[Paraview] Render a Tile

[Moreland, Kenneth]

> -----Original Message-----
> From: Mario [mailto:mario.orefice at gmail.com]
> Sent: Thursday, December 14, 2006 2:37 AM
> To: Moreland, Kenneth; paraview at paraview.org
> Subject: Re: [Paraview] Render a Tile
> 
> Finally I'm able to render a tile from the ray cast mapper in my vtk
> application.
> I have two questions for you:
> 
> 1 - When I render a tile with IceT, it casts ray only from that
> selected pixels, or it computes all the image then clips?
> I think the first, infact I captured the last render time and it's
> faster when I only render a tile instead of all the image...

It's not easy to answer that question.  IceT will always render images
the size of the tiles (sort of).  So if each tile is 1024x768, IceT will
always render 786K pixels at a time.  If necessary, IceT will perform
multiple renderings to get all the pixels.  This is often done on a
tile-by-tile basis, which would be the first case you mentioned.
However, IceT also tries to minimize the number of renders it invokes,
so it sometimes "floats" the viewport away from any tile.  In this
particular case, the rendering will have more pixels covered by the
geometry.  In situations such as yours where the rendering is fragment
processing bound, this increases the time for each rendering, but
reduces the overall rendering time.

> 
> 2 - When I don't set tile dimensions and I leave the default mode, it
> composes only a single tile, the entire image... that image is
> rendered in cooperation by all the processes or only by the process 0?
> that is, I had parallel volume rendering or not? I wasn't able to
> prove that because I don't have a cluster or a parallel machine, but I
> simulate it in my desktop pc with MPI....

Again this is difficult to answer because ParaView changes its behavior
to give the best performance in a variety of situations.  Assuming that
you are running in client/server mode AND compositing is on AND the size
of your geometry is above the composite threshold, then yes, parallel
volume rendering should be happening.

-Ken