Height of the game window

HEIGHT = 400

Width of the game window

WIDTH = 400

Background color of the game window

BACKGROUND = "moon.jpg" #colorant"purple"

Globals to store the velocity of the actor

dx = 2
dy = 2

Create an Actor object with an image

a=Actor("alien.png")
txt = TextActor("Hello World", "moonhouse")
txt.pos = (120,180)

Start playing background music

play_music("radetzky_ogg")

The draw function is called by the framework. All we do here is draw the Actor

function draw(g::Game)
    draw(a)
    draw(txt)
end

The update function is called every frame. Within the function, we

• change the position of the actor by the velocity
• if the actor hits the edges, we invert the velocity, and play a sound
• if the up/down/left/right keys are pressed, we change the velocity to move the actor in the direction of the keypress

function update(g::Game)
    global dx, dy
    a.position.x += dx
    a.position.y += dy
    if a.x > 400-a.w || a.x < 2
        dx = -dx
        play_sound("eep")
    end
    if a.y > 400-a.h || a.y < 2
        dy = -dy
        play_sound("eep")
    end

    if g.keyboard.DOWN
        dy = 2
    elseif g.keyboard.UP
        dy = -2
    elseif g.keyboard.LEFT
        dx = -2
    elseif g.keyboard.RIGHT
        dx = 2
    end

end

If the "space" key is pressed, change the displayed image to the "hurt" variant. Also schedule an event to change it back to normal after one second.

function on_key_down(g, k)
    if k == Keys.SPACE
        alien_hurt()
        schedule_once(alien_normal, 1)
    end
end

We define functions to change the image for the actor. These functions are called from the keydown and scheduled events.

alien_hurt() = a.image = "alien_hurt.png"
alien_normal() = a.image = "alien.png"