Comment by convolvatron

there were at least two renderers written for the CM2 that used strips. at least one of them used scans and general communication, most likely both.

1) for the given processor set, where each process holds an object 'spawn' a processor in a new set, one processor for each span. (a) spawn operation consists of the source processor setting the number of nodes in the new domain, then performing an add-scan, then sending the total allocation back to the front end the front end then allocates a new power-of-2 shape than can hold those the object-set then uses general communication to send scan information to the first of these in the strip-set (the address is left over from the scan) (b) in the strip-set, use a mask-copy-scan to get all the parameters to all the the elements of the scan set. (c) each of these elements of the strip set determine the pixel location of the leftmost element (d) use a general send to seed the strip with the parameters of the strip (e) scan those using a mask-copy-scan in the pixel-set (f) apply the shader or the interpolation in the pixel-set

note that steps (d) and (e) also depend on encoding the depth information in the high bits and using a max combiner to perform z-buffering.

Edit: there must have been an additional span/scan in a pixel space that is then sent to image space with z buffering, otherwise strip seeds could collide, and be sorted by z which may miss pixels from the losing strip