# (lisppad turtle)

This is a library implementing a simple graphics window for displaying turtle graphics. The library supports one graphics window per LispPad session which gets initialized by invoking

`init-turtle`

. `init-turtle`

will create a new turtle and display its drawing on a graphics window. If there is already an existing graphics window with the given title, it will be reused.Once

`init-turtle`

was called, the following functions can be used to move the turtle across the plane:`(pen-up)`

: Lifts the turtle`(pen-down)`

: Drops the turtle`(pen-color color)`

: Sets the current color of the turtle`(pen-size size)`

: Sets the size of the turtle pen`(home)`

: Moves the turtle back to the origin`(move x y)`

: Moves the turtle to position`(x, y)`

`(heading angle)`

: Sets the angle of the turtle (in radians)`(turn angle)`

: Turns the turtle by the given angle (in radians)`(left angle)`

: Turn left by the given angle (in radians)`(right angle)`

: Turn right by the given angle (in radians)`(forward distance)`

: Moves forward by`distance`

units drawing a line if the pen is down`(backward distance)`

: Moves backward by`distance`

units drawing a line if the pen is down

This library provides a simplified, interactive version of the API provided by library

`(lispkit draw turtle)`

.**(init-turtle)**

**(init-turtle scale)**

**(init-turtle scale title)**

Initializes a new turtle and displays its drawing in a graphics window.

`init-turtle`

gets two optional arguments: `scale`

and `title`

. `scale`

is a scaling factor which determines the size of the turtle drawing. `title`

is a string that defines the window name of the turtle graphics. It also acts as the identify of the turtle graphics window; i.e. it won't be possible to have two sessions with the same name but a different graphics window.**(close-turtle-window)**

Closes the turtle window and resets the turtle library.

**(turtle-drawing)**

Returns the drawing associated with the current turtle.

**(pen-up)**

Lifts the turtle from the plane. Subsequent

`forward`

and `backward`

operations don't lead to lines being drawn. Only the current coordinates are getting updated.**(pen-down)**

Drops the turtle onto the plane. Subsequent

`forward`

and `backward`

operations will lead to lines being drawn.**(pen-color**

*color***)**

Sets the drawing color of the turtle to

*color*.*color*is a color object as defined by library`(lispkit draw)`

.**(pen-size**

*size***)**

Sets the pen size of the turtle to

*size*. The pen size corresponds to the width of lines drawn by`forward`

and `backward`

.**(home)**

Moves the turtle to its home position.

**(move**

*x y***)**

Moves the turtle to the position described by the coordinates

*x*and*y*.**(heading**

*angle***)**

Sets the heading of the turtle to

*angle*.*angle*is expressed in terms of degrees.**(turn**

*angle***)**

Adjusts the heading of the turtle by

*angle*degrees.**(right**

*angle***)**

Adjusts the heading of the turtle by

*angle*degrees.**(left**

*angle***)**

Adjusts the heading of the turtle by

*-angle*degrees.**(forward**

*distance***)**

Moves the turtle forward by

*distance*units drawing a line if the pen is down.**(backward**

*distance***)**

Moves the turtle backward by

*distance*units drawing a line if the pen is down.Last modified 7mo ago