Mazes - The Essential Guide to HTML5 - page 252

Code Explanation

case 39: //right arrow

mypent.moveit(unit,0);

break;

case 40: //down arrow

mypent.moveit(0,unit);

break;

default:

window.removeEventListener
('keydown',getkeyAndMove,false) ;

}

drawall();

}

function intersect(sx,sy,fx,fy,cx,cy,rad) {

var dx;

var dy;

var t;

var rt;

dx = fx-sx;

dy = fy-sy;

t =0.0-((sx-cx)*dx+(sy-
cy)*dy)/((dx*dx)+(dy*dy));

if (t<0.0) {