[pygame] Proposed additions to Transform: connected components, upper and lower thresholding, and centroids

["Nirav Patel" <olpc@xxxxxxxxxxxxxx>]

As part of my project to add computer vision stuff to pygame, I'd like
to write a function or functions that do the following.

For vision purposes, it would be very useful to have thresholding with
both upper and lower boundaries, returning both the number of pixels
within the threshold and the centroid of those pixels.  This is a
trivial addition to the existing transform.threshold() function, but
is it acceptable to modify the input options and the output of an
existing function?  Would it break compatibility with existing pygame
games?  Would it make sense to have a second function so similar to an
existing one?

The other function, which is also similar (and could even just be an
option in thresholding), is thresholding with connected component
detection.  This would involve supplying an upper and lower threshold,
a Surface, and optionally a mask.  The function would find the largest
blob of pixels in the Surface within the threshold, make a mask of
those pixels if desired, and return the centroid and number of pixels
in the blob.

It could also be useful to have multiple connected component
detection, for "multi-touch" without having to use different colored
objects (or if you are using IR LEDs like the Wii does), but I'm not
sure how to handle that in a single pass of the array.  Actually, I'm
not really sure how I'm going to handle both detection and creating a
mask in a single pass either.  It may be necessary to store the
starting pixel, ending pixel, and size of each connected component on
the first pass, keeping track of which was the largest yet, and then
have a shorter second pass to create the mask that only starts at the
starting pixel and ends at the ending pixel.

Any comments, reality checks, questions, or suggestions would be
greatly appreciated.

Nirav