The Reverse utility simply reverses an input. The following math occurs:

Output = 1 - Input

Thus, an input of 1 produces 0 and an input of 0 produces 1. At the same time, the Reverse utility will make larger numbers negative or positive. For instance, an input of 100 produces −99 and an input of −100 produces 101. Only an input of 0.5 will lead to an unchanged output.

For example, in Figure 8.1 the Specular Roll Off of a material is automatically reduced as it becomes more transparent. The transparency attribute of a blinn material node is connected to the input of a reverse node. The outputX of the reverse node is connected back to the specularRollOff of the blinn. If a vector attribute (RGB) is connected to the reverse node, it is not necessary to utilize all three channels on the output. Without this network, a specular highlight of the blinn will remain visible even if its transparency is turned up to 100 percent. Although you can keyframe the Specular Roll Off attribute, this network is easy to set up.

Figure 8.1. The Specular Roll Off of a Blinn material is driven by its Transparency attribute with the aid of a Reverse utility. This scene is included on the CD as reverse.ma.

The Multiply Divide utility applies multiplication, division, or power operations to zero, one, or two inputs. If no inputs exist, you can enter numbers into the Input1 and Input2 attribute fields. If the Multiply Divide utility has one input, you can enter numbers into the unconnected Input1 or Input2 attribute fields. Regardless of the number of inputs, the Multiply Divide utility follows this logic:

Input1 / Input2
Input1 * Input2
Input1 ^ Input2

If the utility's Operation attribute is set to Multiply, the order makes no difference. If the utility's Operation is set to Divide or Power, however, the order is critical, as in this example:

10 / 2 = 5 while 2 / 10 = 0.2
10 ^ 2 = 100 while 2 ^ 10 = 1024

A chain of Multiply Divide nodes can emulate fairly complex math. Although Maya expressions can easily handle math work, the Multiply Divide utility offers an alternative method that allows the user to stay within the Hypershade window. For example, in Figure 8.2 the generic formula y = 1 / (x^(x / 2)) is re-created.

Figure 8.2. A generic formula is re-created with Multiply Divide utilities. This network is included on the CD as multiply_generic.ma.

To view the custom network, follow these steps:

In this case, (x / 2) is provided by multiplyDivideA. x is entered manually into the Input1X field. Input2X is set to 2. The Operation attribute is set to Divide.

x ^ is provided by multiplyDivideB. x is entered manually into the Input1X field. The Operation attribute is set to Power. outputX of multiplyDivideA is connected to input2X of multiplyDivideB.

1 / is provided by multiplyDivideC. Input1X is set to 1. Operation is set to Divide. outputX of multiplyDivideB is connected to input2X of multiplyDivideC. Ultimately, outputX of multiplyDivideC equals the answer, or in this case, y. If x is 1, then y equals 1. If x is 4, then y equals 0.0625. If x is 15, then y = 1.51118e-009. In Maya, e-009 is equivalent to ×10⁻⁹. If the outputX of multiplyDivideC is connected to the input1X of a fourth multiplyDivide node, the input1X field will display 0.000. Since the Input1 and Input2 fields of the Multiply Divide utility are limited to three floating points, they will not display numbers with an excessive number of digits. However, the correct value of multiplyDivideC's outputX can always be retrieved by entering getAttr multiplyDivideC.outputX in the Script Editor.

The Plus Minus Average utility supports addition, subtraction, and average operations. It operates on single, double, and vector input attributes. If single attributes are connected, they are not visible in the Plus Minus Average utility's Attribute Editor tab. However, double and vector attributes are indicated by input fields (see Figure 8.3).

Figure 8.3. A Plus Minus Average utility with single, double, and vector inputs

The Plus Minus Average utility provides Add New Item buttons in the Input 2D and Input 3D sections of its Attribute Editor tab. When you click one of these buttons, a new set of input fields is added to the appropriate section. The input fields are not connected to a node, which allows you to enter values by hand. However, you can choose to make a custom connection to the new input.

