The envelope of light rays reflected or refracted by a curved surface is called a Caustic.
All the light rays incident on the caustic surface are tangent to it.
The next time you take a sip from your coffee mug, be sure to take a look at its soul that it benevolently exhibits.
In the case of a circle, the caustic shape/curve formed is the cardioid.
Even water produces some really interesting caustic patterns
and so does wine in a glass.
Some of the images that have portrayed in the post have been made using computer graphic rendering systems. They trace the possible paths of light beam, accounting for refraction and reflection.
Have a great day!