Vray fur problem

[simmsimaging]

Hi All -

Been playing with Vray fur to make some grass and it was working okay but I have run into an intermittent problem with some buckets rendering oddly - pls. see the attachments. They are noisy but that doesn't affect the issue at all. The problem looks kind of like jpg artifacting or a DR problem - but it isn't either of those.

The fuzzy background is a plane of Vray fur (actually 3 of them to add variety) and the foreground object is another set of 3 vray fur objects growing out of an object. I get this issue with 1, 2 or 3 of the vray fur active.

This happens with or without DOF on - it's just easier to see the pattern with it, and it happens with all the different GI methods, with and without DR active, and with varying bucket sizes. The odd thing is that sometimes just turning off the Vray fur item or changing a parameter seems to make it go away or render differently (the odd buckets do vary every time you render it though)

It's a bit hard to predict and it ruined a 4 hour render today - is this a known bug or there something that might cause this?

[simmsimaging]

I've been playing some more and I think it's a material/UV issue with Vray Fur. I had been using a Vray BlendMat and if I just use a simple VrayMat it seems to clear up consistently. I'll test some more and post it if I figure it out.

Where does the Vray Fur object get it's UV coordinates from - the source object, or does it have it's own implicit UV's? I had thought it just picked up the surface colour from whatever the source object was at the point of origin for strand of fur - is that right?

Thanks,

b

[vlado]

Which V-Ray version are you using for this? There were similar issues at some point, but they should have been fixed.

Best regards,
Vlado

[simmsimaging]

Which V-Ray version are you using for this? There were similar issues at some point, but they should have been fixed.

Best regards,
Vlado

I'm using 1.5 SP2.

The file definitely renders fine with a simple VrayMat - ran it last night. I am not clear yet if it is the BlendMat that caused the problem itself, or just the bitmap used to blend the two VrayMats within it due to some kind of UV oddness.

b

[vlado]

What kind of mapping modes are you using for the bitmaps? I think explicit channel should work fine, not sure about others (object/world XYZ). If there are still issues, you can send me the scene to vlado@chaosgroup.com and we'll take a look.

Best regards,
Vlado

[simmsimaging]

What kind of mapping modes are you using for the bitmaps? I think explicit channel should work fine, not sure about others (object/world XYZ). If there are still issues, you can send me the scene to vlado@chaosgroup.com and we'll take a look.

Best regards,
Vlado

It was explicit mapping for sure. I don't know that it is a problem with just UV's per se, as a single Vray mat rendered fine, but a Vray blendmat with a bitmapped blending mask caused this issue. I have not had a chance to go back and test to see if it was the blend map or the blend material causing the problem. I can separate out the elements and send you the file if you wish.

About the Vray fur UVS: when you click "generate uvs" does that give each strand mappable uv's, or what exactly does that do? I ask because I'd like to figure out a way to create some variation in tone along the length of a strand of fur - just not sure if it's possible.

Thanks Vlado
b

[vlado]

It is possible, yes - you just have to make sure the texture takes the W coordinate into consideration (not just the U and V).

Best regards,
Vlado