Daz 4.9 - Iray -- Reflections stopped working?

TabascoJack

I was noticing some strange behavior with lighting, so ran a test scene with Modern Attic Bedroom.

I set the floor to a mirror and aimed a spotlight with tight focus along the side of the wall, aimed at the floor.  

I expected to see the light reflect off the floor and show up on the far wall.  Instead, nothing.  

I dropped a chess set on the floor to show where the light was hitting, and also to see if the shadow from it would be refelected.   Nada.

Attached is the render. 

Any thoughts?

TabascoJack

Of course, now I'm starting to question if it ever worked as I expected and I just never noticed before.....

 

 

AndyGrimm

while your render looks in fact a little bit strange - i think this is correct behavior..  a mirror dosent show light (beams) because there is no diffuse scattering ... while the chess board scatters the light in all directions.....

If you want to see the light SOURCE (a mirror would reflect the lamp - but maybe not on your point of view) you need to switch on geometry on the light.

Edit: the chess board .. hmmm....   where exactly is your spotlight? i can just guess.. because something IS strange in your render

TabascoJack

AndyGrimm said:

while your render looks in fact a little bit strange - i think this is correct behavior..  a mirror dosent show light (beams) because there is no diffuse scattering ... while the chess board scatters the light in all directions.....

If you want to see the light SOURCE (a mirror would reflect the lamp) you need to switch on geometry on the light.
 

Agreed.  I didn't expect to see the light on the floor itself.  I was expecting to see the reflection of the light on the far wall.

Different example which better shows what I'm talking about.  The only light source is the emissive plane aimed just before the white chess pieces.  Light reflected off the floor should cause the chess pieces to cast shadows on the wall, which they don't.

Again, I may be confused and it's always acted like this.  I just don't remember.

 

AndyGrimm

hmm...  you are right - direct reflections seems not to work in iray... 

render one : 100% - light beam should be reflected on the wall but is not there...only the direct spot light.
render two: 50% rough...  diffuse reflections are there

 

Richard Haseltine

Have you tried the Architectural sampler option? Or nmore likely the Caustic Sampler. Both are in the Optimisations group in Render Settings.

AndyGrimm

ok...  here it is... render settings - caustic ON

AndyGrimm

I did not expect that i had it switched off. is normaly on - maybe the update, dont remember..

good Iray

TabascoJack

That seems to have solved it, thanks!

 

So in layman's terms, what does the Caustic Sampler do and when should we be using it?

Tobor

Here are to (among several) nVidia blog posts about the caustic sampler. As noted, it is a render flag that allows for a higher definition of ray calculations. While Iray is a physically-based renderer, it takes many shortcuts in order to provide a scene within a reasonable period of time. Its standard render algorithms may not be sufficient for all scenes, particularly those involving complex ray tracing through objects, or when reflected off multiple objects.

http://blog.irayrender.com/post/51722647664/the-architectural-and-caustic-samplers

http://blog.irayrender.com/post/89741414098/caustic-and-architectural-sampler-revisited

AndyGrimm

thx Tobor - i thought that caustic is only needed for light effects which shines TROUGH a transparent object (refraction).. i also expected "simple" light rays/traces to be reflected on ONE flat surfaces such as the mirror floor above...  nvidias links are also not clear on that - so,  you well spotted this strange "behaviour" @TabascoJack ....