Blender Fluid produces spikes in mesh

[Mitsuma]

It is a problem with every GPU renderer but I don't know why.
And it is not a problem which happens during the export.
I think it has something to do with the BVH building.

[aLeXXtoR]

It is a problem with every GPU renderer but I don't know why.
And it is not a problem which happens during the export.
I think it has something to do with the BVH building.

I tried rendering wit Cycles — CPU and GPU renderings produce same results. I think that problem is somwhere else, than GPU.

[aLeXXtoR]

Concerning that spikes — I found that their shape is affected by modifiers. For example, if I use Smooth modifier on the fluid (Domain) mesh, spikes' shape becomes more solid if I increase smoothing value. That could mean that this bug appears before applying modifiers to objects while exporting. Is Blender core doing this, or any stand-alone (exporter's) module?

[yoyoz]

I've opened a bug for it, let's see if someone picks it up.

The exporter uses modifiers if the option is enabled in the export settings (it's on by default). When the exporter queries blender for the objects, it just says if modifiers have to be applied or not (only applied for the export time of course). This apply to all modifiers, you cannot select or exclude specific ones.

[aLeXXtoR]

I've opened a bug for it, let's see if someone picks it up.

Thank you, Lionel!

The exporter uses modifiers if the option is enabled in the export settings (it's on by default). When the exporter queries blender for the objects, it just says if modifiers have to be applied or not (only applied for the export time of course). This apply to all modifiers, you cannot select or exclude specific ones.

I understand that.
I just ment to say that modifiers affect that spikes with Octane and Cycles as well. I don't know exact mechanism of the exporters but I suppose that the order is about this: 0) taking source mesh > 1) applying modifiers 2 mesh > 2) converting resulting mesh 2 OBJ represerntation > 3) exporting > 4) rendering. If it so and modifiers affect spikes that can mean that spikes appear before step 1. So it is possible that spikes is not a exporter's bug, but some Blender bug that happens when Blender calls some other exporter than standard...
Anyway that's only my suppositions. )

[yoyoz]

Yep, that's the way it works. It seems to me that internal renderer is not affected because it can deal with non-triangle/quad-based geometry while that's what is required for cycles or export. Anyway this is internal issue and cannot be fixed by the scripts.

[regionfive]

Hi there,

after I gave the fluidsimulator another try with the new version, I found something!

The problem itself comes directly from the simulator. When you look closely on the frames in the Viewport in shaded mode,
you´ll see tiny holes in the mesh of the fluid, right from where the spike arises. I guess these holes can´t be interpreted by the exporter.
Cheers.
René

[steveps3]

I had the same problem a while back. I found the problem. It is caused by faces that have less that 3 verts (essentially an edge). I did find a way of eliminating them. uumm. I think that what I did was to select all faces and then invert the select. I may be wrong but I think this will select the offending odd faces.

I did spot that during the google summer of code that someone will be working on a tool to get of exactly this problem. I can't find the link now

If it helps, here is the thread that I started a while back http://render.otoy.com/forum/viewtopic.php?f=32&t=22425

[regionfive]

Hi Steve,
thanks for your reply.
The fluid Simulation only makes sense for me if i can use it in an animation. does your workaround (import obj.) mean,
I have to render all spike frames manually? 400 fluid frames can produce around 50-100 spike frames.. that is very annoying.
I hope they fixed that at GSOC. but cool you found the reason and how to eliminate them!! at least this is a progress.
Cheers

[steveps3]

Fraid so.

Hopefully the GSOC will come up with a solution sooner rather than later. Keep an eye on graphicall.org.