Sphere +distant light. Why does it look so ugly?

works for me
Houdini 14.0.228

rotate your light. works for me without rotation too

It's related to Ray Bias (on the ROP). You can raise the Bias or Subdivide the sphere to prevent self-shadowing intersections of this kind.

jason_iversen
thank you!

But why they keep this value so low by default? What possible artifacts if increase it too much?

Evgeny_rus
Sphere +distant light. Why does it look so ugly?

Please see the attaced PDF which explains the cause of this in detail.

mark
thank you for good explanation!

This is called the “terminator artifact”, and other renderers usually compensate for it. It involves adjusting the bias on a per-sample basis. (I even have some mental ray shader code somewhere from the stone age that does it – as the computation had to be redone after bump mapping.)

The wonder of the internets: I found the code in a blog post about 7 years old. (There's both code and explanation there.) Perhaps the same thing could be done in a mantra shader.

https://blueriviera.wordpress.com/2008/07/31/how-to-recalculate-shadow_tol/ [blueriviera.wordpress.com]

The reason I needed this for was, although mental ray compensated for this artifact correctly, if you wrote a bump shader you had to recalculate the tolerance by hand, otherwise this arfiact reappeared. (I remember it annoyed the hell out of me at the time.)

Evgeny_rus
jason_iversen
thank you!

But why they keep this value so low by default? What possible artifacts if increase it too much?

The value has to be as low as possible, or else you'll get another artifact, namely shadows getting “detached from objects”, something like this:

http://www.digitalrune.com/Portals/0/Blog/Files/11/218/Windows-Live-Writer-Shadow-Acne_D184-clip_image007_2.jpg [digitalrune.com]

riviera
The wonder of the internets: I found the code in a blog post about 7 years old. (There's both code and explanation there.) Perhaps the same thing could be done in a mantra shader.

Oh, God. My past comes back to haunt me.

halfdan

riviera
The wonder of the internets: I found the code in a blog post about 7 years old. (There's both code and explanation there.) Perhaps the same thing could be done in a mantra shader.

Oh, God. My past comes back to haunt me.

Mine too, if that's any consolation.

Btw, how about implementing this thing in mantra then? Or would it cause trouble elsewhere?

riviera
The value has to be as low as possible, or else you'll get another artifact, namely shadows getting “detached from objects”, something like this:

http://www.digitalrune.com/Portals/0/Blog/Files/11/218/Windows-Live-Writer-Shadow-Acne_D184-clip_image007_2.jpg [digitalrune.com]

Thank you

riviera

halfdan

riviera
The wonder of the internets: I found the code in a blog post about 7 years old. (There's both code and explanation there.) Perhaps the same thing could be done in a mantra shader.

Oh, God. My past comes back to haunt me.

Mine too, if that's any consolation.

Btw, how about implementing this thing in mantra then? Or would it cause trouble elsewhere?

Yes, mantra should do some thing avoid this. Render as subdivide is not able in some situations.

Sorry to bump an old thread like this, but in case anyone finds this thread in the future, the issue was fixed in Houdini 15.0.

ndickson
Sorry to bump an old thread like this, but in case anyone finds this thread in the future, the issue was fixed in Houdini 15.0.

Neil Dickson FTW 8)

pusat

ndickson
Sorry to bump an old thread like this, but in case anyone finds this thread in the future, the issue was fixed in Houdini 15.0.

Neil Dickson FTW 8)

It wasn't me who fixed it! I was just going through my… *cough*700+*cough*… open Firefox tabs, and found this thread, so I figured it'd be worth posting an update.

ndickson

pusat

ndickson
Sorry to bump an old thread like this, but in case anyone finds this thread in the future, the issue was fixed in Houdini 15.0.

Neil Dickson FTW 8)

It wasn't me who fixed it! I was just going through my… *cough*700+*cough*… open Firefox tabs, and found this thread, so I figured it'd be worth posting an update.

SESI FTW 8)

Is this a recent fix? If not, how did you know it was fixed? You have 700 tabs open in Visual Studio?

pusat

ndickson

pusat

ndickson
Sorry to bump an old thread like this, but in case anyone finds this thread in the future, the issue was fixed in Houdini 15.0.

Neil Dickson FTW 8)

It wasn't me who fixed it! I was just going through my… *cough*700+*cough*… open Firefox tabs, and found this thread, so I figured it'd be worth posting an update.

SESI FTW 8)

Is this a recent fix? If not, how did you know it was fixed? You have 700 tabs open in Visual Studio?

https://www.sidefx.com/index.php?option=com_journal&Itemid=213&page=index&journal=default&view=FULL&logfile=ALL&icon=mantra&version=ALL&buildstart=&buildend=221&perpage=20&search=vm_smoothP&find=Find [sidefx.com]

pusat
Is this a recent fix? If not, how did you know it was fixed?

Well, I knew it had been fixed because a few of us had strong opinions about it, and were eager to see the results when someone decided to tackle it. It's been fixed since the first public version of 15.0.

The way the fix works is not 100% obvious that it'd work in most cases, but it seems to do well unless you have geometry close to a low-res curved surface. For example, two boxes with point normals near each other may get odd shading artifacts, but who has boxes with point normals? *cough*cough*

It's also apparently in the What’s new in Houdini 15: Lighting, shading, and rendering [sidefx.com] page, but I didn't know that until I checked the commit logs. :wink:

You have 700 tabs open in Visual Studio?

Well, I might, if Visual Studio didn't lose my newly-opened tabs whenever it crashes, and boy, is VS2015 ever crashy.