To understand a bit more about shaders, consider what makes objects
appear as they do in the real world. The short answer is light. The way light
bounces off an object defines how you see that object. The surface of the object may
have pigments that affect the wavelength of light that reflects off it, giving the
surface color. Other features of that object’s surface also dictate how light is
reflected.
For the most part, shader types address the differences in how light
bounces off surfaces. Most light, after it hits a surface, diffuses across an area of that surface. It may also reflect a hot spot
called a specular highlight. The shaders in Maya differ
in how they deal with specular and diffuse parameters according to the specific math
that drives them. As you learn about the shader types, think of the things around
you and what shader type would best fit them. Some Maya shaders are specific to
creating special effects, such as the Hair Tube shader and the Use Background
shader. It’s important to learn the fundamentals first, so we’ll cover the shading
types you’ll be using right off the bat.
The Lambert Shader Type
The most common shader type is Lambert, an evenly diffused shading type found in dull or matte
surfaces. A sheet of paper, for example, is a Lambert surface.
A Lambert surface diffuses and scatters light evenly across its surface
in all directions, as you can see in Figure 7-2.
The Phong Shader Type
Phong shading brings to a
surface’s rendering the notions of specular highlight and reflectivity. A Phong
surface reflects light with a sharp hot spot, creating a specular highlight that
drops off sharply, as shown in Figure
7-3. You’ll find that glossy objects such as plastics, glass, and most
metals take well to Phong shading.
The Blinn Shader Type
The Blinn shading method brings to
the surface a highly accurate specular lighting model that offers superior control
over the specular’s appearance. (See Figure 7-4.) A Blinn surface reflects light with a hot spot, creating a
specular that diffuses somewhat more gradually than a Phong. The result is a shader
that is good for use on shiny surfaces and metallic surfaces.
The Phong E Shader Type
The Phong E shader type expands the Phong shading model to
include more control over the specular highlight. A Phong E surface reflects light
much as a regular Phong does, but it has more detailed control over the specular
settings to adjust the glossiness of the surface. (See Figure 7-5.) This creates a surface with a specular that
drops off more gradually and yet remains sharper than a Blinn. Phong E also has
greater color control over the specular than do Phong and Blinn, giving you more
options for metallic reflections.
The Anisotropic Shader Type
The Anisotropic shader is good to use on surfaces that are
deformed, such as a foil wrapper or warped plastic. (See Figure 7-6.)
Anisotropic refers to something whose
properties differ according to direction. An Anisotropic surface reflects light
unevenly and creates an irregular-shaped specular highlight that is good for
representing surfaces with directional grooves, like CDs. This creates a specular
highlight that is uneven across the surface, changing according to the direction you
specify on the surface. In contrast with Blinn and Phong types, the specular
highlight is evenly distributed to make a circular highlight on the surface.
The Layered Shader Type
A Layered shader allows the
stacking of shaders to create complex shading effects, which is useful for creating
objects composed of multiple materials. (See Figure 7-7.) By using the Layered shader to texture
different materials on different parts of the object, you can avoid using excess
geometry.
You control Layered shaders by using transparency maps to define which
areas show which layers of the shader. You drag material nodes into the top area of
the Attribute Editor and stack them from left to right, the left being the topmost
layer assigned to the surface.
Layered shaders are valuable resources to control compound and complex
shaders. They’re perfect for putting labels on objects or adding dirt to aged
surfaces. You’ll use a Layered shader in the axe-texturing exercise later in this
chapter.
The Ramp Shader Type
A Ramp
texture is a gradient that can be attached to almost any
attribute of a shader as a texture node. Ramps can
create smooth transitions between colors and can even be used to control particles.
(See Chapter 12, “Maya Dynamics and Effects,” to see how a ramp is used to control
particles.) When used as a texture, a ramp can be connected to any attribute of a
shader to create graduating color scales, transparency effects, increasing glow
effects, and so on. You’ll use Ramp textures later in this chapter.
The Ramp shader is a self-contained shader
node that automatically has several Ramp texture nodes attached to its attributes.
These ramps are attached within the shader itself, so there is no need to connect
external Ramp texture nodes. This makes for a simplified editing environment for the
shader because all the colors and handles are accessible through the Ramp shader’s
own Attribute Editor, as shown in Figure
7-8.
To create a new color in any of the horizontal ramps, click in the
swatch to create a new ramp position. Edit its color through its Selected Color
swatch. You can move the position by grabbing the circle right above the ramp and
dragging left or right. To delete a color, click the box beneath it.
Ramp textures are automatically attached to the Color, Transparency,
Incandescence, Specular Color, Reflectivity, and Environment attributes of a Ramp
shader. In addition, a special curve ramp is attached to the Specular Roll Off to
allow for more precise control over how the specular highlight diminishes over the
surface.
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