Open the carScene_v01.ma scene from the chapter10scenes directory on the DVD. The scene has the three-wheeled vehicle in a futuristic setting created by Anthony Honn.

Create a render from the renderCam (make sure mental ray is chosen as the current renderer).

Currently there is a basic white Lambert shader applied to the car and a gray Lambert shader applied to the scenery. The default light is enabled in the Render Settings window.

Open the Outliner, and Shift+click all of the group nodes and the glass object. From the Rendering menu set choose Lighting/Shading

Figure 10.2. Apply a surface shader to the geometry in the scene.

Open the Hypershade window (Window

On the left column of the Hypershade, set the mode of the Create tab to Create mental ray Nodes. Expand the Textures rollout, and click the mib_amb_occlusion button to create an ambient occlusion texture. It should appear in the Work Area of the Hypershade.

In the Work Area of the Hypershade, MMB-drag the mib_amb_occlusion1 node on top of the surfaceShader1 node, and choose Default from the pop-up. This connects the ambient occlusion node to the outColor channel of the surface shader (see Figure 10.3).

Surface shaders are the simplest of all shaders. They do not react to the lighting in the scene at all. The outColor channel applies a flat color to all the geometry that uses the shader. By connecting the ambient occlusion texture to the out color, you'll see only the effects of the ambient occlusion node on the geometry. Any lighting or other surface properties in the scene will be overridden by the ambient occlusion texture.

Figure 10.3. Apply a surface shader to the geometry in the scene.

In the render view, create a test render of the scene from the renderCam camera (see Figure 10.4).

The render takes a while (two minutes on my machine), partly because of the car's complex geometry and partly because the occlusion texture needs to be tuned to maximize efficiency. You'll also notice the image is very grainy. To fix these problems, let's look at how ambient occlusion is calculated.

Figure 10.4. Render the scene using a surface shader with an ambient occlusion node connected to the outColor channel.

Ambient occlusion uses ray tracing to determine how the shading of a surface is colored. When a ray from the camera intersects with geometry that has the ambient occlusion texture applied, a number of secondary rays are shot from the point of intersection on the surface back into the scene. Imagine all the secondary rays as a hemisphere above each point on the surface that receives an initial ray from the camera. If the secondary ray detects another object (or part of the same object) within a given distance from the original surface, that point on the original surface has a dark color applied. If no other nearby surfaces are detected, then a light color is applied. The level of dark or light color is determined by the proximity of nearby surfaces.

In the Render View window, store the current image so you can compare it with future renders. Select the mib_amb_occlusion node in the Hypershade, and open its Attribute Editor.

The Samples attribute adjusts the overall quality of the ambient occlusion shading. Raising this setting improves quality but also increases render times. Set this to 32.

The bright and dark colors determine how a surface is shaded based on the proximity of other surfaces or parts of the same surface. If you reverse these colors, you'll see the negative image of the previous render.

The Max Distance attribute determines how much of the scene is sampled. Think of this as the distance the secondary rays travel in the scene as they search out nearby surfaces. If a nearby object is beyond the Max Distance, then it will not affect how ambient occlusion is calculated because the secondary rays will never reach it. When Max Distance is set to 0, the entire scene is sampled; the Max Distance is essentially infinite.

One of the best ways to increase efficiency in the scene is to establish a value for Max Distance. This decreases the render time and improves the look of the image. Determining the proper value for Max Distance often takes a little experimentation and a few test renders. You want to find the value that offers the type of shadowing you need within a reasonable render time.

Spread determines the distance of the shading effect across the surface. Think of this as the size of the shadow. Higher values produce larger areas of shadowing on the surface; lower values produce tighter shadows.

Set Max Distance to 20 and create another test render; compare this with the previous render.

The render takes about half the time as the original render, and there is less noise in the lighter areas. The overall image is brighter because fewer objects are within the range of Max Distance, and thus there are fewer objects creating shadows on the surface.

The Falloff attribute modifies Max Distance. Lowering this value will produce darker shadows in crevices and softer shadows at the edges of the Max Distance. In practice, use Spread, Max Distance, and Falloff together to tune the look of the ambient occlusion shading (see Figure 10.5).

Figure 10.5. The attributes for the ambient occlusion texture

The Id Incexcl and Id Nonself attributes are two ways in which you can segregate occlusion shading by surface. If you have a scene in which there are multiple ambient occlusion textures applied to different objects, setting the Id Incexcl setting to a non-zero value either includes or excludes the surfaces from the effects of ambient occlusion.

If you set Id Incexcl to a positive value, the object is excluded from ambient occlusion; if you set it to a negative value, the object is included. A value of zero means that the object is always included in the ambient occlusion calculation.

Save the scene as car_scene_v02.ma. To see a version of the scene, open carScene_v02.ma from the chapter10scenes directory on the DVD.

