diff --git a/packages/shader-ast-stdlib/src/index.ts b/packages/shader-ast-stdlib/src/index.ts
index 50033ea896..fa80cda419 100644
--- a/packages/shader-ast-stdlib/src/index.ts
+++ b/packages/shader-ast-stdlib/src/index.ts
@@ -62,6 +62,7 @@ export * from "./sdf/smooth-isec";
 export * from "./sdf/smooth-sub";
 export * from "./sdf/smooth-union";
 export * from "./sdf/sphere";
+export * from "./sdf/sub";
 export * from "./sdf/torus";
 export * from "./sdf/tri";
 export * from "./sdf/union";
diff --git a/packages/shader-ast-stdlib/src/sdf/union.ts b/packages/shader-ast-stdlib/src/sdf/union.ts
index ebc2d29cc6..f7cebdd0ea 100644
--- a/packages/shader-ast-stdlib/src/sdf/union.ts
+++ b/packages/shader-ast-stdlib/src/sdf/union.ts
@@ -1,4 +1,4 @@
-import { FloatTerm, min } from "@thi.ng/shader-ast";
+import { $x, defn, FloatTerm, lt, min, ret, ternary } from "@thi.ng/shader-ast";
 
 /**
  * Inline function. SDF shape union (a || b).
@@ -7,3 +7,14 @@ import { FloatTerm, min } from "@thi.ng/shader-ast";
  * @param b - float
  */
 export const sdfUnion = (a: FloatTerm, b: FloatTerm) => min(a, b);
+
+/**
+ * SDF shape union for vec2 terms, i.e. the common form where the X coord
+ * defines distance and Y an object or material ID.
+ *
+ * @param a -
+ * @param b -
+ */
+export const sdfUnion2 = defn("vec2", "sdfUnion2", ["vec2", "vec2"], (a, b) => [
+    ret(ternary(lt($x(a), $x(b)), a, b)),
+]);