I have code of finding the perpendicular distance from a point to a 3D plane. But in this case, the plane is infinite. If the plane is not infinite, but limited to a certain piece, such as the face of an object, then how to find the minimum distance from a point to that face?

An example:

If the 3 points defining a "piece" of plane are:

1 0 0

0 1 0

0 0 0

And the query point is:

1 1 1

Then the answer will be .

Is there any implementation in C++ for this problem? If yes, then could someone please provide it? And if not, then sharing the idea of solving it will also help. Thanks in advance.