Continue with the scene from the previous section or open the carScene_v02.ma file from the chapter10scenes directory on the DVD.

In the Outliner, expand the platform group and select the platformSurface object. Apply a Lambert shader to this object (Lighting/Shading

Open the Attribute Editor for the new Lambert material, and click on the checkered box to the right of the Bump Mapping field. From the Create Render Node pop-up, click the Textures tab and choose SolidFractal from the 3D Textures section.

Open the Hypershade, and switch to the Textures tab. With the new Lambert shader open in the Attribute Editor, MMB-drag the mib_amb_occlusion1 node from the Textures section of the Hypershade on top of the Incandescence channel of the Lambert shader.

Set the Color of the Lambert Shader to black so lighting from the scene does not affect the shader. Create a test render of the scene; the bump texture appears on the platform as part of the ambient occlusion shading (see Figure 10.6). This will also work for displacement maps and normal maps.

Figure 10.6. Render the scene using a surface shader with an ambient occlusion node connected to the outColor channel.

By using the same ambient occlusion texture for the surface shader and the Lambert shader, you only have to worry about changing the setting on one ambient occlusion node.

Save the scene as carScene_v03.ma. To see a version of the scene to this point, open the carScene_v03.ma file from the chapter10scenes directory on the DVD.

Open the carScene_v04.ma file from the chapter10scenes directory on the DVD.

In this version of the scene, a Physical Sun and Sky network has been added to the scene, and Final Gathering is enabled. A Blinn texture named wheelShader has been applied to the wheels of the car. The Reflectivity of the Blinn is at 1 (or 100 percent), so the wheels will resemble chrome when rendered.

Create a render from the renderCam camera in the Render View window.

The wheels are 100 percent reflective, which makes them appear somewhat unrealistic (see Figure 10.7). You can tone down the reflectivity in the crevices of the wheel geometry, which will help make them appear more realistic and the details more visible.

Figure 10.7. The wheels are 100 percent reflective, making them appear less realistic. Much of the detail of the wheels is lost in the reflection.

Open the Hypershade window, and MMB-drag the wheelShader from the Materials library down to the Work Area.

Set the Create column on the left side of the Hypershade window to Create mental ray Nodes. Expand the Textures section, and click the mib_amb_occlusion button to create an ambient occlusion node.

When you connect the ambient occlusion texture to a shader, you want to use the outColor attribute of the texture as the output. The outColor attribute is a vector, meaning it has three components (the red channel, the blue channel, and the green channel). To modify the Blinn texture, connect the color output of the ambient occlusion texture into the Reflectivity attribute of the wheelShader. However, the Reflectivity channel accepts only an input that has a single component, not a vector. To make the two channels compatible, you can use the Luminance color utility. This converts the vector output of the ambient occlusion texture into a single value, which can then be connected to the Reflectivity channel of the wheelShader.

In the Create column on the left of the Hypershade, set the mode to Create Maya Nodes.

Scroll down to the Color Utilities section, expand it, and click the Luminance button to create the Luminance utility.

In the Work Area of the Hypershade, MMB-drag the mib_amb_occlusion1 node on top of the luminance node. Choose Value from the pop-up window.

MMB-drag the luminance node on top of the wheel shader. Choose Other from the pop-up window. This opens the Connection Editor.

In the Connection Editor, select outValue on the left and the Reflectivity channel on the right (you may need to scroll to the bottom of the list; see Figure 10.8).

Open the Attribute Editor for the mib_amb_occlusion1 node. Set Samples to 32 and Max Distance to 20, and activate the Reflective option.

Create a test render from the renderCam camera, and compare it to the original render created at the start of the section (see Figure 10.9).

Figure 10.8. Connect the ambient occlusion texture to the Reflectivity channel of the wheelShader using a Luminance color utility node.

Figure 10.9. The reflection occlusion helps bring out the detail of the wheels and makes much more realistic-looking chrome.

The ambient occlusion texture makes the wheels look more realistic by controlling the amount of reflectivity in the cracks and crevices of the surface to bring out the detail. The wheels are now a bit closer to looking realistic.

You can use a reflection occlusion texture to create a separate render pass the same way that you created an ambient occlusion pass at the start of the chapter. All you need to do is use an ambient occlusion texture with the Reflective option activated for reflective surfaces and a standard ambient occlusion texture for diffuse surfaces. Render them all out in a single pass, or split them into separate passes and use the images to modify the render in your compositing software.

Save the scene as carScene_v05.ma. To see a version of the scene to this point, open the carScene_v05.ma file from the chapter10scenes folder on the DVD.

Open the crystalGlobe_v01.ma file from the chapter10scenes directory on the DVD.

The scene shows the crystal globe and stand. The scene uses the Physical Sun and Sky network to create simple lighting.

