From da9030fa90d188e245051f976ad236726061afe8 Mon Sep 17 00:00:00 2001
From: fnicon <mybeddrom@gmail.com>
Date: Sat, 21 Mar 2026 11:18:58 +0900
Subject: [PATCH] putting together magic_number, fix friction, add magic boost
 and magic slowdown

---
 .../love_src/src/world/top_down_race/init.lua |  4 +-
 .../world/top_down_race/system/velocity.lua   | 74 ++++++++++++++++---
 2 files changed, 66 insertions(+), 12 deletions(-)

diff --git a/game/love_src/src/world/top_down_race/init.lua b/game/love_src/src/world/top_down_race/init.lua
index b770e51..aaa5998 100644
--- a/game/love_src/src/world/top_down_race/init.lua
+++ b/game/love_src/src/world/top_down_race/init.lua
@@ -32,10 +32,10 @@ function wrapper:load(_args)
       assemblage = racer.assemble,
       data = {
         accel = 20.0,
-        brake = 1.0,
+        brake = 10.0,
         grip = 1.0,
         max_speed = 50.0,
-        steer = 1.0,
+        steer = 5.0,
         velocity = 0.0,
         inertia = {0.0, 0.0},
         drag = 1.0,
diff --git a/game/love_src/src/world/top_down_race/system/velocity.lua b/game/love_src/src/world/top_down_race/system/velocity.lua
index f40bb10..b3abbb9 100644
--- a/game/love_src/src/world/top_down_race/system/velocity.lua
+++ b/game/love_src/src/world/top_down_race/system/velocity.lua
@@ -144,20 +144,50 @@ local function grip_force(grip, friction)
   return friction * grip
 end
 
-local function add_friction(force, grip, friction, tire_c, floor_c)
+local function add_friction(force, friction_direction, grip, friction, tire_c, floor_c)
   local f_grip = grip_force(grip, friction)
   if (force > 0) then
     -- tire - floor
-    force = force + tire_c * f_grip - floor_c * f_grip
+    force = force + friction_direction * tire_c * f_grip - friction_direction * floor_c * f_grip
   elseif (force < 0) then
-    force = force - tire_c * f_grip + floor_c * f_grip
+    force = force + friction_direction * tire_c * f_grip - friction_direction * floor_c * f_grip
   else
     force = force
   end
   return force
 end
 
-local function add_drag(force, drag)
+local function add_friction_lateral(force, grip, friction, tire_c, floor_c)
+  local f_grip = grip_force(grip, friction)
+  if (force > 0) then
+    -- tire - floor
+    force = force + tire_c * f_grip - floor_c * f_grip
+    if (force < 0) then
+      force = 0.1
+    end
+  elseif (force < 0) then
+    force = force - tire_c * f_grip + floor_c * f_grip
+    if (force > 0) then
+      force = -0.1
+    end
+  else
+    force = force
+  end
+  return force
+end
+
+local function add_drag(force, drag_direction, drag)
+  if (force > 0) then
+    force = force + drag_direction * drag
+  elseif (force < 0) then
+    force = force + drag_direction * drag
+  else
+    force = force
+  end
+  return force
+end
+
+local function add_drag_lateral(force, drag)
   if (force > 0) then
     force = force - drag
   elseif (force < 0) then
@@ -201,6 +231,16 @@ local function get_friction(pos_x, pos_y, floors)
   return friction
 end
 
+local magic_n = {
+  tire_c = 1.0,
+  floor_c = 1.5,
+  scale_x = 100000.0,
+  scale_y = 100000.0,
+  centrifugal_r = 1.0,
+  magic_slowdown = 10.0,
+  magic_boost = 5000.0
+}
+
 function system:update(dt)
   for _, e in ipairs(self.pool) do
     local accel, brake, grip, max_speed, steer, velocity, drag, inertia, mass = get(e)
@@ -217,18 +257,32 @@ function system:update(dt)
     local f_forward = accel_force(up, down, accel, brake, inertia[1])
     local f_lateral = steer_force(left, right, steer, inertia[2])
 
-    f_forward = add_friction(f_forward, grip, friction, 1.0, 0.5)
-    f_lateral = add_friction(f_lateral, grip, friction, 1.0, 0.5)
+    if (not up) then
+      f_forward = f_forward - magic_n.magic_slowdown
+    elseif (up and velocity == 0) then
+      f_forward = f_forward + magic_n.magic_boost
+    end
 
-    f_forward = add_drag(f_forward, drag)
-    f_lateral = add_drag(f_lateral, drag)
+    if (velocity > 0) then
+      f_forward = add_friction(f_forward, 1.0, grip, friction, magic_n.tire_c, magic_n.floor_c)
+    elseif (velocity < 0) then
+      f_forward = add_friction(f_forward, -1.0, grip, friction, magic_n.tire_c, magic_n.floor_c)
+    end
+    f_lateral = add_friction_lateral(f_lateral, grip, friction, magic_n.tire_c, magic_n.floor_c)
+
+    if (velocity > 0) then
+      f_forward = add_drag(f_forward, -1.0, drag)
+    elseif (velocity < 0) then
+      f_forward = add_drag(f_forward, 1.0, drag)
+    end
+    f_lateral = add_drag_lateral(f_lateral, drag)
 
     if (mass == 0) then
       mass = 1
     end
 
     local new_velocity = racing_phy.accelerate(dt, 1, velocity, max_speed, f_forward*dt/mass, 0)
-    local centrifugal = racing_phy.centrifugal_force(dt, mass, new_velocity, max_speed)
+    local centrifugal = racing_phy.centrifugal_force(dt, mass, new_velocity * magic_n.centrifugal_r, max_speed)
     f_lateral = add_centrifugal(f_lateral, centrifugal)
 
     e[race.dict.inertia].data = {f_forward * dt, f_lateral * dt}
@@ -237,7 +291,7 @@ function system:update(dt)
     e["race.angle"].data = new_angle
     e[race.dict.velocity].data = new_velocity
 
-    local goal_x, goal_y = racing_phy.drift(dt, pos_x, pos_y, new_velocity, max_speed, new_angle, 100000, 100000)
+    local goal_x, goal_y = racing_phy.drift(dt, pos_x, pos_y, new_velocity, max_speed, new_angle, magic_n.scale_x, magic_n.scale_y)
     -- print("force_forward", f_forward, "f_lateral", f_lateral, "velocity", new_velocity, "angle", new_angle, "goal_x", goal_x, "goal_y", goal_y)
 
     e["race.pos"].data[1] = goal_x