Particle shader alpha error

[Inaxis]

Hello!

I encountered a strange error in the alpha element and this wasn't the first time. When using particle shader in point mode, you may experience some unusual results as the attached screenshot shows. I've tried multiple setting in Vray render settings but its clearly related to the pixel size in particle shader. Did anyone find a cure for this issue?

[georgi.zhekov]

Hello,

Two things you can try to remedy these:

1 - Try turning off the Volume light cache in the Particle Shader options or reduce it to a lower value than the default of 0.9
2 - You can change the ptSizeExtra script option of the Particle Shader. It is 0 by default and can be increased to suppress grid artifacts. Increasing the value too much might slow down the rendering considerably.

for the second option just select the Particle Shader and in the MaxScript editor type

$.ptSizeExtra = 1

You can try increasing the value to 2,3,4 and so on until the artifacts vanish, but note that the larger the value the slower the render will be so use the lowest value that works.

Cheers!

[Inaxis]

1. the Volume light cache was already off

2. here are my results with different $.ptSizeExtra values:




Apart from brightness, there is not much difference.

Any other thoughts?

[georgi.zhekov]

Looks strange for sure.

Can you send over the scene along with a few cache files so that we can take a look?

You can send it via support.chaos.com (Submit a request at top right)

Thanks!

[Inaxis]

Sure, I will prepare a simplified version for the support. Thank you for your help Georgi!

[Inaxis]

Ticket submitted with Id #256833. Thank you for your help in advance!

[georgi.zhekov]

Hello,

Thanks a lot for the scene. Looks like the issue is coming from the large Point Pixel Radius for the Mist Particle Shader.
When you have too many particles and when the radius is very large you get these artifacts - we will have to investigate if we can do something about in the code.

Meanwhile as a workaround - how about using the Fog mode instead?

You're already making the points very large - so you should be able to get similar look by using Fog mode with larger Voxel size.
In your scene setting the Voxel Size to 30cm and using a density of 0.6 yields a similar result and it renders a lot faster.

[Inaxis]

Thanks for the help Georgi! Fog mode works almost the same in this case.