Timestep independence, finally

.nvim.lua

@@ -0,0 +1,2 @@
+vim.opt_global.makeprg = "./build_hot_reload.sh"
+vim.opt.errorformat = "%f(%l:%c)\\ %m"

game/game.odin

@@ -62,7 +62,7 @@ Car :: struct {
 }
 
 SOLVER_CONFIG :: physics.Solver_Config {
-	timestep            = 1.0 / 120,
+	timestep            = 1.0 / 104,
 	gravity             = rl.Vector3{0, -9.8, 0},
 	substreps_minus_one = 4 - 1,
 }
@@ -245,20 +245,20 @@ update_runtime_world :: proc(runtime_world: ^Runtime_World, dt: f32) {
 			},
 		)
 
-		car_body := physics.get_body(&world.physics_scene, runtime_world.car_handle)
+		// car_body := physics.get_body(&world.physics_scene, runtime_world.car_handle)
 
 		camera := &runtime_world.camera
 
 		camera.up = rl.Vector3{0, 1, 0}
 		camera.fovy = 60
 		camera.projection = .PERSPECTIVE
-		camera.position = physics.body_local_to_world(
-			car_body,
-			physics.body_world_to_local(
-				car_body,
-				physics.body_local_to_world(car_body, rl.Vector3{1, 0, -2}),
-			),
-		)
+		// camera.position = physics.body_local_to_world(
+		// 	car_body,
+		// 	physics.body_world_to_local(
+		// 		car_body,
+		// 		physics.body_local_to_world(car_body, rl.Vector3{1, 0, -2}),
+		// 	),
+		// )
 		camera.target = physics.get_body(&world.physics_scene, runtime_world.car_handle).x
 		if runtime_world.camera.position == {} {
 			runtime_world.camera.position = runtime_world.camera.target - rl.Vector3{10, 0, 10}
@@ -333,8 +333,8 @@ update_runtime_world :: proc(runtime_world: ^Runtime_World, dt: f32) {
 		drive_wheels := []physics.Suspension_Constraint_Handle{wheel_rl, wheel_rr}
 		turn_wheels := []physics.Suspension_Constraint_Handle{wheel_fl, wheel_fr}
 
-		DRIVE_IMPULSE :: 1
-		BRAKE_IMPULSE :: 2
+		DRIVE_IMPULSE :: 20
+		BRAKE_IMPULSE :: 50
 		TURN_ANGLE :: -f32(30) * math.RAD_PER_DEG
 
 		for wheel_handle in drive_wheels {
@@ -520,7 +520,12 @@ draw :: proc() {
 			car_matrix := rl.QuaternionToMatrix(car_body.q)
 			car_model.transform = car_matrix
 
-			rl.DrawModel(car_model, car_body.x + runtime_world.car_com, 1, rl.WHITE)
+			rl.DrawModel(
+				car_model,
+				physics.body_local_to_world(car_body, -runtime_world.car_com),
+				1,
+				rl.WHITE,
+			)
 		} else {
 			if g_mem.draw_car {
 				rl.DrawModel(car_model, 0, 1, rl.WHITE)
@@ -572,6 +577,8 @@ draw :: proc() {
 		rl.BeginMode2D(ui_camera())
 		defer rl.EndMode2D()
 
+		rl.DrawFPS(0, 0)
+
 		if g_mem.editor {
 			rl.DrawText("Editor", 5, 5, 8, rl.ORANGE)
 
@@ -782,7 +789,7 @@ game_init_window :: proc() {
 	rl.InitWindow(1280, 720, "Odin + Raylib + Hot Reload template!")
 	rl.SetExitKey(.KEY_NULL)
 	rl.SetWindowPosition(200, 200)
-	rl.SetTargetFPS(60)
+	rl.SetTargetFPS(120)
 }
 
 @(export)

game/physics/simulation.odin

@@ -48,7 +48,7 @@ simulate :: proc(scene: ^Scene, state: ^Solver_State, config: Solver_Config, dt:
 	state.accumulated_time += dt
 
 	num_steps := 0
-	for state.accumulated_time > config.timestep {
+	for state.accumulated_time >= config.timestep {
 		num_steps += 1
 		state.accumulated_time -= config.timestep
 
@@ -135,17 +135,21 @@ simulate_step :: proc(scene: ^Scene, config: Solver_Config) {
 		for _, i in scene.suspension_constraints {
 			v := &scene.suspension_constraints_slice[i]
 			if v.alive {
+				body_idx := int(v.body) - 1
 				body := get_body(scene, v.body)
 
 				if body.alive && v.hit {
+					prev_x, prev_q := body_states[body_idx].prev_x, body_states[body_idx].prev_q
+
 					wheel_world_pos := body_local_to_world(body, v.rel_pos)
+					prev_wheel_world_pos := prev_x + lg.quaternion_mul_vector3(prev_q, v.rel_pos)
+
+					vel_3d := (wheel_world_pos - prev_wheel_world_pos) * inv_dt
 					dir := body_local_to_world_vec(body, v.rel_dir)
 					body_state := body_states[i32(v.body) - 1]
 
 					// Spring damping
 					if true {
-						vel_3d := body_velocity_at_local_point(body, wheel_world_pos - body.x)
-
 						vel := lg.dot(vel_3d, dir)
 						damping := -vel * min(v.damping * dt, 1)
 
@@ -166,8 +170,6 @@ simulate_step :: proc(scene: ^Scene, config: Solver_Config) {
 						total_impulse := v.drive_impulse - v.brake_impulse
 						forward := body_local_to_world_vec(body, rl.Vector3{0, 0, 1})
 
-						corr := total_impulse * forward * dt
-
 						apply_constraint_correction_unilateral(
 							dt,
 							body,
@@ -176,7 +178,6 @@ simulate_step :: proc(scene: ^Scene, config: Solver_Config) {
 							forward,
 							wheel_world_pos,
 						)
-						apply_correction(body, corr, wheel_world_pos)
 						body_solve_velocity(body, body_state, inv_dt)
 					}