add sf_ring

src/experimental/sf_ring.scad

@@ -0,0 +1,36 @@
+use <experimental/_impl/_sf_square_surfaces.scad>;
+use <experimental/sf_solidify.scad>;
+use <experimental/tf_ring.scad>;
+
+/*
+    levels : A list of numbers (0 ~ 255).
+    radius: The radius of the arc after being bent
+    thickness: shell thickness
+    angle: The central angle of the arc..
+    invert: inverts how the gray levels are translated into height values.
+*/
+
+module sf_ring(levels, radius, thickness, angle = 360, invert = false) {
+    surface = _sf_square_surfaces(levels, thickness, invert);
+    rows = len(levels);
+    columns = len(levels[0]);
+    size = [columns - 1, rows - 1];
+    
+    offset_z = invert ? thickness : 0;
+    sf_solidify(
+        [
+            for(row = surface[0]) 
+            [
+                for(p = row) 
+                    tf_ring(size, p, radius, angle, 0) + + [0, 0, offset_z]
+            ]
+        ],
+        [
+            for(row = surface[1]) 
+            [
+                for(p = row) 
+                    tf_ring(size, p, radius, angle, 0)
+            ]
+        ]
+    );
+}