3 files changed, 537 insertions, 1 deletions

diff --git a/src/crepe/system/CollisionSystem.cpp b/src/crepe/system/CollisionSystem.cpp
index c74ca1d..9ca8b3a 100644
--- a/src/crepe/system/CollisionSystem.cpp
+++ b/src/crepe/system/CollisionSystem.cpp
@@ -1,5 +1,359 @@
+#include <cmath>
+#include <algorithm>
+#include <cstddef>
+#include <utility>
+#include <variant>
+
+#include "api/Event.h"
+#include "api/EventManager.h"
+#include "api/BoxCollider.h"
+#include "api/CircleCollider.h"
+#include "api/Vector2.h"
+#include "api/Rigidbody.h"
+#include "api/Transform.h"
+
+#include "ComponentManager.h"
 #include "CollisionSystem.h"
+#include "Collider.h"
 
 using namespace crepe;
 
-void CollisionSystem::update() {}
+void CollisionSystem::update() {
+	// Get collider components and keep them seperate
+	ComponentManager & mgr = this->component_manager;
+	std::vector<std::reference_wrapper<BoxCollider>> boxcolliders	= mgr.get_components_by_type<BoxCollider>();
+	std::vector<std::reference_wrapper<CircleCollider>> circlecolliders	= mgr.get_components_by_type<CircleCollider>();
+	
+	// Check between all colliders if there is a collision
+	std::vector<std::pair<CollidedInfoStor,CollidedInfoStor>> collided = check_collisions(boxcolliders,circlecolliders);
+
+	// For both objects call the collision handler 
+	for (auto& collision_pair : collided) {
+		collision_handler(collision_pair.first,collision_pair.second);
+		collision_handler(collision_pair.second,collision_pair.first);
+	}
+}
+
+void CollisionSystem::collision_handler(CollidedInfoStor& data1,CollidedInfoStor& data2){
+
+	// Data needed for collision handler info
+	const Collider* collider1 = nullptr;
+	const Collider* collider2 = nullptr;
+	Vector2 move_back;
+
+	// Check collision type and get values for handler
+	if (std::holds_alternative<std::reference_wrapper<BoxCollider>>(data1.collider)) {
+		if (std::holds_alternative<std::reference_wrapper<BoxCollider>>(data2.collider)) {
+			
+			// Get colliders from variant to be used to determine collision handler info
+			const BoxCollider& box_collider1 = std::get<std::reference_wrapper<BoxCollider>>(data1.collider).get();
+			const BoxCollider& box_collider2 = std::get<std::reference_wrapper<BoxCollider>>(data2.collider).get();
+			collider1 = &box_collider1;
+			collider2 = &box_collider2;
+
+			// TODO: send with the collider info to this function because this is calculated previously
+			// Get the current position of the collider
+			Vector2 final_position1 = current_position(box_collider1,data1.transform,data1.rigidbody);
+			Vector2 final_position2 = current_position(box_collider2,data2.transform,data2.rigidbody);
+
+			// Determine move_back value for smallest overlap (x or y)
+			move_back = box_box_collision_move_back(box_collider1,box_collider2,final_position1,final_position2);
+			
+		}
+		else {
+			// TODO: calcualte Box - Circle collision info
+			const BoxCollider& box_collider = std::get<std::reference_wrapper<BoxCollider>>(data1.collider).get();
+			const CircleCollider& circle_collider = std::get<std::reference_wrapper<CircleCollider>>(data2.collider).get();
+			collider1 = &box_collider;
+			collider2 = &circle_collider;
+		}
+	}
+	else {
+		if (std::holds_alternative<std::reference_wrapper<CircleCollider>>(data2.collider)) {
+			// TODO: calcualte Circle - Circle collision info
+			const CircleCollider& circle_collider1 = std::get<std::reference_wrapper<CircleCollider>>(data1.collider).get();
+			const CircleCollider& circle_collider2 = std::get<std::reference_wrapper<CircleCollider>>(data2.collider).get();
+			collider1 = &circle_collider1;
+			collider2 = &circle_collider2;
+		}
+		else {
+			// TODO: calcualte Circle - Box collision info
+			const CircleCollider& circle_collider = std::get<std::reference_wrapper<CircleCollider>>(data1.collider);
+			const BoxCollider& box_collider = std::get<std::reference_wrapper<BoxCollider>>(data2.collider);
+			collider1 = &circle_collider;
+			collider2 = &box_collider;
+		}
+	}
+
+	// One vaue is calculated for moving back. Calculate the other value (x or y) relateive to the move_back value.
