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Thread: Luminous surfaces & transparency -??

  1. #1
    Axes grinder- Dongle #99
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    Question Luminous surfaces & transparency -??

    So, just about to go to bed but I'm playing w/radiosity and luminous surfaces, and it appears that if a Surface has even 1% of transparency, the LW renderer stops treating it like it's luminous at all.

    Is that correct?

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    \\ is sparkling // Iain's Avatar
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    If you look at real world luminous elements, the item emanating light is almost always opaque (filaments, diodes etc) and the transparent or translucent part just lets the light through. This is usually referred to as efficacy.
    You should approach this the same way in cg i.e. put your emitter behind the transparent/translucent surface.
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    I'm not a squirrel! Mitja's Avatar
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    Iain is right. To tell the truth I never even tried to make a transparent object luminous, so yours is quite a revelation to me!
    Another good idea is to evaluate the need of the transparent object. Example, interior renders: if you want to simulate the artificial lighting, the glass of the light bulb is useless, you can't see it in the final render. Contrarily, if you want to make a closeup of the light bulb, you will need that glass. A good idea (I almost always do so) is to put the glass in separate layer and make it unseen by radiosity: faster and cleaner renders.
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  4. #4
    To be fair any bulb which has a phosphor coating is both transparent and emissive - such as flourescent tubes - which are not completelly opaque. Either way I 'think' what you need to do is enable 'use transparency' in the radiosity prefs. without this setting transparent objects are ignored by radiosity. Converselly though if you have this enabled radiosity won't transmit through transparent objects - so say sky light through windows - unless you have 'directional rays' enabled - which allows mtl in LW - however this is SLOW - so best avoided unless you need the pretty causrics effects it gives ( albeit monochrome). in such cases you need to treat window glass as a special case and make it a seperate object 'unseen by transparency.

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    Axes grinder- Dongle #99
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    Cool

    Quote Originally Posted by Iain View Post
    If you look at real world luminous elements, the item emanating light is almost always opaque (filaments, diodes etc...
    Flame, neon gas. Thus I refute thee.

    Also, big glowing SF holograms, which the camera goes behind while the protagonist addresses the screen.
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  6. #6
    \\ is sparkling // Iain's Avatar
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    Quote Originally Posted by jeric_synergy View Post
    Flame, neon gas. Thus I refute thee.

    Also, big glowing SF holograms, which the camera goes behind while the protagonist addresses the screen.
    I'm not sure you can refute me when you quoted me saying 'almost always'
    But still, ionized neon gas is what produces the light, not the glass tubing and that was my point; for a realistic effect (and of course, all cg is just an effect, even Maxwell-type engines merely simulate reality through mathematics) having your light source behind a transparent or translucent surface is highly convincing.
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  7. #7
    Axes grinder- Dongle #99
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    That's the issue for me here: I'd like for the luminous object to be behind a refracting tube, but the math used seems to make that severely inconvenient.

    Maybe some slight-of-hand with gradients....
    They only call it 'class warfare' when we fight back.
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  8. #8
    Neither flame nor ionised gas have a surface, so technically you are wrong, in that their surfacing properties would contribute to lighting.. they are not a surface, but a gas or plasma, however there are examples of transparent luminous surfaces regardless

    If you want to create physically convincing conventional light sources though Iain is right, you should ideally place them behind glass, though it's quite possible to make transparent surfaces emissive, as I explained above, anyway.

  9. #9
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    Quote Originally Posted by jeric_synergy View Post
    Is that correct?
    It's bug in VPR.

    But you must remember that full render is paying attention whether Use Transparency is toggled in Render Globals > GI. If it's not toggled on, surface is ignored in GI stage immediately completely.

    You must understand - it doesn't matter what is plugged or set in Luminosity. What matters is sum of all Diffuse + Luminosity + Translucency, called simply Diffuse Shading.

    If you will use Const > Scalar 10.0 and plug it to Diffuse, then it'll almost like plugging to Luminosity or Translucency (from GI point of view).

    Try plugging Const > Scalar 10.0 directly to Diffuse Shading..
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    Last edited by Sensei; 08-10-2012 at 06:46 PM.

  10. #10
    Axes grinder- Dongle #99
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    Quote Originally Posted by Tobian View Post
    If you want to create physically convincing conventional light sources though Iain is right,
    But, not Luminous Surfaces, without compositing, right?
    They only call it 'class warfare' when we fight back.
    Praise to Buddha! #resist
    Chard's Credo-"Documentation is PART of the Interface"
    Film the cops. Always FILM THE COPS. Use this app.

  11. #11
    Quote Originally Posted by Sensei View Post
    It's bug in VPR.
    It's a bug in VPR that it won't show 'use transparency' objects, yes. Just tested it, works, as I said it would. VPR can only go so far!

    JS: Not sure what you are talking about: Compositing?
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