Add noise-gradient-fractal-value function (similar to noise-fractal-value, but use noise-gradient-value instead of noise-value).

src/base-generation/noise.rkt

@@ -9,7 +9,8 @@
   make-noise
   noise-value
   noise-gradient-value
-  noise-fractal-value)
+  noise-fractal-value
+  noise-gradient-fractal-value)
 
 ; Structure
 (struct s-noise
@@ -185,3 +186,18 @@
                 coords)))))
     0
     (build-list octaves values)))
+
+; Same as above, but use the noise-gradient-value instead of the noise-value
+(define (noise-gradient-fractal-value ns octaves persistance . coords)
+  (foldl
+    (lambda (i res)
+      (+ res
+         (* (expt persistance i)
+            (apply
+              noise-gradient-value
+              ns
+              (map
+                (lambda (x) (* (+ i 1) x))
+                coords)))))
+    0
+    (build-list octaves values)))