Struct Turtle

pub struct Turtle { /* private fields */ }

A turtle with a pen attached to its tail

The idea: You control a turtle with a pen tied to its tail. As it moves across the screen, it draws the path that it follows. You can use this to draw any picture you want just by moving the turtle across the screen.

See the documentation for the methods below to learn about the different drawing commands you can use with the turtle.

Implementations

impl Turtle

pub fn new() -> Turtle

Create a new turtle.

This will immediately open a new window with the turtle at the center. As each line in your program runs, the turtle shown in the window will update.

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    // Do things with the turtle...
}

Note: If you do not create the Turtle right at the beginning of main(), call turtle::start() in order to avoid any problems.

pub fn forward(&mut self, distance: Distance)

Move the turtle forward by the given amount of distance. If the pen is down, the turtle will draw a line as it moves.

The turtle takes very small steps (measured in “pixels”). So if you want it to move more, use a bigger value to make the turtle walk further. The distance can be a negative value in which case the turtle will move backward.

Example

// Move forward 10 tiny turtle steps, drawing a line as you move
turtle.forward(10.0);

// Move forward 100 tiny turtle steps, drawing a much longer line
turtle.forward(100.0);

// Move backward 223 tiny turtle steps, without drawing anything
turtle.pen_up();
turtle.forward(-223.0);

pub fn backward(&mut self, distance: Distance)

Move the turtle backwards by the given amount of distance. If the pen is down, the turtle will draw a line as it moves.

The turtle takes very small steps (measured in “pixels”). So if you want it to move more, use a bigger value to make the turtle walk further. The distance can be a negative value in which case the turtle will move forward.

Example

// Move backward 10 tiny turtle steps, drawing a line as you move
turtle.backward(10.0);

// Move backward 100 tiny turtle steps, drawing a much longer line
turtle.backward(100.0);

// Move forward 179 tiny turtle steps, without drawing anything
turtle.pen_up();
turtle.backward(-179.0);

pub fn right(&mut self, angle: Angle)

Instruct the turtle to turn right (clockwise) by the given angle. Since the turtle rotates in place, its position will not change and it will not draw anything while it turns.

The angle parameter is a floating point number that represents how much you want the turtle to rotate. The unit of angle is “degrees” by default. You can change that by using the use_degrees() or use_radians() methods.

Example

// rotate right by 30 degrees
turtle.right(30.0);

// rotate right by 1 radian (57.2957795 degrees)
turtle.use_radians();
turtle.right(1.0);
// Use PI for precise angles in radians
use std::f64::consts::PI;
// This is the same as turning 45.0 degrees
turtle.right(PI/4.0);

pub fn left(&mut self, angle: Angle)

Instruct the turtle to turn left (counterclockwise) by the given angle. Since the turtle rotates in place, its position will not change and it will not draw anything while it turns.

The angle parameter is a floating point number that represents how much you want the turtle to rotate. The unit of angle is “degrees” by default. You can change that by using the use_degrees() or use_radians() methods.

Example

// rotate left by 30 degrees
turtle.left(30.0);

// rotate left by 1 radian (57.2957795 degrees)
turtle.use_radians();
turtle.left(1.0);
// Use PI for precise angles in radians
use std::f64::consts::PI;
// This is the same as turning 45.0 degrees
turtle.left(PI/4.0);

pub fn wait(&mut self, secs: f64)

Waits for the specified number of seconds before executing the next command.

turtle.forward(100.0);
turtle.wait(2.0);
// The turtle will stop for 2 seconds before proceeding to this line
turtle.forward(50.0);

pub fn drawing(&self) -> &Drawing

Retrieve a read-only reference to the drawing.

