When the Use Depth Map Shadows attribute is checked for a spot, directional, point, area, or volume light, Maya creates a temporary depth map (see Figure 3.1).

Figure 3.1. The Depth Map Shadow Attributes section of a spot light's Attribute Editor tab

The depth map represents the distance between surfaces in the scene and the shadow-casting light from the light's point-of-view. This information is stored as a monochromatic Z-depth buffer (see Figure 3.2). Objects far from the light receive dark pixels, and objects closer to the light receive light pixels.

Figure 3.2. A depth map

When a surface point is rendered, its distance to the shadowing light is compared to the distance encoded in the corresponding depth map pixel. If the distance is greater than that encoded in the depth map pixel, it's assumed that another surface occludes the surface point's view of the light and the surface point is therefore shadowed. For example, in Figure 3.2 a distant building is partially occluded by a pair of gas pumps. The gas pumps are assigned brighter pixels because they are fairly close to the light. The part of the building that's not occluded has fairly dark pixels. Since the distance value of the dark pixels is equal to the actual distance that the surface points are from the light, no shadows occur in that area (with the exception of self-shadowing, which is discussed later in this section).

By default, depth maps are temporarily written to disk during a render but are not saved. You can force Maya to save the depth map as a Maya IFF bitmap, however, by switching the Disk Based Dmaps attribute (found in the shadow-casting light's Attribute Editor tab) from Off to one of the two following options:

By default, Maya writes out at least two IFF files per depth map per frame. The following naming convention is used:

ShadowMapFileName_lightName_sceneName.SM.iffframeNumber
ShadowMapFileName_lightName_sceneName.MIDMAP.SM.iffframeNumber

When a depth map is calculated, Maya shoots a shadow ray from the light view plane through each pixel of the depth map. The first surface point that the ray encounters is recorded in the SM map. The MIDMAP.SM map is created by the Use Mid Dist attribute.

Adjusting Use Mid Dist and Bias

By default, Use Mid Dist is checked for each light type that supports depth map shadows. This attribute significantly reduces self-shadowing artifacts, which often appear as bands across flat surfaces or a degradation of the shadow as it wraps around a curved surface (see Figure 3.4).

Figure 3.4. Extreme to subtle depth map artifacts

The artifacts are generally caused by one of two reasons:

• Surface points are misinterpreted as existing "below" or "behind" adjacent surface points. This can occur when surface points are sampled within the boundary of a depth map pixel and are discovered to be farther from the light than the distance value encoded in that pixel (see Figure 3.5). Since the distance value stored in a depth map pixel is based on a single sample—one taken at the point which the shadow ray intersects the surface—this problem occurs frequently.

  

  Figure 3.5. A simplified representation of the depth map artifacts

• The pixels of a depth map, which may cover relatively large surface areas, are unable to accurately sample areas of high curvature. In such a case, surface points are incorrectly considered "behind" or "below" adjacent surface points.

In either of these situations, the artifacts are not visible in the depth map bitmap itself. The artifacts occur only during the render of the final image. As a solution, you can increase the depth map Resolution value. Unfortunately, this will reduce the size of the artifacts but will not necessarily eradicate them.

The Use Mid Dist attribute, on the other hand, artificially pushes the surface points closer to the light by comparing the distance from the light to the surface point and the distance from the light to a point halfway between the first surface encountered by the shadow ray and the second surface encountered (see Figure 3.6). The second surface encounters are recorded in the MIDMAP.SM depth map.

If a second surface is not encountered, the light's far clipping plane value is used. Again, the basic depth map algorithm works in the following manner:

• If the distance between a surface point and the light is less than or equal to the distance encoded in the depth map pixel that contains the surface point in its boundary, the surface point is in light.

• If the distance between a surface point and the light is greater than the distance encoded in the depth map pixel that contains the surface point in its boundary, the surface point is shadowed.

In this situation, Use Mid Dist forces the depth map to encode distances that are greater than the actual distance to the first surface encountered. Hence, surface points sampled during the render have a greater likelihood of possessing a smaller distance value when compared to the distance encoded in the corresponding depth map pixel.

