fix gravity

Author: julerex

server/src/main.rs

@@ -127,8 +127,9 @@ async fn main() -> anyhow::Result<()> {
         loop {
             interval.tick().await;
             let mut game = game_state_for_physics.write().await;
-            // Step physics with delta time of 1/60 second
-            game.step_physics(1.0 / 60.0);
+            // Step physics with delta time of 1.0 game second
+            // Each real-time step (1/60 second) represents 1 game second (60x time scale)
+            game.step_physics(1.0);
         }
     });
 

server/src/physics.rs

@@ -127,11 +127,15 @@ impl PhysicsWorld {
             impulse_joint_set: ImpulseJointSet::new(),
             multibody_joint_set: MultibodyJointSet::new(),
             ccd_solver: CCDSolver::new(),
-            // Earth gravity scaled for 60x time scale (1 real second = 60 game seconds)
-            // Base gravity: 9.81 m/s² = 981 cm/s²
-            // Scaled by 60² = 3600 (since acceleration = distance/time²)
-            gravity: vector![0.0, -981.0 * 3600.0, 0.0], // 3,531,600 cm/s² in game time
-            integration_parameters: IntegrationParameters::default(),
+            // Earth gravity: 9.81 m/s² = 981 cm/s²
+            // Physics steps represent game time (1 step = 1 game second), so use normal gravity
+            gravity: vector![0.0, -981.0, 0.0], // 981 cm/s²
+            integration_parameters: IntegrationParameters {
+                // Each physics step represents 1 game second (60x time scale)
+                // Real-time step is 1/60 second, but we simulate 1 game second per step
+                dt: 1.0, // 1 game second per step
+                ..IntegrationParameters::default()
+            },
             entity_handles: HashMap::new(),
         }
     }
@@ -152,10 +156,10 @@ impl PhysicsWorld {
         use rand::Rng;
 
         // Random initial velocity for trajectory variation
-        // Scaled by 60 for 60x time scale (1 real second = 60 game seconds)
+        // Velocities are in game-time units (cm/game-second)
         let mut rng = rand::thread_rng();
-        let vel_x = rng.gen_range(-100.0..100.0) * 60.0;
-        let vel_z = rng.gen_range(-100.0..100.0) * 60.0;
+        let vel_x = rng.gen_range(-100.0..100.0);
+        let vel_z = rng.gen_range(-100.0..100.0);
         let vel_y = 0.0; // Zero vertical velocity
 
         let rigid_body = RigidBodyBuilder::dynamic()
@@ -248,11 +252,11 @@ impl PhysicsWorld {
                 if let Some(body) = self.rigid_body_set.get_mut(*handle) {
                     let mut linvel = *body.linvel();
                     // Random perturbation to velocity for trajectory variation
-                    // Scaled by 60 for 60x time scale
+                    // Velocities are in game-time units (cm/game-second)
                     if linvel.y < 6.0 && linvel.y > -6.0 {
                         // Near ground, add random horizontal component to maintain speed
-                        linvel.x += rng.gen_range(-20.0..20.0) * 60.0;
-                        linvel.z += rng.gen_range(-20.0..20.0) * 60.0;
+                        linvel.x += rng.gen_range(-20.0..20.0);
+                        linvel.z += rng.gen_range(-20.0..20.0);
                         body.set_linvel(linvel, true);
                     }
                 }