See the documentation for the Drawing struct for a complete listing of the information that you can retrieve from the drawing.

pub fn drawing_mut(&mut self) -> &mut Drawing

Retrieve a mutable reference to the drawing

See the documentation for the Drawing struct for a complete listing of the ways that you can manipulate the drawing.

pub fn speed(&self) -> Speed

Returns the current speed of the turtle.

turtle.set_speed(8);
assert_eq!(turtle.speed(), 8);

See the documentation for the Speed struct for more information.

pub fn set_speed<S: Into<Speed>>(&mut self, speed: S)

Set the turtle’s movement and rotation speed to the given value. A higher value will make the turtle’s walking and turning animations faster.

You can pass either a number or certain strings like "slow", "normal", and "fast". See the documentation for the Speed struct for all of the different options as well as the valid range of numbers that can be used for speeds.

turtle.set_speed("normal");
turtle.set_speed("fast");
turtle.set_speed(2);
turtle.set_speed(12);
turtle.set_speed("slower");
// Constructing a Speed directly works too, but the syntax above is often more convenient
turtle.set_speed(Speed::from(2));

Any invalid string or numeric value outside of the valid range will cause the program to panic! at runtime.

Moving Instantly

Setting the speed to "instant" results in no animation. The turtle moves instantly and turns instantly. This is often used to position the turtle before you start to draw something. You can set the speed to instant, move the turtle into the position you want to start your drawing from and then set the speed back to "normal".

let mut turtle = Turtle::new();
turtle.set_speed("instant");
// Move to a position 300 steps to the left of the start position
turtle.right(90.0);
turtle.backward(300.0);

// The turtle is in position we want it to start at,
// so let's set the speed back to normal
turtle.set_speed("normal");
// Start drawing from here...

Conversion Traits

So how does this method work? Why can it accept completely different types as input to the same function?

Using this method is an excellent way to learn about the conversion traits From and Into. This method takes a generic type as its speed parameter. By specifying the type as S: Into<Speed>, we are telling the Rust compiler that we want to accept any type that can be converted into a Speed.

// This is (essentially) how Turtle::set_speed is implemented
fn set_speed<S: Into<Speed>>(&mut self, speed: S) {
    // Calling `.into()` converts the value of `speed` into type `Speed`.
    // The `.into()` method is defined in the `Into` trait and is implemented by `Speed`
    // for `i32` and `&str`
    // `S: Into<Speed>` makes the compiler guarantee that this method exists and returns
    // exactly the type that we expect
    let speed: Speed = speed.into();
    self.speed = speed;
}

// This makes it possible to pass in any type that can be converted into a `Speed`
fn main() {
    let mut turtle = Turtle::new();

    // The following works because `Speed` defined a conversion from `i32`
    turtle.set_speed(1);

    // The following works because `Speed` defined a conversion from `&str`
    turtle.set_speed("fast");
}

The Speed documentation describes the different types that it can be converted from in detail. For other types and in other crates where this may not be explicitly documented, you can always find this information by looking for implementations of the From trait.

Speed implements From for several types:

• impl From<&str> for Speed
• impl From<i32> for Speed
• etc.

Why look for From and not Into? It turns out that the Rust compiler knows a rule that says “if some type A can be converted from type B, type B can be converted into type A.” That is why most types only implement From and leave Into to automatically be derived based on the rule. See the documentation of the Into trait for the “blanket implementation” which defines that rule.

pub fn position(&self) -> Point

Returns the turtle’s current location (x, y)

turtle.forward(100.0);
let pos = turtle.position();
assert_eq!(pos.round(), Point {x: 0.0, y: 100.0});

pub fn go_to<P: Into<Point>>(&mut self, position: P)

Moves the turtle directly to the given position. See the Point struct documentation for more information.

