+
+# Immutable relative anchors for reference points on `camera`
+private class CameraAnchor
+ super IPoint3d[Float]
+
+ # Reference camera
+ var camera: UICamera
+
+ # Reference position, the top left of the screen
+ var ref: Point3d[Float] = camera.position is lazy
+
+ # X position as proportion of the screen width
+ var relative_x: Float
+
+ # Y position as proportion of the screen height
+ var relative_y: Float
+
+ redef fun x do return ref.x + relative_x*camera.width
+ redef fun y do return ref.y + relative_y*camera.height
+ redef fun z do return ref.z
+
+ redef fun offset(x, y, z) do return new OffsetPoint3d(self, x.to_f, y.to_f, z.to_f)
+end
+
+# Position relative to another point or usually a `CameraAnchor`
+private class OffsetPoint3d
+ super Point3d[Float]
+
+ autoinit ref, offset_x, offset_y, offset_z
+
+ # Reference point to which the offsets are applied
+ var ref: IPoint3d[Float]
+
+ # Difference on the X axis
+ var offset_x: Float
+
+ # Difference on the X axis
+ var offset_y: Float
+
+ # Difference on the X axis
+ var offset_z: Float
+
+ redef fun x do return ref.x + offset_x
+ redef fun y do return ref.y + offset_y
+ redef fun z do return ref.z + offset_z
+
+ redef fun x=(value) do if value != null then offset_x += value - x
+ redef fun y=(value) do if value != null then offset_y += value - y
+ redef fun z=(value) do if value != null then offset_z += value - z
+
+ redef fun offset(x, y, z) do return new OffsetPoint3d(self, x.to_f, y.to_f, z.to_f)
+end