Diffusion

Diffusion describes how a light ray is reflected off a rough surface. Think of light rays striking concrete. Concrete is a rough surface covered in tiny bumps and crevices. As a light ray hits the bumpy surface, it is reflected back into the environment at different angles, which diffuse the reflection of light across the surface (see Figure 8.1).

You see the surface color of the concrete mixed with the color of the lighting, but you generally don’t see the reflected image of nearby objects. A sheet of paper, a painted wall, and clothing are examples of diffuse surfaces.

In standard Maya shaders, the amount of diffusion is controlled by using the Diffuse slider. As the value of the Diffuse slider is increased, the surface appears brighter because it is reflecting more light back into the environment.

Reflection

When a surface is perfectly smooth, light rays bounce off the surface and back into the environment. The angle at which they bounce off the surface is equivalent to the angle at which they strike the surface—this is the incidence angle. This type of reflection is known as a specular reflection. You can see the reflected image of surrounding objects on the surface of smooth, reflective objects. Mirrors, polished wood, and opaque liquids are examples of reflective surfaces. A specular highlight is a reflection of the light source on the surface of the object (see Figure 8.2).

Logically, smoother surfaces, or surfaces that have a specular reflectivity, are less diffuse. However, many surfaces are composed of layers (think of glossy paper) that have both diffuse and specular reflectivity.

A glossy reflection occurs when the surface is not perfectly smooth but not so rough as to diffuse the light rays completely. The reflected image on a surface is blurry and bumpy and otherwise imperfect. Glossy surfaces can represent those surfaces that fit between diffuse reflectivity and specular reflectivity.

Refraction

A transparent surface can change the direction of the light rays as they pass through the surface (see Figure 8.3). The bending of light rays can distort the image of objects on the other side of the surface. Think of an object placed behind a glass of water. The image of the object as you look through the glass of water is distorted relative to an unobstructed view of the object. Both the glass and the water in the glass bend the light rays as they pass through.

Shaders use a refractive index value to determine how refractions will be calculated. The refraction index is a value that describes the amount by which the speed of the light rays is reduced as it travels through a transparent medium, as compared to the speed of light as it travels through a vacuum. The reduction in speed is related to the angle in which the light rays are bent as they move through the material. A refraction index of 1 means that the light rays are not bent. Glass typically has a refractive index between 1.5 and 1.6; water has a refractive index of 1.33.

If the refracting surface has imperfections, this can further scatter the light rays as they pass through the surface. This creates a blurry refraction.

The controls for refraction are found in the Raytrace Options section of the Attribute Editor of standard Maya shaders. A shader must have some amount of transparency before refraction has any visible effect.

The Fresnel Effect

The Fresnel effect is named for the nineteenth-century French physicist Augustin-Jean Fresnel (pronounced with a silent s). This effect describes the amount of reflection and refraction that occurs on a surface as the viewing angle changes. The glancing angle is the angle at which you view a surface. If you are standing in front of a wall, the wall is perpendicular to your viewing angle, and thus the glancing angle is 0. If you are on the beach looking out across the ocean, the glancing angle of the surface of the water is very high. The Fresnel effect states that as the glancing angle increases, the surface becomes more reflective than refractive. It’s easy to see objects in water as you stare straight down into water (low glancing angle); however, as you stare across the surface of water, the reflectivity increases, and the reflection of the sky and the environment makes it increasingly difficult to see objects in the water.

Opaque, reflective objects also demonstrate this effect. As you look at a billiard ball, the environment is more easily seen reflected on the edges of the ball as they turn away from you than on the parts of the ball that are perpendicular to your view (see Figure 8.4).

Anisotropy

Anisotropic reflections appear on surfaces that have directionality to their roughness, which causes the reflection of light to spread in one direction more than another. When you look at the surface of a compact disc, you see the tiny grooves that are created when data is written to the disc to create the satin-like anisotropic reflections. Brushed metal, hair, and satin are all examples of materials that have anisotropic specular reflections.

The resulting stretch or compression of an anisotropic reflection is defined in U and V directions. Anisotropy works in conjunction with the UV coordinates defined on a piece of geometry. (UV texture layout will be covered in Chapter 9, “Texture Mapping”.)

