add tf_torus

src/experimental/tf_torus.scad

@@ -0,0 +1,20 @@
+use <rotate_p.scad>;
+
+function tf_torus(size, point, radius, angle = [360, 360], twist = 0) =
+    let(
+        xlen = size[0],
+        ylen = size[1],
+        x = point[0],        
+        y = point[1],
+        R = radius[0],
+        r = radius[1],
+        A = angle[0],
+        a = angle[1],
+        ya_step = a / xlen,
+        za_step = A / ylen,
+        twa_step = twist / ylen,
+        ya = 180 - x * ya_step,
+        za = za_step * y,
+        twisted = rotate_p([r * cos(ya), 0, r * sin(ya)], [0, twa_step * y, 0])
+    ) 
+    rotate_p(twisted + [R + r, 0, 0], za);