Frames.

Each animation step is displayed in a new frame. We will now draw a rectangle of the size of the canvas, with a different random color.

sdl offers methods to draw basic shapes, like rectangles, this needs to be imported. It also offers methods that convert our u8 values into RGB colors, that can be displayed.

#![allow(unused_variables)]
fn main() {
use sdl2::rect::Rect;
use rand;

}

rand is another library we are using. To activate it, add it to your Cargo.toml as a dependency. It should now look like this:

[dependencies]
sdl2 = "0.30.0"
rand = "0.7"

Add the following function to your program.

#![allow(unused_variables)]

fn main() {
fn display_rectangle (
    renderer: &mut Canvas<Window>,
    canvas_width: &u32,
    canvas_height: &u32,

) {
    let red: u8 = rand::random();
    let green: u8 = rand::random();
    let blue: u8 = rand::random();

    renderer.clear();

    let drawing_color = Color::RGB(red, green, blue);
    renderer.set_draw_color(drawing_color);

    let square_definition = Rect::new(0, 0, *canvas_width, *canvas_height);
    renderer.fill_rect(square_definition);

    renderer.present();
}

}

The function takes the canvas, as well as the canvas width and height as arguments. It does not return a value. In the body of the function, the variables red, green and blue are assigned random u8 numbers. The clear() method is called on the renderer, this clears the canvas. When, like in our case, the entire canvas is drawn over, this does not really matter, but it's a good habit to think of this. Then, the drawing color is defined. We use a function that is provided by sdl2. The function takes in three u8 values and returns a color. The method set_draw_color() is called on the renderer, with drawing_color as argument.

We create a new rectangle with its minimum and maximum x and y values as arguments and bind it to the variable square_definition. This variable is then passed to the method fill_rect(). Our square is rendered and put into the back buffer.

The last line updates the screen with all the rendering done since the last update.

Do you notice anything peculiar about some of the type declarations in this function?

Try calling this function for every 'game loop iteration in your main program.

Run the program.