How to hide the portion of a graphic that is outside of a circle

Sometimes one might want to display a graphic such that only the portion inside a circle with a certain radius is displayed. The plot of a Sin wave below will be used as an example where only the portion of the graphic inside a circle centered at the origin with radius 0.85 is displayed.

The graphic made by the next cell is used to demonstrate how one can hide the portion of the above plot outside the desired circle.

The next input displays the mask from above on-top of the Sin wave made earlier.

The next cell makes a circle with lots of points, and ensures the mask covers the whole circle.

In the next cell the mask is invisible since it's the same color as the bacgkround.

Created by Mathematica (May 16, 2004)