add sf_thicken

src/surface/sf_thicken.scad

@@ -0,0 +1,67 @@
+use <sf_solidify.scad>;
+use <util/sum.scad>;
+
+module sf_thicken(points, thickness, slicing = "SLASH") {
+    function tri_normal(tri) =
+        let(v = cross(tri[2] - tri[0], tri[1] - tri[0])) v / norm(v);    
+
+    function vertex_normal(sf, xi, yi) = 
+        let(
+            xy = [xi, yi],
+            // clockwise
+            vi = [for(coord_offset = [[1, 0], [0, -1], [-1, 0], [0, 1]]) coord_offset + xy],
+            normals = [
+                for(i = [0:3])
+                let(
+                    vi0 = xy,
+                    vi1 = vi[i],
+                    vi2 = vi[(i + 1) % 4],
+                    v1 = sf[vi0[1]][vi0[0]], 
+                    v2 = sf[vi1[1]][vi1[0]], 
+                    v3 = sf[vi2[1]][vi2[0]]
+                )
+                if(v1 != undef && v2 != undef && v3 != undef) 
+                    tri_normal([v1, v2, v3])
+            ]
+        )
+        sum(normals) / len(normals);
+
+    vertex_normals = [
+        for(y = [0:len(points) - 1])
+        [
+            for(x = [0:len(points[0]) - 1])
+                vertex_normal(points, x, y)
+        ]
+    ];
+
+
+    half_thickness = thickness / 2;
+    surface_top = points + half_thickness * vertex_normals;
+    surface_bottom = points - half_thickness * vertex_normals;    
+
+    sf_solidify(surface_top, surface_bottom, slicing);
+}
+
+/*
+use <surface/sf_thicken.scad>;
+
+function f(x, y) = 
+	30 * (
+		cos(sqrt(pow(x, 2) + pow(y, 2))) + 
+		cos(3 * sqrt(pow(x, 2) + pow(y, 2)))
+	);
+
+thickness = 3;
+min_value =  -200;
+max_value = 200;
+resolution = 10;
+
+surface1 = [
+    for(y = [min_value:resolution:max_value])
+        [
+            for(x = [min_value:resolution:max_value]) 
+                [x, y, f(x, y) + 100]
+        ]
+];
+sf_thicken(surface1, thickness);
+*/