From 6ac6f55538b4852bb2eb51af40291fbd43f072f0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lu=C3=ADs=20Fonseca?= <luis@lhf.pt>
Date: Sun, 12 Nov 2023 16:47:11 +0000
Subject: [PATCH] feat(collisions): emit event on collision

---
 .../engine/collisions/collision_event.hpp     | 23 ++++++++
 engine/src/cubos/engine/collisions/plugin.cpp | 54 +++++++++++++++++++
 2 files changed, 77 insertions(+)
 create mode 100644 engine/include/cubos/engine/collisions/collision_event.hpp

diff --git a/engine/include/cubos/engine/collisions/collision_event.hpp b/engine/include/cubos/engine/collisions/collision_event.hpp
new file mode 100644
index 000000000..7f5634a5a
--- /dev/null
+++ b/engine/include/cubos/engine/collisions/collision_event.hpp
@@ -0,0 +1,23 @@
+/// @file
+/// @brief Event @ref cubos::engine::CollisionEvent.
+/// @ingroup collisions-plugin
+
+#pragma once
+
+#include <glm/vec3.hpp>
+
+#include <cubos/core/ecs/entity/entity.hpp>
+
+namespace cubos::engine
+{
+    /// @brief Represents a collision event.
+    /// @ingroup collisions-plugin
+    struct CollisionEvent
+    {
+        cubos::core::ecs::Entity entity; ///< Entity involved in the collision.
+        cubos::core::ecs::Entity other;  ///< Other entity involved in the collision.
+        float penetration;               ///< Penetration depth of the collision.
+        glm::vec3 position;              ///< Position of contact on the surface of the entity.
+        glm::vec3 normal;                ///< Normal of contact on the surface of the entity.
+    };
+}; // namespace cubos::engine
diff --git a/engine/src/cubos/engine/collisions/plugin.cpp b/engine/src/cubos/engine/collisions/plugin.cpp
index 08dbf9912..0e1b0b503 100644
--- a/engine/src/cubos/engine/collisions/plugin.cpp
+++ b/engine/src/cubos/engine/collisions/plugin.cpp
@@ -1,13 +1,17 @@
 #include "broad_phase/plugin.hpp"
 
+#include <cubos/core/ecs/system/event/writer.hpp>
 #include <cubos/core/ecs/system/query.hpp>
 
+#include <cubos/engine/collisions/broad_phase/candidates.hpp>
 #include <cubos/engine/collisions/collider.hpp>
+#include <cubos/engine/collisions/collision_event.hpp>
 #include <cubos/engine/collisions/plugin.hpp>
 #include <cubos/engine/collisions/shapes/box.hpp>
 #include <cubos/engine/collisions/shapes/capsule.hpp>
 #include <cubos/engine/transform/plugin.hpp>
 
+using cubos::core::ecs::EventWriter;
 using cubos::core::ecs::Query;
 using cubos::core::ecs::Read;
 using cubos::core::ecs::Write;
@@ -51,16 +55,66 @@ static void setupNewCapsulesSystem(Query<Read<CapsuleCollisionShape>, Write<Coll
     }
 }
 
+/// TODO: This is a temporary system should be removed once narrow phase is implemented.
+static void emitCollisionEventSystem(Query<Read<Collider>> query, Read<BroadPhaseCandidates> candidates,
+                                     EventWriter<CollisionEvent> events)
+{
+    for (const auto& [ent1, ent2] : candidates->candidates(BroadPhaseCandidates::CollisionType::BoxBox))
+    {
+        auto [collider1] = query[ent1].value();
+        auto [collider2] = query[ent2].value();
+
+        auto c1 = collider1->worldAABB.center();
+        auto b1 = collider1->worldAABB.box();
+
+        auto c2 = collider2->worldAABB.center();
+        auto b2 = collider2->worldAABB.box();
+
+        auto d = c2 - c1;
+        auto p = (b2.halfSize + b1.halfSize) - glm::abs(d);
+
+        auto s = glm::sign(d);
+
+        float penetration = 0.0F;
+        glm::vec3 normal{0.0F};
+        glm::vec3 pos{0.0F};
+
+        if (p.x < p.y && p.x < p.z)
+        {
+            penetration = p.x;
+            normal.x = s.x;
+            pos.x = c1.x + (b1.halfSize.x * s.x);
+        }
+        else if (p.y < p.x && p.y < p.z)
+        {
+            penetration = p.y;
+            normal.y = s.y;
+            pos.y = c1.y + (b1.halfSize.y * s.y);
+        }
+        else
+        {
+            penetration = p.z;
+            normal.z = s.z;
+            pos.z = c1.z + (b1.halfSize.z * s.z);
+        }
+
+        events.push(CollisionEvent{ent1, ent2, penetration, normal, pos});
+    }
+}
+
 void cubos::engine::collisionsPlugin(Cubos& cubos)
 {
     cubos.addPlugin(transformPlugin);
 
     cubos.addPlugin(broadPhaseCollisionsPlugin);
 
+    cubos.addEvent<CollisionEvent>();
+
     cubos.addComponent<Collider>();
     cubos.addComponent<BoxCollisionShape>();
     cubos.addComponent<CapsuleCollisionShape>();
 
     cubos.system(setupNewBoxesSystem).tagged("cubos.collisions.setup");
     cubos.system(setupNewCapsulesSystem).tagged("cubos.collisions.setup");
+    cubos.system(emitCollisionEventSystem).tagged("cubos.collisions").after("cubos.collisions.setup");
 }