Squashed 'l1/' content from commit 670aa58

git-subtree-dir: l1
git-subtree-split: 670aa582df99e87fca7c247b949baf452e8c234f

sexp_effects/effects/blend.sexp

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+;; Blend effect - combines two video frames
+;; Streaming-compatible: frame is background, overlay is second frame
+;; Usage: (blend background overlay :opacity 0.5 :mode "alpha")
+;;
+;; Params:
+;;   mode - blend mode (add, multiply, screen, overlay, difference, lighten, darken, alpha)
+;;   opacity - blend amount (0-1)
+
+(require-primitives "image" "blending" "core")
+
+(define-effect blend
+  :params (
+    (overlay :type frame :default nil)
+    (mode :type string :default "alpha")
+    (opacity :type float :default 0.5)
+  )
+  (if (core:is-nil overlay)
+    frame
+    (let [a frame
+          b overlay
+          a-h (image:height a)
+          a-w (image:width a)
+          b-h (image:height b)
+          b-w (image:width b)
+          ;; Resize b to match a if needed
+          b-sized (if (and (= a-w b-w) (= a-h b-h))
+                    b
+                    (image:resize b a-w a-h "linear"))]
+      (if (= mode "alpha")
+        (blending:blend-images a b-sized opacity)
+        (blending:blend-images a (blending:blend-mode a b-sized mode) opacity)))))