Irradiance map calculation also computes secondary bounces?

[stefan]

I was wondering about this for quite some time now because I experienced the following:

When I render a scene with GI and secondary bounces (direct compute, not the photon map) it obviously takes longer to render compared to the same scene without secondary bounces. But: also the Irradiance map computation takes longer, and not only the second (the final) render process. I always thought that the whole Idea of the Irradiance map is to have a quick, one-bounce GI solution and that it doesn´t care about secondary bounces at all, so why are they evaluated during this process when they are also computed later again during the final render process (which also takes longer) after its calculation? It seems to be a double negative speed hit, first during irradiance map calculation, then again during the final render process. Since nobody seems to question this I guess it´s supposed to be that way but why?

Stefan

[vlado]

The irradiance map stores the complete indirect illumination - secondary bounces and all. When you use the irradiance map, during the rendering no GI is computed at all - it all comes from the irradiance map.

Best regards,
Vlado

[stefan]

All right, I get the picture. I previously had the impression that also the render process takes longer if secondary bounces are directly computed. But looking at the new render message window I seee that rendertimes are exactly the same with or without secondary bounces. Only irradiance map computation takes longer. Thanks Vlado for pointing me into the right direction.