Particle Color - Unexpected Behavior (color changes with camera movment)

At the first image you can see particles. (bigger and small dust).
Now on second image I have slightly rotated camera up and all particles suddenly disapeared (not entirely but they are barerly visible).

I expected that ParticleColor node in Material editor will just change color, not affect color based on how you look at particles.
Material setup is very simple. One texture multiplied by ParticleColor (RGB for Color and Alpha for Opacity) and pluged into Color and Opacity slots.
If I plug to Emissive slot instead of Color behavior changes to what I would expect (color stays the same regardless of my position).

But I’m not sure if it is all that intuitive. When I plug something into emissive slot I expect it to emit light, and to color slot to just change color without external influences, like angle and position from what I’m looking at my particles.

Hi Lukasz,

I am attempting to reproduce this issue on Beta 3 and on an internal build. I am not having much luck. The material I have created has a texture that runs into a multiply ‘A’ with a ParticleColor running to ‘B’. The multiply is attached to BaseColor and Opacity. It is two-sided and Translucent.

I apply this to a particle effect’s required material and bring it into the editor. I am not sure what settings you have on the particle. With just this, there is no change in opacity when I move the camera angle.

Could you please let me know how you have the particle set up. Also please give me your hardware specs. Once I have more information I will be able to investigate further.

Thank you,

Alexander

I just uploaded my setup on ftp:—

Edit:

I Uploaded wrong file, I have now uploaded the right one that shows the issue:

Lukasz_Particles_UDN_Question_FIX

The particle effect in question is:

M_FX_Dust_Small

As for my spec:

Core i750 (3.2GHz)

12GB Ram

Radeon HD 7850

Windows 8.

Hi Lukasz,

Thank you for the assets. I recreated the scene and played with what was available. Unfortunately my machine was not reproducing this error. We built a machine to meet the specs you gave (except Radeon HD 7870, we didn’t have a 7850) and built a test. On the FTP there is a file named Alexander_Particle_Lukasz_Test. Please upload it and open the project. Let me know if the error is occurring with the dust particle in the Particletest.umap provided.

Thank you,
Alexander

It’s intresting but it seems to be working just fine. I think the problem is connected with this specific map. I also had other issues with it that I had reported here:

https://rocket.unrealengine.com/questions/3327/build-1711197-very-big-perfomance-diffrence-betwee.html

It might be connected.

I have also created blank map, and it’s working fine on it.

Well, unfortunately in that case it is somewhere on your side of the project settings. I will not be able to do much with that without knowing every change you have ever made. However, since we are now aware that it is a project specific issue, could you please let me know if you find out what settings may have caused this? It may help with future issues. Thank you for your help during this investigation.

Thanks,
Alexander

It seems I have found issue. On the level I have two Post Process Volumes. One global and one for my building. There is Ambient Cupemap both of those volumes.

When the settings are on default (Intensity and Tint unchecked), the particles doesn’t receive any lighting from certain angle and the are became black (or inside my building change color to be slighlty more transparent).

Another thing I have discovered is that global post process override Ambient Cubemap settings on my second volume if they are turned on. It doesn’t matter if the another volume have diffrent settings or not.

The thing is perfectly replicable. Just seup quite dark room and particle emitter with quite big particles and alpha set to one in initial color (so the issue will be easier to spot). Then disable ambient light, change directional light to movable, and add single SpotLight inside room, with very low brigthness.
Then comapre results with and without ambient map. In my case most of the particles are grey. With ambient light on they are pretty much the same color. Although you can still notice at least small color changes.

I believe the issue is coming from dynamic shadows, as I spoted particles that are going away from camera and they change color like they were transition thorugh shadow acne.

I think the issue might be in how particles are lit.

Thank you very much for this information Lukasz. I will investigate into the cause and may end up making a report if it is not already reported. If there is anything else you need assistance with or if you find another issue, please let us know and we will be happy to help.

Thanks,
Alexander

I also found a type of solution:
I tried changing lighting in sceene, but it didnt help.
I needed to change values in material provided by game. In my case i was using gas smoke and u had to add new pin to emmisive color. When particles wanted to turn black, thay have been countered by emmisive color. Only disandvage is that when light in scene goes dark, for ex. you turn off lights in room, particles would still emit light. The way to solve it is just to set niagara to visible:false