diff --git a/collects/graphics/scribblings/traditional-turtles.scrbl b/collects/graphics/scribblings/traditional-turtles.scrbl index 444d7b6a84..660d185f42 100644 --- a/collects/graphics/scribblings/traditional-turtles.scrbl +++ b/collects/graphics/scribblings/traditional-turtles.scrbl @@ -5,6 +5,9 @@ @defmodule[graphics/turtles] +To use any of the turtle drawing functions, you first need to +initialize the turtles by calling @racket[(turtles #t)]. + @defproc*[([(turtles [on? any/c]) void?] [(turtles) void?])]{ @@ -126,7 +129,8 @@ The fern functions below demonstrate more advanced use of @defmodule[graphics/turtle-examples] The @racketmodname[graphics/turtle-examples] library's source is meant -to be read, but it also exports the following examples. +to be read, but it also exports the following examples. To display these +examples, first initialize the turtle window with @racket[(turtles #t)]. @defproc[(regular-poly [sides exact-nonnegative-integer?] [radius real?]) void?]{ diff --git a/collects/graphics/turtles.rkt b/collects/graphics/turtles.rkt index 72f4540275..e0b0ea5986 100644 --- a/collects/graphics/turtles.rkt +++ b/collects/graphics/turtles.rkt @@ -220,7 +220,8 @@ (clear-window)) (define (update-icon) - (send turtles:window refresh)) + (when turtles:window + (send turtles:window refresh))) (define (home) (set! turtles-cache empty-cache)