+	Direction move_back_direction = Direction::NONE;
+	if(move_back.x != 0 && move_back.y > 0) {
+		move_back_direction = Direction::BOTH;
+	} else if (move_back.x != 0) {
+		move_back_direction = Direction::X_DIRECTION;
+		if(data1.rigidbody.data.linear_velocity.y != 0)	
+		move_back.y = data1.rigidbody.data.linear_velocity.y * (move_back.x/data1.rigidbody.data.linear_velocity.x);
+	} else if (move_back.y != 0) {
+		move_back_direction = Direction::Y_DIRECTION;
+		if(data1.rigidbody.data.linear_velocity.x != 0) 
+		move_back.x = data1.rigidbody.data.linear_velocity.x * (move_back.y/data1.rigidbody.data.linear_velocity.y);
+	}
+
+	// collision info
+	crepe::CollisionSystem::CollisionInfo collision_info{
+            .first={ *collider1, data1.transform, data1.rigidbody },
+            .second={ *collider2, data2.transform, data2.rigidbody },
+						.move_back_value = move_back,
+						.move_back_direction = move_back_direction,
+        };
+
+	// Determine if static needs to be called
+	determine_collision_handler(collision_info);	
+}
+
+
+Vector2 CollisionSystem::box_box_collision_move_back(const BoxCollider& box_collider1,const BoxCollider& box_collider2,Vector2 final_position1,Vector2 final_position2)
+{
+	Vector2 resolution; // Default resolution vector
+	Vector2 delta = final_position2 - final_position1;
+
+	// Compute half-dimensions of the boxes
+	double half_width1 = box_collider1.width / 2.0;
+	double half_height1 = box_collider1.height / 2.0;
+	double half_width2 = box_collider2.width / 2.0;
+	double half_height2 = box_collider2.height / 2.0;
+
+	// Calculate overlaps along X and Y axes
+	double overlap_x = (half_width1 + half_width2) - std::abs(delta.x);
+	double overlap_y = (half_height1 + half_height2) - std::abs(delta.y);
+
+	// Check if there is a collision
+	if (overlap_x > 0 && overlap_y > 0) {//should always be true check if this can be removed
+		// Determine the direction of resolution
+		if (overlap_x < overlap_y) {
+			// Resolve along the X-axis (smallest overlap)
+			resolution.x = (delta.x > 0) ? -overlap_x : overlap_x;
+		} else if (overlap_y < overlap_x) {
+			// Resolve along the Y-axis (smallest overlap)
+			resolution.y = (delta.y > 0) ? -overlap_y : overlap_y;
+		} else {
+			// Equal overlap, resolve both directions with preference
+			resolution.x = (delta.x > 0) ? -overlap_x : overlap_x;
+			resolution.y = (delta.y > 0) ? -overlap_y : overlap_y;
+		}
+	}
+
+	return resolution;
+}
+
+void CollisionSystem::determine_collision_handler(CollisionInfo& info){
+	// Check rigidbody type for static
+	if(info.first.rigidbody.data.body_type != Rigidbody::BodyType::STATIC)
+	{
+		// If second body is static perform the static collision handler in this system
+		if(info.second.rigidbody.data.body_type == Rigidbody::BodyType::STATIC){
+			static_collision_handler(info);
+		}; 
+		// Call collision event for user
+		CollisionEvent data(info);
+		EventManager::get_instance().trigger_event<CollisionEvent>(data, info.first.collider.game_object_id);
+	}		
+}
+
+void CollisionSystem::static_collision_handler(CollisionInfo& info){
+	// Move object back using calculate move back value 
+	info.first.transform.position += info.move_back_value;
+
+	// If bounce is enabled mirror velocity
+	if(info.first.rigidbody.data.bounce) {
+		if(info.move_back_direction == Direction::BOTH)
+		{
+			info.first.rigidbody.data.linear_velocity.y = -info.first.rigidbody.data.linear_velocity.y * info.first.rigidbody.data.elastisity;
+			info.first.rigidbody.data.linear_velocity.x = -info.first.rigidbody.data.linear_velocity.x * info.first.rigidbody.data.elastisity;
+		}
+		else if(info.move_back_direction == Direction::Y_DIRECTION) {
+			info.first.rigidbody.data.linear_velocity.y = -info.first.rigidbody.data.linear_velocity.y * info.first.rigidbody.data.elastisity;
+		}
+		else if(info.move_back_direction == Direction::X_DIRECTION){
+			info.first.rigidbody.data.linear_velocity.x = -info.first.rigidbody.data.linear_velocity.x * info.first.rigidbody.data.elastisity;
+		}
+	}
+	// Stop movement if bounce is disabled
+	else {
+		info.first.rigidbody.data.linear_velocity = {0,0};
