Start implementing engine simulation

assets/ae86_rpm_torque.csv

@@ -0,0 +1,63 @@
+rpm,torque
+1000,63.6
+1100,72.3
+1200,79.5
+1300,85.7
+1400,90.9
+1500,95.5
+1600,99.4
+1700,102.9
+1800,106.1
+1900,108.9
+2000,111.4
+2100,113.6
+2200,115.7
+2300,117.6
+2400,119.3
+2500,120.9
+2600,122.4
+2700,123.7
+2800,125
+2900,126.2
+3000,127.3
+3100,128.3
+3200,129.3
+3300,130.2
+3400,131
+3500,131.8
+3600,132.6
+3700,133.3
+3800,134
+3900,134.6
+4000,135.2
+4100,135.8
+4200,136.4
+4300,136.9
+4400,137.4
+4500,137.9
+4600,138.3
+4700,138.8
+4800,139.2
+4900,139.6
+5000,140
+5100,140
+5200,139.8
+5300,139.6
+5400,139.3
+5500,138.9
+5600,138.4
+5700,137.8
+5800,137.2
+5900,136.4
+6000,135.6
+6100,134.7
+6200,133.7
+6300,132.6
+6400,131.4
+6500,130.1
+6600,128.8
+6700,126.3
+6800,123
+6900,118.7
+7000,113.6
+7100,107.7

game/assets/assets.odin

@@ -1,9 +1,6 @@
 package assets
 
-import "core:bytes"
 import "core:c"
-import "core:encoding/csv"
-import "core:io"
 import "core:log"
 import "core:math"
 import lg "core:math/linalg"
@@ -194,57 +191,12 @@ get_curve_2d :: proc(assetman: ^Asset_Manager, path: string) -> (curve: Loaded_C
 		return
 	}
 
-	bytes_reader: bytes.Reader
+	err2: Curve_Parse_Error
-	bytes.reader_init(&bytes_reader, data)
+	curve, err2 = parse_curve_2d(data, context.temp_allocator)
-	bytes_stream := bytes.reader_to_stream(&bytes_reader)
 
-	csv_reader: csv.Reader
+	if err2 != nil {
-	csv.reader_init(&csv_reader, bytes_stream, context.temp_allocator)
+		log.errorf("Failed to parse curve: %s, %v", path, err2)
-
-	tmp_result := make([dynamic][2]f32, context.temp_allocator)
-
-	skipped_header := false
-	for {
-		row, err := csv.read(&csv_reader, context.temp_allocator)
-		if err != nil {
-			if err != io.Error.EOF {
-				log.errorf("Failed to read curve %v", err)
 	}
-			break
-		}
-
-		if len(row) != 2 {
-			log.errorf("Curve expected 2 columns, got %v", len(row))
-			break
-		}
-
-		ok: bool
-		key: f64
-		val: f64
-		key, ok = strconv.parse_f64(row[0])
-		if !ok {
-			if skipped_header {
-				log.errorf("Curve expected numbers, got %s", row[0])
-				break
-			}
-			skipped_header = true
-			continue
-		}
-		val, ok = strconv.parse_f64(row[1])
-		if !ok {
-			if skipped_header {
-				log.errorf("Curve expected numbers, got %s", row[1])
-				break
-			}
-			skipped_header = true
-			continue
-		}
-
-		append(&tmp_result, [2]f32{f32(key), f32(val)})
-	}
-
-	curve.points = make([][2]f32, len(tmp_result), context.temp_allocator)
-	copy(curve.points, tmp_result[:])
 
 	return
 }

game/assets/assets_test.odin

@@ -0,0 +1,42 @@
+package assets
+
+import "core:testing"
+
+@(private = "file")
+test_csv := `
+rpm,torque
+1000,100
+2000,110.5
+5000,354.123
+`
+
+
+@(private = "file")
+test_invalid_csv := `
+rpm,torque
+rpm,torque
+1000,100
+2000,110.5
+5000,354.123
+`
+
+
+@(test)
+test_curve_parsing :: proc(t: ^testing.T) {
+	curve, err := parse_curve_2d(transmute([]u8)test_csv, context.temp_allocator)
+
+	testing.expect_value(t, err, nil)
+	testing.expect_value(t, len(curve.points), 3)
+	testing.expect_value(t, curve.points[0], [2]f32{1000, 100})
+	testing.expect_value(t, curve.points[1], [2]f32{2000, 110.5})
+	testing.expect_value(t, curve.points[2], [2]f32{5000, 354.123})
+}
+
+@(test)
+test_curve_parsing_error :: proc(t: ^testing.T) {
+	curve, err := parse_curve_2d(transmute([]u8)test_invalid_csv, context.temp_allocator)
+	defer free_all(context.temp_allocator)
+
+	testing.expect_value(t, err, Curve_Parse_Error.ExpectedNumber)
+	testing.expect_value(t, len(curve.points), 0)
+}