You can connect single attributes to input1D[n] of a plusMinusAverage node. You can connect double attributes, such as uvCoord, to input2D[n]. You can connect vector attributes, such as outColor, to input3D[n]. n represents the order with which attributes have been connected, with the [0] position being the first. There is no limit to the number of attributes that may be connected. For example, in Figure 8.4 the translateX attributes of four primitive polygon shape transform nodes are connected to input1D[n] of a plusMinusAverage node with the node's Operation set to Subtract. To illustrate the result, the output1D of the plusMinusAverage node is connected to the translateX of a locator. To see this custom network, follow these steps:

Figure 8.4. Two Plus Minus Average utilities subtract translation and average texture color for four polygon shapes. This scene is included on the CD as plus_simple.ma.

The locator position represents the result of the following math:

shape1.tx - shape2.tx - shape3.tx - shape4.tx

If the Operation attribute of the plusMinusAverage node is switched to Sum, the same logic applies. However, if the Operation attribute is switched to Average, the following math occurs:

(shape1.tx + shape2.tx + shape3.tx + shape4.tx) / 4

You can apply the Average operation to color attributes as well. In the same example, the outColor attributes of four textures are connected to the input3D[n] of a second plusMinusAverage node. The utility's output3D is connected to the color of a blinn material node, which is assigned to all four shapes. The following happens to the red channel of an individual pixel:

(water.colorR + ramp.colorR + mountain.colorR + bulge.colorR ) / 4

Maya expressions offer the most efficient and powerful way to incorporate math calculations into a custom shading network. Although a deeper discussion on expressions is beyond the scope of this book, here are a few items to keep in mind:

The Set Range utility maps one range of values to a second range of values. The underlying math for the utility follows:

outValue = Min + (((value-oldMin)/(oldMax-oldMin)) * (Max-
Min))

As an example illustrated by Table 8.1, five different ValueX inputs are processed by a Set Range utility, resulting in new Out ValueX outputs. For this example, Old MinX of the utility is set to −100, Old MaxX is set to 100, Min X is set to 0, and MaxX is set to 1.

The mid-value of the Old MinX and Old MaxX range (0) becomes the mid-value of the new MinX and MaxX range (0.5). Any value greater than the Old MaxX is clamped to the Old MaxX value before it is remapped. Hence, 500 becomes 100, which is then remapped to 1. Min, Max, Old Min, Old Max, and Value are vector attributes. The individual channels (for example MinX, MinY, MinZ) can carry different values.

In a working example, the Set Range utility is used to create diffuse shadows on a directional light. Diffuse shadows are a product of diffuse lighting. A diffuse light source is one that either produces divergent light rays or is physically large enough that it produces multiple overlapping shadows. One feature of a diffuse shadow is an increased edge softness over distance. A second feature is a shadow color that becomes lighter over distance (see the photo at the top of Figure 8.5).

Since depth map shadows are calculated using a single point-of-view of a light, Maya is unable to produce a diffuse effect. A light's Filter Size attribute blurs the edge of a depth map shadow, but the blur is equally intense whether or not it's close to the object casting the shadow. Raytraced shadows, on the other hand, can be adjusted to have a larger spread and thus a softer edge over distance; however, high-quality raytrace shadows can be time intensive. (See Chapter 3 for more information on shadow quality settings.) Nonetheless, you can emulate diffuse shadows with the shading network illustrated in Figure 8.5. To view this custom shading network, follow these steps:

Figure 8.5. The diffuse quality of a depth map shadow is controlled by a Set Range utility. This scene is included on the CD as setrange_shadow.ma.

For the 3D render at the bottom of Figure 8.5, a directional light named Key is placed behind a polygon cube. The light's Use Depth Map Shadows attribute is checked. Two locators are placed in the scene. The first locator, named shadow_begin, is placed at a point on the ground where the shadow begins (close to the cube). A second locator, named shadow_end, is placed on the ground where the shadow ends.