Select the ground plane and apply a Blinn material. Set the Reflectivity of the Blinn material to 1 and the Diffuse value to 0. Then render the scene in the render view from the renderCam camera.

Open the Attribute Editor for the Blinn shader that is applied to the ground. Expand the mental ray section and increase Mi Reflection Blur to 3. Create another test render, and compare this to the render in the previous step (Figure 10.17).

Figure 10.17. Add a blurred reflection to the ground plane (right image).

Continue with the scene from the previous section. In the Outliner, expand the globe group and select the crystal object. Assign a Blinn shader to the object.

Set Reflectivity of the new Blinn texture to 0 so you can clearly see the refractions.

Set Transparency of the object to light gray.

Expand Raytrace Options, and activate the Refractions option. Set Refractive Index to 1.4.

Render the scene from the renderCam camera, and store the image in the Render View window.

Expand the mental ray section in the Blinn's Attribute Editor. Set Mi Refraction Blur to 5, and create another test render (Figure 10.18).

Save the scene as crystalGlobe_v02.ma. To see a version of the scene, open the crystalGlobe_v02.ma file from the chapter10scenes directory on the DVD.

Open the helmet_v01.ma scene from the chapter10scenes directory on the DVD.

Open the render view, and create a render using the renderCam camera. Store the render in the Render View window.

The scene has a very simple light setup. The key lighting is provided by a mental ray area light, which can be seen as a specular highlight on the orange metal of the helmet and on the glass face shield. The fill lighting is supplied by two directional lights; these lights have their specularity turned off so they are not seen as reflections on the surface of the helmet (see Figure 10.19).

The helmet uses standard Maya shaders. The metal of the helmet uses an orange Blinn, the face shield uses a transparent Blinn, and the helmet details and the woman's head use Lambert shaders. The grainy quality of the shadows results from the low sampling level set for the area light. By keeping the samples low, the image renders in a fairly short amount of time (under a minute on my machine). The reflection of the checkerboard plane beneath the helmet is clearly seen in the metal of the helmet and on the face shield.

Open the Hypershade window. In the Create tab on the left column, switch the mode to Create mental ray Nodes. Under Materials, click the dgs_material twice to create two DGS material nodes. Name the first one helmet_dgs and the second shield_dgs.

Figure 10.19. The space helmet rendered with simple lighting and standard Maya shaders

In the Outliner, select the group labeled helmetSurfaces. In the Hypershade, right-click the helmet_dgs shader and choose Assign dgs_material1SG from the marking menu. This assigns the material to all the objects in the group.

In the Outliner, select the shield surface. In the Hypershade, right-click the shield_dgs material, and choose Assign dgs_material2SG from the marking menu.

In the Hypershade, select the helmet_dgs material and open its Attribute Editor. Set the Diffuse color to bright orange. Set Glossy to black and Specular to white.

In the Hypershade, select the shield_dgs material. Set Transparency to 0.8. Set Glossy to black and Specular to white.

In the render view, render the scene from the renderCam camera. Compare this render to the previous render. Immediately you'll notice a lot of strange things going on with the materials you just applied (see Figure 10.20).

If you compare Figure 10.20 with Figure 10.19, you should notice a few details:

Select the area light in the Hypershade and open its Attribute Editor. In the areaLightShape1 tab, expand the mental ray attributes and activate the Visible option.

Render the scene again. This time you can see a reflection of the light in the surfaces. You can clearly see that the light is square shaped.

Glossy reflections, on the other hand, automatically render the reflection of a light source regardless of whether the light source is set to visible or not. The Glossy attribute on the DGS shader controls how reflections are scattered across the surface of an object. The term specular highlight with regard to shading models implies a certain amount of glossiness. Understandably, it's confusing when talking about specular reflections and specular highlights as two different things. The bottom line is this: To make a specular highlight appear in a DGS shader, either the light has to be visible when the Specular attribute is above zero and Glossy is set to zero or the Glossy setting must be above zero.

Glossy reflections can be blurry or sharp. To control the blurriness of a glossy reflection, you need to adjust the Shiny setting. Lower Shiny values create blurry reflections; higher Shiny values create sharp reflections.

Select the helmet_dgs shader and open its Attribute Editor. Set Glossy to a medium gray; set the Specular color to black. Set Shiny to 10 and create another render. This time the surface of the helmet appears more like painted metal and less like a mirror (upper-left image in Figure 10.21).

The Shiny U and Shiny V settings control the blurriness of the glossy reflection when Shiny is set to 0. Using these settings you can create an anisotropic type of reflection. Anisotropic reflections appear on surfaces that have a directionality to their roughness. When you look at the surface of a compact disc, the tiny grooves that are created when data is written to the disk create the satinlike anisotropic reflections. Brushed metal, hair, and satin are all examples of materials that have anisotropic specular reflections.

