Having a problem rendering what should be a simple scene.  It’s a room with four walls (back, floor, sideR, sideL) made of cubes, which fall away and disappear over 400ish frames.  There are 516 cubes total, so I’d prefer it stays systematic, but open to building it in a completely different way. 

The walls are (hidden) polygon grids that emit a point cloud: one cube per polygon position.  At the particles’ age limit (turbulized, so it’s somewhat random), they die and spawn a single new particle with non-zero mass and a new age limit (the mass makes the particle affected by the wind, and start moving).  The new particles change color from white to black over their age. 

In the shader for the instance geometry (Instance Shape node into Emit from Position shape port; the Set Instance Geometry node had some problems) and point clouds, there is an Attribute_Color node plugged into the cutout_opacity port of a MIA shader, so in theory the color of the particles drives the cutout_opacity of the shader on the instance geometry: the cubes start opaque (white) and fade out (black) over about a second after they start moving. 

I have also tried it with a separate matte pass, just a constant with Attribute_Color plugged directly into its color port, but I’d prefer to do it “in render” because the surface is reflective and a matte pass isn’t a “real” solution (but would have been cool for animatic).

The render crashes.  A lot.  No error message in the logs/script, just normal prep/loading stuff (sometimes even a few buckets of render) then freeze.  I am almost certain the problem is using the Attribute_Color node on instanced geometry (and not on a point cloud’s shader only).  When I disconnect this part of the shader, it renders, fast.  Oddly, with the matte pass, the region renders quickly with no errors but a real render freezes immediately.  Further complication: the crash behavior is inconsistent, sometimes a frame renders ok, sometimes it freezes, and I haven’t been able to see a pattern.

Anyone know the “right” way to connect things so it renders, or a different way to set it up?

the 1st thing I’d try is to cache the particles..

Yes, me too; the particles are cached, it’s not that, it’s not lots of things.  There seems to be a similar issue being discussed here[FONT=arial][SIZE=2], but I don’t understand the recommendations: “write to per point data”, “write to a vertex color map”, etc… that sounds promising, but I don’t know how to execute them.

I decided to build the scene in a different way: with actual separate object cubes, instead of a particle cloud, which solves several problems, but “unsolves” a few also.  I got the material change: the cubes “swim” through a gradient texture that drives a mix2color node.  However, the animation of the cubes falling away is a problem.  [B]I’d like to be able to clone or instantiate (say) one cube, offset the clones’ animation, but then still be able to change the shape of the posz fcurve if the client wants the cubes to behave differently (while still retaining the time offset on all the clones).[/B] Or maybe “turn off” the offset, make the change to hundreds of curves simultaneously, and “turn the offset back on”. But apparently there is no way to offset instances’ animation, and clones appear to consider geometry but not animation.  Another thought I had was to put the posz animation in a mixer clip, to theoretically feed 200-some animation clips, and be able to edit the source to change them all… but I can’t figure out how to apply a clip from Object A’s posz onto Object B’s posz.  May not be possible.

Any ideas?
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do the clouds emit the same number of particles ?

my xsi crashes when using instance shape + attribute color if the clouds have different particles count !