+	}
+}
+
+std::vector<std::pair<CollisionSystem::CollidedInfoStor,CollisionSystem::CollidedInfoStor>> CollisionSystem::check_collisions(const std::vector<std::reference_wrapper<BoxCollider>>& boxcolliders, const std::vector<std::reference_wrapper<CircleCollider>>& circlecolliders) {
+	ComponentManager & mgr = this->component_manager;
+	std::vector<std::pair<CollidedInfoStor,CollidedInfoStor>> collisions_ret;
+
+	// TODO:
+	// If no colliders skip
+	// Check if colliders has rigidbody if not skip
+
+	// TODO:
+	// If amount is higer than lets say 16 for now use quadtree otwerwise skip
+	// Quadtree code
+	// Quadtree is placed over the input vector
+
+	// Check collisions for each collider
+	for (size_t i = 0; i < boxcolliders.size(); ++i) {
+		// Fetch components for the first box collider
+		if(!boxcolliders[i].get().active) continue;
+		int game_object_id_1 = boxcolliders[i].get().game_object_id;
+		Transform& transform1 = mgr.get_components_by_id<Transform>(game_object_id_1).front().get();
+		if(!transform1.active) continue;
+		Rigidbody& rigidbody1 = mgr.get_components_by_id<Rigidbody>(game_object_id_1).front().get();
+		if(!rigidbody1.active) continue;
+		
+		// Check BoxCollider vs BoxCollider
+		for (size_t j = i + 1; j < boxcolliders.size(); ++j) {
+			if(!boxcolliders[j].get().active) continue;
+			// Skip self collision
+			int game_object_id_2 = boxcolliders[j].get().game_object_id;
+			if (game_object_id_1 == game_object_id_2) continue;
+
+			// Fetch components for the second box collider
+			Transform & transform2 = mgr.get_components_by_id<Transform>(boxcolliders[j].get().game_object_id).front().get();
+			if(!transform2.active) continue;
+			Rigidbody & rigidbody2 = mgr.get_components_by_id<Rigidbody>(boxcolliders[j].get().game_object_id).front().get();
+			if(!rigidbody2.active) continue;
+			// Check collision
+			if (check_box_box_collision(boxcolliders[i], boxcolliders[j], transform1, transform2, rigidbody1, rigidbody2)) {
+				collisions_ret.emplace_back(std::make_pair(
+				CollidedInfoStor{boxcolliders[i].get(), transform1, rigidbody1}, 
+				CollidedInfoStor{boxcolliders[j].get(), transform2, rigidbody2}
+				));
+			}
+		}
+
+		// Check BoxCollider vs CircleCollider
+		for (size_t j = 0; j < circlecolliders.size(); ++j) {
+			if(!circlecolliders[j].get().active) continue;
+			// Skip self collision
+			int game_object_id_2 = circlecolliders[j].get().game_object_id;
+			if (game_object_id_1 == game_object_id_2) continue;
+
+			// Fetch components for the second collider (circle)
+			Transform & transform2 = mgr.get_components_by_id<Transform>(circlecolliders[j].get().game_object_id).front().get();
+			if(!transform2.active) continue;
+			Rigidbody & rigidbody2 = mgr.get_components_by_id<Rigidbody>(circlecolliders[j].get().game_object_id).front().get();
+			if(!rigidbody2.active) continue;
+
+			// Check collision
+			if (check_box_circle_collision(boxcolliders[i], circlecolliders[j], transform1, transform2, rigidbody1, rigidbody2)) {
+				
+				collisions_ret.emplace_back(std::make_pair(
+				CollidedInfoStor{boxcolliders[i].get(), transform1, rigidbody1}, 
+				CollidedInfoStor{circlecolliders[j].get(), transform2, rigidbody2}
+				));
+			}
+		}
+	}
+	// Check CircleCollider vs CircleCollider
+	for (size_t i = 0; i < circlecolliders.size(); ++i) {
+		if(!circlecolliders[i].get().active) continue;
+		// Fetch components for the first circle collider
+		int game_object_id_1 = circlecolliders[i].get().game_object_id;
+		Transform & transform1 = mgr.get_components_by_id<Transform>(circlecolliders[i].get().game_object_id).front().get();
+		if(!transform1.active) continue;
+		Rigidbody & rigidbody1 = mgr.get_components_by_id<Rigidbody>(circlecolliders[i].get().game_object_id).front().get();
+		if(!rigidbody1.active) continue;
+
+		for (size_t j = i + 1; j < circlecolliders.size(); ++j) {
+			if(!circlecolliders[j].get().active) continue;
+			// Skip self collision
+			int game_object_id_2 = circlecolliders[j].get().game_object_id;
+			if (game_object_id_1 == game_object_id_2) continue;
+
