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Where can portal go?

Posted: Wed Sep 26, 2012 10:19 pm
by treddie
I am a little confused on the use of portals. In the manual's example, the portal is placed inside a window hole, filling the entire hole and replacing any glass that would have been there. But the manual also suggests using one portal to cover many holes, since ALL holes must be covered for the portals to work. In that case, it sounds like since one portal can be used to cover many holes, it cannot sit inside the holes but can hover in front of them all. Is this correct?

Along those same lines, the manual also states that a portal and glass cannot work together yet. Why can't the portal be placed in front of the glass pane and work with it that way? If a portal only works with direct rays (my assumption) would not putting the portal between the light source and the glass work, with the portal very close to the glass?

Re: Where can portal go?

Posted: Thu Sep 27, 2012 8:33 am
by roeland
Octane doesn't trace shadow rays through glass objects. Because of that, if you make a scene with a daylight environment, you don't see sunlight shining through glass windows. Portals in windows have the same problem, Octane will sample the portals but because of the glass it will assume the light from the environment is not directly reaching the scene (when sampling portals the rays don't stop at the portals, in case there is some geometry outside, like trees).

For both problems the solution is not putting any glass in the windows. If you want to see some reflections you can put a perfectly smooth glossy material with a high transparency instead of the glass. Use a falloff node in the opacity input if you want more reflections at grazing angles.

The portals should be placed in any opening where skylight is entering the scene. Using portals will have the most benefit in scenes where a large part of the light comes from the environment through a few small windows. The rendered image will still be correct if some openings are not fully covered, or the portal geometry is bigger than the actual openings, but the rendering will be less efficient.

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Roeland

Re: Where can portal go?

Posted: Thu Sep 27, 2012 1:34 pm
by gabrielefx
roeland wrote:Octane doesn't trace shadow rays through glass objects. Because of that, if you make a scene with a daylight environment, you don't see sunlight shining through glass windows. Portals in windows have the same problem, Octane will sample the portals but because of the glass it will assume the light from the environment is not directly reaching the scene (when sampling portals the rays don't stop at the portals, in case there is some geometry outside, like trees).

For both problems the solution is not putting any glass in the windows. If you want to see some reflections you can put a perfectly smooth glossy material with a high transparency instead of the glass. Use a falloff node in the opacity input if you want more reflections at grazing angles.

The portals should be placed in any opening where skylight is entering the scene. Using portals will have the most benefit in scenes where a large part of the light comes from the environment through a few small windows. The rendered image will still be correct if some openings are not fully covered, or the portal geometry is bigger than the actual openings, but the rendering will be less efficient.

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Roeland
I really can't use glossy mats for architectural windows (especially if they are colored) because the rendering performance heavily will slow down.
Also with glossy mat you can't have refractions. In architecture glass panels are used everywhere and sometime the borders are visible, you notice the refraction.
Also it's impossible to achieve good alpha through transparent glossy thin panels, the result it's so fake that I have to delete these meshes and photoretouch them in photoshop loosing all the beautiful Octane's photorealism.

The only way is to create an architectural glass material similar to the vray one that reacts to reflections, refraction and has a credible alpha channel.

Re: Where can portal go?

Posted: Fri Sep 28, 2012 9:01 am
by treddie
Then, in the virtual camera thing I was doing recently, you can't put a portal in the middle of the aperture because of glass on both sides? If so, isn't the problem only there when using a Daylight node? Or is it the same problem with emitter objects or HDR images?

The only thing I had noticed with using a Daylight node was that shadows cast by a refractive material were completely opaque as if the material was completely opaque. Emitter Objects and HDR don't seem to have that limitation.