinates_on_line(p1, p2) {
 	    for w in &self.wall_grid.cells[c.x][c.y] {
 		if let Intersection::Point(p) = Intersection::lines(p1, p2, w.p1, w.p2) {
-		    let wall = Wall {
-			region: Rc::clone(&self.walls[w.region]),
-			edge: Rc::clone(w),
-		    };
-		    return IntersectResult::Intersection(wall, p)
+		    if w.point_is_in_front(p1) {
+			let wall = Wall {
+			    region: Rc::clone(&self.walls[w.region]),
+			    edge: Rc::clone(w),
+			};
+			return IntersectResult::Intersection(wall, p)
+		    }
 		}
 	    }
 	}
@@ -243,6 +245,13 @@ struct WallEdge {
     pub p2: Point<f64>,
 }
 
+impl WallEdge {
+    fn point_is_in_front(&self, p: Point<f64>) -> bool {
+	let cross = (self.p2 - self.p1).cross_product(p - self.p1);
+	cross > 0.0
+    }
+}
+
 ////////// WALL ////////////////////////////////////////////////////////////////
 
 pub struct Wall {
diff --git a/src/geometry.rs b/src/geometry.rs
index 2d5a70c..7ddc3ec 100644
--- a/src/geometry.rs
+++ b/src/geometry.rs
@@ -38,6 +38,10 @@ impl Point<f64> {
 	    y: self.y as i32,
 	}
     }
+
+    pub fn cross_product(&self, p: Self) -> f64 {
+        return self.x * p.y - self.y * p.x;
+    }
 }
 
 macro_rules! impl_point_op {
-- 
2.11.0