Re: upstream vs. downstream

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Yair Kurzion (yair++at++polygon.engr.sgi.com)
Mon, 11 Oct 1999 13:19:45 -0700 (PDT)

> I've seen several references to the terms upstream and downstream.
> Could someone please clarify what is intended with this terminology?

Kevin,

Performer is an implementation of a 3-stage pipeline. The three stages are:
App, Cull and Draw. If App is running its n'th frame, Cull is busy processing
the (n-1)'th frame and Draw is drawing the (n-2)'th frame. At the end of each
frame, each pipeline stage hands over the results from its current frame to the
process DOWNSTREAM from it. App hands to Cull, Cull hands to Draw.

So, a process B is downstream from process A if A hands the result of its
frame to B. Upstream is the exact opposite.

A thing to note: Information never travels upstream. If you change a node on
the scene graph in a Cull process callback, the changes will not propagate
upstream to the App process.

-yair

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