From 5fa358a465d32d1420a8cdfd23dd1a88ca4ae797 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Tue, 14 Jan 2025 13:32:02 +0100
Subject: feat(engine): add simple collision

---
 engine/src/mesh.rs | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

(limited to 'engine/src/mesh.rs')

diff --git a/engine/src/mesh.rs b/engine/src/mesh.rs
index de0af70..a9914e7 100644
--- a/engine/src/mesh.rs
+++ b/engine/src/mesh.rs
@@ -1,5 +1,6 @@
 use ecs::Component;
 
+use crate::vector::Vec3;
 use crate::vertex::Vertex;
 
 pub mod cube;
@@ -30,4 +31,103 @@ impl Mesh
     {
         self.indices.as_deref()
     }
+
+    /// Finds the vertex positions that are furthest in every 3D direction. Keep in mind
+    /// that this can be quite time-expensive if the mesh has many vertices.
+    pub fn find_furthest_vertex_positions(&self) -> DirectionPositions<'_>
+    {
+        let mut point_iter = self.vertices().iter().map(|vertex| &vertex.pos).into_iter();
+
+        let first_point = point_iter.next().unwrap();
+
+        point_iter
+            .fold(
+                FurthestPosAcc {
+                    up: FurthestPos::new(&first_point, &Vec3::UP),
+                    down: FurthestPos::new(&first_point, &Vec3::DOWN),
+                    left: FurthestPos::new(&first_point, &Vec3::LEFT),
+                    right: FurthestPos::new(&first_point, &Vec3::RIGHT),
+                    back: FurthestPos::new(&first_point, &Vec3::BACK),
+                    front: FurthestPos::new(&first_point, &Vec3::FRONT),
+                },
+                |mut furthest_pos_acc, pos| {
+                    furthest_pos_acc.up.update_if_further(pos);
+                    furthest_pos_acc.down.update_if_further(pos);
+                    furthest_pos_acc.left.update_if_further(pos);
+                    furthest_pos_acc.right.update_if_further(pos);
+                    furthest_pos_acc.back.update_if_further(pos);
+                    furthest_pos_acc.front.update_if_further(pos);
+
+                    furthest_pos_acc
+                },
+            )
+            .into()
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct DirectionPositions<'mesh>
+{
+    pub up: &'mesh Vec3<f32>,
+    pub down: &'mesh Vec3<f32>,
+    pub left: &'mesh Vec3<f32>,
+    pub right: &'mesh Vec3<f32>,
+    pub back: &'mesh Vec3<f32>,
+    pub front: &'mesh Vec3<f32>,
+}
+
+impl<'mesh> From<FurthestPosAcc<'mesh>> for DirectionPositions<'mesh>
+{
+    fn from(acc: FurthestPosAcc<'mesh>) -> Self
+    {
+        Self {
+            up: acc.up.pos,
+            down: acc.down.pos,
+            left: acc.left.pos,
+            right: acc.right.pos,
+            back: acc.back.pos,
+            front: acc.front.pos,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct FurthestPosAcc<'mesh>
+{
+    up: FurthestPos<'mesh>,
+    down: FurthestPos<'mesh>,
+    left: FurthestPos<'mesh>,
+    right: FurthestPos<'mesh>,
+    back: FurthestPos<'mesh>,
+    front: FurthestPos<'mesh>,
+}
+
+#[derive(Debug)]
+struct FurthestPos<'mesh>
+{
+    pos: &'mesh Vec3<f32>,
+    dot_prod: f32,
+    direction: &'mesh Vec3<f32>,
+}
+
+impl<'mesh> FurthestPos<'mesh>
+{
+    fn new(pos: &'mesh Vec3<f32>, direction: &'mesh Vec3<f32>) -> Self
+    {
+        Self {
+            pos,
+            dot_prod: direction.dot(&pos),
+            direction,
+        }
+    }
+
+    fn update_if_further(&mut self, point: &'mesh Vec3<f32>)
+    {
+        let point_dot_prod = self.direction.dot(point);
+
+        if point_dot_prod > self.dot_prod {
+            self.pos = point;
+            self.dot_prod = point_dot_prod;
+        }
+    }
 }
-- 
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