Import L1 (celery) as l1/

l1/sexp_effects/effects/xector_feathered_blend.sexp

@@ -0,0 +1,44 @@
+;; Feathered blend - blend two same-size frames with distance-based falloff
+;; Center shows overlay, edges show background, with smooth transition
+
+(require-primitives "xector")
+
+(define-effect xector_feathered_blend
+  :params (
+    (inner-radius :type float :default 0.3 :range [0 1] :desc "Radius where overlay is 100% (fraction of size)")
+    (fade-width :type float :default 0.2 :range [0 0.5] :desc "Width of fade region (fraction of size)")
+    (overlay :type frame :default nil :desc "Frame to blend in center")
+  )
+  (let* (
+         ;; Get normalized distance from center (0 at center, ~1 at corners)
+         (dist (dist-from-center frame))
+         (max-dist (βmax dist))
+         (dist-norm (α/ dist max-dist))
+
+         ;; Calculate blend factor:
+         ;; - 1.0 when dist-norm < inner-radius (fully overlay)
+         ;; - 0.0 when dist-norm > inner-radius + fade-width (fully background)
+         ;; - linear ramp between
+         (t (α/ (α- dist-norm inner-radius) fade-width))
+         (blend (α- 1 (αclamp t 0 1)))
+         (inv-blend (α- 1 blend))
+
+         ;; Background channels
+         (bg-r (red frame))
+         (bg-g (green frame))
+         (bg-b (blue frame)))
+
+    (if (nil? overlay)
+        ;; No overlay - visualize the blend mask
+        (let ((vis (α* blend 255)))
+          (rgb vis vis vis))
+
+        ;; Blend overlay with background using the mask
+        (let* ((ov-r (red overlay))
+               (ov-g (green overlay))
+               (ov-b (blue overlay))
+               ;; lerp: bg * (1-blend) + overlay * blend
+               (r-out (α+ (α* bg-r inv-blend) (α* ov-r blend)))
+               (g-out (α+ (α* bg-g inv-blend) (α* ov-g blend)))
+               (b-out (α+ (α* bg-b inv-blend) (α* ov-b blend))))
+          (rgb r-out g-out b-out)))))