[Bf-cycles] Light leaks

[Brecht Van Lommel]

Only a small percentage of rays will slip through, so it's unlikely
this has a big impact on performance. Regardless, it's not something
that's simple to fix, we have these because efficient ray-triangle
intersection algorithms are less precise, and if we use a slower but
more precise algorithm it will make overall render time even longer.

I'd like to improve this once and there probably exist fast algorithms
that are more precise than what we have now, but it's a quite complex
problem, especially combined with instancing support.

Brecht.

On Sun, Apr 14, 2013 at 6:51 PM, David Black <db4tech at yahoo.co.uk> wrote:
> Hi Brecht,
>
> After carrying out several tests I have a question, is it possible that
> light leaks (see attached image) will slow down convergence performance with
> harder to find light sources due to extra calculations being performed?  It
> seems light leaks happen with all solid objects, this gets progressively
> worse when a Subsurf modifier is added, higher the subdivision modifier
> setting the more light penetration calculations are performed showing
> increasing light leaks. To help rule out recent code changes and SSS
> integration, tested with version 2.66a and 2.66.5.
>
> Cycles Light Leaks test Method:
> •    With the default scene, select Cycles render, delete the light
> •    Add default material to the cube
> •    Duplicate the cube and reduce in size (so it is inside the default
> cube), change the material so the smaller cube is a powerful emission source
> •    Duplicate the main cube again and greatly enlarge, so it encompass all
> objects within the scene including camera, there should now be three cubes
> in the scene, each inside the other.
> •    Select camera view and render several passes
> •    Add a Subsurf modifier to the default main cube and re-render
>
> To help reduce mailing list bandwidth, please find attached single image,
> will post a selection of test images showing progressive light leaks on
> blenderartists.org Brecht’s Easter egg surprise thread.
>
> Thank you for your time and great SSS coding work,
> David
>
> --
>
> 3d-designs-davidblack.blogspot.com
>
>
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