Figure 3.6. A simplified representation of the Use Mid Dist process

Although Use Mid Dist is responsible for a huge improvement in the quality of the render, it cannot eliminate 100 percent of the artifacts. The Bias attribute, which operates on similar principles, is designed to work in conjunction with Use Mid Dist.

Bias holds true to its name and "biases" the surface points toward the light casting the shadow. Whereas Use Mid Dist forces the depth map to take its distance value from a point midway between the first encountered surface and the second, Bias simply multiplies the actual surface point position by a factor that transforms it closer to the light. For spot and point lights, the number entered into the Bias field is multiplied by the distance value derived from the depth map, the result of which is used to determine how far to offset the surface point in world space. Hence, large Bias numbers tend to make the shadow disappear or develop large holes. For directional lights, the Bias attribute is not multiplied by the depth map values but is used as is.

Trial and error is often the best solution when choosing a Bias value. When changing the value, incrementally step from 0.001 to 1. For example, in Figure 3.7 depth map artifacts appear along the edge of a convoluted surface. Although a 0.25 Bias value reduces the problem, a value of 0.5 removes the artifacts completely. Higher values erode the self-shadowing on the surface.

Figure 3.7. Depth map artifacts are eliminated by adjusting the Bias attribute. This scene is included on the CD as bias_values.ma.

With most scenarios, checking Use Mid Dist and leaving Bias at its default value is satisfactory for a scene. However, if you find it necessary to change the Bias value, proceed with caution. A Bias value that removes an artifact at one point on a surface can introduce an artifact at another point. For example, an incorrect Bias value will often "disconnect" a surface from a ground or floor. In Figure 3.8, a thin NURBS leg loses its connection with a plane.

Figure 3.8. Three Bias values affect the connection of a depth map shadow to a NURBS leg. This scene is included on the CD as bias_leg.ma.

Note

The Depth Map Shadow Attributes section includes a Use Macro field, which is designed to call externally scripted macros to control the creation of depth maps. You can write the macros in such scripting languages as Perl or Python.

Creating Multiple Depth Maps

If necessary, you can generate more than two depth maps per spot light. If a scene is large in world space or necessitates a large Resolution size, you can uncheck the Use Only Single Dmap attribute. When this attribute is unchecked, six additional attributes become available with the following naming convention: Use Axis+/– Map (see Figure 3.9).

Figure 3.9. The Use Only Single shadow-casting spot light's section of the Attribute Editor tab

If one of these new attributes is checked, a depth map is rendered from the point of view of the light in one axis direction. For example, Use X+ Map writes a depth map aligned to the positive X axis. In this case, if Use Mid Dist is checked and Disk Based Dmaps is not set to Off, two depth maps are written out to the disk with the following names:

ShadowMapFileName.XP.iff
ShadowMapFileName.MIDMAP.XP.iff

P stands for positive axis direction. P is replaced by N if the axis direction is negative. The ability to choose direction is particularly useful for a spot light that must cover a large model. For example, in Figure 3.10 a spot light with a 120-degree Cone Angle value is placed close to the model of a building. Use X+ Map, Use X– Map, and Use Z– Map are checked. The resulting render creates two depth maps—one standard and one for Use Mid Dist—in each axis direction. If Use Only Single Dmap had been checked, the left and right sides of the model would have been excluded from the depth map. If the spot light were moved farther from the model to avoid this problem, a significantly larger Resolution would be required to maintain the map's detail.

By default, point lights create six standard depth maps and six corresponding depth maps for Use Mid Dist. These maps surround the point light in a virtual cube. You can turn off particular directions to save render time. For example, if no critical geometry exists below the point light, you can uncheck Use Y– Map. If a particular direction is completely empty, the corresponding depth map is ignored automatically.

Figure 3.10. Six depth maps are generated for one spot light.

