i3d vs sprites

[TheDunadan]

Hi, I've been playing around with houdini's particle system now and I was wondering on the following. ~2-3 Years ago, I think almost everyone who had to deal with particle effects auch as tornados relied on sprites for rendering output, at least in almost any discussions about this subject most people seemed to agree that prman sprites was the way to go.

So far I haven't played around with i3d and volumetric shaders much yet, but I guess others have . Are they still way too expensive cpu-wise to use and everyone tries to get away with sprites or is the use of raymarchers a valid option now ? Does motion blur work sufficiently well for things such as Tornados ? Are there ways to add the motion blur in the post process by rendering out some velocity vectors seperatly, to speed up rendering, since i assume brute force motionblur with a raymarcher yields killer-render times.

I'd welcome any tips, tricks & ideas on this subject. I believe some small hardly known company was working on such effects just recently and in x-men 2 , any hints on how they tackled the rendering problem would be very intresting.

[old school]

Sprites still rule from what I can see. Although i3d certainly does have it's place for clouds.

There is a third option where you use i3d to generate the sprite flipbook images.

[edward]

Were the tornadoes in Day After Tomorrow done with VoxelBitch? If so, then is that an argument for the volumetric approach?

[Marc]

Well, arguing for the volumetric approach, and arguing for i3d are two totally different arguments .

But, yes. The twisters in Day After Tomorrow were done using voxelbitch (and the whitewater in the water sequence). And I believe the twisters in X2 were done with jig, which is also a volumetric solution.

On the other hand though, the movie I'm now working on uses a sprite based solution for all volumetric style renderings (fog, clouds, steam etc.) and its alarmingly quick and successful.

So, I guess the answer is, either will work very well it just depends on who's doing it and how much time you have to render them.

Ciao

Marc

[TheDunadan]

Thanks for the info.

Somewhat more specific on houdini, what are the options in houdini to render volumetric shaders on particles except doing the i3d file first and using this file as texture for the fog shader of the atmosphere object in return.

I couldn't find any "volumetric primitive types" except the atmosphere object type that I could assign any volumetric shop to. Is there something similar to the "cloud/tube sw shader"-type of Maya in Houdini. I half-expected there would be something similar to the mantra sprite procedure for this, but there isn't

Jens

[Jason]

What I experimented with in VoxelBitch during DAY was to render a volumetric sprite. I rendered a single splash with variations with the lighting baked into the voxeldata. (i.e., now the voxel data contained RGB-density instead of just density)

Solutions may differ hugely but the nature of voxelbitch allowed me to Copy/Stamp these smaller voxelbuffers in to my main rendering one. This might take some fancy i3d shenanigans to do it this way, but it should be possible. It'd be slower due to the "pull" nature of i3d generation. Voxelbitch works the other way round. Directly stamping voxel buffers into a master buffer is easy, and in VB directly drawing voxels into the buffer is possible and very, very fast compared to having to render an entire 800x800x800 buffer when all you may want to do is draw a few thousand voxels.