The center attribute of the shadow_begin transform node is connected to the point1 of a distanceBetween node (distanceBetweenB). The center of shadow_end is connected to point2 of distanceBetweenB. The Center attribute provides the location of an object's bounding box in world space. Ultimately, distanceBetweenB determines the length of the shadow. The center of shadow_end is also connected to the point2 of a second distanceBetween node (distanceBetweenA). The pointWorld attribute of a samplerInfo node is connected to the point1 of the distanceBetweenA. The Point World attribute stores the world position of the point being sampled during the render. Hence, distanceBetweenA determines the distance between the end of the shadow and the point being sampled. The distance of distanceBetweenA is connected to the inputX of a reverse node (reverseA). The outputX of the reverseA is connected to the valueX and valueY of a setRange node.

In the meantime, the distance of the distanceBetweenB node is connected to its own reverse node (reverseB). The outputX of reverseB is connected to oldMinX and oldMinY of the setRange node. The setRange node's MinX is set to 2 and its MaxX is set to 32. This represents the range of values that can be used as a Filter Size for the directional light. Since the Old Min value is fed by distanceBetweenB, and has been made negative by reverseB, the Old Max is set to 0. This negative range (–n to 0) matches the negative distance value provided by reverseA. These negative values are necessary to place the diffuse effect at the shadow end and not the shadow beginning. In this case, if a point near the end of the shadow is sampled, the distance between that point and the shadow_end is small and outputX of reverseA will be a small negative number (for example, −1). As a number, −1 is relatively high in the Old Min and Old Max range (close to 0) and is thus remapped to a number close to 32. Again, distanceBetweenB and reverseB represent the length of the shadow and therefore supply the Old Min values. If a point near the beginning of the shadow is sampled, the distance between that point and the shadow_end is large and outputX of reverseA will be a large negative number, such as −15. As a number, −15 is relatively low in the Old Min and Old Max range (not close to 0) and is thus remapped to a number close to 2.

Returning to the network, the outValueX of the setRange node is connected to the dmapFilterSize of the directional light KeyShape node. A dmapFilterSize of 0 produces no additional blur. A dmapFilterSize value of 32 creates the maximum amount of blur on the shadow. The outValueY of the setRange node is also connected to the shadColorR, shadColorG, and shadColorB of the light KeyShape node. The MinY of the setRange node is set to 0 and the MaxY is set to 0.5. This converts the Old Min and Old Max range into a range usable as a color. The end effect is a shadow that becomes lighter as it travels farther away from the cube. Increasing the value of MaxY will create a lighter shadow. This network works best with depth map shadows that have a relatively large Resolution value (for example, 1024). Smaller Resolution values will reveal the transitions between different Filter Size values. Nevertheless, this offers an alternative way to produce a diffuse shadow effect without the necessity of potentially time-consuming raytracing.

The Array Mapper utility is designed to control per-particle attributes on particle nodes. The attributes can affect particle size, dynamic behavior, color, and opacity. (An array is an ordered list of values.)

The simplest way to see the Array Mapper utility work is to create an RGB PP attribute for hardware-rendered particles. Since the process is a little unusual, I recommend you use the following steps:

You can manually connect the Array Mapper utility (found in the General Utilities section of the Create Maya Nodes menu). For example, in Figure 8.7 the outColor of a ramp texture node is connected to the computeNodeColor of an arrayMapper node. The message of the ramp is also connected to the computeNode of the arrayMapper. The outColorPP of the arrayMapper node is connected to the rgbPP of the particleShape node. In turn, the ageNormalized of the particleShape node is connected to the vCoordPP of the arrayMapper node. The Min Value and Max Value attributes of the Array Mapper utility serve as a clamp for the outColorPP and outValuePP attributes (outValuePP is the single-attribute version of outColorPP). You can replace the ramp texture with other types of textures, but the results will be unpredictable.