You can view a depth map IFF file by choosing File > View Image and browsing for the filename. The FCheck window opens. Press the Z key while the mouse arrow is over the window or click the Z Buffer button. Since the depth information is stored in the Z channel of the IFF file, the depth map cannot be seen in Photoshop or other standard digital-imaging program. However, if you choose File > Save Image in FCheck while the depth map is visible, you can export the monochromatic image to any of the image formats supported by Maya. In this case, the information is written as RGB. Unfortunately, the converted file cannot be read by a Maya renderer because a depth map with an IFF extension and a Z channel is expected during the shadow-casting process.

Maya depth maps possess other attributes that are critical to the quality of their render. These include Resolution, Filter Size, Shadow Color, and Use Auto Focus. In addition, a specialized mental ray depth map and area light offers an alternative approach to creating shadows.

Setting the Resolution, Filter Size, and Shadow Color

Resolution sets the pixel size of the depth map. Filter Size controls the amount of edge blur applied to the shadow. As a general rule of thumb, you can follow this guideline:

• A crisp edge requires high Resolution and low Filter Size.

• A soft edge requires low Resolution and high Filter Size.

Aside from softening the shadow's edge, the Filter Size attribute is designed to disguise depth map limitations. Since depth maps are restricted by a fixed number of pixels, the pixels are often visible in the render. For example, in Figure 3.11 three different Filter Size values are applied to a depth map with its Resolution set to the default value of 512.

Figure 3.11. A depth map with a 512 Resolution and three different Filter Size values

The blur created by Filter Size is applied to the shadow map equally at all edge points. Hence, it cannot replicate a diffuse shadow that changes edge quality over distance. You can overcome this limitation, however, by creating a custom shading network. For a demonstration of this, see Chapter 7.

Shadow Color tints the color of the shadow, thus emulating bounced light. Choosing a lighter color also creates a shadow that is less intense and gives the appearance that a greater amount of fill light is present.

Setting a Light's Focus

The Use Auto Focus attribute automatically fits objects in the light's view to the resolution of the depth map. That is, if the objects are surrounded by empty space, the light view is "zoomed" in to maximize the number of pixels dedicated to the objects. Use Auto Focus is available on spot, directional, and point lights. Area and volume lights do not possess the attribute.

Note

If the cone of a spot light cuts objects out of the spot light's view, the Use Auto Focus attribute will not widen the view for the depth map. To avoid this problem, you will have to increase the light's Cone Angle, move the light backward, or manually set the light's Focus attribute.

In some situations, a scene will benefit if Use Auto Focus is unchecked and the light's Focus value is set manually. For example, if a depth map shadow is not critical for objects on the fringe of a scene, you can choose a Focus value that allows the light to concentrate on the scene's most important elements.

To choose an appropriate Focus value for a spot light, use the following steps:

1. Select the spot light and open its Attribute Editor tab. Uncheck Use Auto Focus. The Focus attribute becomes available.

2. With the light selected, choose Display > Rendering > Camera/Light Manipulator > Cone Angle. In a workspace view, choose Panels > Look Through Selected. The view through the light appears.

3. Click-drag the Cone Angle manipulator until the cone circle surrounds the objects in the scene that require a depth map shadow. Do not allow the cone circle to "split" a shadow-casting object in half; the resulting shadow will come to an abrupt stop in the render. Note the Cone Angle value and enter the number in the Focus attribute field. Move the manipulator back to its original position so that the original Cone Angle value is once again achieved.

4. Switch Disk Based Dmaps to Reuse Existing Dmap(s), enter a name into the Shadow Map File Name field, and render out a test frame. (This assumes that no depth maps have been written out.) Double-check the resulting depth map with FCheck. In the workspace view used to look through the light, choose an orthographic view through the Panels menu; this removes the temporary camera attached to the light by the Look Through Selected command.