The U and V values control the direction of the anisotropic reflections across the surface. For best results set one value higher than the other.

Set Shiny to 0. Set the Shiny U value to 3 and the Shiny V value to 10, and create another render; the helmet now appears more like brushed metal (upper-right image in Figure 10.21).

The Shiny U and Shiny V settings simulate the anisotropic reflections on the material by stretching the reflection along the U or V direction. In this case this is not physically accurate and does not simulate how tiny grooves in the surface affect the reflection.

When rendering transparent surfaces using the DGS shader, the Specular, Glossy, Transparency, and Refraction settings all work together to create the effect. For transparency to work, the shader must have a Transparency setting higher than zero and either a Specular or a Glossy setting above zero. If Transparency is set to 1 and both Specular and Glossy are set to black, the surface will render as opaque, the same as if Transparency were set to 0.

The Specular color can be used to color the transparent surface, and the Glossy setting can be used (along with the Shiny settings) to create the look of a translucent material, such as plastic, ice, or frosted glass.

Select the shield_dgs material. Set the Specular color to a light green, and set Transparency to 0.8.

Set Index Of Refraction to 1.1. This makes the glass appear thicker as the light rays are bent as they pass through the glass.

Create another test render. Notice that the green specular color tints both the objects behind the glass as well as the reflections on the surface (lower-left image in Figure 10.21).

To create the look of frosted glass, set Diffuse to light gray, Specular to black, Glossy to light gray, Shiny to 20, Transparency to 0.8, and Index Of Refraction to 1.2.

Create another test render to see the result (lower-right image in Figure 10.21).

Figure 10.21. Rendering using different settings for the DGS materials applied to the helmet metal and face shield.

A few details are worth noting about using the Glossy settings:

Save the scene as helmet_v02.ma. To see a finished version of the scene, open the helmet_v02.ma scene from the chapter10scenes directory on the DVD.

Open glass_v01.ma from the chapter10scenes directory on the DVD.

In this scene a simple glass has been modeled and split into four surfaces. Each surface represents one of the three transitions that will be simulated using the Dielectric material. To make this easier to visualize, each surface each has a colored Lambert shader applied. The scene is lit using a single spotlight that casts ray trace shadows.

The four surfaces are named air_glass1, air_glass2, liquid_glass1, and liquid_air1.

Open the Hypershade window. Set the Create tab on the left to Create mental ray Nodes.

Expand the Materials section, and click the dielectric_material button. Name the new dielectric_material1 node air2GlassShader.

Create two more materials and name one glass2LiquidShader and the other liquid2AirShader.

Apply the air2GlassShader to both the airGlass1 and airGlass2 objects. Apply glass2LiquidShader to the liquid_glass1 object and liquid2AirShader to liquid_air1.

Select the air2glassShader and open its Attribute Editor.

The Index Of Refraction (IOR) for glass is typically 1.5, and the IOR for air is 1. Look at the settings for the air2Glass shader. The Index Of Refraction setting defines the IOR for the material; the Outside Index Of Refraction setting defines the IOR for the medium outside the material. The default settings for the Dielectric material are already set to the proper glass-to-air transition. Index Of Refraction should be set to 1.5, and Outside Index of Refraction should be set to 1.

Set Phong Coefficient to 100 and turn on Ignore Normals.

The Phong Coefficient creates a specular reflection on the glass. The Dielectric material uses the surface normals of the object to create the refraction effect. If you activate the Ignore Normals option, the shader bases the normal direction on the camera view. For a basic glass model such as this one, you can safely use the Ignore Normals feature.

Select the glass2LiquidShader and open its Attribute Editor. Set Index Of Refraction to 1.33 (the IOR of water is 1.33) and Outside Index Of Refraction to 1.5. Set Phong Coefficient to 100, and turn on Ignore Normals.

Click on the color swatch next to the Col attribute. This determines the color of the shader (why spell out Index Of Refraction in the interface but at the same time abbreviate Color? One of the many mysteries of Maya). In the Color Chooser set Hue (H) to 180, Sat (S) to 0.45, and Value (V) to 1.

Select the liquid2AirShader. Set Index Of Refraction to 1.33 and leave Outside Index Of Refraction at 1. Set Phong Coefficient to 100, and turn on Ignore Normals.

Select the Col swatch, and use the same HSV values in the Color Chooser that you set in step 9.

Open the Render View window, and create a test render from the renderCam camera (see Figure 10.22).

Figure 10.22. Render the glass using the Dielectric material (left image). Add transparent shadows by rendering with caustics (right image).

Open the helmet_v03.ma scene from the chapter10scenes folder on the DVD. This scene currently uses standard Maya shaders applied to the geometry.

Open the Hypershade window, and set the mode of the Create tab to Create mental ray Nodes.

