From 5c797145ae45a4313851c2afc3dba516ab30087a Mon Sep 17 00:00:00 2001
From: sergeypdev <sergeypoznyak@protonmail.com>
Date: Sun, 27 Apr 2025 12:40:46 +0400
Subject: [PATCH] Fixed power delivery from engine, now 0-100 time seems to be
 in the right ballpark

---
 game/game.odin               |  6 ++--
 game/physics/scene.odin      |  1 +
 game/physics/simulation.odin | 60 +++++++++++++++++++++++++++---------
 3 files changed, 49 insertions(+), 18 deletions(-)

diff --git a/game/game.odin b/game/game.odin
index 916e5a0..2680aae 100644
--- a/game/game.odin
+++ b/game/game.odin
@@ -402,13 +402,13 @@ update_runtime_world :: proc(runtime_world: ^Runtime_World, dt: f32) {
 			physics.Engine_Config {
 				rpm_torque_curve = assets.get_curve_2d(&g_mem.assetman, "assets/ae86_rpm_torque.csv").points,
 				lowest_rpm = 1000,
-				inertia = 0.0264,
-				internal_friction = 0.00,
+				inertia = 0.264,
+				internal_friction = 0.01,
 				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,
+					diff_type = .Open,
 					final_drive_ratio = 4.1,
 				},
 			},
diff --git a/game/physics/scene.odin b/game/physics/scene.odin
index 9ebce02..a94a4ee 100644
--- a/game/physics/scene.odin
+++ b/game/physics/scene.odin
@@ -177,6 +177,7 @@ Suspension_Constraint :: struct {
 }
 
 Diff_Type :: enum {
+	Open,
 	Fixed,
 	// TODO: LSD
 }
diff --git a/game/physics/simulation.odin b/game/physics/simulation.odin
index 6f07feb..64ef176 100644
--- a/game/physics/simulation.odin
+++ b/game/physics/simulation.odin
@@ -587,27 +587,57 @@ pgs_solve_engines :: proc(sim_state: ^Sim_State, config: Solver_Config, dt: f32,
 				gear_ratio := lookup_gear_ratio(gear_ratios, engine.gear)
 
 				if engine.gear != 0 {
-					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_ratio * engine.axle.final_drive_ratio
+					inv_ratio := f32(1.0 / (ratio))
 
-						ratio := gear_ratio * engine.axle.final_drive_ratio
-						inv_ratio := f32(1.0 / (ratio))
+					drive_wheel1 := &engine.axle.wheels[0]
+					wheel1 := get_suspension_constraint(sim_state, drive_wheel1.wheel)
 
-						w1 := wheel.inv_inertia
-						w2 := f32(1.0 / (engine.inertia * ratio * ratio))
+					drive_wheel2 := &engine.axle.wheels[1]
+					wheel2 := get_suspension_constraint(sim_state, drive_wheel2.wheel)
 
-						w := w1 + w2
-						inv_w := f32(1.0 / w)
+					w1 := f32(1.0 / (engine.inertia * ratio * ratio))
+					w2 := wheel1.inv_inertia
+					w3 := wheel2.inv_inertia
 
-						delta_omega := wheel.w * ratio - (-engine.w)
+					w := w1 + w2 + w3
+					inv_w := f32(1.0 / w)
 
-						incremental_impulse := -inv_w * delta_omega
-						// drive_wheel.impulse += incremental_impulse
+					avg_wheel_vel := (wheel1.w + wheel2.w) * 0.5
 
-						wheel.w += incremental_impulse * w1 * inv_ratio
-						engine.w += incremental_impulse / (engine.inertia * ratio * ratio)
-					}
+					delta_omega := avg_wheel_vel * ratio - (-engine.w)
+
+					incremental_impulse := -inv_w * delta_omega
+
+					engine.w += incremental_impulse * w1
+					wheel1.w += incremental_impulse * w2 * inv_ratio
+					wheel2.w += incremental_impulse * w3 * inv_ratio
+				}
+			}
+
+			// Diff
+			{
+				switch engine.axle.diff_type {
+				case .Open:
+				case .Fixed:
+					drive_wheel1 := &engine.axle.wheels[0]
+					wheel1 := get_suspension_constraint(sim_state, drive_wheel1.wheel)
+
+					drive_wheel2 := &engine.axle.wheels[1]
+					wheel2 := get_suspension_constraint(sim_state, drive_wheel2.wheel)
+
+					w1 := wheel1.inv_inertia
+					w2 := wheel2.inv_inertia
+
+					w := w1 + w2
+					inv_w := f32(1.0 / w)
+
+					delta_omega := wheel2.w - wheel1.w
+
+					incremental_impulse := -inv_w * delta_omega
+
+					wheel1.w += -incremental_impulse * wheel1.inv_inertia
+					wheel2.w += incremental_impulse * wheel2.inv_inertia
 				}
 			}
 		}