Cardio is a fun web app for drawing Cardioids and related mathematical figures with nothing but straight lines. A Cardioid is what you get when following a point on a circle that is rolling around another circle of the same radius, or the pattern refractured light makes in a cup, or, in this case, the envelope of lines arranged in a circle (and many other things!). On here you'll get a Cardioid when "X Degree" and "Y Degree" (which are most definitely mathematically incorrect labels) are both equal to 2. Whenever X & Y Degree are equal, you'll get a more general form of a Cardioid, an Epicycloid. I have no idea what the mathematical term for the patterns that develop when X & Y Degree are different are, but they look cool anyway :D
I built this website because 1) watching straight lines build these patterns is mesmerizing, 2) screwing with parameters is fun, and 3) the actual drawing process is surprisingly simple. See this section on Wikipedia for an explanation. The X and Y Degree on here just dictate how much the second point gets moved. The entire drawing logic is in this component if you want to take a look at it.
Optimize for mobile. Currently trying to figure out how to make the canvas look sharp on mobile devices without screwing up the layout of the page D: