[Sig12] [PBS] Disney's physically based lighting

Http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_slides_v2.pdf

Http://blog.selfshadow.com/publications/s2012-shading-course/burley/s2012_pbs_disney_brdf_notes.pdf

Disney explained the physically based lighting they used in the new cartoon wreck it Ralph.

Transformation

At the beginning, Disney used hair rendering based on a real physical model in <tangled> (MAGIC romance). The effect was superb, encouraging Disney.

Hair rendering based on physical models brings a rich set of real senses, and art can be fully controlled, this allows Disney to decide to use the light and Material System Based on the physical model in the next movie.

There are a lot of models available in the academic world, but what about the convincing effects and efficiency in actual industrial use? Next, Disney conducted extensive research. In this process, Disney developed a BRDF viewer to render the physical model and obtain the direct feeling.

Disney gains a lot in studying and observing these models through the viewer.

At the same time, Disney does not blindly follow academic theories. First, he starts from the true BRDF. On the basis of the truth, he examines the theory in turn. There is a great project here, called NLP:

Each small image directly shows a typical BRDF feature:

Diffuse

Diffuse is generally called diffuse reflection. Disney thinks that it is the subsurface scattering of light on the material (the light is reflected in the material for scattering, absorption, and other processes, and then comes out again ).

In contrast, Pixar believes that apart from subsurface scattering, as the material surface is rough, the multiple ejection between particles is also considered.

This is why metals do not usually have diffuse.

We generally talk about the lambert model,

In fact, this is not accurate. In the place where normal and line of sight tend to be vertical, Fresnel causes more light reflection and a few refraction, And the diffuse of this part should be reduced.

In this regard, Oren-Nayar and Hanrahan-Krueger have a further description of the model, which can be further described based on interests and needs:

Other parts... There is not much to say, it is a comparison between some shading models and real BRDF...

BRDF used by Disney

Principles for designing the BRDF model:

• Parameters must be intuitive, not abstract as physical paramter
• As few parameters as possible
• The value range must be simple, ranging from 0 to 1. If it is large or small, scale it by yourself, but the value must be simple.
• If needed, a parameter can be within the hackable value range)
• The combination of parameters requires robust and reasonable

Disney parameters: a great way to explain the meaning of each parameter

Here

• Specular is a familiar specular color.
• Roughness and specular power express similar meaning
• Anisotropic: the opposite sex, widely used in hair silk
• Sheen: Used to render clothes and process grazsing angle (normal and line of sight vertical)
• Clearcoat: a secondary specular that is used as a supplement to the primary specular. This is different from the secondary specular (usually obtained using envmap) mentioned in realtime physically based lighting. It is the secondary specular on the material.

DiffuseDisney uses a self-developed method:
Here we can see that the two points mentioned above are combined:

• Diffuse will become stronger with the increase of roughness (or the decrease of specular power)
• It will become weak in areas with strong Fresnel

This model is very popular with Disney's art and looks like the shader before physically based shading ).
Specular's distribution & Fresnel & geometry is not much to say.
Material MixingIf the artist wants to mix multiple materials, all the parameters need to be interpolated:

Some experiences in "Invincible ship"

• The uniform material BRDF makes the material library much simpler.
• And there is a good mix, art can be selected from the material library some of the needs, quickly make a new mix of Materials
• The use of image based lighting, detailed this article more details: http://blog.csdn.net/ccanan/article/details/7647964
• Real-time WYSIWYG material BRDF Editor: This is very common in the game's material editor.
• Thanks to a stable physical model, there is almost no rework for illumination.