hilbert turtle

docs/src/animation.md

@@ -76,7 +76,9 @@ Sometimes you want to construct an animation that has different components, laye
 
 As an example, consider a simple example showing the sun for each hour of a 24 hour day.
 
- sun24demo = Movie(400, 400, "sun24", 0:23)
+```
+sun24demo = Movie(400, 400, "sun24", 0:23)
+```
 
 The `backgroundfunction()` draws a background that's used for all frames (animated GIFs like constant backgrounds):
 

docs/src/transforms.md

@@ -53,7 +53,7 @@ nothing # hide
 ![scale](assets/figures/scale.png)
 
 
-`rotate()` rotates the current workspace by the specifed amount about the current 0/0 point. It's relative to the previous rotation, not to the document's original.
+`rotate()` rotates the current workspace by the specified amount about the current 0/0 point. It's relative to the previous rotation, not to the document's original.
 
 ```@example
 using Luxor, Random # hide

docs/src/turtle.md

@@ -57,6 +57,50 @@ nothing # hide
 
 ![many turtles](assets/figures/manyturtles.svg)
 
+A turtle graphics approach lends itself well to recursive programming. This short recursive function draws a Hilbert curve.
+
+```@example
+using Luxor, Colors # hide
+Drawing(400, 400, "assets/figures/hilbertturtle.svg") # hide
+origin() # hide
+background("black") # hide
+
+function hilbert(t::Turtle, level, angle, lengthstep)
+    level == 0 && return
+
+    HueShift(t, 0.1)
+
+    Turn(t, angle)
+    hilbert(t, level-1, -angle, lengthstep)
+
+    Forward(t, lengthstep)
+    Turn(t, -angle)
+    hilbert(t, level-1, angle, lengthstep)
+
+    Forward(t, lengthstep)
+    hilbert(t, level-1, angle, lengthstep)
+
+    Turn(t, -angle)
+    Forward(t, lengthstep)
+    hilbert(t, level-1, -angle, lengthstep)
+
+    Turn(t, angle)
+end
+
+setline(2)
+setlinecap("round")
+
+hilbert(Turtle(first(BoundingBox()) + (12, 12), true, 0, (1, 0, 0)),
+        6,  # level
+        90, # turn angle, in degrees
+        6   # steplength
+        )
+finish() # hide
+nothing # hide
+```
+
+![hilbert turtle](assets/figures/hilbertturtle.svg)
+
 ```@docs
 Turtle
 Forward

src/Turtle.jl

@@ -175,7 +175,8 @@ end
     HueShift(t::Turtle, inc=1.0)
 
 Shift the Hue of the turtle's pen forward by `inc`. Hue values range between
-0 and 360.
+0 and 360. (Don't start with black, otherwise the saturation and brightness values
+will be black.)
 """
 function HueShift(t::Turtle, inc=1.0)
     r, g, b = t.pencolor