Expand the Materials section; you'll see a number of mib materials toward the bottom (see Figure 10.23).

Click the mib_illum_cooktorr button to create a Cook-Torrance material, and open its Attribute Editor.

Figure 10.23. Some of the mental ray base shaders are available in the Materials section of the Create mental ray Nodes menu.

The Cook-Torrance shader creates physically accurate isotropic specular highlighting, meaning that the specular highlights on surfaces are scattered as if the surface was covered with tiny microfacets arranged randomly.

The look of the highlight is created by setting the Specular color to a value above zero. The Roughness slider determines the spread of the highlight. The shader has three separate controls to determine the Index Of Refraction for each color channel (red, green, and blue). When light is reflected from the tiny bumps on an isotropic surface, the directionality of each light wave changes. The three IOR sliders allow you to specify this directional change for each color channel. This gives the specular highlight the appearance of "color fringing"—a slight tint on the edge of the highlight (this appears as blue fringe in the shader's preview). The color fringing around the highlight make this shader very useful for creating realistic-looking metals.

The Ward (mib_illum_ward) material is similar to the Cook-Torrance but offers more options for creating realistic anisotropic specularity. The Ward material works best on NURBS surfaces; the mib_illum_ward_deriv shader is a little easier to use, giving you two simple sliders to control the direction of the anisotropy along the U and V coordinates of the surface.

In the Outliner, select the helmetSurfaces group. In the Hypershade, right-click on the mib_illum_cooktorr1 shader, and choose Assign Material To Selection from the marking menu.

In the Attribute Editor, set the Diffuse color to light orange. Set the Specular channel to light gray.

Set Roughness to 0.19.

To create an orange fringe around the highlight, set Index Of Refraction, Red to 80, Index Of Refraction, Green to 10, and Index Of Refraction, Blue to 8.

In the Render View window, create a test render using the renderCam camera (Figure 10.24).

Figure 10.24. The Cook-Torrance shader creates fairly realistic metallic highlights.

The helmet has a very convincing metallic look, but you'll notice there are no reflections. To add reflections you can combine the Cook-Torrance shader with a glossy reflection node.

In the Create tab of the Hypershade, click the mib_glossy_reflection button. Assign the new mib_glossy_reflection1 node to the helmet surfaces group. This overwrites the Cook-Torrance shader that has been applied.

Open the Attribute Editor for the mib_glossy_reflection1 node. From the Hypershade window, MMB-drag the mib_cook_torr1 node from the Hypershade to the Base Material slot of the mib_glossy_reflection1 node (see Figure 10.25).

Figure 10.25. Connect the Cook-Torrance shader to the Base Material slot of the mib_glossy_reflection1 node.

Set Reflection Color to white (white sets the shader to maximum reflectivity; darker shades create a less-reflective material), and create another render.

The default settings create a glossy reflection in the helmet surfaces. To adjust the quality and glossiness of the reflections, increase the Samples value to 32.

The U Spread and V Spread sliders control the glossiness of the reflections, much like the Shiny U and Shiny V settings on the DGS shader. Higher values produce glossier reflections. Using a different value for U than V creates anisotropic specular highlights. Ideally you want to match the glossiness of the reflections on the mib_glossy_reflection1 shader with the glossiness of the highlight on the mib_cooktorr shader.

You can blend between a reflection of the objects in the scene and an environment reflection. To do this, you first need to create an environment reflection node.

Open the Attribute Editor for the mib_glossy_reflection1 node. Click on the checkered box to the right of the Environment field. From the mental ray tab of the Create Render Node window, scroll down to the Environments section. Click the mib_lookup_background button.

This connects a mib_lookup_background node to the Environment slot of the mib_glossy_reflection1 node. You can use any of the environment nodes to map an image to the reflection of the environment. Mib_lookup_background works with standard rectangular images. The node sizes the background image to fit the resolution of the rendering camera.

The Attribute Editor should open to the mib_lookup_background1 node. Click on the checkered box next to the Texture tab to add a mental ray texture node. This allows you to map an image to the background.

In the Attribute Editor for the mentalRayTexture1 node, click on the folder next to Image Name. Load the desert.jpg image found in the sourceimages directory in the Chapter10 folder on the DVD.

Select the mib_glossy_reflection1 node, and in its Attribute Editor, set Environment Color to medium gray. This sets the strength of the reflectivity of the environment.

The shader can create a smooth transition from the reflections of objects in the scene and the environment reflections. The Max Distance attribute sets a limit in the scene for tracing reflections. When reflection rays reach this limit, they stop sampling reflections of objects in the scene and start sampling the image mapped to the environment. The Falloff value determines the smoothness of the transition. The Falloff value is a rate of change. A setting of 1 creates a linear falloff; higher values create a sharper transition.

