Broaden solid core in ball falloff

app.py

@@ -930,7 +930,7 @@ def compose_frame(state: AppState, frame_idx: int, remove_bg: bool = False) -> I
                 if ball_mask is not None:
                     combined_mask = np.maximum(
                         combined_mask,
-                        _apply_radial_falloff(np.clip(ball_mask.astype(np.float32), 0.0, 1.0)),
+                        _apply_radial_falloff(np.clip(ball_mask.astype(np.float32), 0.0, 1.0), strength=1.0, solid_ratio=0.8),
                     )
             result_np = _apply_cutout_fx(state, frame_np, combined_mask)
             out_img = Image.fromarray(result_np)
@@ -944,7 +944,7 @@ def compose_frame(state: AppState, frame_idx: int, remove_bg: bool = False) -> I
             if BALL_OBJECT_ID in masks:
                 ball_mask = masks[BALL_OBJECT_ID]
                 if ball_mask is not None:
-                    ball_alpha = _apply_radial_falloff(ball_mask)
+                    ball_alpha = _apply_radial_falloff(ball_mask, strength=1.0, solid_ratio=0.8)
                     if ball_alpha is not None and ball_alpha.max() > FX_EPS:
                         base_np = np.array(out_img).astype(np.float32) / 255.0
                         color = np.array(state.color_by_obj.get(BALL_OBJECT_ID, (255, 255, 0)), dtype=np.float32) / 255.0
@@ -1137,7 +1137,7 @@ def _build_ball_trail_mask(state: AppState, frame_idx: int) -> np.ndarray | None
         if mask_np.ndim == 3:
             mask_np = mask_np.squeeze()
         mask_np = np.clip(mask_np, 0.0, 1.0)
-        mask_np = _apply_radial_falloff(mask_np)
+        mask_np = _apply_radial_falloff(mask_np, strength=1.0, solid_ratio=0.8)
         if trail_mask is None:
             trail_mask = np.zeros_like(mask_np, dtype=np.float32)
         if trail_mask.shape != mask_np.shape:
@@ -1169,7 +1169,7 @@ def _compute_mask_centroid(mask: np.ndarray) -> tuple[int, int] | None:
     return cx, cy
 
 
-def _apply_radial_falloff(mask: np.ndarray, strength: float = 1.5) -> np.ndarray:
+def _apply_radial_falloff(mask: np.ndarray, strength: float = 1.0, solid_ratio: float = 0.8) -> np.ndarray:
     if mask is None:
         return None
     mask_np = np.clip(mask.astype(np.float32), 0.0, 1.0)
@@ -1189,8 +1189,10 @@ def _apply_radial_falloff(mask: np.ndarray, strength: float = 1.5) -> np.ndarray
     max_dist = dist[mask_np > FX_EPS].max() if np.any(mask_np > FX_EPS) else 0.0
     if max_dist <= FX_EPS:
         return mask_np
-    falloff = 1.0 - np.clip(dist / max_dist, 0.0, 1.0)
-    falloff = np.power(falloff, strength)
+    if solid_ratio >= 1.0:
+        return mask_np
+    clipped_dist = np.clip((dist / max_dist - solid_ratio) / (1.0 - solid_ratio), 0.0, 1.0)
+    falloff = 1.0 - np.power(clipped_dist, strength)
     return np.clip(mask_np * falloff, 0.0, 1.0)