mia water caustic problem

[MasterZap]

This is - possibly - a newly discovered bug in the "fresnel" feature.

It will be fixed in a future version, but you can get around that fairly easily: Turn off brdf_fresnel, and set your brdf_0_degree to about 0.05 and brdf_90_degree to 1.0, and brdf_curve to 5. This results in pretty much the same angular falloff as the fresnel feature gives you, but without the bright-spot bug.

/Z

[Lamster]

Very nice article MasterZap. It's very very useful that you explained the transition bit.

Terence

[djx]

MasterZap, thanks for the tip. I'll try that tomorrow.
(Great blog, by the way!)

cheers
-- David

[djx]

I tried MasterZap's suggestion regarding the fresnel problem, but in my scene turning off the "Fresnel" flag made things worse.
http://www.djx.com.au/cgtalk/mia_water_caustics02.jpg
Next I tried all the possible combinations of roundCorners/displacement(ocean)/fresnel.
Here is a summary of what resulted:

1. roundCorners+displacement(ocean)+fresnel = small number of random spots
2. roundCorners+displacement(ocean)+no fresnel = white spots fill frame
3. displacement(ocean)+fresnel = no problems
4. displacement(ocean)+no fresnel = white spots fill frame
5. roundCorners+fresnel = small number of random spots
6. roundCorners+no fresnel = no problems
7. no round corners, no displacement(ocean) + fresnel = no problems

(In all cases with problems some frames still rendered perfectly - approx 1 in 3)

Since roundCorners needs the "no fresnel" fix and displacement(ocean) MUST have fresnel on I cant use both together. This is something I would like to figure out though. The roundCorners really adds that little extra highlight that makes it look more real.

This is my 8.5 scene file (http://www.djx.com.au/cgtalk/miaWater_DJ040.rar) if anybody has time to take a look.

Here are screen shots of the mia attributes that I started with
http://www.djx.com.au/cgtalk/miaWaterAttr01.jpg
http://www.djx.com.au/cgtalk/miaWaterAttr02.jpg

thanks
David

[Ash-Man]

Dave
Out of crusty
Do you have other render elements in the scene such as sky system/FG

PS I coudlnt get your file
not working


Edit
neverminde
got the file

[sixbysixx]

EDIT: oops - just rendering the whole sequence and there are still a few frames with those artifacts. Wasn't quite as easy as I thought:-(

---------------------------------------------------------------

It looks to me like a FG problem (in combination with the shaders I guess)
No FG no artifacts, so started to play a bit with the FG settings.
When I change the FG settings of your scene to Accuracy 100, Point Denisty 0.1 every frame seems to render flawlessly for me (and in less than half of the time...)

It still leaves a few questions if you have to use higher settings I guess, but for this scene it does the trick (for me anyway;-)

Good Luck - Christoph

[djx]

Christoph, thanks for taking the time to render the sequence. At least I know it's not just me now.

By the way, I've just remembered that I used JS_wood (one of pixero's textures) on the floor - probably should have removed that for the test scene.

Ash-Man - yeah, I used the physicalSky - but you probably worked that out by now.

thanks
David

[razorback]

Ive seen something like that before, but possibly from a totally different cause. Might be unrelated at all.

I did a project a couple of months back using the mia materials that yahsu converted from max. It seemed that the artifacts were caused by an unclampled lanczos / mitchell filter that would sometimes return negative values which in my compositing package returned as white.

[Ash-Man]

OK this might not be the best answer, but here is my 2 cents on the topic

Lowering the reflection cutoff to a very small values will bounce back these wired artifacts
I increased it to 0.1 and it got it smaller (I think they still there..but they very small)
Maybe this should be enough to get your project out of the door

Best of luck

Note:I didn’t render the entire sequence...just couple of frames

[djx]

razorback, I'm pretty sure that in this case its not a filtering problem. These artifacts are too big and circular.

Ash-Man, I tried setting both the reflection and refraction cutoffs to 0.1 (seperately and together). I rendered 10 frames of the sequence, 3 frames had those artifacts. I havent had time to try higher cut-off values yet (been too busy this week).

I think this bug is just something I have to live with. I probably will just ditch the roundCorners texture for now.

Thanks for taking an interest. It's appreciated.

-- David

[glim]

your shader is don't set properly. u use refraction fallof but in the zap description iit's using reflection fallof ...

[MasterZap]

your shader is don't set properly. u use refraction fallof but in the zap description iit's using reflection fallof ...


Actually he is right, and my description (now fixed) was wrong.

/Z

[Sphere♥]

BTW MasterZap, is that Fresnel FG spots bug fixed? I've had to avoid it all this time because it often gave crazy bright spots, but it would be nice to just click that check box and have it work.

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