once more i post a correction to something i said -not really explicitly- but could have mislead or confused someone, sorry if it happened ..
i guess this is natural in forums, i discuss and study things even if i'm no expert , but since post are public material they can be seen as 'manuals' , often it's also easier to write a post like a manual (with disclaimer) and correct later ..
I see professional forums as a blend of 'friends talikng about job at pub' and 'international science research magazine' ..can be kind of hard to say how proven is what you're reading , right ?
So, this is the issue : in path tracing rays are cast from camera not from lightsource
i said they started from the light source, i was wrong.
It's Photon map that casts rays from the lightsource ( bidirectional does both ).
" The distributed path tracer is an extension of the regular path tracer. Instead of selecting a single reflection direction, it will select multiple and spawn additional rays along each direction. The number of rays to spawn is configurable per material type (diffuse, specular and refraction)"
(quote from lux documentation "render settings")
I got the first hint (that i was wrong) when Jeanphi posted about distributed path (and how direct light is handled in this integrator) he said DP shoots a ray from the camera ..and i understand now that's just normal pathtracing behaviour.
Sorry again if i confused anyone , this infos are in the manual , i swear i read it many times before, but.. took time to really get into my head
On to something different, a comparison pic , about how mlt can be good for speed :
What's interesting about this pic is that MLT is converging faster in this scene.
--top: MLT (lmprob 0.014 , max.rej 16)
--bottom: HILBERT samples 16
distributed path 3diffuse bounces, 0 glossy
mesh emitters for artificial lights , mesh plane on windows for sky
time: (each pic.) 30mins , 2 cores q6600 (luxrender rc5)
(WARNING: This are very biased settings , as such, depending on the scene they might produce artifacts , generally incorrect lighting or simply not bring any advantage respect to reccomended settings !!. again, the interesting thing of this scene is just that mlt is clearing faster than LD )