Although directional lights possess the Focus attribute, choosing an appropriate value requires a different strategy. By default, directional lights possess direction but have no true position; despite the location of the light icon, they are considered to be an infinite distance from the subject. Hence, a directional light automatically includes all the objects in a scene for a depth map shadow. As a result, two new attributes become available when Use Auto Focus is unchecked: Width Focus and Use Light Position. Use the following steps to set these attributes:

1. Select the directional light and open its Attribute Editor tab. Uncheck Use Auto Focus and check Use Light Position.

2. In a workspace view, choose Panels > Look Through Selected. The view through the light appears. With Alt+RMB, dolly the light in or out so that the shadow-casting objects fill the view.

3. Using the workspace view menu, choose View > Camera Attribute Editor. In the camera's Attribute Editor tab, note the value in the Orthographic Width field in the Orthographic Views section. The Orthographic Width attribute represents the width of the visible scene as measured from the left side to the right side of the current view. Enter the value into the Width Focus field of the directional light.

4. Switch Disk Based Dmaps to Reuse Existing Dmap(s), enter a name into the Shadow Map File Name field, and render out a test frame. (This assumes that no depth maps have been written out.) Double-check the resulting depth map with FCheck. If the foreground appears clipped, the light icon is below, intersecting, or otherwise too close to the clipped surface. Simply dolly the light back in the workspace view and render another test. If shadow-casting objects are cut off at the left or right side of the depth map, gradually increase the Width Focus value and render additional tests.

The process of setting the focus for a point light is also unique. The point light Focus attribute does not correspond to either the Cone Angle or Orthographic Width attribute. You can determine an appropriate Focus value, however, by employing the following formula:

Focus = depth map world space width * 12

You can determine the world space width of a desired depth map by measuring across a scene with the Distance tool (choose Create > Measure Tools > Distance Tool). For example, in Figure 3.12 a desired depth map includes three center cones but not the outer two cones. The Distance tool is used to determine the maximum distance between the outer cones. The number, approximately 6.1, is multiplied by 12. The result is rounded off to 73 and entered into the Focus field. This formula represents a rough approximation. Multiple tests may be necessary to determine the best value.

Figure 3.12. The Focus value of a point light is determined with the assistance of the Distance tool. This scene is included on the CD as point_focus.ma.

Using mental ray Shadow Maps and Area Lights

The mental ray renderer supports standard Maya depth maps. In addition, mental ray can produce its own shadow map variation. You can also adapt a standard spot or area light by activating the mental ray area light options. (To render the mental ray light and shadow variations, switch the Render Using attribute, in the Render Settings window, to mental ray.)

When checked, the Use mental ray Shadow Map Overrides attribute (found in the Shadows subsection of the mental ray section of a spot, directional, area, or point light's Attribute Editor tab) overrides the standard Maya depth map shadow. (With Maya 8.5, you must uncheck the Derive From Maya attribute.) The Shadow Map Format attribute, found just above Use mental ray Shadow Map Overrides, controls the type of mental ray shadow map. The Regular Shadow Map option produces mental ray depth maps, which are more advanced than the Maya equivalent due to additional attributes. The Detail Shadow Map option supports object transparency and is discussed in Chapter 11. If you click the Take Settings From Maya button, the applicable values from the Depth Map Shadow Attributes section are transferred to the mental ray Shadow Map Overrides subsection. The following attributes control the look of the resulting mental ray shadow:

Resolution

Sets the pixel size of the depth map.

Samples

Sets the number of subpixel samples taken per pixel. Low values create grainy results.

Softness

Controls the spread of the light. Values above 0 create a softer, more diffuse shadow edge. Higher values necessitate higher Samples values to create acceptable results (see Figure 3.13). High values tend to smear the shadow at surface corners.

Figure 3.13. mental ray depth map shadows with two attribute settings

Bias

Functions in the same manner as the default Maya depth map Bias attribute by offsetting surface points to avoid self-shadowing artifacts. This attribute, if above 0, overrides the Shadow Map Bias attribute in the Shadow Map subsection of the Render Options section of the mental ray tab in the Render Settings window. Maya documentation recommends a Bias value that is less than the world distance between the light and the shadowed object. (Additional shadow attributes, including those found in the mental ray tab of the Render Settings window, are discussed in detail in Chapter 11.)