game/assets/parsers.odin

@@ -0,0 +1,79 @@
+package assets
+
+import "core:bytes"
+import "core:encoding/csv"
+import "core:io"
+import "core:log"
+import "core:strconv"
+
+Curve_Parse_Error :: enum {
+	Ok,
+	TooManyColumns,
+	ExpectedNumber,
+}
+
+parse_curve_2d :: proc(
+	data: []byte,
+	allocator := context.allocator,
+) -> (
+	curve: Loaded_Curve_2D,
+	error: Curve_Parse_Error,
+) {
+	bytes_reader: bytes.Reader
+	bytes.reader_init(&bytes_reader, data)
+	bytes_stream := bytes.reader_to_stream(&bytes_reader)
+
+	csv_reader: csv.Reader
+	csv.reader_init(&csv_reader, bytes_stream, context.temp_allocator)
+	defer csv.reader_destroy(&csv_reader)
+
+	tmp_result := make([dynamic][2]f32, context.temp_allocator)
+
+	skipped_header := false
+	for {
+		row, err := csv.read(&csv_reader, context.temp_allocator)
+		if err != nil {
+			if err != io.Error.EOF {
+				log.warnf("Failed to read curve %v", err)
+			}
+			break
+		}
+
+		if len(row) != 2 {
+			log.warnf("Curve expected 2 columns, got %v", len(row))
+			error = .TooManyColumns
+			break
+		}
+
+		ok: bool
+		key: f64
+		val: f64
+		key, ok = strconv.parse_f64(row[0])
+		if !ok {
+			if skipped_header {
+				log.warnf("Curve expected numbers, got %s", row[0])
+				error = .ExpectedNumber
+				break
+			}
+			skipped_header = true
+			continue
+		}
+		val, ok = strconv.parse_f64(row[1])
+		if !ok {
+			if skipped_header {
+				log.warnf("Curve expected numbers, got %s", row[1])
+				error = .ExpectedNumber
+				break
+			}
+			skipped_header = true
+			continue
+		}
+
+		append(&tmp_result, [2]f32{f32(key), f32(val)})
+	}
+
+	curve.points = make([][2]f32, len(tmp_result), allocator)
+	copy(curve.points, tmp_result[:])
+
+	return
+}

game/fs.odin

@@ -15,7 +15,9 @@ init_physfs :: proc(args: []string) {
 
 	physfs.init(strings.clone_to_cstring(args[0], context.temp_allocator))
 	physfs.setSaneConfig("serega", "gutter-runner", "zip", 0, 1)
+}
 
+init_physifs_raylib_callbacks :: proc() {
 	rl.SetLoadFileDataCallback(raylib_load_file_data_physfs)
 	rl.SetSaveFileDataCallback(raylib_save_file_data_physfs)
 	rl.SetLoadFileTextCallback(raylib_load_file_text_physfs)

game/game.odin

@@ -394,6 +394,25 @@ update_runtime_world :: proc(runtime_world: ^Runtime_World, dt: f32) {
 			},
 		)
 
+		engine := physics.immediate_engine(
+			&world.physics_scene,
+			&runtime_world.solver_state,
+			#hash("engine", "fnv32a"),
+			physics.Engine_Config {
+				rpm_torque_curve = assets.get_curve_2d(&g_mem.assetman, "assets/ae86_rpm_torque.csv").points,
+				lowest_rpm = 1000,
+				inertia = 10,
+				internal_friction = 8,
+				gear_ratios = []f32{3.48, 3.587, 2.022, 1.384, 1, 0.861},
+				axle = physics.Drive_Axle_Config {
+					wheels = {wheel_rl, wheel_rr},
+					wheel_count = 2,
+					diff_type = .Fixed,
+					final_drive_ratio = 4.3,
+				},
+			},
+		)
+
 		drive_wheels := []physics.Suspension_Constraint_Handle{wheel_rl, wheel_rr}
 		turn_wheels := []physics.Suspension_Constraint_Handle{wheel_fl, wheel_fr}
 		front_wheels := turn_wheels
@@ -426,11 +445,7 @@ update_runtime_world :: proc(runtime_world: ^Runtime_World, dt: f32) {
 			wheel.brake_impulse = brake_input * (1.0 - BRAKE_BIAS) * BRAKE_IMPULSE
 		}
 
