added friction

.gitignore

@@ -0,0 +1,2 @@
+.venv/*
+__pycache__/*

main.py

@@ -49,31 +49,82 @@ def main():
 
     physics = PhysicsSystem()
 
+    linecollider = RectCollider((495, 1))
+
     ball_transform = Transform(position=pg.Vector2(250,250), rotation=pi/8.0)
     square_transform = Transform(position=pg.Vector2(250, 100))
+    #ball2_transform = Transform(position=pg.Vector2(250, 50))
 
     ball = Square(ball_transform, 20)
 
     ball2 = Square(square_transform, 20, color=(0,255,0,255))
 
+    #ball3 = Ball(ball2_transform, 10)
+
     physics.add_body(
         RigidBody(
             ball_transform,
             RectCollider((20,20)),
             velocity=pg.Vector2(0,-400),
-            restitution=1.0,
+            restitution=0.2,
+            coef_friction=0.4
         )
     )
 
+    """physics.add_body(
+        RigidBody(
+            ball2_transform,
+            CircleCollider(20),
+            velocity=pg.Vector2(0,0)
+        )
+    )"""
+
     physics.add_body(
         RigidBody(
             square_transform,
             RectCollider((20,20)),
             pg.Vector2(0,0),
-            restitution=1.0
+            restitution=0.2,
+            coef_friction=0.2
+        )
+    )
+
+    physics.add_body(
+        RigidBody(
+            Transform(pg.Vector2(250,0)),
+            linecollider,
+            pg.Vector2(0,0),
+            mass=0.0
         )
     )
     
+    physics.add_body(
+        RigidBody(
+            Transform(pg.Vector2(250,500)),
+            linecollider,
+            pg.Vector2(0,0),
+            mass=0.0
+        )
+    )
+    
+    physics.add_body(
+        RigidBody(
+            Transform(pg.Vector2(0,250),rotation=pi/2.0),
+            linecollider,
+            pg.Vector2(0,0),
+            mass=0.0
+        )
+    )
+
+    physics.add_body(
+        RigidBody(
+            Transform(pg.Vector2(500,250),rotation=pi/2),
+            linecollider,
+            pg.Vector2(0,0),
+            mass=0.0
+        )
+    )
+
     while running:
         
         dt = clock.tick(144) / 1000
@@ -82,6 +133,7 @@ def main():
         physics.update(dt)
         ball.draw(screen)
         ball2.draw(screen)
+        #ball3.draw(screen)
         pg.display.flip()
         for event in pg.event.get():
             

rigidbody.py

@@ -14,6 +14,12 @@ class RigidBody:
     angular_velocity: float = 0
     mass: float = 1.0
     restitution: float = 0.5
+    coef_friction: float = 0.6
+
+    def apply_impulse(self, j: pg.Vector2, point: pg.Vector2) -> None:
+        moment_arm = point - self.transform.global_position
+        self.velocity += j * self.inv_mass
+        self.angular_velocity += moment_arm.cross(j) * self.inv_moment_of_inertia
 
     @property
     def inv_mass(self) -> float:
@@ -57,20 +63,30 @@ class PhysicsSystem:
         if b.mass != 0.0:
             b.transform.position -= correction
 
+        restitution = a.restitution * b.restitution
+        friction = a.coef_friction * b.coef_friction
+        tangent = collision.normal.rotate(90)
+        v_rel_linear = pg.Vector2(a.velocity - b.velocity)
+        a_w = a.angular_velocity
+        b_w = b.angular_velocity
+
         for point in collision.points:
             r_a = point - a.transform.position
             r_b = point - b.transform.position
 
-            w_cross_r_a = pg.Vector2(-r_a.y * a.angular_velocity, r_a.x * a.angular_velocity) #omega is not encoded as a vector, so we pretend it is
-            w_cross_r_b = pg.Vector2(-r_b.y * b.angular_velocity, r_b.x * b.angular_velocity)
-            v_rel = a.velocity + w_cross_r_a - b.velocity - w_cross_r_b
-            restitution = a.restitution * b.restitution
-            impulse = -(1+restitution)*(v_rel.dot(collision.normal))\
+            w_cross_r_a = pg.Vector2(-r_a.y * a_w, r_a.x * a_w) #omega is not encoded as a vector, so we pretend it is
+            w_cross_r_b = pg.Vector2(-r_b.y * b_w, r_b.x * b_w)
+            v_rel = v_rel_linear + w_cross_r_a - w_cross_r_b
+            v_rel_tangent = v_rel.dot(tangent)
+            
+            collision_impulse = -(1+restitution)*(v_rel.dot(collision.normal))\
                 / (a.inv_mass + b.inv_mass + (r_a.cross(collision.normal)**2 * a.inv_moment_of_inertia)\
                 + (r_b.cross(collision.normal)**2 * b.inv_moment_of_inertia)) / len(collision.points)
-            a.velocity += collision.normal*impulse*a.inv_mass
-            b.velocity -= collision.normal*impulse*b.inv_mass
-            a.angular_velocity += (r_a.cross(impulse*collision.normal)) * a.inv_moment_of_inertia
-            b.angular_velocity -= (r_b.cross(impulse*collision.normal)) * b.inv_moment_of_inertia
+            friction_impulse = (-v_rel_tangent / (a.inv_mass + b.inv_mass +\
+                (r_a.cross(tangent))**2 * a.inv_moment_of_inertia +\
+                (r_b.cross(tangent)**2  * b.inv_moment_of_inertia))) / len(collision.points)
+            friction_impulse = pg.math.clamp(friction_impulse, -abs(collision_impulse)*friction, abs(collision_impulse)*friction)
+            a.apply_impulse(collision.normal*collision_impulse + friction_impulse * tangent, point)
+            b.apply_impulse(-1 * collision.normal*collision_impulse - friction_impulse * tangent, point)
 
     

transform.py

@@ -7,7 +7,7 @@ import pygame as pg
 class Transform:
     
     position: pg.Vector2
-    rotation: pg.Vector2 = 0.0
+    rotation: float = 0.0
     scale: float = 1.0
     parent: 'Transform' = None