Shadow Map File Name

When a name is entered into this field, mental ray shadow maps are written to disk in the renderDatamentalrayshadowMap folder within the project directory. The maps are overwritten with each new render. The depth map files are written in a native mental ray format and cannot be viewed with FCheck. Point lights automatically produce six depth map files, while other lights produce one each.

You can convert a spot light into a mental ray area light by checking the Area Light attribute (found in the Area Light subsection of the mental ray section of a spot light's Attribute Editor tab). You can convert a standard Maya area light into a mental ray area light by checking Use Light Shape (found in the same subsection). In both cases, mental ray adapts the chosen light by grafting a specialized mental ray area light onto the light icon (see Figure 3.14).

Figure 3.14. When the Area Light attribute is checked, a mental ray light is grafted onto the spot light icon.

The added area light acts as a light spread, thus creating a diffuse, soft-edged shadow. The result is most noticeable when combined with a default raytrace shadow, which produces a hard edge in its default state (see Figure 3.15).

Figure 3.15. (Left) Raytrace shadow with a mental ray area light grafted onto a spot light. (Right) Default raytrace shadow with same spot light. This scene is included on the CD as area_spot.ma.

You can adjust the resulting shadow with the following attributes:

Type

Determines the shape of the area light. Options include Rectangle, Disc, Sphere, Cylinder, and User. If Type is set to Cylinder, the area light sends shadow rays above, below, and behind the parent light. If Type is set to Sphere, the area light sends shadow rays in all directions. The User option allows you to apply a custom mental ray light shader to the area light.

High Samples

Sets the number of shadow rays emitted from the area light, as measured in the X and Y direction of the light's icon. Default values leave the shadow very grainy. High values create an excellent result but slow the render.

High Sample Limit

Represents the maximum number of times a shadow ray is permitted to reflect or refract before it must employ the Low Samples attribute. By switching to Low Samples, fewer shadow light rays are involved when calculating reflections and refractions.

Low Samples

The number of shadow rays employed when the High Sample Limit is reached.

Visible

If the parent light is a Maya area light, the Visible attribute determines whether the mental ray area light icon is visible in the render. If Visible is checked, Shape Intensity becomes available and controls the strength of the visibility. If Shape Intensity is set above 0, the icon renders as a solid white rectangle but does not affect the light striking surfaces in the scene. Maya documentation recommends using the mental ray area light in conjunction with the Maya area light as it requires lower sampling levels to produce higher-quality shadows.

Light gaps, which look like thin, bright lines, often appear along the intersection of two surfaces. For example, in Figure 3.16 two primitive planes sit at a right angle and intersect slightly. A spot light, placed behind the surfaces, casts a default depth map shadow. A light gap appears along the intersection seam. Such gaps are due to a mismatch of the depth map to the render of the geometry. Depth maps do not receive anti-aliasing, which leads to stair-stepping. (See Chapter 10 for information on render quality issues.) In this situation, the depth map will not accurately line up with the anti-aliased render, and the bright surface appears in the resulting "gap." The light's Filter Size attribute, which blurs the shadow edge, widens the gap if raised above 0.

Figure 3.16. A light gap is visible at the intersection of two planes. This scene is included on the CD as light_gap.ma.

In this situation, higher Bias values make the error worse. You can increase the light's Resolution, which will reduce the strength of the light gap. However, the increased Resolution will not make the error disappear completely (see Figure 3.16). Switching to raytrace shadows will solve the problem but requires a more time-intensive render. Another solution involves the following steps:

In another common depth map scenario, a shadow stops short of a hard corner on a surface. For example, in Figure 3.17 a tire-shaped polygon casts a depth map shadow onto a stand. The shadow stops short of the stand edge, producing a thin white line. In addition, a similar white line is visible along the inner edge of the tire that is in shadow. When the Filter Size is raised, the artifacts become worse. Once again, this problem arises from the mismatch of the aliased depth map with the anti-aliased final render. In this case, an increased Resolution value will reduce the intensity of the white lines.