Figure 8.7. The shading network for a per-particle attribute

Although color is used in the previous example, a number of other per-particle attributes are available, including incandescencePP, radiusPP, and opacityPP. You can access these attributes by clicking the General button in the Add Dynamics Attributes section of the particle shape's Attribute Editor tab and choosing the Particle tab of the Add Attribute: particleShape window (see Figure 8.8). In addition to the PP attributes, the Particle tab carries a long list of more esoteric attributes, any of which can be utilized for per-particle operations through an expression.

Figure 8.8. The Particle tab of the Add Attribute window. Only a small portion of the available PP attributes are shown.

In a second example, a single Array Mapper utility drives the color, opacity, and acceleration of a point particle node (see Figure 8.9).

Figure 8.9. A point particle node receives its color, opacity, and acceleration from an Array Mapper utility. This scene is included on the CD as array_point.ma. A QuickTime movie is included as array_point.mov.

To view the shading network, follow these steps:

With this network, the Noise attribute of the connected ramp node is set to 1 and its Noise Freq attribute is set to 50, which creates a random pattern throughout the ramp. Although rgbPP receives its color directly from the ramp node, an expression controls the particle node's opacity, acceleration, and lifespan. The expression follows:

particleShape.opacityPP=arrayMapper.outValuePP;
particleShape.acceleration=arrayMapper.outValuePP*-500;
particleShape.lifespanPP=rand(1,3);

To view the expression, follow these steps:

In the first line of the expression, outValuePP of the arrayMapper node drives opacityPP. In the second line of the expression, outValuePP drives the particle's acceleration attribute. The acceleration attribute controls the rate of velocity change on a per-particle basis (although it's not listed as a "PP"). You can see the effect of the variable acceleration if the particle count is reduced to a low number. Some particles move rapidly, while others fall very slowly. The outValuePP is multiplied by −500, which makes the acceleration more rapid and the particles' direction in the negative X, Y, and Z direction. The ability to use outValuePP as an input for multiple particle attributes eliminates the need for additional arrayMapper and ramp nodes.

In the third line of the expression, the particle lifespan is assigned a random number from 1 to 3 with the rand() function. The outValuePP attribute is automatically connected to input[0] of the arrayMapper node; this represents the use of outValuePP in an expression. When an expression is created for a per-particle attribute, the expression is carried by the particle shape node and no separate expression node is generated.

As for other particle settings, the emitter is set to a cube volume shape with 0, −1, 0 Direction values. A turbulence field with a Magnitude value of 500 is also assigned to the particles. The field adds additional random motion; although the turbulence affects direction, it does not impact the overall acceleration. The end result is a glitter-like fall of particles. The point particles are rendered with the Hardware Render Buffer with Multi-Pass Rendering.

Unfortunately, the Array Mapper utility will not work with software-rendered particles—unless it is used in conjunction with a Particle Sampler utility. The Particle Sampler utility serves as a go-between, retrieving attribute information from a particle shape node and passing it on to a material assigned to the software-rendered particles. For example, in Figure 8.10 the example from Figure 8.9 is reused with the addition of a Particle Sampler utility. The Particle Render Type of the particle shape node is switched to Blobby Surface. The particle node is assigned to a blinn material node. The Noise value of the original ramp texture node is reduced and the ramp colors are adjusted. The Rate(Particles/Sec) value of the particle node is reduced for easier viewing. A directional light is added to the scene.

Figure 8.10. A Blobby Surface particle node receives its color, opacity, and acceleration through Array Mapper and Particle Sampler utilities. This scene is included on the CD as array_blobby.ma. A QuickTime movie is included as array_blobby.mov.

