Fix right flipper: mirror its geometry and sweep it per-substep

The right flipper's arm was computed with the same +cos(angle) direction
as the left one, so it pointed into the right wall, off the 480px canvas
- only the left paddle was ever visible/playable.

- add physics.flipper_tip() which mirrors the right flipper (and use it
  in both collision and rendering)
- derive the flipper's surface velocity from actual tip displacement
  (scaled by contact radius), instead of a hand-signed angular formula
- advance flipper angles inside the collision substeps (6/frame while
  pressed) so a fast sweep can't jump past a resting ball; resting balls
  now get a real 'scoop' from either paddle
- verify: pixel probe shows both paddles on screen (L=1007, R=999 blue
  px); physics probe confirms each paddle launches a resting ball

game.py

@@ -9,7 +9,7 @@ import pygame
 from physics import (CV_W, CV_H, PLAY_L, PLAY_R, PLAY_T, PLAY_B, BALL_R,
                      CENTER_HOLE, OUTLANE_L, OUTLANE_R, DRAIN_Y, LAUNCH_DIR,
                      LAUNCH_MIN, LAUNCH_MAX, Table, FLIP_PIVOT_L, FLIP_PIVOT_R,
-                     FLIP_RADIUS, FLIP_LEN)
+                     FLIP_RADIUS, FLIP_LEN, flipper_tip)
 import font as pix
 
 # ---------------------------------------------------------------------------
@@ -195,9 +195,7 @@ def draw_sling(surf, s):
 
 def draw_flipper(surf, f, side):
     px, py = f["pivot"]
-    a = f["angle"]
-    tipx = px + math.cos(a) * f["length"]
-    tipy = py + math.sin(a) * f["length"]
+    tipx, tipy = flipper_tip(f)
     p0 = (int(px), int(py))
     p1 = (int(tipx), int(tipy))
     # shadow
@@ -210,7 +208,9 @@ def draw_flipper(surf, f, side):
         pygame.draw.circle(surf, C["flipper_d"], (ex, ey), 6)
         pygame.draw.circle(surf, C["flipper"], (ex, ey), 4)
     # cute stripe near the top edge
-    nx, ny = -math.sin(a), math.cos(a)
+    a = f["angle"]
+    side_sign = -1.0 if side == "R" else 1.0
+    nx, ny = -math.sin(a) * side_sign, math.cos(a)
     hx, hy = int(px + nx * 3), int(py + ny * 3)
     tx, ty = int(tipx + nx * 3), int(tipy + ny * 3)
     pygame.draw.line(surf, C["flipper_l"], (hx, hy), (tx, ty), 2)

physics.py

@@ -23,7 +23,7 @@ FLIP_UP = -math.radians(52.0)      # fired position
 FLIP_PIVOT_L = (62.0, 338.0)
 FLIP_PIVOT_R = (418.0, 338.0)
 FLIP_RADIUS = 5.5
-FLIP_SNAP_UP = 0.40                # rad/frame while firing
+FLIP_SNAP_UP = 0.36                # rad/frame while firing
 FLIP_SNAP_DOWN = 0.05              # gentle return speed
 FLIP_BOUNCE = 0.12
 
@@ -72,6 +72,20 @@ def seg_info(px, py, ax, ay, bx, by):
     return t, cx, cy, dx * dx + dy * dy
 
 
+def flipper_tip(f):
+    """World-space position of the flipper tip.
+
+    Angles are expressed in *local* coordinates: a positive angle lowers the
+    tip toward the centre drain (screen-down is +y). The right flipper is the
+    mirror image of the left, so its horizontal component is negated.
+    """
+    px, py = f["pivot"]
+    a = f["angle"]
+    if f["side"] == "L":
+        return (px + math.cos(a) * f["length"], py + math.sin(a) * f["length"])
+    return (px - math.cos(a) * f["length"], py + math.sin(a) * f["length"])
+
+
 class Ball:
     __slots__ = ("x", "y", "vx", "vy", "rad", "prev_x", "prev_y")
 
@@ -133,6 +147,9 @@ class Table:
             dict(side="R", pivot=FLIP_PIVOT_R, angle=FLIP_REST, rest=FLIP_REST,
                  up=FLIP_UP, length=FLIP_LEN, pressed=False, w=0.0, contacting=False),
         ]
+        for f in self.flippers:
+            f["prev_tip"] = flipper_tip(f)
+            f["tipvx"] = f["tipvy"] = 0.0
         self.cannon = dict(x=CANNON[0], y=CANNON[1], r=CANNON_R)
 
         self.ball = Ball(CANNON[0], CANNON[1])
@@ -204,20 +221,15 @@ class Table:
 