Set Max Distance to 5 and Falloff to 2. Turn off Single Env Sample, and create another test render. You can see the blue sky of the desert image reflected in the metal of the helmet.

To increase the realism of the reflections, you can add an ambient occlusion node to decrease the intensity of the reflections in the crevices of the model.

Open the Attribute Editor of the mib_glossy_reflection node. Click on the checkered box next to Reflection Color. From the Create Render Node pop-up, switch to the mental ray tab, and click on the Mib_amb_occlusion node in the Textures section.

Open the Attribute Editor for the mib_mab_occlusion node, set Samples to 32, Bright Color to medium gray, and Dark Color to a very dark gray (but not black). Set Max Distance to 5, and turn on Reflective.

Create another test render of the scene. Now the reflections on the model look much more believable (see Figure 10.26).

Figure 10.26. The Cook-Torrance shader is combined with a glossy reflection shader (left image). An environment is added to the reflectivity (center image), and an ambient occlusion node is used to modify the reflectivity (right image).

Figure 10.27 shows the shader network for this material.

This gives you a basic idea of how to work with the mental ray base materials. Of course, you can make many more complex connections between nodes to create even more realistic and interesting surface materials. Experimentation is a good way to learn which connections work best for any particular situation.

Save the scene as helmet_v04.ma. To see a version of the scene to this point, open the helmet_v04.ma scene from the chapter10scenes directory on the DVD.

Open the carScene_v06.ma scene from the chapter10scenes directory on the DVD. This scene uses the Physical Sun and Sky network for lighting.

Open the Hypershade window, and set the mode of the Create column on the left to Create mental ray Nodes. Expand the Materials section, and click on the mi_car_paint_phen_x shader (see Figure 10.28).

Figure 10.28. The car paint materials are found in the Materials section of the Create mental ray Nodes column in the Hypershade.

Open the Outliner and select the carBody group; apply the mi_car_paint_phen1 material to this group. This group consists of the surfaces that make up the body of the car.

Open the Attribute Editor for the mi_car_paint_phen1 material.

The Diffuse Parameters section determines 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.

Set Base Color to dark navy blue; this is the main color of the base layer. If you wanted to add a texture map to apply decals to the car, you would use this channel.

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

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

Lit Color is the color seen in the surface areas that face the light source. Set this color to a bright purplish-blue.

Lit Color Bias works on the same principle as Edge Color Bias. Lower values (above zero) create a wider spread in the Lit Color.

Diffuse Weight and Diffuse Bias set the overall strength of the Diffuse colors. A lower Diffuse Bias value (0 to 1) flattens the color; higher values (1 to 2) increase intensity toward the lit areas. Set Diffuse Bias to 2.

The Specular Parameters settings define the look of the specular highlight on the surface. The highlight has two components: a bright center highlight and a surrounding secondary highlight. The Spec Glazing feature adds a polished shiny quality to the highlight, which works well on new cars. Turn this feature off when you want to create the look of an older car with a duller finish.

Spec Weight and Spec Sec Weight are multipliers for the primary specular and secondary specular colors (respectively). Spec Exp and Spec Sec Exp determine the tightness of the highlight; higher values (30 and higher) produce tighter highlights. Generally Spec Sec Exp should be lower than Spec Exp.

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

Flake Reflect adds ray-tracing reflectivity to the flakes. This means that the flakes contribute to reflections of objects in the scene. For most situations a value of 0.1 is sufficient.

Flake Exp is the specular exponent for the flakes. Much like Spec Exp, higher values create a tighter highlight.

Flake Density determines the number of flakes visible in the paint. The values range from 0.1 to 10. In many situations a high value actually means that the individual flakes are harder to see.

Flake Decay optimizes rendering times by setting a limit to the visibility of the flakes. Beyond the distance specified by this value the Flakes are no longer rendered, which can keep render times down and reduce render artifacts, especially if Flake Density is set to a high value.

Flake Strength varies the orientation of the flakes in the paint. Setting this to 0 makes all 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 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 than another part of the car, 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 the parts of the car.

Set Flake Density to 0.6, Flake Strength to 1, and Flake Scale to 0.08.

The Reflection Parameters settings are similar to those for the reflection parameters on the glossy reflection material. The reflectivity of the surface is at its maximum when Reflection Color is set to white. When this is set to black, reflections are turned off.

Edge Factor determines the transition between the reflection strength at glancing angles and the reflection strength at facing angles.

Reflection Edge Weight sets the strength of reflectivity at glancing angles, and Reflection Base Weight sets the reflectivity at facing angles. Generally the base weight should be lower than the edge weight to create a proper Fresnel reflection effect.

Samples sets the sampling for glossy reflections. Unless you want to create glossy reflections, which are best used for older, duller cars, you can leave Samples at 0.

Glossy Spread defines the glossiness of the reflections. Max Distance sets the point where reflection rays start sampling environment shaders and stop sampling the geometry in the scene.

