add spiral_ripples

examples/spiral/spiral_ripples.scad

@@ -0,0 +1,42 @@
+use <noise/nz_cell.scad>
+use <golden_spiral.scad>
+use <noise/nz_perlin2.scad>
+use <surface/sf_thicken.scad>
+use <util/radians.scad>
+
+amplitude = 2;
+angle_step = 30;
+voxel_step = 0.2;
+wave_step = 0.1;
+thickness = 0.5;
+dist = "euclidean"; // [euclidean, manhattan, chebyshev, border] 
+seed = 51;
+
+spiral_ripples();
+
+module spiral_ripples() {
+    phi = (1 + sqrt(5)) / 2;
+    degrees = 720;
+    points = [
+        for(d = [0:angle_step:degrees])
+        let(
+            theta = radians(d),
+            r = pow(phi, theta * 2 / PI)
+        )
+        r * [cos(d), sin(d)]
+    ];
+
+    sf = [
+        for(y = [-45:voxel_step:30]) 
+        [
+            for(x = [-40:voxel_step:70]) 
+            let(
+                nz = nz_cell(points, [x, y], dist),
+                n = amplitude * nz_perlin2(nz + x * wave_step, nz + y * wave_step, seed)
+            )
+            [x, y, n]
+        ]
+    ];
+
+    sf_thicken(sf, thickness);
+}