moire pattern in teapot example?

Deprecated Krakatoa 1.0 Beta Discussion
1

Hi Folks,



I’ve gotten some free time to run through the krakatoa manual and have a proper play. One thing I notices with the teapot example is as particle counts go higher, the image gets darker and moire patterns start to appear. Here’s the teapot example with 50,000 particles and 200,000 particles - the higher particle count example is darker and also displays a moire type pattern. I’ve tried upping the subdivs of the teapot and the integration step of pflow but to no avail. which parameter is causing this?



http://www.joconnell.com/uploads/krakatoa/krakatoa_200k_vs_50k.jpg

2

It will be a combination of the density and shadow map size.



As the particle counts increase, you may need to reduce the density setting.

Likewise, increasing the shadow map size will reduce the moire patterns.


3

Ah okay, so it’s a case of the increased density having more opacity thus making a more solid surface to recieve shadows?

4

Generally, if the particles are created in a grid, instead of randomly, Moire patterns are likely because of that patterning.



Another thing that causes Moire is extremely high densities, due to interaction with the attenuation buffer of the light. With a really high density, the particles don’t blend, behaving more like a nearest neighbor filter than a bilinear or bicubic filter, which causes the artifacts. In that case, reducing the density is the solution, and you will likely be able to reduce it a fair bit before the collective particles start to become transparent.



-Mark

5

Good to know, thanks mark.

6

Is there some guideline for spacial density? I’ve been trying to work more with spacial density than with opacity density, and just limiting the number of particles to control the apparent density, but I’m having a hard time controling my shadows either way.


  • Chad
7

Another thing, is the moire pattern in the shadows a bug or no? Meaning, will it be fixed, or is it something we can expect to have to work around?


  • Chad
8

Another thing, is the moire pattern in the shadows a bug or no? Meaning,

will it be fixed, or is it something we can expect to have to work around?<<



Unless I hear otherwise from the developers, I would consider this a bug.



Mind you, this is a different class of bug than the crashes, memory leaks

and functional failures we typically log. It is more of a render quality

issue. There may be some algorithmic or heuristic approach we can use to

make this easier to eliminate. I would love to have rendering defaults be

as close to perfect as possible. (You know… That mythical “make art”

button!)