Alpha Lighting Through Portals

April 16, 2008

The technology itself is a bit broken (I’m rewriting it), but the base idea is here, and it works well enough for screen shots 🙂

Lookin’ good…

So far, a little light bleeding in floating portals…

Better when on walls.

Just another screeny…

Ah, the beauty… level, props, everything soft self shadows through portals =D


15 Responses to “Alpha Lighting Through Portals”

  1. Futil1ty said

    Where’s my video?

  2. Peabnuts123 said

    I posted a comment.

    Looks good though, lol.

  3. ms said

    That looks really nice, please do keep the nice work up!

  4. bbarrett said

    Implementation issues aside, it would appear you have the method down at least. Looking forward to the final product. Oh, and congrats on the new blog 😉

  5. nullsquared said


    I got the correct algorithm down now – it’s pretty cool, you can shine a light at two portals in a corner and then 2 lights come out of the portals and they both shadow stuff. Which is actually not too slow, considering there’s only 1 shadow map, which is the original light’s shadow map 😉

    Futil1ty: no video until bug free (and since there is no sentence that can truly combine “bug” and “free”, I’ll rephrase myself with “most bugs eliminated”).

  6. Jallen said

    Looking good, i see you have made a softshadow demo for Ogre too. Nice one.

  7. alesto said

    Impressive work 😉
    I’ve seen also your last portal demo and was very surprised. How do you draw the portals. Do you use something like a stencil buffer?

  8. Block said

    Oh god the puzzles you could create with this…Nice blog!

  9. nullsquared said


    You guys will be a lot more impressed with the next beta compared to the “last portal demo” ;). I draw the portals with the stencil buffer, yes (just the way Valve does it). Except, my whole rendering technology (other than the fact that we both use the stencil buffer) is way different from Valve. This allows around 100 portal iterations (with complete normal mapped lighting and soft shadowing from 2 lights) at ~20FPS on my 8800GTS (including PTP lighting).

    I’ll be posting a new blog with updated PTP lighting (0% light leaking, unlike this blog), the new PTP lighting technology is something I innovated today – hasn’t been used until now, I’d say. It’s really a “branch” of an existing technique, except it’s used for the opposite effect.


  10. alesto said

    I’m planning to implement portals, too. I promised myself to accelerate rendering process at some points. I find them useful to connect rooms and indoor-outdoor environment.
    But how complicated would be calculations through portals? For example, a simple thing like getting distance from point to point? Beside the problem, that there are more than one possible result …

  11. nullsquared said

    Are you thinking of zone-culling portals, maybe? They’re a bit of a different concept.

    Calculations through portals… depends on what you’re doing. But when you have portals, you have to basically account for everything being seen/heard through them, and that means everything. Otherwise they aren’t portals, they’re just smoke and mirrors 😉

    I’d love to see other portal implementations (other than the ND/Valve team, obviously 😀 ).

  12. Truly inspiring. Keep up the good work!

  13. anachron said

    It’s been a month now, with no news. That’s a long time when you check this page every day 🙂

    When you’re done, you should make a “clone” of Peter Molyneux’ demo “The Room”, that would be awesome!

  14. […] productive than him) now has a blog with some interesting commentary on his efforts as well as some gorgeous screenshots. It doesn’t look like it’ll be open source any time soon but I don’t think […]

  15. Olav said

    the design of the cubes are very artistic!

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