// Utility functions for a game to 
// detect collisopns and allow objects
// to bouce off the edges or
// be constrained to them

function randomlyPlace(thing)
{
    thing.x = Math.random() * (gCanvas.width - thing.width);
    thing.y = Math.random() * (gCanvas.height - thing.height);
}

// reverse the x and y speeds if overlapping the edges
function bounceOffEdges(thing)
{
    // bounce off the edges in Y direction
    if (thing.y + thing.height > gCanvas.height)
    {
        thing.y = gCanvas.height - thing.height;
        thing.yspeed *= -1;
    }else if (thing.y < 0){
        thing.y = 0; 
        thing.yspeed *= -1;
    }

    // bounce off the edges in X direction
    if (thing.x + thing.width > gCanvas.width)
    {
        thing.x = gCanvas.width -  thing.width;
        thing.xspeed *= -1;
    }else if (thing.x < 0){
        thing.x = 0;
        thing.xspeed *= -1;
    }

}

// limit the x and y positions if they would 
// go outside the canvas area
function constrainToEdges(thing)
{
    // if beyond the edges, limit in the X direction
    if (thing.x < 0){
        thing.x = 0;
    }else if (thing.x > gCanvas.width - thing.width){
        thing.x = gCanvas.width - thing.width;
    }

    // if beyond the edges, limit in the X direction
    if (thing.y < 0){
        thing.y = 0;
    }else if (thing.y > gCanvas.height - thing.height){
        thing.y =  gCanvas.height - thing.height;
    }
}


// detect whether two objects have collided
function detectCollision(thing1,thing2)
{
    var collided = true;

    if (thing1.x>  thing2.x + thing2.width) collided = false;
    if (thing1.x + thing1.width < thing2.x ) collided = false;
    if (thing1.y > thing2.y + thing2.height) collided = false;
    if (thing1.y + thing1.height < thing2.y) collided = false;
    return collided;
}