Aside from these adjustments, all the old network connections and the old expression are intact. As an addition, the rgbPP of a particleSamplerInfo node is connected to the color and the ambientColor of the blinn. The opacityPP of the particleSamplerInfo node is also connected to the transparencyR, transparencyG, and transparencyB of the blinn. The end result is a color distribution, opacity, lifespan, and acceleration roughly identical to Figure 8.9 but with a software-rendered particle node. The Particle Sampler utility also carries a long list of read-only attributes (see the left side of Figure 8.10). These attributes remotely read attribute information from the particle shape node that is assigned to the material. (For this to work, the material must share the shading network with the Particle Sampler utility.) The attributes are intuitively named (for example, particleSamplerInfo.rgbPP remotely reads particleShape.rgbPP). You can connect these attributes to any attribute of a material that may prove useful.

Vectors are useful for determining direction within Maya. Matrices, on the other hand, are an intrinsic part of 3D and are necessary for converting various coordinate spaces. Comparing the direction of lights, cameras, and surface components within different coordinate spaces can provide information useful for custom shading networks. Before I discuss such networks, however, a review of vector math, the Vector Product utility, and Maya matrices is warranted.

An Overview of Maya Matrices

Maya uses a 4 × 4 matrix for transformations (see Figure 8.11). The position of an object is stored in the first three numbers of the last row. The object's scale is stored as a diagonal from the upper left. The object's rotation is indirectly stored within the first three vertical and horizontal positions from the upper-left corner; the rotation values are stored as sine and cosine values. When an object is created, or has the Freeze Transformations tool applied to it, its transform matrix is an identity matrix. An identity matrix is one that produces no change when it is multiplied by a second transform matrix. In other words, an object with an identity matrix has no translation, rotation, or increased/decreased scale.

Figure 8.11. Maya's 4 × 4 transformation matrix

Converting Camera Space to World Space

As an example of camera space to world space conversion, in Figure 8.12 the Xform Matrix of a polygon cube is used to convert a Normal Camera vector of a Sampler Info utility into a world space vector. The results are illustrated by applying the resulting vector to the color of a material.

Figure 8.12. The Xform Matrix attribute of a polygon cube drives the color of a material. This scene is included on the CD as xform_matrix.ma. A QuickTime movie is included as xform_matrix.mov.

The xformMatrix of the pCube1 transform node is connected to the matrix of a vectorProduct node. (pCube1 is the small gray cube in Figure 8.12.) The normalCamera of a samplerInfo node is connected to the input1 of the vectorProduct node. The vectorProduct Operation value is set to Vector Matrix Product. The output of the vectorProduct node is connected directly to outColor of a surfaceShader material node, which is assigned to a second, larger polygon shape.

As a result of the custom connections, the faces of the larger shape that point toward the camera render blue until pCube1 is rotated. This is a result of the Normal Camera attribute existing in camera space. A normal that points directly toward the camera always has a vector of 0, 0, 1. At the same time, while pCube1 is at its rest position, its xformMatrix is an identity matrix and has no effect on the normalCamera value. Thus, the values 0, 0, 1 are passed to outColor of the surfaceShader node. When pCube1 is rotated, however, the normalCamera value is multiplied by the new xformMatrix and hence the color of the shape is affected. For instance, if pCube1 is rotated −45, −45, 0, a pale green results on the faces of the larger shape that point toward camera. The resulting math is illustrated in Figure 8.13.

Figure 8.13. A matrix calculation based on pCube1's rotation of −45, −45, 0. The matrix numbers have been rounded off for easier viewing.

When representing the matrix calculation, as with Figure 8.13, the extra number 1 at the right side of the Normal Camera vector (and at the bottom-right corner of the Xform Matrix) is necessary for this type of math operation; however, these numbers do not change as the corresponding objects go through various transformations.

Note

As with many custom networks, the material icon in the Hypershade window, as well as the workspace view, may not provide an accurate representation of the material. To see the correct result for the previous example, use the Render View window.

Note

You can retrieve the current Xform Matrix value of a node by typing getAttr name_of_node.xformMatrix; in the Script Editor.

The Condition utility functions like a programming If Else statement. If Else statements are supported by Maya expressions and are written like so:

if ($test < 10){
     print "This Is True";
} else {
     print "This Is False";
}

If the $test variable is less than 10, Maya prints "This Is True" on the command line. The If Else statement serves as a switch of sorts, choosing one of several possible outcomes depending on the input. The function of the Condition utility, when written in the style of an If Else statement, would look like this:

if (First Term  Operation  Second Term){
     Color If True;
} else {
     Color If False;
}

First Term and Second Term attributes each accept a single input or value, while the Color If True and Color If False attributes accept vector values or inputs. The Operation attribute has six options: Equal, Not Equal, Greater Than, Less Than, Greater Or Equal, and Less Or Equal.

With the Condition utility, you can apply two different textures to a single surface. By default, all surfaces in Maya are double-sided but only carry a single UV texture space. Hence, a plane receives the same texture on the top and bottom. You can avoid this, however, with the shading network illustrated by Figure 8.14.

The flippedNormal of a samplerInfo node is connected to firstTerm of a condition node. The Flipped Normal attribute indicates the side of the surface that is renderable. If the attribute's value is 1, then the "flipped," or secondary, side is sampled. If the value is 0, the nonflipped, or primary, side is sampled. The nonflipped side is the side that is visible when the Double Sided attribute of the surface is unchecked.

Returning to the network, the outColor of a checker texture node is connected to the colorIfTrue of the condition node. The outColor of a file texture node is connected to the colorIfFalse attribute of the same condition node. A bitmap image of a hundred dollar bill is loaded into the file texture node. The condition's Second Term is set to 1 and Operation is set to Equal. Last, the outColor of the condition node is connected to the color of a blinn material node. Thus, the flipped side of a primitive plane receives the Checker texture while the nonflipped side receives the File texture.

Figure 8.14. A single surface receives two textures with the help of a Condition utility. This scene is included on the CD as condition_flipped.ma.

Switch utilities provide multiple outputs from a single node. That is, they switch between different values in order to create different results among the geometry assigned to their shading network. Since the application of a Switch utility is unique in Maya, a step-by-step guide for a Triple Switch utility follows:

Although these steps apply the switch to a material, you can apply them to any node. That said, Triple Switches are designed for vector values and are best suited for any attribute that uses RGB colors or XYZ coordinates.

Single switches, on the other hand, are designed for scalar values and are best suited for such attributes as Diffuse, Eccentricity, Reflectivity, or Bump Value. The Single Switch utility automatically chooses the outAlpha attribute when a texture is chosen. In this case, the outAlpha of each texture connects to the input[n].inSingle of the singleShadingSwitch node. The n in input[n].inSingle corresponds to the slot number of the Switch Attributes list. The first slot is 0, the second is 1, and so on. Although geometry is also connected to the singleShadingSwitch node, the connection lines are initially hidden. Nevertheless, the instObjGroups[n] of each geometry shape node must be connected to the input[n].inShape of the singleShadingSwitch node. In this situation, the n of the instObjGroups[n] attribute refers to the hierarchy position of an instanced attribute. (See Chapter 7 for information on attribute instancing.) In most cases, n is 0. The instObjGroups[n] convention applies equally to Double, Triple, and Quad Switch utilities. In addition, all the switches possess variations of the input[n].inSingle input.

Double switches are designed for paired or double attributes. This makes the utility well suited for controlling UVs. For example, in Figure 8.16 a Cloth texture receives standard UV coordinates from a default place2dTexture node. The Repeat UV values, however, are supplied by a Double Switch utility. In this case, the repeatUV attributes of three additional place2dTexture nodes are connected to the input[n].inDouble attributes of the doubleShadingSwitch node. place2dTexture1 has a Repeat UV value of 5, 5. place2dTexture2 has a Repeat UV value of 25, 25. place2dTexture3 has a Repeat UV value of 50, 50. This shading network offers the ability to adjust UVs on multiple objects without affecting the base texture or necessitating the duplication of the entire shading network.