+			// Fetch components for the second circle collider
+			Transform & transform2 = mgr.get_components_by_id<Transform>(circlecolliders[j].get().game_object_id).front().get();
+			if(!transform2.active) continue;
+			Rigidbody & rigidbody2 = mgr.get_components_by_id<Rigidbody>(circlecolliders[j].get().game_object_id).front().get();
+			if(!rigidbody2.active) continue;
+
+			// Check collision
+			if (check_circle_circle_collision(circlecolliders[i], circlecolliders[j], transform1, transform2, rigidbody1, rigidbody2)) {
+				collisions_ret.emplace_back(std::make_pair(
+				CollidedInfoStor{circlecolliders[i].get(), transform1, rigidbody1}, 
+				CollidedInfoStor{circlecolliders[j].get(), transform2, rigidbody2}
+				));
+			}
+		}
+	}
+	return collisions_ret;
+}
+
+bool CollisionSystem::check_box_box_collision(const BoxCollider& box1, const BoxCollider& box2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2)
+{
+	// Get current positions of colliders
+	Vector2 final_position1 = current_position(box1,transform1,rigidbody1);
+	Vector2 final_position2 = current_position(box2,transform2,rigidbody2);
+
+	// Calculate half-extents (half width and half height)
+	double half_width1 = box1.width / 2.0;
+	double half_height1 = box1.height / 2.0;
+	double half_width2 = box2.width / 2.0;
+	double half_height2 = box2.height / 2.0;
+
+	// Check if the boxes overlap along the X and Y axes
+	return !(final_position1.x + half_width1 <= final_position2.x - half_width2 ||  // box1 is left of box2
+						final_position1.x - half_width1 >= final_position2.x + half_width2 ||  // box1 is right of box2
+						final_position1.y + half_height1 <= final_position2.y - half_height2 || // box1 is above box2
+						final_position1.y - half_height1 >= final_position2.y + half_height2);  // box1 is below box2
+}
+
+bool CollisionSystem::check_box_circle_collision(const BoxCollider& box1, const CircleCollider& circle2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2) {
+	// Get current positions of colliders
+	Vector2 final_position1 = current_position(box1, transform1, rigidbody1);
+	Vector2 final_position2 = current_position(circle2, transform2, rigidbody2);
+
+	// Calculate box half-extents
+	double half_width = box1.width / 2.0;
+	double half_height = box1.height / 2.0;
+
+	// Find the closest point on the box to the circle's center
+	double closest_x = std::max(final_position1.x - half_width, std::min(final_position2.x, final_position1.x + half_width));
+	double closest_y = std::max(final_position1.y - half_height, std::min(final_position2.y, final_position1.y + half_height));
+
+	// Calculate the distance squared between the circle's center and the closest point on the box
+	double distance_x = final_position2.x - closest_x;
+	double distance_y = final_position2.y - closest_y;
+	double distance_squared = distance_x * distance_x + distance_y * distance_y;
+
+	// Compare distance squared with the square of the circle's radius
+	return distance_squared <= circle2.radius * circle2.radius;
+}
+
+bool CollisionSystem::check_circle_circle_collision(const CircleCollider& circle1, const CircleCollider& circle2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2) {
+	// Get current positions of colliders
+	Vector2 final_position1 = current_position(circle1,transform1,rigidbody1);
+	Vector2 final_position2 = current_position(circle2,transform2,rigidbody2);
+
+	double distance_x = final_position1.x - final_position2.x;
+	double distance_y = final_position1.y - final_position2.y;
+	double distance_squared = distance_x * distance_x + distance_y * distance_y;
+
+	// Calculate the sum of the radii
+	double radius_sum = circle1.radius + circle2.radius;
+
+	// Check if the distance between the centers is less than or equal to the sum of the radii
+	return distance_squared <= radius_sum * radius_sum;
+}
+
+Vector2 CollisionSystem::current_position(const Collider& collider, const Transform& transform, const Rigidbody& rigidbody) {
+	// Get the rotation in radians
+	double radians1 = transform.rotation * (M_PI / 180.0);
+
+	// Calculate total offset with scale
