camera accelerating like in unity and faster/slower with modifier keys

include/camera.hpp

@@ -9,6 +9,8 @@ class Camera : private MouseListener {
 private:
 	glm::vec3 position {0, 0, 5};
 
+	float velocityMultiplier = 0;
+
 	float phi = 0;
 	float theta = 0;
 

src/camera.cpp

@@ -14,13 +14,26 @@ const std::map<int, glm::vec3> moveDirections {
 };
 
 void Camera::update(float dt) {
-	glm::vec3 add {};
+	glm::vec3 velocity {};
 
 	for (const auto &[key, dir] : moveDirections)
 		if (Input::KeyIsDown[key])
-			add += dir;
+			velocity += dir;
 
-	position += localToWorld(add) * dt;
+	if (velocity == glm::vec3(0))
+		velocityMultiplier = 0;
+
+	const float baseModifier = 3;
+	float modifier = 1;
+	if (Input::KeyIsDown[GLFW_KEY_LEFT_SHIFT])
+		modifier *= baseModifier;
+	if (Input::KeyIsDown[GLFW_KEY_LEFT_CONTROL])
+		modifier /= baseModifier;
+
+	velocityMultiplier += modifier * dt;
+	velocity *= (1 + velocityMultiplier) * modifier;
+
+	position += localToWorld(velocity) * dt;
 }
 
 glm::mat4 Camera::view() const {