The Dirt Parameters settings allow you to add a layer of dirt to the surface of the car. Dirt Weight specifies the visibility strength of the dirt. For best results you can connect a painted texture map to Dirt Color if you want to add splashes of mud and grime.

Set Edge Factor to 4, and leave the other settings at their defaults (see Figure 10.29).

Figure 10.29. The settings for the car paint shader

Figure 10.30. The car paint material is applied to the body of the car and rendered with the physical sun and sky lighting.

In the Render View window, create a test render from the renderCam camera (Figure 10.30).

Save the scene as carScene_v07.ma. To see a finished version of the scene, open the carScene_v07.ma file from the chapter10scenes directory on the DVD.

Open the helmet_v05.ma scene from the chapter10scenes directory on the DVD. The surfaces in the model have been grouped by material type to make it easier to apply shaders.

Open the Hypershade window, and set the mode of the Create column on the left to Create mental ray Nodes. Expand the Materials section, and click the mia_material_x button to create a material. Name the material metalShader.

In the Outliner, select the helmetMetalSurfaces group, and apply the metalShader material to this group (right-click on the material in the Hypershade, and choose Assign mia_material_x1SG To Selection).

Open the Attribute Editor for the metalShader. Click the Presets button in the upper right, and choose Copper

Open the Render View window, and create a render from the renderCam camera. It really looks like copper. Save the render in the render view.

The material could use a little tweaking to make it look less like a kitchen pot. Click the Presets button again, and choose SatinedMetal

In the Attribute Editor, set Color to a medium grayish-blue (the color should be fairly unsaturated; otherwise the helmet will look very disco!). In the Reflection section, set Color to a light blue and turn on Metal Material—this adds a bluish tint to the reflections.

Create another test render and compare it with the previous render (Figure 10.31).

You can tweak many of the settings to create your own custom metal, but already it looks pretty good. The Glossiness setting adds blur to the reflections. Turning on Highlights Only creates a more plastic-like material—with this option activated the Reflection settings apply only to specular highlights.

Next you can add chrome to the helmet. Create a new mia_material_x shader, and name it chromeShader. Select the chromeParts group in the Outliner, and apply the chromeShader to the group.

Open the Attribute Editor for the chromeShader material. Click the Presets button, and apply the Chrome preset to the shader.

Create another mia_material_x shader. Name it rubberShader. Apply this shader to the rubberParts group. Use the Presets button to apply the rubber preset.

Create another test render and compare it to the previous renders.

The rubber shader can use a little tweaking. A slight bump can increase the realism.

Figure 10.31. The MIA material comes with a number of presets that can be blended together to create novel materials.

Scroll down in the Attribute Editor, and click on the checkered box next to Standard Bump. In the Create Render Nodes pop-up, switch to the Textures tab, and select the Leather texture. The Attribute Editor opens to the leather node. Use the following settings (Figure 10.32):

If the bump seems too strong, you can either adjust the cell and crease colors so that the shades of gray are closer together or switch to the Bump3D1 node and lower the Bump Depth value.

When you use the mia_material_x shader, you have a choice of bump styles. When Standard Bump is enabled and No Diffuse Bump is activated, the bump appears only in the specular and reflective parts of the material, which can be useful for creating the look of a lacquered surface. Standard Bump works much like a typical bump shader on a standard Maya shader.

Figure 10.32. The Leather texture is added as a bump to the rubber MIA material.

3D Textures

The Leather texture is a 3D texture. It does not use UV coordinates to determine the texture's placement on the surface; the texture exists in 3D space. This means that if the object is animated, the texture will appear stationary as the object moves, creating a very strange swimming effect in the texture. To fix this you must either parent the 3D texture node to the animated object or, if the object is deformed, create a texture reference object. To do this, select the object and choose Texturing

The Overall Bump shader can be used for bump textures as well (the No Diffuse Bump setting has no effect on textures used for the Overall Bump shader); however, the Overall Bump slot is really intended for use with the mia_roundcorners texture. The mia_roundcorners texture adds a slight bevel to the edges of a surface in the render. This means you do not need to create beveled edges directly in the geometry. A very slight edge bevel can improve the realism of the model (sharp edges on surface are often a tell-tale sign that the object is computer generated). Let's take a look at the roundcorners texture in action by applying it to the chrome material. You can apply the roundcorners texture to the Overall Bump shader and another texture to the Standard Bump shader.

In the Hypershade, select the chromeShader and open its Attribute Editor. Scroll down to the Bump section, and click on the checkered box to the right of Overall Bump. In the Create Render Nodes pop-up, switch to the mental ray tab and expand the Textures section. Click the Mia_roundcorners button to create this node.

