AWS Thinkbox Discussion Forums

flickering pattern on nparticles

I am getting flickering pattern on the sphere. I have attached the maya file as well as the render. I am not sure what is causing it.

render Sequence (12.4 KB)

Working with volumetric shadows in Krakatoa is an art on itself, it is not magic. Understanding how the attenuation maps work and when they produce strange results is key to getting better results, just like with Depth Shadow Maps that have their requirements.

First of all, Krakatoa defaults to 512 attenuation map size for any light source that does not specify otherwise. In Maya, you can enable Depth Map Shadows and change the default 512 resolution to a higher or lower number. This will produce a more or less precise shadow map and thus influence the quality of the shadows.
A word of warning - on multi-core systems, each light will create as many map buffers during rendering as there are threads. Setting the map size to 4096 and rendering with several Point lights on 8 or 16 threads could potentially use up all your memory. In such cases, we recommend to reduce the number of threads in the Misc. panel of the Krakatoa settings. Rendering with 1, 2 or 4 threads would reduce the memory consumption at the cost of some performance decrease…

Then, we have Point lights vs. Spot lights issue. Point lights are the easiest to set up (since they illuminate in all directions), but the worst to get looking right (because they create a cubic map by rendering attenuation maps in all 6 directions and stitching them together). The problem is that the 6 maps have specific orientation in space, and the particles might happen to be at the edge between two or three sides, where the calculations will be the least precise. Sometimes simply rotating the light could change the look. But in general Point lights should be used only when a light is inside a cloud of particles and has to shine in all directions. We recommend using Spots to illuminate a scene from the side. Also, Point Lights don’t work in Voxel mode.

We have already illustrated in the documentation that moire effects could be produced under certain circumstances. But in this particular case I suspect that the particles are moving slightly and the attenuation / shadow map size does not have enough resolution to capture fine detail, thus large texels are being switched on and off as a tiny sphere is moving across the cubic map. Moving the lights closer to the subject could potentially improve the quality, together with tweaking the map resolution. On top of that, you can switch the Self-Shadow filtering to Bilinear and play with the Filter Size which defaults to 1 - larger values will blur the shadows, which would counteract the added sharpness from increased map resolution.

But I would really recommend to start with 3 Spots pointing at the area where the particles are moving, and setting the cones to enclose the area of interest as tightly as possible to use every last texel of the attenuation map to store useful information. With a Point light, most of that is wasted on the 360 degrees particle-less environment.

I suspect you will get significant changes in the shadows quality (for good or bad) if you start tweaking the parameters described above. What settings will match your needs is something only you can decide, so please explore and see if you can get the results that you want.

Hope this helps!

Thanks for sharing all the information. I was unaware about the difference of spot light vs point light. I used spot light with tight cone angle which solved my issue. :slight_smile:



This makes me VERY happy! :slight_smile:
I will make sure this information is moved to the KMY documentation which I admit does not explain all the fine detail of lighting techniques. :blush:

You should definitely put tip and trick column :stuck_out_tongue:… Also i will share the video on which i worked on here when my project is released by the clients i worked for.



hey Bobo check at 5:33 of the clip. the tiger and elephant were made using krakatoa…

Awesome, thanks for sharing! :slight_smile:

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