Figure 3.17. Edge artifacts of two objects are reduced by increasing the depth map Resolution. This scene is included on the CD as depth_edge.ma.

Unfortunately, an increased Resolution cannot remove the artifacts along the surface edges completely. Raytrace shadows, on the other hand, do not produce this type of artifact.

Each light in Maya imparts distinctive qualities to the shadow it casts. Familiarity with the quirks and strengths of each light will help you make the proper decisions when lighting a scene. As a side-by-side comparison, each light type has been placed in an identical location on a test set (see Figure 3.18). A row of vertical cylinders illustrates the omnidirectional or multidirectional qualities of many of the lights.

Figure 3.18. The light test set

All the lights, except for the ambient, cast depth map shadows with a Resolution set to 2048 and a Filter Size set to 2 (see Figure 3.19). The ambient light, which cannot cast depth map shadows, casts raytrace shadows with default setting. The area light casts both depth map and raytrace shadows since it possesses a unique, physical-based lighting method. The spot light is rendered with two cone sizes. All the lights, except for the volume, are left at their default scale. The volume light is scaled to surround the test set. The lights are turned on, one at a time, with the Illuminates By Default check box.

When the shadows of each light are compared, many qualities are identical; a few, however, stand out. In particular, the short shadows of the directional display the parallel quality of the light type. Even though the directional has the same Intensity value as all the other lights, it imparts the most illumination to the surface. In terms of realism, the area light with raytrace shadows is by far the best. Even though the raytrace attributes are left at their default settings, the area shadows become more diffuse with distance, mimicking light properties in the real world. In comparison, the area light with a depth map shadow creates a look similar to the volume light. Both the area and the volume have the most aggressive light decay.

Figure 3.19. The shadow qualities of Maya's six light types. This scene is included on the CD as light_set.ma.

Aside from the directional light, all the other lights have almost identical shadow patterns. In all these cases, if the light were moved farther from the cylinders, the shadows would become more parallel and less spread out. The spot light shows slight variations in the pattern when its Cone Angle is increased from 85 to 120. The directional and ambient lights provide the most even lighting, with the intensity of the surface changing little over its length and width. All the other lights create hot spots near the cylinders.

Light Fog supports depth map shadows with the Maya Software renderer. More important, Light Fog will fail to interact properly with objects in a scene unless Use Depth Map Shadows is checked. Unfortunately, raytrace shadows and the mental ray renderer will not work with Light Fog. However, several mental ray shaders produce their own volume fog. (For more information, see Chapter 12.)

Two additional fog attributes, Fog Shadow Intensity and Fog Shadow Samples, are included in the Depth Map Shadow Attributes section of spot, point, and volume lights. Fog Shadow Intensity dictates the darkness of shadows appearing in the body of the fog (see Figure 3.21).

Figure 3.21. Light Fog shadow with three different Fog Shadow Intensity settings. This scene is included on the CD as fog_shadow.ma.

The higher the Fog Shadow Intensity value, the less fog remains in the shadowed area. A value of 10 generally removes all the fog in the shadowed area and leaves a clean alpha channel (assuming there are no objects behind the fog).

Fog Shadow Samples, on the other hand, reduces potential fog graininess by applying additional sampling. Although there is no built-in maximum for the attribute, the default value of 20 is generally sufficient for a smooth render.