-		for wheel_handle in drive_wheels {
+		physics.get_engine(sim_state, engine).throttle = gas_input
-			wheel := physics.get_suspension_constraint(sim_state, wheel_handle)
-
-			wheel.drive_impulse = gas_input * DRIVE_IMPULSE
-		}
 
 		car_body := physics.get_body(sim_state, runtime_world.car_handle)
 		turn_vel_correction := clamp(30.0 / linalg.length(car_body.v), 0, 1)
@@ -1040,6 +1055,8 @@ game_init :: proc() {
 
 	g_mem^ = Game_Memory{}
 
+	init_physifs_raylib_callbacks()
+
 	physics.init_physics_scene(&g_mem.runtime_world.world.physics_scene, 100)
 
 	game_hot_reloaded(g_mem)

game/physics/helpers.odin

@@ -1,6 +1,7 @@
 package physics
 
 import "collision"
+import "core:math"
 import lg "core:math/linalg"
 import "game:halfedge"
 
@@ -150,3 +151,11 @@ body_get_aabb :: proc(body: Body_Ptr) -> (aabb: AABB) {
 
 	return aabb
 }
+
+rpm_to_angular_velocity :: proc(rpm: f32) -> f32 {
+	return 2.0 * math.PI * (rpm / 60.0)
+}
+
+angular_velocity_to_rpm :: proc(w: f32) -> f32 {
+	return (w / (2.0 * math.PI)) * 60.0
+}

game/physics/immediate.odin

@@ -71,10 +71,40 @@ immediate_suspension_constraint :: proc(
 	return
 }
 
+immediate_engine :: proc(
+	scene: ^Scene,
+	state: ^Solver_State,
+	id: u32,
+	config: Engine_Config,
+) -> (
+	handle: Engine_Handle,
+) {
+	sim_state := get_sim_state(scene)
+	if id in state.immediate_engines {
+		engine := &state.immediate_engines[id]
+		if engine.last_ref != state.simulation_frame {
+			engine.last_ref = state.simulation_frame
+			state.num_referenced_engines += 1
+		}
+		handle = engine.handle
+		update_engine_from_config(sim_state, get_engine(sim_state, handle), config)
+	} else {
+		state.num_referenced_engines += 1
+		handle = add_engine(sim_state, config)
+		state.immediate_engines[id] = {
+			handle   = handle,
+			last_ref = state.simulation_frame,
+		}
+	}
+
+	return
+}
+
 prune_immediate :: proc(scene: ^Scene, state: ^Solver_State) {
 	tracy.Zone()
 	prune_immediate_bodies(scene, state)
 	prune_immediate_suspension_constraints(scene, state)
+	prune_immediate_engines(scene, state)
 }
 
 // TODO: Generic version
@@ -134,3 +164,30 @@ prune_immediate_suspension_constraints :: proc(scene: ^Scene, state: ^Solver_Sta
 		remove_suspension_constraint(get_sim_state(scene), handle)
 	}
 }
+
+prune_immediate_engines :: proc(scene: ^Scene, state: ^Solver_State) {
+	if int(state.num_referenced_engines) == len(state.immediate_engines) {
+		return
+	}
+
+	num_unreferenced_engines := len(state.immediate_engines) - int(state.num_referenced_engines)
+	assert(num_unreferenced_engines >= 0)
+
+	engines_to_remove := make([]u32, num_unreferenced_engines, context.temp_allocator)
+
+	i := 0
+	for k, &v in state.immediate_engines {
+		if v.last_ref != state.simulation_frame {
+			engines_to_remove[i] = k
+			i += 1
+		}
+	}
+
+	assert(i == len(engines_to_remove))
+
+	for k in engines_to_remove {
+		handle := state.immediate_engines[k].handle
+		delete_key(&state.immediate_engines, k)
+		remove_engine(get_sim_state(scene), handle)
+	}
+}

game/physics/scene.odin

@@ -2,6 +2,7 @@ package physics
 
 import "collision"
 import lg "core:math/linalg"
+import "game:container/spanpool"
 
