This is a animated space-filling Hilbert Curve in Processing.

The first three quarters of the curve are colored black, but the last quarter reveals a still image of Rick Astley.

There are some settings you can change by changing variable values:

1. lerpStep: Reduce/Increase it to make the curve smoother/dotted and make the animation run faster/slower
2. onlyTopRightCorner: Set this value to false if you want to reveal the image over the whole curve
3. skipNodes and skipAmount: if skipNodes is true, every skipAmount-th Node will be skipped

Have fun. You can see this program in action here (edited for entertainment purposes).