Initializing the Canvas

Our game needs a canvas on which all the games' graphics will be rendered. Let's initialize it.

Functions and variables

Let's take a closer look at fn init.

main.rs


#![allow(unused_variables)]

fn main() {
// this function initializes the canvas
fn init(width: u32, height: u32) -> (Canvas<Window>, EventPump) {
    let sdl_context = sdl2::init().unwrap();
    let video_subsystem = sdl_context.video().unwrap();

    let window = video_subsystem
        .window("Rusty Snake", width as u32 + 1, height as u32 + 1)
        .position_centered()
        .build()
        .unwrap();

    let mut canvas = window.into_canvas().present_vsync().build().unwrap();

    canvas.set_draw_color(Color::RGB(0, 0, 0));
    canvas.clear();
    canvas.present();

    let event_pump = sdl_context.event_pump().unwrap();
    (canvas, event_pump)
}

}

fn declares the function, init is its name. The function takes two parameters, x and y. Rust is a type safe language, so the types of the parameters need to be explicitly indicated. In this example, the type of both parameters is u32, a 32bit unsigned integer. The return types also need to be specifically named. fn init returns two values in a bracket, separated by a comma. The types of these values are defined in the sdl2-crate. We'll ignore the body of the function for now.

In main(), delete the println! statement.
Declare the variables canvas_width and canvas_height, each with the value 720_u32. _u32 makes this number explicitly an unsigned 32bit integer.

Call the function by adding the following line:


#![allow(unused_variables)]
fn main() {
let (canvas, events) = init(canvas_width, canvas_height);
}

In the terminal enter cargo run. What happens?