 MAX_CONTACTS :: 1024 * 16
 
@@ -43,18 +44,26 @@ contact_container_copy :: proc(dst: ^Contact_Container, src: Contact_Container)
 Sim_State :: struct {
 	bodies:                                    #soa[dynamic]Body,
 	suspension_constraints:                    #soa[dynamic]Suspension_Constraint,
+	engines:                                   [dynamic]Engine,
 	// Number of alive bodies
 	num_bodies:                                i32,
+	num_engines:                               i32,
 
 	// Slices. When you call get_body or get_suspension_constraint you will get a pointer to an element in this slice
 	bodies_slice:                              #soa[]Body,
 	suspension_constraints_slice:              #soa[]Suspension_Constraint,
 	first_free_body_plus_one:                  i32,
 	first_free_suspension_constraint_plus_one: i32,
+	first_free_engine_plus_one:                i32,
 
 	// Persistent stuff for simulation
 	contact_container:                         Contact_Container,
 	convex_container:                          Convex_Container,
+
+	// NOTE: kinda overkill, but it simplifies copying sim states around a lot
+	// Engine array data
+	rpm_torque_curves_pool:                    spanpool.Span_Pool([2]f32),
+	gear_ratios_pool:                          spanpool.Span_Pool(f32),
 }
 
 Scene :: struct {
@@ -167,12 +176,80 @@ Suspension_Constraint :: struct {
 	next_plus_one:          i32,
 }
 
+Diff_Type :: enum {
+	Fixed,
+	// TODO: LSD
+}
+
+Drive_Wheel :: struct {
+	wheel:   Suspension_Constraint_Handle,
+	impulse: f32,
+}
+
+Drive_Axle :: struct {
+	// Params
+	wheels:            [2]Drive_Wheel,
+	wheel_count:       i32,
+	diff_type:         Diff_Type,
+	final_drive_ratio: f32,
+
+	// State
+	// Diff angular vel
+	w:                 f32,
+	// Impulse that constrains diff and engine motion
+	engine_impulse:    f32,
+	// Impulse that constrains wheels motion relative to each other
+	diff_impulse:      f32,
+}
+
+Engine_Curve_Handle :: distinct spanpool.Handle
+Gear_Ratios_Handle :: distinct spanpool.Handle
+
+// This actually handles everything, engine, transmission, differential, etc. It's easier to keep it in one place
+Engine :: struct {
+	alive:             bool,
+	// Engine Params
+	rpm_torque_curve:  Engine_Curve_Handle,
+	lowest_rpm:        f32,
+	inertia:           f32,
+	internal_friction: f32,
+
+	// Transmission Params
+	// 0 - reverse, 1 - first, etc.
+	gear_ratios:       Gear_Ratios_Handle,
+	axle:              Drive_Axle,
+
+	// Engine State
+	// Angular velocity, omega
+	q:                 f32,
+	w:                 f32,
+
+	// Impulse applied when engine is stalling (rpm < lowest_rpm)
+	unstall_impulse:   f32,
+	// Friction that makes rpm go down when you're not accelerating
+	friction_impulse:  f32,
+	// Impulse applied from releasing throttle
+	throttle_impulse:  f32,
+
+	// Transmission State
+	// -1 - reeverse, 0 - neutral, 1 - first, etc.
+	gear:              i32,
+
+	// Controls
+	throttle:          f32,
+
+	// Free list
+	next_plus_one:     i32,
+}
+
 // Index plus one, so handle 0 maps to invalid body
 Body_Handle :: distinct i32
 Suspension_Constraint_Handle :: distinct i32
+Engine_Handle :: distinct i32
 
