Flycam physics: make it linear (remove drag), use meaningful parameters

src/camera.rs

@@ -2,6 +2,8 @@ use glam::{Mat4, Quat, Vec2, Vec3};
 use std::time::Instant;
 use winit::event::{ElementState, VirtualKeyCode};
 
+const LN2: f32 = 0.6931472;  // TODO figure out how to use lazy_static! or something
+
 pub trait Camera {
     fn get_eye(&self) -> [f32; 4];
     fn get_vp(&self) -> [[f32; 4]; 4];
@@ -28,8 +30,7 @@ pub struct Flycam {
     // constants
     turn_sensitivity: f32,
     thrust_mag: f32,
-    friction_coeff: f32,
-    drag_coeff: f32,
+    damping_coeff: f32,
     aspect: f32,
     fovy: f32,
     znear: f32,
@@ -37,7 +38,9 @@ pub struct Flycam {
 }
 
 impl Flycam {
-    pub fn new(turn_sensitivity: f32, thrust_mag: f32, friction_coeff: f32, drag_coeff: f32) -> Self {
+    /// thrust_speed: top speed when using a single thruster, in units/second
+    /// duration to halve difference between current and target velocity, in seconds
+    pub fn new(turn_sensitivity: f32, thrust_speed: f32, damper_half_life: f32) -> Self {
         Self {
             is_world_up_pressed: false,
             is_world_down_pressed: false,
@@ -55,9 +58,8 @@ impl Flycam {
             velocity: Vec3::new(0.0, 0.0, 0.0),
             position: Vec3::new(0.0, 0.5, 1.0),
             turn_sensitivity,
-            thrust_mag,
-            friction_coeff,
-            drag_coeff,
+            thrust_mag: thrust_speed / damper_half_life * LN2,
+            damping_coeff: LN2 / damper_half_life,
             aspect: 1.0, // TODO compute from size
             fovy: std::f32::consts::FRAC_PI_2,
             znear: 0.01,
@@ -135,7 +137,8 @@ impl Flycam {
     }
 
     fn update_kinematic(&mut self, dt: f32) {
-        let net_acc = self.get_thrust_acc() + self.get_friction_acc() + self.get_drag_acc();
+        /// update velocity and position from acceleration using forward differences
+        let net_acc = self.get_thrust_acc() + self.get_damping_acc();
 
         let delta_vel = net_acc * dt;
         self.velocity += delta_vel;
@@ -161,12 +164,8 @@ impl Flycam {
         self.thrust_mag * thrusters_total
     }
 
-    fn get_friction_acc(&self) -> glam::Vec3 {
-        self.friction_coeff * -self.velocity
-    }
-
-    fn get_drag_acc(&self) -> glam::Vec3 {
-        0.5 * self.drag_coeff * -self.velocity * self.velocity.length()
+    fn get_damping_acc(&self) -> glam::Vec3 {
+        self.damping_coeff * -self.velocity
     }
 
     fn key_axis(negative: bool, positive: bool) -> f32 {

src/main.rs

@@ -149,7 +149,7 @@ async fn make_window_renderer(window: &winit::window::Window) -> Renderer {
 fn main() {
     let event_loop = EventLoop::new();
     let window = WindowBuilder::new().build(&event_loop).unwrap();
-    let mut camera = Flycam::new(0.002, 50.0, 5.0, 5.0);
+    let mut camera = Flycam::new(0.002, 10.0, 0.25);
     let mut is_grabbed = false;
     let mut ren = pollster::block_on(make_window_renderer(&window));
     // let mut state: Box<dyn WorldState> = Box::new(Planets::new(&mut ren));