function myAnimation() {
    ctx.clearRect(0, 0, canvas_size_x, canvas_size_y);

    if (x_icon < 0 || x_icon > canvas_size_x - size_x) {
        stepX = -stepX;
    }
    
    if (y_icon < 0 || y_icon > canvas_size_y - size_y) {
        stepY = -stepY;
    }

    x_icon += stepX;
    y_icon += stepY;

    ctx.drawImage(anim_img, x_icon, y_icon);
}

function draw() {
    var canvas = document.getElementById("canvas");
    ctx = canvas.getContext("2d");
    
    anim_img = new Image(size_x, size_y);
    
    anim_img.onload = function() {
        setInterval('myAnimation()', 5);
    }
    
    anim_img.src = 'http://www.gbtags.com/gb/networks/avatars/80x8013d6393f-a44c-4180-8cb6-7bf0e4776283.png';
}