The Poser 4 renderer renders one 'scan line' at a time.  The Firefly renderer renders little squares across the screen.  Each of these squares is the width and height of a bucket.  Firefly has to allocate memory to handle everything related to rendering the pixels contained within a particular bucket.

So basically, it figures out which polygons are going to be rendered in this bucket and if smoothing is enabled, it creates all the micropolygons for those and (along with the shadow map and other things) it renders that section of the image.  Each rendering thread needs it's own bucket (memory).  pzj99, check your bucket size... if your renders are 'hanging' for long periods of time, try a smaller bucket size.

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