add tf_bend

src/experimental/tf_bend.scad

@@ -0,0 +1,18 @@
+/*
+    size: The size of the rectangle which can contain the point.
+    point: A point in the rectangle.
+    radius: The radius of the arc after being bent
+    angle: The central angle of the arc.
+*/
+
+function tf_bend(size, point, radius, angle) = 
+    let(
+        xlen = size[0],
+        // ignored
+        // ylen = size[1],
+        y = point[0],
+        z = point[1],
+        a_step = angle / xlen,
+        a = a_step * y
+    )
+    [radius * cos(a), radius * sin(a), z];