If the pen is down, this will draw a line. The turtle will not turn to face the direction in which it is moving. It’s heading will stay the same. Use set_speed() to control the animation speed.

let heading = turtle.heading();
assert_eq!(turtle.position(), Point {x: 0.0, y: 0.0});
turtle.go_to([100.0, -150.0]);
// The heading has not changed, but the turtle has moved to the new position
assert_eq!(turtle.heading(), heading);
assert_eq!(turtle.position(), Point {x: 100.0, y: -150.0});

pub fn set_x(&mut self, x: f64)

Goes to the given x-coordinate, keeping the y-coordinate and heading of the turtle the same. See go_to() for more information.

pub fn set_y(&mut self, y: f64)

Goes to the given y-coordinate, keeping the x-coordinate and heading of the turtle the same. See go_to() for more information.

pub fn home(&mut self)

Moves instantaneously to the origin and resets the heading to face north.

let mut turtle = Turtle::new();
let start_position = turtle.position().round();
let start_heading = turtle.heading().round();
turtle.right(55.0);
turtle.forward(127.0);
assert_ne!(turtle.heading().round(), start_heading);
assert_ne!(turtle.position().round(), start_position);
turtle.home();
assert_eq!(turtle.heading().round(), start_heading);
assert_eq!(turtle.position().round(), start_position);

pub fn heading(&self) -> Angle

Returns the turtle’s current heading.

The unit of the returned angle is degrees by default, but can be set using the use_degrees() or use_radians() methods.

The heading is relative to the positive x axis (east). When first created, the turtle starts facing north. That means that its heading is 90.0 degrees. The following chart contains many common directions and their angles.

Cardinal Direction	Heading (degrees)	Heading (radians)
East	0.0°	0.0
North	90.0°	PI/2
West	180.0°	PI
South	270.0°	3*PI/2

You can test the result of heading() with these values to see if the turtle is facing a certain direction.

// Turtles start facing north
let mut turtle = Turtle::new();
// The rounding is to account for floating-point error
assert_eq!(turtle.heading().round(), 90.0);
turtle.right(31.0);
assert_eq!(turtle.heading().round(), 59.0);
turtle.left(193.0);
assert_eq!(turtle.heading().round(), 252.0);
turtle.left(130.0);
// Angles should not exceed 360.0
assert_eq!(turtle.heading().round(), 22.0);

pub fn set_heading(&mut self, angle: Angle)

Rotate the turtle so that its heading is the given angle.

The unit of angle is degrees by default, but can be set using the use_degrees() or use_radians() methods.

The turtle will attempt to rotate as little as possible in order to reach the given heading (between -180 and 179 degrees). Use set_speed() to control the animation speed.

Here are some common directions in degrees and radians:

Cardinal Direction	Heading (degrees)	Heading (radians)
East	0.0°	0.0
North	90.0°	PI/2
West	180.0°	PI
South	270.0°	3*PI/2

See heading() for more information.

Example

// Turtles start facing north
let mut turtle = Turtle::new();
// The rounding is to account for floating-point error
assert_eq!(turtle.heading().round(), 90.0);
turtle.set_heading(31.0);
assert_eq!(turtle.heading().round(), 31.0);
turtle.set_heading(293.0);
assert_eq!(turtle.heading().round(), 293.0);
turtle.set_heading(1.0);
assert_eq!(turtle.heading().round(), 1.0);
// Angles should not exceed 360.0, even when we set them to values larger than that
turtle.set_heading(367.0);
assert_eq!(turtle.heading().round(), 7.0);

pub fn is_using_degrees(&self) -> bool

Returns true if Angle values will be interpreted as degrees.

See use_degrees() for more information.

pub fn is_using_radians(&self) -> bool

Returns true if Angle values will be interpreted as radians.

See use_radians() for more information.

pub fn use_degrees(&mut self)

Change the angle unit to degrees.

assert!(!turtle.is_using_degrees());
turtle.use_degrees();
assert!(turtle.is_using_degrees());

// This will now be interpreted as 1.0 degree
turtle.right(1.0);

pub fn use_radians(&mut self)

Change the angle unit to radians.

assert!(!turtle.is_using_radians());
turtle.use_radians();
assert!(turtle.is_using_radians());

// This will now be interpreted as 1.0 radian
turtle.right(1.0);

pub fn is_pen_down(&self) -> bool

Return true if pen is down, false if it’s up.

assert!(turtle.is_pen_down());
turtle.pen_up();
assert!(!turtle.is_pen_down());
turtle.pen_down();
assert!(turtle.is_pen_down());

pub fn pen_down(&mut self)