Paint Effects is a powerful tool that allows you to interactively paint specialized strokes that create complex geometry as a post-process. Numerous Paint Effects brushes are included with Maya and are grouped in such categories as grasses, trees, fire, and fibers. To create a simple Paint Effects scene, you can follow these basic steps:

A Paint Effects stroke is a specialized set of nodes. The stroke shape and transform nodes generate the geometry visible in the workspace view. The hidden curve node controls the shape of the stroke path. If you select the curve node in the Hypergraph Hierarchy or Outliner window, you can scale, translate, and rotate it like any other curve. You can also manipulate or animate the vertices of the curve to change the shape. The stroke geometry automatically follows the curve. Curve-editing tools, however, cannot be applied to the curve node. If a Paint Effects brush is applied to a surface through Make Paintable, the stroke geometry automatically deforms and moves with the surface. You can apply Paint Effects brushes to any surface that has valid UVs. Last, the brush node, which carries all the brush attributes, is connected to the stroke shape node. You can view the brush node in the Hypergraph Connections window; in addition, the brush node appears beside the stroke shape node in the Attribute Editor. The brush node is named after the brush type (for example, rope1).

The majority of Paint Effects brushes grow special tube geometry as part of the post-process. This is most noticeable with brushes that create plant life. A long list of attributes controls the tube growth; these can be found in the Tubes section of the brush node's Attribute Editor tab. Tubes can generate excellent shadows. In contrast, a few Paint Effects brushes create sprites. With these brushes, a bitmap is applied to a flattened tube with alpha information. No matter what direction the camera points, the sprite bitmap always faces the camera. Although sprites can cast shadows, the results are rough.

Paint Effects strokes cannot cast raytrace shadows. However, two attributes are provided to create depth map and fake shadows. They can be found in the Shadow Effects section of the brush node's Attribute Editor tab (see Figure 3.22).

Figure 3.22. The Shadow Effects section of a Paint Effects brush node's Attribute Editor tab

In addition to shadow effects, Paint Effects strokes include several attributes to create self-shadowing:

The Maya Fur system grows numerous hairs over a surface. You can use depth map shadows with fur if special attributes are added to a spot light. If the special attributes are added to other light types, self-shadowing is available. In addition, you can create raytrace fur shadows with the mental ray renderer.

To create a simple fur setup and cast depth map shadows, follow these steps:

Maya Fur supports raytrace shadows only if the renderer is switched to mental ray. To see raytrace shadows, check Use Ray Trace Shadows in the light's Attribute Editor tab and switch the Quality Presets attribute to Draft or Production in the mental ray tab of the Render Settings window. (The default settings of the mental ray ProductionRapidFur preset are designed for depth map shadows and will not produce raytrace shadows.)

If Maya Software is the renderer of choice, Add To Selected Light must be applied to each spot light that is creating a shadow. You can remove the Fur Shading/Shadowing attributes of a light by selecting the light and choosing Fur > Fur Shadowing Attributes > Remove From Selected Light. If mental ray is the renderer of choice, Add To Selected Light is not needed. If the Fur Shading/Shadowing attributes already exist, mental ray ignores them. Whereas the Maya Software renderer creates the fur as a post-process, mental ray integrates the fur directly into the scene. In general, mental ray raytrace shadows are more accurate than Maya Software depth map shadows, which have a tendency to separate individual hair shadows from the hair bases. You can use any light type when raytracing fur shadows with mental ray. In addition, mental ray possesses the following render capabilities:

If Fur Shading Type is switched to Auto Shading, self-shadowing attributes become available (see Figure 3.24 earlier in this chapter). Auto Shading is available to every light type except volume (which does not support fur shadowing). As with a spot light, the Fur Shading/Shadowing section must be added to the light by choosing Fur > Fur Shadowing Attributes > Add To Selected Light. The following attributes accompany Auto Shading:

The Maya Hair system generates a series of dynamic curves that can simulate hair, ropes, chains, and other thin but long elements. The quickest way to generate hair in Maya is to switch to the Dynamics menu set, choose Hair > Get Hair Example, select a hair icon in the Visor window, right-click, and choose Import Maya File name of hair file from the shortcut menu. A complete scene with a polygon model and hair system is brought in. Otherwise, you can create a hair system from scratch following these steps:

When a hair system is created, many new nodes are included. The hairSystemFollicles node is a group node to which all the follicle shape nodes belong as children. Follicles are small, red circles along the hair-generating surface that create individual clumps of dynamic curves. The hair that is rendered is actually a Paint Effects tube. Hence, pfxHair, pfxHairShape, and hairSystemShape are included. pfxHair serves as a transform node for the hair system. pfxHairShape carries global Paint Effects attributes such as Display Quality. hairSystemShape carries a specialized set of Paint Effects attributes designed for rendering hair.

