Ambient lights and bump mapping

[djsmackmackey]

Does anyone know how to make bump maps show up on objects lit only by ambient lights in a scene? I know it sounds like someone doing something stupid, but I have a very good reason only to use ambient lights. I just need to find a way to get bump maps to work with the ambient lights. Anyone out there able to figure this out?

[wcy93]

bump mapping shouldn't work with ambient lighting. bump mapping is a technique that simply calculates the surface normal, and then offsets, or perturbs that normal depending on a map. the shading is done by calculating the angle between this offset surface normal and the light direction. because ambient lighting is directionless, then no shading occurs, other than the surface colour contribution.

workarounds might be something light putting a little bit of normal lighting in your scene, or use displacement mapping.

[sunil_born2win]

If you intend to have a "flat" looking render, you'd better use surface shaders and directional lights, or whatever ... And you'll have your mapping appear, other way, you'll be unable to have bump map with only ambient lights.

[djsmackmackey]

no, I'm not going for a flat look or anything. I have a very good reason to be using ambient lights, but it's a bit too involved to go into on here. I've sort of painted my way into a corner here. though there is a way around it, it's a looonnnngggg way around. I have to have no illuminating lights and then go into each material's ambient channel and bump channel and make a ton of connections to make the bump show up. But if I could find a way to use an ambient light or two, and get the bumps to show up, then it would be a much faster process. I tried connecting the out normal of the bump node to the normal camera of the ambient light, but that projected the bump from the light in all directions. but if you plug it into the normal camera of the material (like bumps usually do), then it doesn't show up. I think I'm just going in the wrong direction here.
Like I said, I have a very good reason to use ambient lights (and no other light type). I just need to find some kind of workaround to get the bump to show up.

[sumo-kun]

Bump maps imply that there is some sort of directional lighting involved, so I suggest that you create several directional lights and parent them under your camera. THere is no workaround to get ambient light (as modeled by the ambient light node in Maya) to light a bump map. Look at the math involved if you need further proof. Perhaps you are after a dome light?

-MD

[joojaa]

Yeah because bump effect comes from the fact that surfaces gain more light when pointing at the light (and less when not), and bump only changes the normal so that the facing calculations use faked normals. now since the ambient lights shine equaly from all points in speace, all points would therefore be equaly bright/dark...

So no effevt would occur, while you might have something that would seem bumpy it isnt. You can however use displacement which actualy moves the surface around... Altough since you dont have any real lightsources to act on the effect would be a bit flat. At a huge tesselatinon cost.

[djsmackmackey]

Would it help if I showed a picture of the effect I want to get using ambient lights? I know ambience appears flat, but that isn't always the case. I can try to post a picture to help explain, though I don't know that it would help. just let me know.

[jeffd]

Maybe an ambient light with an ambient shade setting?

This basically makes that light an ambient plus a point, though.

Bump maps without a light direction doesn't make any sense, though.

--JeffD

[djsmackmackey]

I tried the ambient shade to see if it would even show a bump map then, but it still didn't show. but I really need the ambient shade set to 0. I want to be able to globally affect the ambience of the scene. kind of like how it works in Soft and XSI. I figured an ambient light with ambient shade set to 0 would suffice, but bump mapping is where I get stuck. and I can't afford the time and memory to use displacement. Maybe when I get a new computer I will be able to. speacking of which, how well does displacement work with Sub-D's?
On another note, how can I post a pic in a message? I've seen people do that and I'm wondering how it's done. do I have to link to a picture on the web, or can I upload one from my hard drive?

[joojaa]

Well because bump map is only a function of the specular and lambert proportions of the shaded surface, ambient wont affect it at all since its added after the fact. If you need the calculations i can point you on your way but youll only realize that fact.

PS however if you have an environment to reflect then bump might do a difference (environment would then act like a global light of a sort), or if you raytrace.

[djsmackmackey]

I understand all that. I'm more or less trying to find a work around. The work around I have involves connecting a shader to the ambient channel of every material in the scene. I guess I could try to figure out how to write a mel script for this, but I'm not much of a programmer. This is a bit out of my field as it is. Does anyone at least know how to write a script to connect an attribute of one node to the ambience of every shader in a scene? something like a wildcard I would imagine. *.ambience or something like that?
If I could figure out how to post a picture in here, it would probably help explain it.

[joojaa]

For some reason the bump wont work on environment only but works fine if lights or raytrace data is available... go figure

[djsmackmackey]

I'm not sure what you mean. envoronment won't work alone but will with raytrace data? what does that mean?

[joojaa]

for some reason maya wont touch the normals unless its lighted properly or raytraced (some optimisation probably, sice you wont gain anything by doing so)

[djsmackmackey]

what environmental stuff are you talking about. like environment textures like envCube, or something else?

[joojaa]

yes an environment texture all else is raytrace data...

[djsmackmackey]

well, I guess I'll just stick with the way I have it working for now, through the ambient channel instead of the ambient light. if anyone figures out a way to get it to work with ambient light, let me know!

[stevesayer]

Let me just try to clarify a little bit here.

We all know how ambient lights work and how bump maps work... right?

So... when you say, 'how can I get a bump map to work with just ambient lights,' what exactly is the effect you're going for?!

If your scene only has ambient lights, then an object--let's say a sphere--must appear to be a flat-colour circle when rendered, because every point on its surface receives an identical amount of light.

Now let's say you've got a bump-map of bright 'bulges' on a dark background.

In a normal scene lit from above (let's say), the bits of the sphere's surface that were on the top part of each bulge would be brighter than before... the bits of surface on the bottom of each bulge would be darker. If you made the light come from below instead of above, this would be reversed. Right? Simple. Fine.

But... in your ambient-only scene... exactly WHAT parts of the map do you want shaded brighter, or darker, or whatever? How will Maya know which parts should be lighter or darker?! With reference to what? The world up? The direction of the camera? The direction of some phantom directional light that isn't actually casting?

As several people have pointed out, saying that you want 'bump maps to work with ambient lights' is, phrased just like that, meaningless (because the concepts are incompatible). You say you understand this. So... you need to be more specific about what you want to achieve.

In this case I think a few screenshots would be worth a thousand words. How about one shot of some test object with your ambient-lighting-only setup and no bumpmap; one shot with the bumpmap and a regular light to show the look you're going for; and one shot of it with that same bumpmap and your current ambient-only workaround?

Good luck!

-Steve

[djsmackmackey]

It's really difficult to explain, and I don't know how to get pictures into my post. or how to get them online somewhere to link to. I could email them directly to someone, but who wants to download attachments from strangers (certainly not me). Ok, let me set up the scenario a bit.
For the sake of argument, let's say you were stuck using ambient lights for all your lighting. (also for the sake of argument, let's say you use the ambient shade option to make it work like a point light, though that's not what I'm doing here). With the ambient shade set all the way up, the light seems to emit from the point of the ambient light, and not from all directions. then, theoretically, you would have areas to brighten and darken to make bump maps. (not a flat color.) Why doesn't ambient light pick up the bump information then?
If I can figure out how to post a picture, it'll probably help explain a bit.

[djsmackmackey]

If you go to cgw.com and look up the article called War Effort, it's about Pearl Harbor and their ambient lighting. Although it looks to me like they're doing the same thing I'm doing, by mapping it to the ambient channel of every object, instead of using ambient lights. That or they made their own little program for it. I'll just stick to my long way of doing it. Thanks anyway for the help everyone.