Pull the pen down so that the turtle draws while moving.

assert!(!turtle.is_pen_down());
// This will move the turtle, but not draw any lines
turtle.forward(100.0);
turtle.pen_down();
assert!(turtle.is_pen_down());
// The turtle will now draw lines again
turtle.forward(100.0);

pub fn pen_up(&mut self)

Pick the pen up so that the turtle does not draw while moving

assert!(turtle.is_pen_down());
// The turtle will move and draw a line
turtle.forward(100.0);
turtle.pen_up();
assert!(!turtle.is_pen_down());
// Now, the turtle will move, but not draw anything
turtle.forward(100.0);

pub fn pen_size(&self) -> f64

Returns the size (thickness) of the pen. The thickness is measured in pixels.

turtle.set_pen_size(25.0);
assert_eq!(turtle.pen_size(), 25.0);

See set_pen_size() for more details.

pub fn set_pen_size(&mut self, thickness: f64)

Sets the thickness of the pen to the given size. The thickness is measured in pixels.

The turtle’s pen has a flat tip. The value you set the pen’s size to will change the width of the stroke created by the turtle as it moves. See the example below for more about what this means.

Example

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();

    turtle.pen_up();
    turtle.right(90.0);
    turtle.backward(300.0);
    turtle.pen_down();

    turtle.set_pen_color("#2196F3"); // blue
    turtle.set_pen_size(1.0);
    turtle.forward(200.0);

    turtle.set_pen_color("#f44336"); // red
    turtle.set_pen_size(50.0);
    turtle.forward(200.0);

    turtle.set_pen_color("#4CAF50"); // green
    turtle.set_pen_size(100.0);
    turtle.forward(200.0);
}

This will produce the following:

Notice that while the turtle travels in a straight line, it produces different thicknesses of lines which appear like large rectangles.

pub fn pen_color(&self) -> Color

Returns the color of the pen.

turtle.set_pen_color("blue");
assert_eq!(turtle.pen_color(), "blue".into());

See the color module for more information about colors.

pub fn set_pen_color<C: Into<Color> + Copy + Debug>(&mut self, color: C)

Sets the color of the pen to the given color.

Any type that can be converted into a color can be passed into this function. See the color module for more information.

Example

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    turtle.drawing_mut().set_background_color("light grey");
    turtle.set_pen_size(3.0);

    let colors = ["red", "green", "blue"];

    for i in 0..36 {
        turtle.set_pen_color(colors[i % colors.len()]);
        turtle.forward(25.0);
        turtle.right(10.0);
    }
}

This will produce the following:

pub fn fill_color(&self) -> Color

Returns the current fill color.

This will be used to fill the shape when begin_fill() and end_fill() are called.

turtle.set_fill_color("coral");
assert_eq!(turtle.fill_color(), "coral".into());

See the color module for more information about colors.

pub fn set_fill_color<C: Into<Color> + Copy + Debug>(&mut self, color: C)

Sets the fill color to the given color.

Note: The fill color must be set before begin_fill() is called in order to be used when filling the shape.

Any type that can be converted into a color can be passed into this function. See the color module for more information.

Example

See begin_fill() for an example.

pub fn is_filling(&self) -> bool

Return true if the turtle is currently filling the shape drawn by its movements.

assert!(!turtle.is_filling());
turtle.begin_fill();
assert!(turtle.is_filling());
turtle.end_fill();
assert!(!turtle.is_filling());

See begin_fill() for more information and an example.

pub fn begin_fill(&mut self)

Begin filling the shape drawn by the turtle’s movements.

Rule of thumb: For every call to begin_fill(), there should be a corresponding call to end_fill().

Example

The following example will draw a circle filled with the color red and then a square with no fill.

Note: The fill color must be set before begin_fill() is called in order to be used when filling the shape.