+	Vector2 total_offset = (rigidbody.data.offset + collider.offset) * transform.scale;
+
+	// Rotate
+	double rotated_total_offset_x1 = total_offset.x * cos(radians1) - total_offset.y * sin(radians1);
+	double rotated_total_offset_y1 = total_offset.x * sin(radians1) + total_offset.y * cos(radians1);
+
+	// Final positions considering scaling and rotation
+	return(transform.position + Vector2(rotated_total_offset_x1, rotated_total_offset_y1));
+
+}
diff --git a/src/crepe/system/CollisionSystem.h b/src/crepe/system/CollisionSystem.h
index c1a70d8..69d1d23 100644
--- a/src/crepe/system/CollisionSystem.h
+++ b/src/crepe/system/CollisionSystem.h
@@ -1,13 +1,193 @@
 #pragma once
 
+#include <vector>
+#include <variant>
+
+#include "api/Rigidbody.h"
+#include "api/Transform.h"
+#include "api/BoxCollider.h"
+#include "api/CircleCollider.h"
+#include "api/Vector2.h"
+
+#include "Collider.h"
 #include "System.h"
 
 namespace crepe {
 
+
+//! A system responsible for detecting and handling collisions between colliders.
 class CollisionSystem : public System {
 public:
 	using System::System;
+private:
+	
+	//! A variant type that can hold either a BoxCollider or a CircleCollider.
+	// using collider_stor = std::variant<BoxCollider, CircleCollider>;
+	using collider_stor = std::variant<std::reference_wrapper<BoxCollider>, std::reference_wrapper<CircleCollider>>;
+
+	/**
+		* \brief A structure to store the collision data of a single collider.
+		* 
+		* This structure stores the collider type, its associated transform, and its rigidbody.
+		*/
+	struct CollidedInfoStor {
+		//! Store either BoxCollider or CircleCollider
+		collider_stor collider; 
+		Transform& transform;
+		Rigidbody& rigidbody;
+	};
+	
+	//! Enum representing movement directions during collision resolution.
+	enum class Direction {
+    NONE,
+    X_DIRECTION,
+    Y_DIRECTION,
+    BOTH
+	};
+
+public:
+	/**
+		* \brief A structure representing the collision information between two colliders.
+		* 
+		* This structure contains both colliders, their associated transforms and rigidbodies,
+		* as well as the movement vector to resolve the collision.
+		*/
+	struct ColliderInfo {
+		const Collider& collider;
+		Transform& transform;
+		Rigidbody& rigidbody;
+	};
+	/**
+		* \brief A structure representing detailed collision information between two colliders.
+		* 
+		* This includes the movement data required to resolve the collision.
+		*/
+	struct CollisionInfo{
+    ColliderInfo first;
+    ColliderInfo second;
+		Vector2 move_back_value;
+		Direction move_back_direction = Direction::NONE;
+	};
+
+public:
+
+	//! Updates the collision system by checking for collisions between colliders and handling them.
 	void update() override;
+
+private:
+	/**
+		* \brief Handles a collision between two colliders.
+		* 
+		* This function calculates the necessary response to resolve the collision, including
+		* moving the objects back to prevent overlap and applying any velocity changes.
+		*
+		* \param data1 The collision data for the first collider.
+		* \param data2 The collision data for the second collider.
+		*/
+	void collision_handler(CollidedInfoStor& data1,CollidedInfoStor& data2);
+	
+	/**
+		* \brief Resolves the movement of two box colliders that are colliding.
+		* 
+		* This function calculates the smallest overlap (along the X or Y axis) and determines
+		* the move-back vector to prevent overlap.
+		*
+		* \param box_collider1 The first box collider.
+		* \param box_collider2 The second box collider.
+		* \param final_position1 The final position of the first box collider.
+		* \param final_position2 The final position of the second box collider.
+		* \return The move-back vector to resolve the collision.
+		*/
+	Vector2 box_box_collision_move_back(const BoxCollider& box_collider1,const BoxCollider& box_collider2,Vector2 position1,Vector2 position2);
+
+	/**
+		* \brief Determines the appropriate collision handler based on the rigidbody types of the colliding objects.
+		* 
+		* This function checks if the second object is static, and if so, it calls the static collision handler.
+		* Otherwise, it triggers a collision event.
