function calculateArrow(x1, x2, y1, y2) {
  var deg = -90;
  var dist_x = x1 - x2;
  var dist_y = Math.abs(y1 - y2);
  if (dist_y != 0) {
    deg = Math.atan(dist_x / dist_y);
  }
  if (y2 < y1) {
    deg = -1 * ((deg + Math.PI) % (2 * Math.PI));
  }
  return deg * 360 / (2 * Math.PI);
}

function renderRadar() {
    var mindist = 10000000000;
    var closest;
    var remainingFound = false;
    for (var S = 0; S < explorer.objects.length; S++) {
        var I = explorer.objects[S];
        if (!I.got) {
            remainingFound = true;
            var dist = distance(explorer.pos.x, explorer.pos.y, I.x1, I.y1);
            if (dist < mindist) {
                mindist = dist;
                closest = I;
            }
        }
    }
    if (!remainingFound) {
        document.getElementById("radar").innerHTML = "You found all coins!";
        return;
    }
    var indicator = "";
    var deg = calculateArrow(closest.x1, explorer.pos.x, closest.y1, explorer.pos.y);
    var dist_x = Math.abs(closest.x1 - explorer.pos.x);
    var dist_y = Math.abs(closest.y1 - explorer.pos.y);
    if (closest.x1 < explorer.pos.x) {
        indicator += ((dist_x < 500)?"slightly ":"") + "left";
    }
    if (closest.x1 > explorer.pos.x) {
        indicator += ((dist_x < 500)?"slightly ":"") + "right";
    }
    if (closest.y1 < explorer.pos.y) {
        indicator += ((dist_y < 500)?"slightly ":"") + " up";
    }
    if (closest.y1 > explorer.pos.y) {
        indicator += ((dist_y < 500)?"slightly ":"") + " down";
    }
    document.getElementById("radar").innerHTML = "Distance: " + mindist.toFixed(1).toString() + "<br/><div id=\"indic\" style=\"transform: rotate(" + deg + "deg)\" title=\"indicator\">&#8593;</div>";
}
setInterval(renderRadar, 100);