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    turtle.right(90.0);
    turtle.set_pen_size(3.0);

    turtle.set_pen_color("blue");
    turtle.set_fill_color("red");
    turtle.begin_fill();
    for _ in 0..360 {
        turtle.forward(2.0);
        turtle.right(1.0);
    }
    turtle.end_fill();

    turtle.set_pen_color("green");
    turtle.forward(120.0);
    for _ in 0..3 {
        turtle.right(90.0);
        turtle.forward(240.0);
    }
    turtle.right(90.0);
    turtle.forward(120.0);
}

This will result in the following:

pub fn end_fill(&mut self)

Stop filling the shape drawn by the turtle’s movements.

Rule of thumb: For every call to begin_fill(), there should be a corresponding call to end_fill().

See begin_fill() for more information.

pub fn is_visible(&self) -> bool

Returns true if the turtle is visible.

let mut turtle = Turtle::new();
assert!(turtle.is_visible());
turtle.hide();
assert!(!turtle.is_visible());
turtle.show();
assert!(turtle.is_visible());

pub fn hide(&mut self)

Makes the turtle invisible. The shell will not be shown, but drawings will continue.

Useful for some complex drawings.

assert!(turtle.is_visible());
turtle.hide();
assert!(!turtle.is_visible());

pub fn show(&mut self)

Makes the turtle visible.

assert!(!turtle.is_visible());
turtle.show();
assert!(turtle.is_visible());

pub fn reset(&mut self)

Delete the turtle’s drawings from the screen, re-center the turtle and reset all of the turtle’s state (speed, color, etc.) back to the default.

turtle.left(43.0);
turtle.forward(289.0);
turtle.set_pen_color("red");
turtle.drawing_mut().set_background_color("green");
let position = turtle.position();
let heading = turtle.heading();
turtle.reset();
assert_eq!(turtle.heading(), 90.0);
assert_eq!(turtle.position(), Point {x: 0.0, y: 0.0});
assert_ne!(turtle.pen_color(), "red".into());
assert_ne!(turtle.drawing().background_color(), "green".into());

pub fn clear(&mut self)

Delete the turtle’s drawings from the screen.

Does not move turtle. Position, speed and heading of the turtle are not affected. The background color and any other settings (pen color, size, etc.) all remain the same.

Example

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    turtle.right(32.0);
    turtle.forward(150.0);

    turtle.wait_for_click();
    turtle.clear();
}

This will produce the following:

Once you click on the screen, the drawings will be cleared:

pub fn turn_towards<P: Into<Point>>(&mut self, target: P)

Rotates the turtle to face the given point. See the Point struct documentation for more information.

If the coordinates are the same as the turtle’s current position, no rotation takes place. Always rotates the least amount necessary in order to face the given point.

Example

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    // moving the turtle to the bottom on the screen in the middle
    turtle.pen_up();
    turtle.go_to([0.0, -300.0]);
    turtle.set_heading(90.0);
    turtle.pen_down();

    // the turtle will go up following an oscillating point
    let mut i: f64 = 0.0;
    // choosing an arbitrary constant to multiply
    // the cos function, result between -5000 and 5000
    let c = 5000.0;
    // just draw a few full cicles
    while i < 15.0 {
        let f = (i).cos()*c;
        // following the oscillating point above at y=1000
        turtle.turn_towards([f, 1000.0]);
        // going forward for a small amount
        turtle.forward(1.0);
        // incrementing the angle
        i = i + 0.01;
    }
}

pub fn wait_for_click(&mut self)

Convenience function that waits for a click to occur before returning.

Useful for when you want the turtle to wait for the user to click before continuing. Use this to force the turtle to wait before it starts drawing at the beginning of your program.

This method uses poll_event() internally and ignores any other events that take place before the click is received.

Example

use turtle::Turtle;

fn main() {
    let mut turtle = Turtle::new();
    turtle.wait_for_click();
    // The turtle will wait for the screen to be clicked before continuing
    turtle.forward(100.0);
}

Trait Implementations

impl Default for Turtle

fn default() -> Self

Returns the “default value” for a type.