[Minitut] Bent Normals
polycounter lvl 10
Recently there has been a lot of people on google+ hanging out and screen sharing. Whenever somebody is baking out/using a bent normal map a lot of questions get asked about what they are, what they do and how to use them. I thought i'd put together a small bit of info on them and what i normally use them for. If you have anything else you'd like to add/dispute please stick it in a comment.
WHAT THE HECK IS THAT?
Like many different map types, a bent normal is achieved through the "baking" process, if you are unfamiliar with baking in general, check the wiki page
A bent normal map is lighting infomation transfered from a highpoly model onto a lowpoly, it made up of RGB channels which each contain their own lighting direction. Typically, red is side lit, green is top lit and Blue is frontal lit.
At first glance, the map doesn't seem all that useful:
Go into the channels though, and its pretty clear that it's light info.
Green channel (top lighting)
SO WHAT CAN I USE THIS FOR?
Lighting information can be used in your textures differently depending on if you are doing a diffuse only character or intend on using normal maps to capture realtime lighting detail.
In both cases, i combine the bent normal green(top lighting) and blue (frontal lighting) into my diffuse texture just as you would with an ambient and cavity map. I like to set the top lighting layer to soft light and set the frontal lighting layer to multiply.
With/without example
It's rather subtle as i want most of the lighting infomation to be captured by the normal map instead of being baked directly into the diffuse, but it's just enough to help the texture pop a little more. It's also a quick and easy way of achieving the "triangle of light" over the face which Hazardous mentioned in his character thread: http://www.polycount.com/forum/showpost.php?p=1615965&postcount=141
If you were working on a diffuse only piece, bent normals are really handy for giving you a strong sense of lighting without even picking up your tablet. With a bit of saturation and more opacity than the previous example you can have something like this;
More examples on using baked light can be found in the dota documentation:
http://media.steampowered.com/apps/d...xtureGuide.pdf
HOW DO I ACHIEVE THIS?
Unfortunately, i only know how to create a bent normal map using Xnormal. If anybody knows of ways of making them in other app's please speak up!
EDIT, maya baking: http://www.polycount.com/forum/showpost.php?p=1629002&postcount=3
I guess just baking out an obj space normal from your baking app works if you don't have xnormal.
In Xnormal, set up your bake as you normally would and simply tick on the Bent Normals box under baking options.
And thats about all there is to it really.
You don't just have to use these on faces, or even characters! lighting info can be really useful for all kinds of environment props and even big scenery pieces.
I hope this was useful to a few people, if there are any other topics like this which you feel there isn't enough infomation about already please PM me and i'l see if i can add some more info on other things in this thread.
WHAT THE HECK IS THAT?
Like many different map types, a bent normal is achieved through the "baking" process, if you are unfamiliar with baking in general, check the wiki page
A bent normal map is lighting infomation transfered from a highpoly model onto a lowpoly, it made up of RGB channels which each contain their own lighting direction. Typically, red is side lit, green is top lit and Blue is frontal lit.
At first glance, the map doesn't seem all that useful:
Go into the channels though, and its pretty clear that it's light info.
Green channel (top lighting)
SO WHAT CAN I USE THIS FOR?
Lighting information can be used in your textures differently depending on if you are doing a diffuse only character or intend on using normal maps to capture realtime lighting detail.
In both cases, i combine the bent normal green(top lighting) and blue (frontal lighting) into my diffuse texture just as you would with an ambient and cavity map. I like to set the top lighting layer to soft light and set the frontal lighting layer to multiply.
With/without example
It's rather subtle as i want most of the lighting infomation to be captured by the normal map instead of being baked directly into the diffuse, but it's just enough to help the texture pop a little more. It's also a quick and easy way of achieving the "triangle of light" over the face which Hazardous mentioned in his character thread: http://www.polycount.com/forum/showpost.php?p=1615965&postcount=141
If you were working on a diffuse only piece, bent normals are really handy for giving you a strong sense of lighting without even picking up your tablet. With a bit of saturation and more opacity than the previous example you can have something like this;
More examples on using baked light can be found in the dota documentation:
http://media.steampowered.com/apps/d...xtureGuide.pdf
HOW DO I ACHIEVE THIS?
Unfortunately, i only know how to create a bent normal map using Xnormal. If anybody knows of ways of making them in other app's please speak up!
EDIT, maya baking: http://www.polycount.com/forum/showpost.php?p=1629002&postcount=3
I guess just baking out an obj space normal from your baking app works if you don't have xnormal.
In Xnormal, set up your bake as you normally would and simply tick on the Bent Normals box under baking options.
And thats about all there is to it really.
You don't just have to use these on faces, or even characters! lighting info can be really useful for all kinds of environment props and even big scenery pieces.
I hope this was useful to a few people, if there are any other topics like this which you feel there isn't enough infomation about already please PM me and i'l see if i can add some more info on other things in this thread.
Replies
Your example looks great as well.
Wouldn't it be better to just bake into the diffuse a little subtle lighting?
have you been using these inengine?
edit also to add something constructive you can bake these in max using the mr ao shader. you change its type to 2 and it outputs the bent normal.
this is just another tool I guess, you dont use any of these things in isolation.
you don't have to. put a grey shader with normalmap applied onto your lowpoly and light it as you like to, then bake it down
Mind blown. I never knew that, so thanks.
That dota link is really nice, i'l add it to the first post
A bent normal map is very similar to an object space normal map, except some AO is also baked into the map. But unless you tweak the occlusion settings you probably won't notice much difference. Unless you're using the bent normal map with a shader that takes advantage of it.
Also, this method works OK most of the time but kind of falls apart if your character is lit from below. The baked-in shading fights with upward-facing light and ends up looking really strange. Depends on your situation I guess.
I do a similar thing with my stuff; I take the green and blue channels of of the bent normal map and put em on top of my ambient occlusion on soft light or overlay mode. It usually takes a bit of tweaking to get the lighting to look consistent and not too directional or strong though.
Here's the layer setup I did on my old guy character
...blarg, didnt notice how small dis image is
In theory, although when I've tried this the bake always came out a bit gash... although I could just be being a bit of pleb and not doing it right.
Yes, but Xnormal is how the cool kids do it.