 INVALID_BODY :: Body_Handle(0)
 INVALID_SUSPENSION_CONSTRAINT :: Suspension_Constraint_Handle(0)
+INVALID_ENGINE :: Engine_Handle(0)
 
 is_body_handle_valid :: proc(handle: Body_Handle) -> bool {
 	return i32(handle) > 0
@@ -180,13 +257,18 @@ is_body_handle_valid :: proc(handle: Body_Handle) -> bool {
 is_suspension_constraint_handle_valid :: proc(handle: Suspension_Constraint_Handle) -> bool {
 	return i32(handle) > 0
 }
+is_engine_handle_valid :: proc(handle: Engine_Handle) -> bool {
+	return i32(handle) > 0
+}
 is_handle_valid :: proc {
 	is_body_handle_valid,
 	is_suspension_constraint_handle_valid,
+	is_engine_handle_valid,
 }
 
 Body_Ptr :: #soa^#soa[]Body
 Suspension_Constraint_Ptr :: #soa^#soa[]Suspension_Constraint
+Engine_Ptr :: ^Engine
 
 _invalid_body: #soa[1]Body
 _invalid_body_slice := _invalid_body[:]
@@ -264,6 +346,25 @@ Suspension_Constraint_Config :: struct {
 	mass:              f32,
 }
 
+Drive_Axle_Config :: struct {
+	wheels:            [2]Suspension_Constraint_Handle,
+	wheel_count:       i32,
+	diff_type:         Diff_Type,
+	final_drive_ratio: f32,
+}
+
+Engine_Config :: struct {
+	rpm_torque_curve:  [][2]f32,
+	lowest_rpm:        f32,
+	inertia:           f32,
+	internal_friction: f32,
+
+	// Transmission Params
+	// 0 - reverse, 1 - first, etc.
+	gear_ratios:       []f32,
+	axle:              Drive_Axle_Config,
+}
+
 calculate_body_params_from_config :: proc(
 	config: Body_Config,
 ) -> (
@@ -335,6 +436,53 @@ update_suspension_constraint_from_config :: proc(
 	constraint.inv_inertia = 1.0 / (0.5 * config.mass * config.radius * config.radius)
 }
 
+add_engine_curve :: proc(sim_state: ^Sim_State, curve: [][2]f32) -> Engine_Curve_Handle {
+	handle := spanpool.allocate_elems(&sim_state.rpm_torque_curves_pool, ..curve)
+	return Engine_Curve_Handle(handle)
+}
+
+remove_engine_curve :: proc(sim_state: ^Sim_State, handle: Engine_Curve_Handle) {
+	spanpool.free(&sim_state.rpm_torque_curves_pool, spanpool.Handle(handle))
+}
+
+get_engine_curve :: proc(sim_state: ^Sim_State, handle: Engine_Curve_Handle) -> [][2]f32 {
+	return spanpool.resolve_slice(&sim_state.rpm_torque_curves_pool, spanpool.Handle(handle))
+}
+
+add_gear_ratios :: proc(sim_state: ^Sim_State, gear_ratios: []f32) -> Gear_Ratios_Handle {
+	handle := spanpool.allocate_elems(&sim_state.gear_ratios_pool, ..gear_ratios)
+	return Gear_Ratios_Handle(handle)
+}
+
+remove_gear_ratios :: proc(sim_state: ^Sim_State, handle: Gear_Ratios_Handle) {
+	spanpool.free(&sim_state.gear_ratios_pool, spanpool.Handle(handle))
+}
+
+get_gear_ratios :: proc(sim_state: ^Sim_State, handle: Gear_Ratios_Handle) -> []f32 {
+	return spanpool.resolve_slice(&sim_state.gear_ratios_pool, spanpool.Handle(handle))
+}
+
+update_engine_from_config :: proc(
+	sim_state: ^Sim_State,
+	engine: Engine_Ptr,
+	config: Engine_Config,
+) {
+	remove_engine_curve(sim_state, engine.rpm_torque_curve)
+	engine.rpm_torque_curve = add_engine_curve(sim_state, config.rpm_torque_curve)
+
+	remove_gear_ratios(sim_state, engine.gear_ratios)
+	engine.gear_ratios = add_gear_ratios(sim_state, config.gear_ratios)
+
+	engine.lowest_rpm = config.lowest_rpm
+	engine.inertia = config.inertia
+	engine.internal_friction = config.internal_friction
+
+	engine.axle.final_drive_ratio = config.axle.final_drive_ratio
+	engine.axle.wheels[0].wheel = config.axle.wheels[0]
+	engine.axle.wheels[1].wheel = config.axle.wheels[1]
+	engine.axle.wheel_count = config.axle.wheel_count
+	engine.axle.diff_type = config.axle.diff_type
+}
 
 add_body :: proc(sim_state: ^Sim_State, config: Body_Config) -> Body_Handle {
 	body: Body
@@ -425,6 +573,54 @@ remove_suspension_constraint :: proc(sim_state: ^Sim_State, handle: Suspension_C
 	}
 }
 