Figure 8.16. Repeat UV is controlled by a Double Switch utility. A simplified version of this scene is included on the CD as double_switch.ma.

The Quad Switch utility is suited for handling a vector attribute and a single attribute simultaneously. For example, in Figure 8.17 the outTriple attribute of the quadShadingSwitch node is connected to the color of a blinn material node. The outSingle attribute of the quadShadingSwitch node is connected the diffuse of the same blinn. To split the switch's output in such a way, it is necessary to use the Connection Editor. The color attributes of three additional blinn nodes are connected to the input[n].inTriple attributes of the quadShadingSwitch node. The diffuse attributes of the blinn nodes are also connected to the input[n].inSingle attributes of the quadShadingSwitch node. Each of the three blinn nodes has the outColor of a different texture connected to their color and diffuse attributes. In this case, the diffuse attributes do not need to correspond with the color attributes. For instance, blinn2's color can be connected to input[0].inTriple and blinn2's diffuse can be connected to input[4].inSingle. This ability to mix and match outputs and inputs allows for a great diversity of results. Hence, the Quad Switch provides the flexibility necessary to texture crowds, flocks, and swarms. Although such custom connections will function properly, they do not appear in the Switch Attributes list of the switch's Attribute Editor tab.

Figure 8.17. Three different Blinn materials are dispersed among nine spheres using a Quad Switch utility. This scene is included on the CD as quad_switch.ma.

As Stencil is the third texture application radio button listed in the 2D Textures section of the Create Maya Nodes menu (following Normal and As Projection). If a texture is chosen with As Stencil selected, the new texture automatically receives a Stencil utility and two place2dTexture nodes. The Stencil utility stencils the new texture on top of the material color. For example, in Figure 8.18 a red logo is applied to a wall map with this technique. Although the Stencil utility produces results similar to the Blend Colors utility (see Chapter 6), its methodology is fairly different.

Figure 8.18. A logo is applied to a wall with a Stencil utility. This scene is included as on the CD as stencil.ma.

In the example shading network, a red logo bitmap is loaded into a File texture named fileColor. The outColor of fileColor is connected to image of a stencil node. Standard UV connections run from the first place2dTexture node to fileColor. The second place2dTexture node is connected to the stencil node with similar (albeit fewer) standard UV connections. The outUV of the stencil's place2dTexture node is connected to the uvCoord of fileColor's place2dTexture node. The outUvFilterSize of the stencil's place2dTexture node is also connected to the uvFilterSize of fileColor's place2dTexture node.

Normally, this minimal set of connections will cause the fileColor texture to completely overtake the blinn's color. To avoid this, the outAlpha of a second file texture node, named fileMask, is connected to the mask of the stencil node. The Mask attribute controls where the new texture will show over the material color. In this case, a black and white bitmap is loaded into the fileMask node. Where the bitmap is white, the material color shows through; where the bitmap is black, the red logo is rendered.

At this point, the material color that is revealed by the Mask attribute can be only the solid color of the material's Color attribute. To avoid this, the outColor of a third file texture node, named fileWall, is connected to the defaultColor of the stencil node. In this example, a bitmap photo of a wall is loaded into the fileWall node. If fileWall was connected directly to the Color attribute of the blinn, it would not be visible.

The Optical FX utility (found in the Glow section of the Create Maya Nodes menu in the Hypershade window) is automatically created whenever Light Glow is applied to a directional, area, or spot light. The utility controls the look of the glow, halo, or lens flare. (For a discussion on this and other fog effects, see Chapter 2.)

