Find Perimeter Of Points

It is possible to find borders between cells with and without content, and to make a contour from the pieces. The first part can be done e.g. by using algorithms from voxel rendering, like marching cubes (but adapted to 2D, of course). Having determined which of and how the 4 sides of a cell are passed by borders, you can chain borders by following the border in those neighbored cells that are determined by the border configuration of the current cell.

What you're asking about is a simple case of a classical image processing problem. Just google "contour tracing" or "contour extraction". Also I have a python implementation of contour extraction in the general case here although it isn't the clearest code in the world and is overkill for what you need (I think).

You'll have to do some post-processing to clip corners to get diagonals like you want though.

Thanks! I did a google search and came across this which looks promosing. And I shall check out your code jwezoewk.

The method I currently use which doesn't work in all cases involves searching neighbouring pixels for a "candidate" next pixel, then moving to the candidate most in the direction back to the starting position.