Creating Reflections and Refractions

Standard Maya shaders, such as the Blinn and Phong shaders, take advantage of mental ray reflection and refraction blurring to simulate realistic material behaviors. These options are available in the mental ray section of the shader’s Attribute Editor. However, turning these options on does not make the shader physically correct. They can also take a while to render. By using a mila shader, you can optimize your shading network and achieve a more realistic look.

Reflection

Reflection is easy to use, and it helps make objects look photo real. This exercise demonstrates how to add reflection and roughness to a surface using mila shaders. This scene contains a model of a coffeemaker above a checkered ground plane.

1. Open the reflections_v01.ma file from the chapter8scenes folder at the book’s web page (www.sybex.com/go/masteringmaya2016).
2. In the Outliner, select the glass surface from the coffeePot hierarchy.
3. Open the Hypershade window, and select Create ➢ mental ray Materials ➢ mila_material. Name the shader mila_glass_MAT.
4. RMB over mila_glass_MAT, and choose Graph Network from the marking menu. The network is now exposed in the Node Editor panel.
5. In the Material Viewer panel, change the renderer from Hardware to mental ray.

6. Under the Base rollout, in the Property Editor, choose black for the color.

7. mila materials work in layers. Since you are creating glass, your next step is to add a layer of transparency. Choose the +Layer button from the Property Editor. A new window appears with three options. Choose Weighted Layer.
8. Another window reveals a list of elemental components. Choose Transparency (see Figure 8.7).
9. The shader is completely transparent. It’s time to add some reflectivity. Choose the +Layer button, and then add a Weighted Layer ➢ Specular Reflection component.
10. The Material Viewer shows that your material is a mirror instead of reflective glass. Change the Weight value under the Specular Reflection rollout to 0.5. Figure 8.8 shows the rendered coffeepot.
11. At this point, you have a clean reflective surface. To add a touch of blur and some highlights, add a Weighted Glossy Reflection.
12. Change the Roughness to 0.2. The Roughness defines microscopic variations in the surface, causing the light that hits it to bounce off in different directions. Ultimately, this creates a blurring effect (see Figure 8.9).
13. Save the scene as reflections_v02.ma.

Many surfaces are more reflective than you may realize. An unpolished wooden tabletop, or even asphalt, can have a small amount of reflection. Adding a low reflectivity value plus reflection blurring to many surfaces increases the realism of the scene.

Refractions

Refractions cause the light passing through a surface to bend in different directions. The refraction component works just like the reflection component. Adding roughness causes microscopic variations in the surface. As a result, it can cause distortion and blurring of the objects that appear behind a transparent surface. The following exercise continues where the previous one left off.

1. Open the reflections_v02.ma file from the chapter8scenes folder at the book’s web page (www.sybex.com/go/masteringmaya2016).
2. Select backSplash from within the coffeeMaker hierarchy, and assign the checker_MAT to it. Having a textured object behind your glass pot will help you determine how much of a blur effect to add.
3. Select the mia_glass_MAT shader. Under the Property Editor panel in the Hypershade, choose the +Layer button and add a Weighted Glossy Transmission component.
4. Set the Weight value to 0.7.
5. Change the Roughness to 0.7 to increase the amount of blur. Figure 8.10 shows the results.
6. Light is not being refracted as expected. The reason for this is that you added a transparency component for the shader’s first layer in the previous exercise. Scroll to the Transparency layer in the Property Editor. Click the trashcan icon to delete the layer.
7. Render the coffeepot again and you’ll see that the problem has been fixed. Light passing through the glass is now bent accordingly (see Figure 8.11).
8. The effect of the refraction is too extreme. Reduce the Roughness to 0.2. The result is shown in Figure 8.12.
9. Save the scene as refractions_v01.ma.

To see a version of the scene, open the refractions_v01.ma file from the chapter8scenes folder at the book’s web page.

Creating Metals and Plastics

In this exercise, you’ll work on defining materials for the coffeemaker. The chapter8 eference folder at the book’s web page contains a photo of the appliance to help you match the look. The example scene uses the Physical Sun and Sky lighting network and Final Gathering to light the scene.