Oddly enough, the Optical FX utility can be "grafted" onto a surface. For example, in Figure 8.19 the worldMatrix[0] attribute of a polygon lightbulb shape node is connected to the lightWorldMat of an opticalFX node. This connection ensures that the optical effect will occur in the center of the lightbulb regardless of the lightbulb's position. The color of the blinn node is connected to lightColor of the opticalFX node. The blinn Color attribute is set to gold, which is picked up by the opticalFX glow. (The lightbulb surface is also assigned to the blinn.) Last, the Ignore Light attribute of the opticalFX node is checked; this informs the program that no light is present. The result is a glow that follows the lightbulb wherever it goes. Unfortunately, since the opticalFX node creates a post-process effect, the size of the glow will not change. You can animate the Glow Spread and Halo Spread attributes of the opticalFX node, however, if necessary.

Figure 8.19. An Optical FX utility is attached t0o a lightbulb model, thereby creating a traveling glow. A simplified version of this scene is included on the CD as optical_bulb.ma. A QuickTime movie is included as optical_bulb.mov.

The Unit Conversion node, while not accessible in the Create Maya Nodes menu, automatically appears in many custom networks. For example, in Figure 8.20 the translateX of a cone transform node is connected to the rotateX of a sphere transform node. To view the connection, follow these steps:

By default, Maya calculates the translation of objects using Linear working units. At the same time, Maya calculates the rotation of objects using Angular working units. Whenever two dissimilar working units, such as Linear and Angular, are used in the same network, Maya must employ a Unit Conversion node to create accurate calculations. In the example illustrated in Figure 8.20, a Unit Conversion node is automatically provided with a Conversion Factor attribute set to 0.017. You can change Conversion Factor to achieve an exaggerated effect. If the Conversion Factor attribute is changed to 1, for example, the sphere will spin at a much greater speed when the cone is transformed.

Figure 8.20. A Unit Conversion node converts two dissimilar units of measure. The scene is included on the CD as unit_conversion.ma.

Render Partition, Default Light Set, and Light Linker nodes sit the farthest downstream in any shading network (see Figure 8.21). The Render Partition utility defines which shading group nodes are called upon during a render.

Figure 8.21. Scene nodes in a network

The Default Light Set utility carries a list of lights that illuminate all objects within a scene. The instObjGroups[0] attribute of each light's transform shape node is connected automatically to the dagSetMembers[0] attribute of the defaultLightSet node. If you uncheck the Illuminates By Default attribute in a light's Attribute Editor tab, the connection is removed until the attribute is once again checked.

The message of the defaultLightSet node is connected automatically to link[n].light and shadowLink[n].shadowLight of the lightLinker utility node. The Light Linker utility defines the relationship between lights and objects. If a light is connected through to defaultLightSet node to the link[n].light attribute, the light illuminates all shading groups connected to the lightLinker node. If a light is connected through the defaultLightSet node to the shadowLink[n].shadowLight attribute, then the light creates shadows for all shading groups connected to the lightLinker node. All shading group nodes are connected automatically to the lightLinker node. However, if you manually delete the connections, the shading group and the shading group's materials are ignored by the lights in the scene.

The Light Linker utility also stores broken links between lights, shadows, and surfaces. If a light link is broken through the Break Light Links tools, a connection is made between the message attribute of the surface shape node to the ignore[n].objectIgnored of the lightLinker node. A connection is also made between the message of the light shape node and ignore[n].lightIgnored of the lightLinker node. If the Make Light Links tool is applied, the connections are removed. Similar connections are made between the surface and light shape nodes' message and the lightLinker node when the Break Shadow Links tool is applied.

If a light is linked or unlinked in the Relationship Editor, the connections are identical to those made with the Make Light Links and Break Light Links tools. For more information on the Relationship Editor, Make Light Links, and Break Light Links, see Chapter 2.

The Default Render Utility List node holds a list of all render utilities in Maya. Although it cannot be used for any other purpose, it will show up in custom shading networks connected to each and every utility node.