In the Attribute Editor for the mia_roundcorners1 node, set Radius to 0.1. Create another test render and compare it to the previous renders. You'll see that the chrome trim around the helmet has a light roundness to it, making it look a little more believable (see Figure 10.33, right image).

Figure 10.33. Adding the mia_roundcorners texture to the chromeShader's Overall Bump channel creates a slight beveled edge to the geometry in the render (right image).

In the Hypershade, create two new mia_material_x nodes. Name one thinGlass and the other thickGlass.

Apply the thinGlass shader to the glassShield object in the Outliner. Apply the thickGlass material to the lampShields group in the Outliner.

In the Attribute Editor for the thinGlass material, use the Preset button to apply the glassThin preset. In the Attribute Editor for the thickGlass shader, apply the glassThick preset.

Create another test render.

The thin glass of the face shield looks extremely believable, especially with regard to the shading on the inside of the helmet. The lamps at the top of the helmet have a chrome reflector behind the thick glass, which adds to the reflectivity of the material. The settings to control thickness are found under the Advanced Refractions controls. Along with the standard Index Of Refraction setting, there is an option for making the material either thin walled or solid. You also have the option of choosing between a transparent shadow and a refractive caustic that is built into the material (the caustics render when caustic photons are enabled and the light source emits caustic photons; for more information on caustics, consult Chapter 9).

Open the Hypershade window, and create another mia_material_x node. Name this one plasticShader. Apply this shader to the plasticParts in the Outliner.

Open the Attribute Editor for the plasticShader, and apply the translucentPlasticFilmLightBlur preset. Create another test render.

This preset creates very translucent plastic using glossy refractions. In this situation it seems a little too transparent. Use the following settings to make the plastic look a little more substantial.

Create another test render (see Figure 10.34).

Save the scene as helmet_v06.ma. To see a finished version of the scene, open the helmet_v06.ma scene from the chapter10scenes directory on the DVD.

Open the helmet_v07.ma scene from the chapter10scenes directory in the DVD. Currently this scene has no lighting. All the materials on the helmet are the same MIA materials described in the previous section.

Open the Render Settings window, and switch to the Indirect Lighting tab. Click the Create button next to Image Based Lighting.

In the Attribute Editor for the mentalrayibl1 node, click on the folder next to Image Name. Select the building_probe image from the chapter10sourceimages directory on the DVD. This is a typical, high-dynamic range image.

Set Mapping to Angular. In the Render Stats section, turn off Primary Visibility so that the IBL sphere is not visible in the render.

Enable Final Gathering in the Indirect Lighting tab of the Render View window, and set Accuracy to 200.

Create a test render in the Render View window using the renderCam camera, and store the image in the Render View window.

The rendered image looks very underexposed; the dark parts are very dark.

In the Outliner, select the renderCam camera and open its Attribute Editor. Expand the mental ray section and click on the checkered box to the right of Lens Shader.

In the Create Render Nodes window, switch to the mental ray tab, expand the Lenses section, and click the button labeled Mia_exposure_simple.

This applies the mia_exposure_simple lens shader to the rendering camera. You need to remember to apply this shader to any of the cameras you'll use for rendering the scene.

Create another test render from the renderCam camera. You'll see a big improvement in the image using the default settings of the mia_exposure_simple lens shader (see Figure 10.36).

Save the scene as helmet_v08.ma. To see a finished version of the scene open the helmet_v08.ma scene from the chapter10scenes directory on the DVD.

Following is a brief description of the shader's attributes.

Open the carContour.ma scene from the chapter10scenes directory on the DVD. This scene shows the car modeled by Anthony Honn. A simple Lambert material is applied to the car.

Open the Render Settings window, and select the Features tab. Expand the Contours section, and click Enable Contour Rendering. This makes contour rendering possible, but you won't see any results until you activate a few more options.

Expand the Draw By Property Difference section. These settings define how the contours will be drawn. One of these options must be activated or contour rendering will not take place. Click Between Different Instances. This means lines will be drawn around each piece of geometry in the scene (see Figure 10.37).

Figure 10.37. To render contour lines, you must check Enable Contour Rendering and choose a Draw By Property Difference option.

Open the Hypershade window, select the whiteLambert material, and graph its input and output connections. In the Work Area of the Hypershade, select the whiteLambertSG node that is attached to the whiteLambert shader, and open its Attribute Editor.

In the Contours section of the mental ray rollout in the Attribute Editor, check the Enable Contour Rendering option. Set Color to red (Figure 10.38).

Figure 10.38. Contour Rendering also needs to be enabled in the shader's shading group node settings.

Create a test render in the Render View window from the renderCam camera. The contours are added after the scene renders, on top of the shaded view of the geometry.

Open the Render Settings window. In the Features tab, in the Contours section, activate Hide Source, and set Flood Color to a dark blue. Create another test render (see Figure 10.39).