Figure 3.26. (Left) Maya Hair without shadows. (Right) Maya Hair with depth map shadows rendered with mental ray. This scene is included on the CD as hair.ma.

You can render hair with raytrace shadows if the mental ray renderer is selected. Whereas the Maya Software renderer creates hair as a post-process, mental ray integrates the hair directly into the scene. As such, mental ray possesses the following render capabilities:

You can turn on or off the hair's reflection visibility, refraction visibility, and the ability to receive shadows by checking the Visible In Reflections, Visible In Refractions, and Receive Shadows attributes in the Render Stats section of the hairSystemShape node's Attribute Editor tab.

With nCloth, Maya provides a robust dynamic simulation system with which you can realistically emulate cloth objects. nCloth adapts preexisting polygon surfaces. To create a simple scene with nCloth, follow these steps:

When the Create nCloth tool is applied, an nCloth shape node is created. The original polygon shape node is connected to the nCloth shape node and is used as an input mesh. Because the original polygon surface is not destroyed, it provides UV and other material information to the nCloth mesh. Therefore, you can render nCloth with standard materials and depth map or raytraced shadows (see Figure 3.27).

Figure 3.27. An nCloth plane with mental ray depth map shadows. This scene is included on the CD as ncloth.ma.

The Maya Toon system emulates the "ink and paint" method of traditional 2D cel animation. Solid "ink" outlines are applied to areas of solid-color "paint." The outlines are specialized tube geometry that is applied to the assigned surfaces. The areas of color are created by Surface Shader and Ramp Shader materials, which are assigned by the Toon system.

The quickest way to apply the Toon system is to switch to the Rendering menu set, choose Toon > Get Toon Example, select a Toon icon in the Visor window, right-click, and choose Import Maya File name of Toon file from the shortcut menu. A complete scene with a Toon system is brought in. Otherwise, you can apply the Toon system with the following steps:

Surface Shader materials ignore all lighting and shadowing information in a scene. Therefore, the Solid Color fill shader does not create shadows. However, if you choose Toon > Assign Fill Shader > Shaded Brightness Two Tone or Shaded Brightness Three Tone, shadows are generated. In this situation, a Ramp Shader is assigned to the surfaces. The Color Input of the Ramp Shader is set to Brightness, which forces Maya to apply the colors of the Ramp Shader's Color gradient based on the brightness of the surface. Shadowed surface areas, which receive little or no light, pick up the left-hand side of the gradient (see Figure 3.28). This works with both depth map and raytrace shadows. Although the mental ray renderer supports the Ramp Shader material, it does not render the Toon outlines. (For more information on the Ramp Shader material, see Chapter 7.)

Figure 3.28. A pair of primitives are assigned a Toon outline and the Shaded Brightness Two Tone fill shader. The render is raytraced. This scene is included on the CD as toon_shadow.ma.

Other Fill Shaders are accessible through Toon > Assign Fill Shader > name of shader. Light Angle Two Tone applies a Ramp Shader, but sets the Color Input attribute to Light Angle. The Light Angle option chooses colors from the gradient based on the angle between the surface normals and the illuminating lights. Oddly enough, Light Angle Two Tone generates shadows. Rim Light, on the other hand, uses a Ramp Shader material, but adds a white color handle to the Incandescence gradient and therefore creates a thin white line around the surface's edge. Circle Highlight is similar, but inserts a white handle into Specular Color gradient, thereby creating an artificial specular highlight on the brightest potion of the surface. Both Rim Light and Circle Highlight options generate shadows.

When the Add New Toon Outline tool is applied, a pfxToon transform and pfxToon shape node are created. The pfxToon shape node generates the tube geometry for the "ink" outline and hosts a long list of attributes that affect the outline position, color, and behavior.