+invalid_engine: Engine
+
+get_engine :: proc(sim_state: ^Sim_State, handle: Engine_Handle) -> Engine_Ptr {
+	index := int(handle) - 1
+	if index < 0 || index >= len(sim_state.bodies_slice) {
+		return &invalid_engine
+	}
+
+	return &sim_state.engines[index]
+}
+
+add_engine :: proc(sim_state: ^Sim_State, config: Engine_Config) -> Engine_Handle {
+	sim_state.num_engines += 1
+
+	engine: Engine
+	update_engine_from_config(sim_state, &engine, config)
+
+	engine.alive = true
+
+	if sim_state.first_free_engine_plus_one > 0 {
+		index := sim_state.first_free_engine_plus_one
+		new_engine := get_engine(sim_state, Engine_Handle(index))
+		next_plus_one := new_engine.next_plus_one
+		new_engine^ = engine
+		sim_state.first_free_engine_plus_one = next_plus_one
+		return Engine_Handle(index)
+	}
+
+	append(&sim_state.engines, engine)
+	index := len(sim_state.engines)
+	return Engine_Handle(index)
+}
+
+remove_engine :: proc(sim_state: ^Sim_State, handle: Engine_Handle) {
+	if is_handle_valid(handle) {
+		engine := get_engine(sim_state, handle)
+
+		remove_engine_curve(sim_state, engine.rpm_torque_curve)
+		remove_gear_ratios(sim_state, engine.gear_ratios)
+
+		engine.alive = false
+		engine.next_plus_one = sim_state.first_free_engine_plus_one
+		sim_state.first_free_engine_plus_one = i32(handle)
+		sim_state.num_engines -= 1
+	}
+}
+
+
 _get_first_free_body :: proc(sim_state: ^Sim_State) -> i32 {
 	return sim_state.first_free_body_plus_one - 1
 }
@@ -434,7 +630,10 @@ destry_sim_state :: proc(sim_state: ^Sim_State) {
 	delete_soa(sim_state.suspension_constraints)
 	delete_soa(sim_state.contact_container.contacts)
 	delete_map(sim_state.contact_container.lookup)
+	delete(sim_state.engines)
 	convex_container_destroy(&sim_state.convex_container)
+	spanpool.destroy_spanpool(&sim_state.rpm_torque_curves_pool)
+	spanpool.destroy_spanpool(&sim_state.gear_ratios_pool)
 }
 
 destroy_physics_scene :: proc(scene: ^Scene) {

game/physics/simulation.odin

@@ -9,6 +9,7 @@ import "core:math"
 import lg "core:math/linalg"
 import "core:math/rand"
 import "core:slice"
+import "game:container/spanpool"
 import "libs:tracy"
 
 _ :: rand
@@ -31,13 +32,16 @@ Solver_State :: struct {
 	// Number of immediate bodies referenced this frame
 	num_referenced_bodies:                 i32,
 	num_referenced_suspension_constraints: i32,
+	num_referenced_engines:                i32,
 	immedate_bodies:                       map[u32]Immedate_State(Body_Handle),
 	immediate_suspension_constraints:      map[u32]Immedate_State(Suspension_Constraint_Handle),
+	immediate_engines:                     map[u32]Immedate_State(Engine_Handle),
 }
 
 destroy_solver_state :: proc(state: ^Solver_State) {
 	delete(state.immedate_bodies)
 	delete(state.immediate_suspension_constraints)
+	delete(state.immediate_engines)
 }
 