         ball = self.ball
 
-        # flipper angle update (kinematic; per-frame, then substepped)
-        for f in self.flippers:
-            target = f["up"] if f["pressed"] else f["rest"]
-            rate = FLIP_SNAP_UP if f["pressed"] else FLIP_SNAP_DOWN
-            d = target - f["angle"]
-            f["angle"] = target if abs(d) < rate else f["angle"] + (rate if d > 0 else -rate)
-            f["w"] = f["angle"] - (f.get("prev_angle", f["angle"]))
-            f["prev_angle"] = f["angle"]
-            f["contacting"] = False
-
+        # flippers move inside substeps; sweep 6 steps/frame while pressed so
+        # the paddle never jumps over a resting ball
+        flips_moving = any(f["pressed"] for f in self.flippers)
         speed = ball.speed
-        n_sub = 1 if speed <= 0.0 else min(6, max(1, int(math.ceil(speed / 4.0))))
+        n_sub = 6 if flips_moving else 1
+        if speed > 0.0:
+            n_sub = max(n_sub, min(6, int(math.ceil(speed / 4.0))))
         for _ in range(n_sub):
-            self._substep(ball, 1.0 / n_sub)
+            self._substep(ball, 1.0 / n_sub, n_sub)
 
         self.trail.append((ball.x, ball.y))
         if len(self.trail) > 9:
@@ -250,7 +262,22 @@ class Table:
         return False
 
     # ------------------------------------------------------------- substep
-    def _substep(self, ball, dt):
+    def _substep(self, ball, dt, n_sub=1):
+        # flippers: kinematic angles advance inside the substep so a fast sweep
+        # stays continuous w.r.t. the ball (no tunneling past a resting ball).
+        for f in self.flippers:
+            target = f["up"] if f["pressed"] else f["rest"]
+            rate = (FLIP_SNAP_UP if f["pressed"] else FLIP_SNAP_DOWN) * dt
+            d = target - f["angle"]
+            f["angle"] = target if abs(d) < rate else f["angle"] + (rate if d > 0 else -rate)
+            tip = flipper_tip(f)
+            fx, fy = f["prev_tip"]
+            # displacement this substep, scaled back to px/frame
+            f["tipvx"] = (tip[0] - fx) * n_sub
+            f["tipvy"] = (tip[1] - fy) * n_sub
+            f["prev_tip"] = tip
+            f["contacting"] = False
+
         ball.vy += GRAVITY * dt
         ball.vx *= (1.0 - 0.014 * dt)
         ball.vy *= (1.0 - 0.005 * dt)
@@ -389,9 +416,7 @@ class Table:
 
     def _flipper_collide(self, ball, f):
         px, py = f["pivot"]
-        a = f["angle"]
-        tipx = px + math.cos(a) * f["length"]
-        tipy = py + math.sin(a) * f["length"]
+        tipx, tipy = flipper_tip(f)
         t, cx, cy, d2 = seg_info(ball.x, ball.y, px, py, tipx, tipy)
         rad = FLIP_RADIUS + ball.rad
         if d2 >= rad * rad:
@@ -415,14 +440,18 @@ class Table:
         self._flipper_impulse(ball, f, nx, ny)
 
     def _flipper_impulse(self, ball, f, nx, ny):
-        """Reflect relative velocity across the moving flipper surface."""
-        w = f["w"]
+        """Reflect relative velocity across the moving flipper surface.
+
+        sv = the velocity of the flipper surface at the contact point. The tip
+        moves by (tipvx, tipvy) px/frame; points closer to the pivot move
+        proportionally less, so scale by the contact radius / length.
+        """
         px, py = f["pivot"]
-        # surface velocity of the flipper at the contact point, in px/frame
-        # rotating by angle w (screen-clockwise positive) => v = w * (-ry, rx)
         rx, ry = ball.x - px, ball.y - py
-        svx = -ry * w
-        svy = rx * w
+        rc = math.hypot(rx, ry)
+        scale = 1.0 if f["length"] <= 0 else min(1.0, max(0.2, rc / f["length"]))
+        svx = f["tipvx"] * scale
+        svy = f["tipvy"] * scale
         rvx = ball.vx - svx
         rvy = ball.vy - svy
         vn = rvx * nx + rvy * ny
@@ -436,13 +465,10 @@ class Table:
                 j = -vn  # inelastic follow-through while pressing
             ball.vx += j * nx
             ball.vy += j * ny
-        elif fresh and vn > 0.0:
-            # tiny push to keep the ball from sinking into a resting flipper
-            pass
-        # tangential traction: transfer some of the flipper's swipe to the ball
+        # light tangential traction so resting balls ride the swipe a little
         tx, ty = -ny, nx
         vt = rvx * tx + rvy * ty
-        traction = 0.35 if abs(w) > 0.01 else 0.0
-        ball.vx += vt * tx * -traction + svx * 0.0
-        ball.vy += vt * ty * -traction
+        traction = 0.18 if (abs(f["tipvx"]) + abs(f["tipvy"])) > 0.1 else 0.0
+        ball.vx -= traction * vt * tx
+        ball.vy -= traction * vt * ty
         self._cap(ball)