1. Open the coffeeMaker_v01.ma scene from the chapter8scenes folder at the book’s web page. The surfaces in the model have been grouped to keep the model organized.
2. You’ll create a brushed aluminum shader first. Create a new mila_material, and name it brushedAluminum_MAT.
3. In the Outliner, expand the coffeePot and coffeeMaker groups. Select silverRing, controlPanel, and backing. Apply the brushed aluminum material to the objects (right-click the material in the Hypershade, and choose Assign Material To Selection).
4. Add a weighted Glossy Reflection component. Change the Weight to 1.0 and the Roughness to 0.3. Use an HSV Color value of 0.6.
5. A render of the coffeemaker shows the aluminum texture. A brushed aluminum surface has special microscopic variations that affect its specular highlights. Instead of the typical rounded highlight shape, it tends to be elongated. Select mila_glossy_reflection2 by selecting the mila_layer2 tab from the Attribute Editor and clicking Go To Input Connection. Expand the Anisotropy rollout. Set Anisotropy to 0.1.
6. Create a test render. The Physical Sun and Sky setup automatically adds gamma to your render. To see the colors correctly, set your Color Management to Raw inside the Render View window under the View Transform drop-down menu (see Figure 8.13).

You can tweak many of the settings to create your own custom metal, but it already looks pretty good. Next, you can add a black plastic material to various parts of the coffeemaker:

1. Create a new mila_material, and name it shinyBlackPlastic_MAT.
2. Add a weighted Specular Reflection component. Change the Weight to 0.2 and the layer’s Color to black.
3. Select the following objects and assign the black plastic material:
   • Backsplash
   • Handle
   • Knobs
   • Lid
   • Spout
   • TopCasing
   • Trim
   • Base
4. Create a test render to see the progress (see Figure 8.14).
5. Save the scene as coffeeMaker_v02.ma.

To see a version of the scene, open the coffeeMaker_v02.ma scene from the chapter8scenes folder at the book’s web page.

Adding Shaders to Individual Polygons

Some areas of the coffeemaker’s control panel are not brushed aluminum. Several polygon faces for the digital readout should have different shaders assigned to them. The following exercise demonstrates applying a shader to these areas:

1. Open the coffeeMaker_v02.ma scene from the chapter8scenes folder at the book’s web page.
2. Select the faces shown in Figure 8.15.
3. RMB-click the shinyBlackPlastic_MAT shader, and choose Assign Material To Selection.
4. Create a new mila material. Name it readout_MAT.
5. Change the Base Color to match the following:
   • H: 68.571
   • S: 0.167
   • V: 0.329
6. Select the two faces inside the shiny black plastic area that you selected in step 1. Assign readout_MAT to the faces.
7. Create a test render of the coffeemaker to see the new materials.
8. Repeat the process and assign the brushed aluminum shader to the inner circle of the control knob. Figure 8.16 shows the rendered results.
9. Save the scene as coffeeMaker_v03.ma.

To see a version of the scene, open the coffeeMaker_v03.ma scene from the chapter8scenes folder at the book’s web page.

Building a Layered Car Paint Shader

In reality, car paint consists of several layers; these layers combine to give the body of a car its special, sparkling quality. Car paint uses a base-color pigment, and the color of this pigment changes hue depending on the viewing angle. This color layer also has thousands of tiny flakes of metal suspended within it. When the sun reflects off these metallic flakes, you see a noticeable sparkling quality. Above these layers is a reflective clear coat, which is usually highly reflective (especially for new cars) and occasionally glossy. The clear coat itself is a perfect study in Fresnel reflections. As the surfaces of the car turn away from the viewing angle, the reflectivity of the surface increases.

In this section, you’ll learn how to use the car paint material by applying it to a model of a truck.

1. Open the truck_v01.ma scene from the chapter8scenes folder at the book’s web page. This scene uses the Physical Sun and Sky network for lighting.

2. Open the Hypershade window, and select Create ➢ mental ray Materials ➢ mila_material.
3. Open the mila_material shader’s Attribute Editor. Change the Base Component to Reflective (Paint) (see Figure 8.17).
4. The truck has several shaders already applied. In the Materials tab in the Hypershade, RMB-click carParts1 and choose Select Objects With Material; this will select all of the polygons on the model that use this shader.
5. Assign the mila_material shader created in step 3 to the selected parts. Parts of the truck body now appear red.
6. Rename the mila_material shader to carPaint1_MAT.
7. Select the faces of carParts2 shader, and assign carPaint1_MAT to it.
8. Select carPaint1_MAT from the Hypershade. Choose the Input and Output Connections icon to graph the material’s connections in the Hypershade Node Editor (see Figure 8.18).