 Immedate_State :: struct($T: typeid) {
@@ -57,9 +61,11 @@ sim_state_copy :: proc(dst: ^Sim_State, src: ^Sim_State) {
 	dst.num_bodies = src.num_bodies
 	dst.first_free_body_plus_one = src.first_free_body_plus_one
 	dst.first_free_suspension_constraint_plus_one = src.first_free_suspension_constraint_plus_one
+	dst.first_free_engine_plus_one = src.first_free_engine_plus_one
 
 	resize(&dst.bodies, len(src.bodies))
 	resize(&dst.suspension_constraints, len(src.suspension_constraints))
+	resize(&dst.engines, len(src.engines))
 
 	dst.bodies_slice = dst.bodies[:]
 	dst.suspension_constraints_slice = dst.suspension_constraints[:]
@@ -70,9 +76,12 @@ sim_state_copy :: proc(dst: ^Sim_State, src: ^Sim_State) {
 	for i in 0 ..< len(dst.suspension_constraints) {
 		dst.suspension_constraints[i] = src.suspension_constraints[i]
 	}
+	copy(dst.engines[:], src.engines[:])
 
 	contact_container_copy(&dst.contact_container, src.contact_container)
 	convex_container_copy(&dst.convex_container, src.convex_container)
+	spanpool.copy(&dst.rpm_torque_curves_pool, src.rpm_torque_curves_pool)
+	spanpool.copy(&dst.gear_ratios_pool, src.gear_ratios_pool)
 }
 
 Step_Mode :: enum {
@@ -204,6 +213,7 @@ simulate :: proc(
 	state.simulation_frame += 1
 	state.num_referenced_bodies = 0
 	state.num_referenced_suspension_constraints = 0
+	state.num_referenced_engines = 0
 }
 
 GLOBAL_PLANE :: collision.Plane {
@@ -474,6 +484,119 @@ pgs_solve_contacts :: proc(
 	}
 }
 
+pgs_solve_engines :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32, inv_dt: f32) {
+	for &engine in sim_state.engines {
+		if engine.alive {
+			rpm_torque_curve := get_engine_curve(sim_state, engine.rpm_torque_curve)
+			gear_ratios := get_gear_ratios(sim_state, engine.gear_ratios)
+
+			// Unstall impulse
+			{
+				engine_lowest_velocity := rpm_to_angular_velocity(engine.lowest_rpm)
+
+				delta_omega := engine_lowest_velocity - engine.w
+
+				inv_w := engine.inertia
+
+				incremental_impulse := inv_w * delta_omega
+				new_total_impulse := max(engine.unstall_impulse + incremental_impulse, 0)
+				applied_impulse := new_total_impulse - engine.unstall_impulse
+				engine.unstall_impulse = new_total_impulse
+
+				engine.w += applied_impulse / engine.inertia
+			}
+
+			// Internal Friction
+			{
+				delta_omega := -engine.w
+
+				inv_w := engine.inertia
+
+				friction :=
+					math.pow(
+						max(engine.w - rpm_to_angular_velocity(engine.lowest_rpm), 0) * 0.001,
+						4,
+					) *
+						engine.internal_friction +
+					engine.internal_friction
+
+				incremental_impulse := inv_w * delta_omega
+				new_total_impulse := math.clamp(
+					engine.friction_impulse + incremental_impulse,
+					-friction,
+					friction,
+				)
+				applied_impulse := new_total_impulse - engine.friction_impulse
+				engine.friction_impulse = new_total_impulse
+
+				engine.w += applied_impulse / engine.inertia
+			}
+
+			// Throttle
+			{
+				rpm := angular_velocity_to_rpm(engine.w)
+
+				torque: f32
+
+				idx, _ := slice.binary_search_by(
+					rpm_torque_curve,
+					rpm,
+					proc(a: [2]f32, k: f32) -> slice.Ordering {
+						return slice.cmp(a[0], k)
+					},
+				)
+
+				if idx > 0 && idx < len(rpm_torque_curve) - 1 {
+					cur_point := rpm_torque_curve[idx]
+					next_point := rpm_torque_curve[idx + 1]
+					rpm_diff := next_point[0] - cur_point[0]
+					alpha := (rpm - cur_point[0]) / rpm_diff
+
+					torque = math.lerp(cur_point[1], next_point[1], alpha)
+				} else {
+					torque = rpm_torque_curve[math.clamp(idx, 0, len(rpm_torque_curve) - 1)][1]
+				}
+
+				torque *= engine.throttle
+
+				engine.w += torque / engine.inertia
+			}
+
+			// Transmission
+			{
+				// TODO: update from game
+				engine.gear = 1
+
+				power_split := 1.0 / f32(engine.axle.wheel_count)
+				for i in 0 ..< engine.axle.wheel_count {
+					drive_wheel := &engine.axle.wheels[i]
+					wheel := get_suspension_constraint(sim_state, drive_wheel.wheel)
+
+					ratio := gear_ratios[1] * engine.axle.final_drive_ratio
+					inv_ratio := f32(1.0 / ratio)
+
+					w1 := wheel.inv_inertia
+					w2 := f32(1.0 / (engine.inertia * ratio))
+
+					w := w1 + w2
+					inv_w := f32(1.0 / w)
+
+					delta_omega := -engine.w - wheel.w * ratio
+
+					incremental_impulse := -inv_w * delta_omega * power_split
+					drive_wheel.impulse += incremental_impulse
+
+					wheel.w += -incremental_impulse * wheel.inv_inertia * inv_ratio
+					engine.w += -(incremental_impulse / engine.inertia)
+				}
+			}
+
+			// tracy.Plot("rpm", f64(angular_velocity_to_rpm(engine.w)))
+			log.debugf("rpm: %v", angular_velocity_to_rpm(engine.w))
+		}
+	}
+}
+
 pgs_solve_suspension :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32, inv_dt: f32) {
 	// Solve suspension velocity
 	for _, i in sim_state.suspension_constraints {
@@ -604,7 +727,7 @@ pgs_solve_suspension :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f
 					slip_len = slip_len == 0 ? 0 : min(slip_len, 1) / slip_len
 					slip_vec *= slip_len
 
