If all you wanted to do was "lerp in 2D", the answer could be rather trivial, for example in the case of a rectangle, where given the values at the four corners, you can trivially interpolate values along two opposing edges, and then get any value in the middle by picking the corresponding pair of points on those edges and interpolate between those. The bit about arbitrary vertices however makes this more complicated.

This is part one of (probably) two. It’ll be a pretty rambly story mostly about why I developed three versions of a terminal video player. There will be a second part that will go deeper into the technical side (like what ffmpeg APIs to call and why, explained in plain english).