[PD] GEM vs Jitter a newbie request for opinions

zmoelnig at iem.at zmoelnig at iem.at
Sun Oct 26 19:32:08 CET 2003

Zitiere Nicholas Colvin <colvin at dvida.net>:

> I have a couple of questions about the tritest.pd examples.  You
> mentioned many triangles, but I only get one triangle, is this correct?
i guess it is correct for you, but i got thousands of them (that is the idea of
the patch), you can also change the number of triangles with the number-box
hanging around.

are you using and old version of gem (non-cvs ?). then the example will most
probably not work (see below)

> Also, why are there multiple [gemhead]s? I wasn't aware of any use for
> this, and I'm really trying hard to understand GEM. I've read the docs
> through a few times, and looked at online tuts a bunch, but haven't
> seen
> anything about multiple gemheads.

multiple gemheads are quite normal, if you have several independent objects...
however, i guess you mean something different, rather "multiple gemheads in one
gemchain" or similar. i'll try to explain:
when rendering, [gemhead] works somehow like a special "Gem-metro" that sends a
"render"-message to the connected gem-objects (who distribute this
render-message further) each rendering frame (in double-buffered mode)
however, you can force a [gemhead] to send out the "render"-message by banging
it (very useful in single-buffered mode).
In version prior to 0.888 (and 0.87-cvs) the "render"-message was somewhat
hidden and did not use pd's messaging system. however this has changed (which is
quite cool, as you can now use "dynamic" render-chains).
now, each frame the first [gemhead] outputs the render_message, which is
converted to a number of bangs (using [until]), which trigger the second
[gemhead] which will then draw the triangles (a number of times each frame).
however the second [gemhead] will also output the render_message once each frame
(independently of the banging it gets from the first [gemhead]), so we will only
use "4999" until-bangs to get 5000 triangles each frame.

the whole patch would have been easier using [repeat] from zexy (and i guess, a
lot of other libraries...), but i wanted it to be plain pd/Gem.


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