-					log.debugf("slip_vec: %v", slip_vec)
+					// log.debugf("slip_vec: %v", slip_vec)
 
 					long_friction :=
 						abs(
@@ -712,6 +835,28 @@ pgs_substep :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32, inv_d
 			}
 		}
 
+		for i in 0 ..< len(sim_state.engines) {
+			e := &sim_state.engines[i]
+
+			if e.alive {
+				gear_ratios := get_gear_ratios(sim_state, e.gear_ratios)
+				e.w += e.unstall_impulse / e.inertia
+
+				e.w += e.friction_impulse / e.inertia
+
+				for i in 0 ..< e.axle.wheel_count {
+					drive_wheel := &e.axle.wheels[i]
+					wheel := get_suspension_constraint(sim_state, drive_wheel.wheel)
+
+					ratio := gear_ratios[1] * e.axle.final_drive_ratio
+					inv_ratio := f32(1.0 / ratio)
+
+					wheel.w += -drive_wheel.impulse * wheel.inv_inertia * inv_ratio
+					e.w += -(drive_wheel.impulse / e.inertia)
+				}
+			}
+		}
+
 		for i in 0 ..< len(sim_state.suspension_constraints) {
 			s := &sim_state.suspension_constraints_slice[i]
 
@@ -739,6 +884,7 @@ pgs_substep :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32, inv_d
 
 	apply_bias := true
 	pgs_solve_contacts(sim_state, config, dt, inv_dt, apply_bias)
+	pgs_solve_engines(sim_state, config, dt, inv_dt)
 	pgs_solve_suspension(sim_state, config, dt, inv_dt)
 
 	for i in 0 ..< len(sim_state.bodies_slice) {
@@ -763,6 +909,12 @@ pgs_substep :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32, inv_d
 		}
 	}
 
+	for i in 0 ..< len(sim_state.engines) {
+		e := &sim_state.engines[i]
+
+		e.q = math.mod_f32(e.q + 0.5 * e.w * dt, math.PI * 2)
+	}
+
 	for i in 0 ..< len(sim_state.suspension_constraints_slice) {
 		s := &sim_state.suspension_constraints_slice[i]
 

libs/physfs/Makefile

@@ -1,7 +1,7 @@
 configure_cmake:
 	cmake -B build ./physfs
 build_physfs: configure_cmake
-	cmake --build build --config Release -j8
+	cmake --build build --config Debug -j8
 libphysfs.a: build_physfs
 	cp ./build/libphysfs.a .
 libphysfs.so: build_physfs

test.sh

@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-odin test game -collection:common=./common -collection:game=./game -collection:libs=./libs -strict-style -vet
+odin test game/assets -collection:common=./common -collection:game=./game -collection:libs=./libs -strict-style -vet -sanitize:memory