About Foggy Window
Everyone has done this. A cold morning, a steamy bathroom mirror, the back window of the car, and you draw on the glass with your finger. A smiley face, your name, a heart with someone's initials. Then you watch it slowly fog back over. It's probably the first drawing surface most of us ever had, and one of the few that cleans itself.
This one is a window on a rainy evening. The street behind it is out of focus, streetlights and car lights and shop signs all smeared into soft circles, the way they look through wet glass. Wipe a patch and the city comes through a little sharper.
How It Works
Fog on a window is condensation. Warm, damp air hits cold glass and turns into millions of tiny droplets, small enough to scatter light in every direction. That's why fogged glass looks milky, and why lights behind it bloom into halos.
When you wipe it, you're really just pushing those droplets together into bigger ones, which is why your finger trails end up with little beads of water along the edges. Get enough of them together and gravity wins, and a drip runs down the glass.
The toy keeps a grid of fog across the window. Your finger clears it, and every bit of it slowly grows back at a slightly different speed, so drawings fade unevenly, edges first. Drips leave a clearer trail that hangs around a bit longer. A drawing takes about a minute to disappear completely.
How to Use It
Drag on the glass to draw. Pick a finger size from the toolbar. Hold still for a moment, or press the breath button, to breathe on the window and fog it back up. Switch the view between night city, dusk and a grey day. The bin fogs the whole window back over.
Try this: write something, then just sit and watch it go.
Sources and Reading
Condensation
on Wikipedia.
Bokeh
on Wikipedia, the name for those soft out-of-focus circles of light.