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View Full Version : LW 11.5 - Negative light not work



aperezg
02-14-2013, 04:51 PM
I don't know if LW 11.5 has different configuration for negative light. But if I have 2 lights, 1 is negative, this light won't substract light, not matter wich kind of light is used in the scene .

Any Ideas ?

or is a Bug

or I miss something

Work fine in positive lights

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jburford
02-14-2013, 05:30 PM
Works fine here! But I am on pc, see that you are on the MAC... maybe is a MAC thing.... or have you tried resetting your configs?

Spinland
02-14-2013, 05:55 PM
I'm seeing the same problem on my Mac. The negative light looks good in VPR but doesn't show up in renders.

aperezg
02-14-2013, 06:04 PM
Works fine here! But I am on pc, see that you are on the MAC... maybe is a MAC thing.... or have you tried resetting your configs?

isn't the configs

Spinland
02-14-2013, 06:09 PM
Attached is the scene file I just tried, as well as the VPR screen shot (looks fine) and the actual F9 render (negative light ignored). My configs are fine, in fact I regenerated them from scratch just a couple of hours ago checking on another issue.

Looks like a Mac bug to me.

111561

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Spinland
02-14-2013, 06:15 PM
Fogbugz case 56788.

aperezg
02-14-2013, 06:18 PM
thanks for testing these lights

my scenes with negative lights, must to stay in LW 11.03

rvankan
02-15-2013, 10:51 AM
I'm on a PC as well and I have the same problem...So, it doesn't seem to be a 'PC vs Mac'-thing...

shrox
02-15-2013, 11:09 AM
I was just thinking about negative lighting, what is a situation where I might use it? I was thinking darkening a corner or something similar.

Spinland
02-15-2013, 11:15 AM
Pretty much. Or say you have a scene all lit but there's one object you want not so brightly lit. A single slightly negative light that affects only that object is an easy way to avoid having to adjust everything else. It's always seemed to me to be more of a simplified tool for certain artistic effects. I'm sure others can come up with other applications.

DonJMyers
02-15-2013, 11:16 AM
I was just thinking about negative lighting, what is a situation where I might use it? I was thinking darkening a corner or something similar.

Yes exactly. You can use negative lights to darken areas.

On the old "I Love Lucy" show they used to paint white or dark grey paint on the walls to fix shadows fast on the set. It's kind of the same thing.

Negative lights can also be used to create cool "negative shadows" which are alien and otherworldly. On the original Simpsons halloween episode an alien spaceship comes down and causes negative shadows.

jeric_synergy
02-15-2013, 12:15 PM
Wait a minute, aren't 'negative shadows' just lights?.... Ohhhh, a 'cast' light, okayyyyy.... Are you always talking volumetric herer, Don?

In the RW, the corners of a box (i.e. a room) are darker than the middle of the sides of the box, it's a physics thing. So pointing a darklightŪ into the corners gives a render that tiny bit of realism it lacks otherwise, without ray-tracing.

Spinland, thanks for being such a good 'LW citizen' and consistantly reporting bugs. It helps us all.

DonJMyers
02-15-2013, 12:18 PM
Wait a minute, aren't 'negative shadows' just lights?.... Ohhhh, a 'cast' light, okayyyyy.... Are you always talking volumetric herer, Don?

Here's an example. A human is standing on flat ground with the sun lighting them on one side. Turn the sun into a negative light and it darkens one side of the figure and it darkens the UNSHADOWED ground. The "dark" side of the figure is unaffected. The "shadow" of the figure is unaffected. Therefore the shadow and dark side end up LIGHTER than the rest of the image which is "anti-illuminated" by the negative light.

jeric_synergy
02-15-2013, 12:26 PM
Nice. Thanks for the explanation!

I hope this isn't an actual universal bug. :(

dwburman
02-15-2013, 12:41 PM
I remember an older tutorial for Maya where they used a two light setup to cast shadow mapped shadows more efficiently. Basically, they moved the shadow-casting light closer to the object so they could use a lower resolution shadow map. Then they cloned the light at set it to negative to negate the shadow casting light's effect.

I'm guessing that even if you wanted to use shadow mapping on a per-object basis in LW it would be simpler to uncheck 'effect diffuse' and 'effect specularity' in the shadow casting light's properties than adding another negative light to the scene.

wyattharris
02-15-2013, 01:15 PM
I usually use it if I've made a hallway or a vent, something long, but didn't actually build it out. The lights in the room usually spoil the illusion by illuminating the back. Throw in a negative light and it sucks all the light out making it appear there is no end.

Never tried it for reverse shadows, I'll have to see how that looks.

shrox
02-15-2013, 01:31 PM
I usually use it if I've made a hallway or a vent, something long, but didn't actually build it out. The lights in the room usually spoil the illusion by illuminating the back. Throw in a negative light and it sucks all the light out making it appear there is no end...

Oh yeah, I see. I have some use for it already then pretty much like you describe!

joelaff
07-12-2013, 08:56 PM
Has this been resolved yet? I have an older scene that is now rendering differently because it uses negative lights,. Build 2519

Ah, nevermind.. 11.5.1 fixed it according to the release notes.