Added partial port of fastnoise-java

orx-noise/src/main/kotlin/SimplexNoise2D.kt

@@ -0,0 +1,63 @@
+package org.openrndr.extra.noise
+
+
+private val G2 = 1.0 / 4.0
+private val F2 = 1.0 / 2.0
+
+fun simplex(seed: Int, x: Double, y: Double): Double {
+    var t = (x + y) * F2
+    val i = (x + t).fastFloor()
+    val j = (y + t).fastFloor()
+
+    t = ((i + j) * G2)
+    val X0 = i - t
+    val Y0 = j - t
+
+    val x0 = x - X0
+    val y0 = y - Y0
+
+    val i1: Int
+    val j1: Int
+    if (x0 > y0) {
+        i1 = 1
+        j1 = 0
+    } else {
+        i1 = 0
+        j1 = 1
+    }
+
+    val x1 = x0 - i1 + G2
+    val y1 = y0 - j1 + G2
+    val x2 = x0 - 1 + F2
+    val y2 = y0 - 1 + F2
+
+    val n0: Double
+    val n1: Double
+    val n2: Double
+
+    t = 0.5 - x0 * x0 - y0 * y0
+    if (t < 0)
+        n0 = 0.0
+    else {
+        t *= t
+        n0 = t * t * gradCoord2D(seed, i, j, x0, y0)
+    }
+
+    t = 0.5 - x1 * x1 - y1 * y1
+    if (t < 0)
+        n1 = 0.0
+    else {
+        t *= t
+        n1 = t * t * gradCoord2D(seed, i + i1, j + j1, x1, y1)
+    }
+
+    t = 0.5 - x2 * x2 - y2 * y2
+    if (t < 0)
+        n2 = 0.0
+    else {
+        t *= t
+        n2 = t * t * gradCoord2D(seed, i + 1, j + 1, x2, y2)
+    }
+
+    return 50.0 * (n0 + n1 + n2)
+}