From d8b1fcfc5d9715342ef08e55aad27f64d1a990a9 Mon Sep 17 00:00:00 2001
From: Darren Eberly <darren@eber.ly>
Date: Sat, 2 Mar 2024 02:45:06 -0500
Subject: [PATCH] Native Polygon Intersection

---
 src/geometry.rs    | 61 ++++++++++++++++++++++++++++++++++++++++++++++
 src/sprite_list.rs |  6 ++---
 2 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/src/geometry.rs b/src/geometry.rs
index b8906aa..3ea7a95 100644
--- a/src/geometry.rs
+++ b/src/geometry.rs
@@ -1,5 +1,66 @@
 use pyo3::prelude::*;
 
+pub fn are_polygons_intersecting_native(
+    poly_a: &Vec<(f32, f32)>,
+    poly_b: &Vec<(f32, f32)>,
+) -> bool {
+    // If either polygon is empty, we should just return False
+    if poly_a.is_empty() || poly_b.is_empty() {
+        return false;
+    }
+    let polygons = [poly_a, poly_b];
+    for polygon in &polygons {
+        for i1 in 0..polygon.len() {
+            let i2 = (i1 + 1) % polygon.len();
+            let projection_1 = polygon[i1];
+            let projection_2 = polygon[i2];
+
+            let normal = (
+                projection_2.1 - projection_1.1,
+                projection_1.0 - projection_2.0,
+            );
+
+            let mut min_a: Option<f32> = None;
+            let mut max_a: Option<f32> = None;
+            let mut min_b: Option<f32> = None;
+            let mut max_b: Option<f32> = None;
+
+            for point in polygons[0] {
+                let projected = normal.0 * point.0 + normal.1 * point.1;
+                match min_a {
+                    Some(x) if projected < x => min_a = Some(projected),
+                    Some(_x) => {}
+                    None => min_a = Some(projected),
+                }
+                match max_a {
+                    Some(x) if projected > x => max_a = Some(projected),
+                    Some(_x) => {}
+                    None => max_a = Some(projected),
+                }
+            }
+
+            for point in polygons[1] {
+                let projected = normal.0 * point.0 + normal.1 * point.1;
+                match min_b {
+                    Some(x) if projected < x => min_b = Some(projected),
+                    Some(_x) => {}
+                    None => min_b = Some(projected),
+                }
+                match max_b {
+                    Some(x) if projected > x => max_b = Some(projected),
+                    Some(_x) => {}
+                    None => max_b = Some(projected),
+                }
+            }
+
+            if max_a <= min_b || max_b <= min_a {
+                return false;
+            }
+        }
+    }
+    true
+}
+
 #[pyfunction]
 pub fn are_polygons_intersecting(poly_a: Vec<(f32, f32)>, poly_b: Vec<(f32, f32)>) -> bool {
     // If either polygon is empty, we should just return False
diff --git a/src/sprite_list.rs b/src/sprite_list.rs
index 64a30ce..89e2807 100644
--- a/src/sprite_list.rs
+++ b/src/sprite_list.rs
@@ -1,4 +1,4 @@
-use crate::geometry::are_polygons_intersecting;
+use crate::geometry::are_polygons_intersecting_native;
 use crate::hitbox::{HitBox, RotatableHitBox};
 use pyo3::prelude::*;
 
@@ -72,7 +72,7 @@ pub fn check_for_collision_with_list(
             panic!("unknown hitbox type");
         };
 
-        let check_2 = are_polygons_intersecting(main_points.to_vec(), other_points);
+        let check_2 = are_polygons_intersecting_native(&main_points, &other_points);
 
         if check_2 {
             final_sprites.push(sprite2.to_object(py));
@@ -149,7 +149,7 @@ pub fn check_for_collision_with_lists(
                 panic!("unknown hitbox type");
             };
 
-            let check_2 = are_polygons_intersecting(main_points.to_vec(), other_points);
+            let check_2 = are_polygons_intersecting_native(&main_points, &other_points);
 
             if check_2 {
                 final_sprites.push(sprite2.to_object(py));