Hi, I have a question about the portal tip. If I have multiple windows throughout my room, would it be better to use one big portal per wall or one portal per window? Are there advantages or disadvantages to using more than one portal?
Hi Josh,
Actually, with multiple windows (depends of course how many, surface-wise), it might be better to not use Portals, because then they become counter-productive.
When you have 1, smaller window, it is helpful when you can tell Cycles, where the light is coming frrom (Portal), but with a large window area, then that would be like telling that the light comes from almost everywhere and you're just stuck with the extra calculation overhead of 'directing the light rays towards the Portals'. I hope that makes a bit of intuitive sense, it's hard for me to explain this in text.
I agree with Martin. But either way, I think one big portal doesn't really work either, because you are telling Blender where the opening is. So if you have one big portal and it's hitting the walls as well as the window openings, then it's counter-productive as well I think.
Think of it this way:
Cycles is shooting rays from the Camera into the Scene (not the other way around!) and they bounce around until they hit their maximum Bounces (set in the Light Paths), or they hit a light source.
Now, if you only have a small window as light source, most of the rays will just get thrown away, because they never hit a light source and thus don't contribute to the Render. So you'll be needing a lot more Samples (light rays per Pixel) to get a decent result. That's when a Portal can be helpful. That is also, why having a lot of small Lights in your Scene isn't optimal for Rendering.