Base Parameters

At the top of the attributes, you’ll find the Base rollout. The settings here determine the color properties of the base pigment layer. As the color of this layer changes depending on the viewing angle, the various settings determine all of the colors that contribute to this layer.

1. Set the Color to a dark red. Choose the default pure red color swatch. Using the HSV color settings, change the value to 0.6. If you wanted to add a texture map to apply decals to the car, you would use this channel. Figure 8.19 shows a render of the truck so far.

2. Set Edge Color to a similar shade of red, but lower the value so that it is almost black. Edge Color is apparent on the edges that face away from the camera. Newer cars and sports cars benefit from a dark Edge Color setting.

   Edge Color Bias specifies the amount of spread seen in Edge Color. Lower values (0.1 to 3) create a wider spread; higher values (4 to 10) create a narrower band of Edge Color.

3. Edge Weight controls the overall contribution of the edge color effect. Set this value to 10.0. Figure 8.20 shows the rendered results.
4. Glossy Color is the color seen in the surface areas that face the light source. Change the Glossy Color settings to match the following values:
   • H: 360.0
   • S: 0.421
   • V: 0.348
5. Use the following Flake settings:
   • Flake Weight: 0.2
   • Flake Scale: 0.001
   • Flake Density: 0.4
   • Flake Strength: 0.1

You can see the rendered version with the new Flake settings in Figure 8.21.

Flake Parameters

The Flake Parameters settings are the most interesting components of the shader. These determine the look and intensity of the metallic flakes in the pigment layer of the car paint:

Flake Color  Should usually be white for new cars.

Flake Weight  A multiplier for Flake Color. Higher values intensify the look of the flakes; 1 is usually a good setting for most situations.

Flake Roughness  Changes the shader from a typical Lambert-style shading at 0 to a more powdery look at 1.0.

Flake Scale  Sets the size of the flakes. It’s important to understand that the size of the flakes is connected to the scale of the object. If you notice that the size of the flakes is different on one part of the car compared to the others, select the surface geometry and freeze the transformations so that the Scale X, Y, and Z values are all set to 1. This will correct the problem and ensure that the flakes are a consistent size across all of the parts of the car.

Flake Density  Determines the number of flakes visible in the paint. The values range from 0.0 to 1.0. In many situations, a high value means that the individual flakes are harder to see.

Flake Strength  Varies the orientation of the flakes in the paint. Setting this to 0 makes all of the flakes parallel to the surface; a setting of 1 causes the flakes to be oriented randomly, making the flakes more reflective at different viewing angles.

Flake Type  Specifies different procedural patterns to define the shape of the flakes.

Flake Cell Style  Forces the pattern specified in the Flake Type setting to be represented as irregular shapes or circles.

Flake Circle Size  Increases or decreases the size of the circular pattern if Circular is chosen for the Flake Cell Style value.

Specular Reflection Layer

A specular layer defines the look of the specular highlight on the surface. By adding a specular layer, you can make the car paint look brand-new or old and dull.

1. Select carParts1_MAT. In its Attribute Editor, choose the +Layer button.
2. From the pop-up window, choose Fresnel Layer.
3. From the next pop-up window, choose Specular Reflection.
4. The layer is added to the mila_material shader. An abridged version of the specular reflection layer’s attributes is displayed within the material node. Change the Fresnel IOR attribute to 1.44 to match the IOR of aluminum. Figure 8.22 shows the rendered results.

Glossy Reflection Parameters

The reflectivity of the surface is at its maximum when Reflection Color is set to white. When this option is set to black, reflections are turned off.

1. Select carParts1_MAT. In its Attribute Editor, choose the +Layer button.
2. From the pop-up window, choose Fresnel Layer.
3. From the next pop-up window, choose Glossy Reflection.
4. The layer is added to the mila_material shader. Change the Fresnel IOR attribute to 1.44.
5. To mimic the crisp reflective proprieties of metal, change the Roughness setting to 0.0. Figure 8.23 shows the results of the glossy layer.
6. Add the carParts1_MAT to the rest of the vehicle’s parts.
7. Save the scene as truck_v02.ma.

To see a finished version of the scene, open the truck_v02.ma file from the chapter8scenes folder at the book’s web page.