feat(shader-ast-stdlib): add fbmNoiseVec34()

packages/shader-ast-stdlib/src/noise/fbm.ts

@@ -0,0 +1,47 @@
+import type { FloatSym, Vec4Sym } from "@thi.ng/shader-ast";
+import { S3D, V3, V4 } from "@thi.ng/shader-ast/api/types";
+import { forLoop } from "@thi.ng/shader-ast/ast/controlflow";
+import { defn, ret } from "@thi.ng/shader-ast/ast/function";
+import { FLOAT05, UINT0, uint, vec4 } from "@thi.ng/shader-ast/ast/lit";
+import {
+	addSelf,
+	div,
+	inc,
+	lt,
+	mul,
+	mulSelf,
+} from "@thi.ng/shader-ast/ast/ops";
+import { sym } from "@thi.ng/shader-ast/ast/sym";
+import { texture } from "@thi.ng/shader-ast/builtin/texture";
+
+/**
+ * Higher order function to compute 3D texture-based FBM noise for given number
+ * of octaves and decay factor (default: 1/octaves). Returns a 2-arg shader
+ * function, taking a sampler3D and vec3 position and which returns summed noise
+ * value as vec4.
+ *
+ * @remarks
+ * Not compatible with WebGL 1.0 (texture type not natively supported).
+ *
+ * @param octaves
+ * @param decay
+ */
+export const fbmNoiseVec34 = (octaves: number, decay = 1 / octaves) =>
+	defn(V4, null, [S3D, V3], (tex, p) => {
+		let res: Vec4Sym;
+		let amp: FloatSym;
+		return [
+			(res = sym(vec4())),
+			(amp = sym(FLOAT05)),
+			forLoop(
+				sym(UINT0),
+				(i) => lt(i, uint(octaves)),
+				inc,
+				() => [
+					addSelf(res, mul(texture(tex, div(p, amp)), amp)),
+					mulSelf(amp, decay),
+				]
+			),
+			ret(res),
+		];
+	});