+		*
+		* \param info The collision information containing the colliders, transforms, rigidbodies, and move-back data.
+		*/
+	void determine_collision_handler(CollisionInfo& info);
+
+	/**
+		* \brief Handles the collision with a static object.
+		* 
+		* This function resolves the collision by moving the object back and applying any bounce or stop behavior.
+		*
+		* \param info The collision information containing the colliders, transforms, rigidbodies, and move-back data.
+		*/
+	void static_collision_handler(CollisionInfo& info);
+private: //detection
+	
+	/**
+		* \brief Checks for collisions between box colliders and circle colliders
+		* and returns the collision pairs that need to be resolved.
+		* 
+		* \param boxcolliders A vector of references to all box colliders.
+		* \param circlecolliders A vector of references to all circle colliders.
+		* \return A vector of pairs containing collision information for the detected collisions.
+		*/
+	std::vector<std::pair<CollidedInfoStor,CollidedInfoStor>> check_collisions(const std::vector<std::reference_wrapper<BoxCollider>>& boxcolliders, const std::vector<std::reference_wrapper<CircleCollider>>& circlecolliders);
+	
+	/**
+		* \brief Checks for a collision between two box colliders.
+		* 
+		* This function checks if two box colliders overlap based on their positions and dimensions.
+		*
+		* \param box1 The first box collider.
+		* \param box2 The second box collider.
+		* \param transform1 The transform component of the first box collider.
+		* \param transform2 The transform component of the second box collider.
+		* \param rigidbody1 The rigidbody component of the first box collider.
+		* \param rigidbody2 The rigidbody component of the second box collider.
+		* \return True if the two box colliders overlap, otherwise false.
+		*/
+	bool check_box_box_collision(const BoxCollider& box1, const BoxCollider& box2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2);
+	
+	/**
+		* \brief Checks for a collision between a box collider and a circle collider.
+		* 
+		* This function checks if a box collider overlaps with a circle collider based on their positions
+		* and dimensions.
+		*
+		* \param box1 The box collider.
+		* \param circle2 The circle collider.
+		* \param transform1 The transform component of the box collider.
+		* \param transform2 The transform component of the circle collider.
+		* \param rigidbody1 The rigidbody component of the box collider.
+		* \param rigidbody2 The rigidbody component of the circle collider.
+		* \return True if the box collider and circle collider overlap, otherwise false.
+		*/
+	bool check_box_circle_collision(const BoxCollider& box1, const CircleCollider& circle2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2);
+	
+	/**
+		* \brief Checks for a collision between two circle colliders.
+		* 
+		* This function checks if two circle colliders overlap based on their positions and radii.
+		*
+		* \param circle1 The first circle collider.
+		* \param circle2 The second circle collider.
+		* \param transform1 The transform component of the first circle collider.
+		* \param transform2 The transform component of the second circle collider.
+		* \param rigidbody1 The rigidbody component of the first circle collider.
+		* \param rigidbody2 The rigidbody component of the second circle collider.
+		* \return True if the two circle colliders overlap, otherwise false.
+		*/
+	bool check_circle_circle_collision(const CircleCollider& circle1, const CircleCollider& circle2, const Transform& transform1, const Transform& transform2, const Rigidbody& rigidbody1, const Rigidbody& rigidbody2);
+	
+	/**
+		* \brief Gets the current position of a collider by combining its transform and rigidbody data.
+		* 
+		* This function calculates the current position of the collider by considering its transform and 
+		* rigidbody velocity.
+		*
+		* \param collider The collider whose position is being determined.
+		* \param transform The transform component associated with the collider.
+		* \param rigidbody The rigidbody component associated with the collider.
+		* \return The current position of the collider as a Vector2.
+		*/
+	Vector2 current_position(const Collider& collider, const Transform& transform, const Rigidbody& rigidbody);
 };
 
 } // namespace crepe
diff --git a/src/crepe/system/RenderSystem.cpp b/src/crepe/system/RenderSystem.cpp
index ad510f5..8f9467e 100644
--- a/src/crepe/system/RenderSystem.cpp
+++ b/src/crepe/system/RenderSystem.cpp
@@ -28,6 +28,8 @@ void RenderSystem::update_camera() {
 
 	if (cameras.size() == 0) throw std::runtime_error("No cameras in current scene");
 
+	if (cameras.size() == 0) throw std::runtime_error("No cameras in current scene");
+
 	for (Camera & cam : cameras) {
 		if (!cam.active) continue;
 		this->context.set_camera(cam);