Soulburn Studios Art Lessons

3) Splitting Visual Details Into Shaders And Patterns

A Surface Shader is a set of equations used to determine the appearance of a surface and how it responds to light. A Shader is combined with Maps (Patterns) to form a Material. Sometimes your material is refereed to as a "shader", but for clarity sake, I will only refer to the Illumination portion of your material as a shader.

Now lets look at your Visual Detail List, what on the list is part of the shader?

Example, Hydrant (3 shaders):

Paint Shader
Metal Shader
Rust Shader

Look at your Visual Detail List, what on the list are patterns?

Example, Hydrant (8 patterns):

Paint requires several colors, has a paintbrush bump pattern, a pattern to change how reflective the surface is, and the paint is worn off to reveal the metal in a specific pattern (4 patterns).
Metal has some slight blemishes in color (1 pattern)
Rust has a specific color, specific bump, and then is placed on the surface of the hydrant in a specific pattern (3 patterns).

4) Shaders

Common Shaders in the CG World:

Lambert (Simple Diffuse)
Phong (Highlight)
Blinn (Highlight, less distortion at glancing angles)
Oren Nayar (Diffuse for Rough Surfaces)
Ward Anisotropic (Anisotropic Highlights)
Cook-Torrance (Metals)
GGX

Now lets choose the most appropriate shaders...

Example, Hydrant:

Paint could be a Lambert with a Blinn shader for shininess
Metal could use a Cook-Torrance shader, or a Lambert/Blinn made to look metallic
Rust could use a lambert, or Oren Nayar since it's very rough, and doesn't need a specular Highlight

Here's a few lessons on shaders...

5) Patterns

Now we look at our list of patterns. To make a successful material, you generally want at least 3 patterns per material...

Color
Bump / Displacement (Disp)
Specular Amount (Spec)

Although some specialty shaders require more patterns like a Translucency amount, subsurface color, etc.

Patterns tend to be chains of nodes (maps) that are layered together and then plugged into a particular channel of a material. Like in this example, a Placement node places a Pattern, that Pattern is Color Corrected (CC), then these Color Corrected Patterns are layered together using a Layer node, the result of that is Color Corrected, and then plugged into your material as a color, a bump, a specular amount etc. At its most basic level, pretty much all Pattern Map Chains you do for any material take on a form like this...

6) Splitting Patterns Into General And Specific Patterns

General Patterns: General Patterns are non-specific, stuff that pretty much covers your entire object. In the Fire Hydrant example, a General Pattern would be the brush strokes in the paint. They don't need to be anywhere specific to read as paint.
Specific Patterns: Specific patterns are patterns that appear in only very specific spots. In the Fire Hydrant example, a Specific Pattern would be the spots that show rust, since that appears only in very specific places on the hydrant (such as where two objects intersect).

Think of this with a traditional painters metaphor. Many painters start by blocking in the basic colors over the entire canvas, then they add details on top. So your basic color would be the General Patterns, and your details would be the Specific Patterns.

Also, some companies have a specific "Shader" job and a specific "Painter" job, usually the Shader handles the Materials and General Patterns, Painters handles Specific Patterns. Or in some companies you have Shader Writers and Painters, in which case the Shader Writer codes the shader, and almost everything else is handled by the Painter. Some companies, one person does both the shader, specific and general patterns.

7) General Patterns

In our Fire Hydrant Example, these are the General Patterns:

Paint Color
Paint Bump
Paint Specularity
Metal Color
Rust Color
Rust Bump

8) Specific Patterns

In our Fire Hydrant Example, these are the Specific Patterns:

Worn Off Paint Placement
Rust Placement

Go To Part 4...