function preload(){
  img1 = loadImage('data/shapes.png');
  img2 = loadImage('data/draw.png');
  img3 = loadImage('data/toner.png');
}
Use an image to check on/off a grid of checkboxes
Shout out to Dan Shiffman's checkbox mirror example
Image credits: Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

KEYS
1                   : load image shapes
2                   : load image letters
3                   : load image map

SLIDER
drag                : drag the slider to adjust the image threshold

CONTRIBUTED BY
[Joey Lee](http://jk-lee.com)

INSPIRED BY
[Dan Shiffman](http://shiffman.net/)