Spotlight bookmarklet

gistfile1.js

// Save this in a bookmarklet and click it on a page:

javascript:(function(){function d(a,c){document.body.style.webkitClipPath="circle("+a+"px, "+c+"px, "+b+"px)"}var b=90;window.addEventListener("mousemove",function(a){d(a.pageX,a.pageY)});window.addEventListener("mousewheel",function(a){if(a.shiftKey){a.preventDefault();var c=a.wheelDeltaY;b+=-c;b=0<c?Math.max(90,b):Math.min(b,window.innerHeight/2);d(a.pageX,a.pageY)}})})();

// Or paste this in the console and mouse over the page.
// SHIFT+mousewheel scroll makes the circle bigger/smaller.

(function() {
var radius = 90; // px

function move(x, y) {
  // CSS clip path - http://dvcs.w3.org/hg/FXTF/raw-file/tip/masking/index.html#the-clip-path
  document.body.style.webkitClipPath = 'circle(' + x + 'px, ' + y + 'px, ' + radius + 'px)';
  document.body.style.mozClipPath = 'circle(' + x + 'px, ' + y + 'px, ' + radius + 'px)';
  document.body.style.msClipPath = 'circle(' + x + 'px, ' + y + 'px, ' + radius + 'px)';
  document.body.style.oClipPath = 'circle(' + x + 'px, ' + y + 'px, ' + radius + 'px)';
  document.body.style.clipPath = 'circle(' + x + 'px, ' + y + 'px, ' + radius + 'px)';
}

window.addEventListener('mousemove', function(e) {
  move(e.pageX, e.pageY);
});

// Holding down SHIFT and scrolling grows/shrinks the circle.
window.addEventListener('mousewheel', function(e) {
  if (!e.shiftKey) {
    return;
  }

  e.preventDefault(); // Prevent scrolling.

  var deltaY = e.wheelDeltaY;
  radius += -deltaY;
  if (deltaY > 0) { // up / shrink
    radius = Math.max(90, radius);
  } else {
    radius = Math.min(radius, window.innerHeight / 2);
  }
  move(e.pageX, e.pageY);
});

})();