Adding Fur to Characters

Editing the Fur Description: Direction You can use the Artisan Brush interface to comb the fur by painting the Direction attribute. 1. Continue with the scene from the previous section, or open the hound_v03.ma scene from the chapter15\scenes directory on the DVD. You’ll notice that there is no Direction or Comb attribute listed in the attributes for the houndFur node. Painting the Direction attribute is the same as painting the Polar attribute. 2. In the houndFur node’s Attribute Editor, set Inclination to 1, and move the Polar slider back and forth. The Polar slider determines the direction in which the fur strands face, but you’ll notice that the direction is not uniform across the surface. Inclinationâã‡â㉠âã‡â㉠Sets the angle at which the hair stands from the surface. A value of 0 is perpendicular to the surface; a value of 1 causes the fur to lie flat against the surface. If the value is 0, then the fur strand sticks straight up, so changing its direction has no visible effect. Rollâã‡â㉠âã‡â㉠Rotates the fur around its root. A value of 0 is -90 degrees; a value of 1 is 90 degrees. Base Curl and Tip Curlâã‡â㉠âã‡â㉠Determine the amount of curling applied to the base and tip of the hair. A value of 0.5 produces straight hair; a value of 0 or 1 curls the hair from one side or the other

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addIng Fur to CharaCters | 811 I prefer doing much of my texture map painting in Pixologic’s ZBrush because of its intuitive poly- gon painting workflow. I like to use ZBrush to carefully paint the baldness and other fur attribute maps, especially when doing something such as creating whiskers for a character’s face. You can just as easily use Mudbox to paint these maps as well. Editing the Fur Description: Direction You can use the Artisan Brush interface to comb the fur by painting the Direction attribute. 1. Continue with the scene from the previous section, or open the hound_v03.ma scene from the chapter15\scenes directory on the DVD. You’ll notice that there is no Direction or Comb attribute listed in the attributes for the houndFur node. Painting the Direction attribute is the same as painting the Polar attribute. 2. In the houndFur node’s Attribute Editor, set Inclination to 1, and move the Polar slider back and forth. The Polar slider determines the direction in which the fur strands face, but you’ll notice that the direction is not uniform across the surface. Inclination Sets the angle at which the hair stands from the surface. A value of 0 is per- pendicular to the surface; a value of 1 causes the fur to lie flat against the surface. If the value is 0, then the fur strand sticks straight up, so changing its direction has no visible effect. Roll Rotates the fur around its root. A value of 0 is -90 degrees; a value of 1 is 90 degrees. Base Curl and Tip Curl Determine the amount of curling applied to the base and tip of the hair. A value of 0.5 produces straight hair; a value of 0 or 1 curls the hair from one side or the other. 812 | Chapter 15 Fur, haIr, and ClothIng The change in direction created by the Polar attribute is based on the direction of the UV texture coordinates. This means that a value applied to fur on one part of the model has a different result than a value applied on another part of the model. To comb the hair correctly, you use the Direction attribute in the Paint Fur Attributes tool to apply a Polar value based on the direction that you drag across the surface. So when you choose to paint the Direction attribute in the Paint Fur Tool options, you’re really painting values for the Polar attribute but in a way that is a bit more intuitive. When painting the direction, set Inclination to a value other than 0, and the Roll value must be something other than 0.5. The Base Curl and Tip Curl values must be something other than 0.5 as well. If these values are not set properly, painting the Direction has no effect. In addition, Color Feedback has no bearing on the direction of the fur, so you can turn this option off in the options for the Artisan tool. 3. Open the Attribute Editor for the houndFur node, and use the following settings: Inclination: 0.8 Roll: 0.2 Base Curl: 0.7 Tip Curl: 0.3 4. Select the houndHead surface. Choose Fur  Paint Fur Attributes Tool  Options. Wait a few moments for Maya to update. 5. In the Options box for the Artisan tool, scroll to the bottom. In the Display options, turn off Color Feedback. 6. In the pop-up options for the Paint Fur Attributes Tool settings, set Fur Attribute to Direction. Make sure Fur Description is set to houndFur and Attribute Map Width and Height are set to 1024. The Paint Operation or Value settings in the Artisan options do not affect how the fur is combed. 7. Drag across the surface to push the fur in the general direction you want it to go. Use Figure 15.10 for reference. Figure 15.11 shows how the paint stroke influences the direc- tion of the fur on the model. Paint lightly and slowly using repeated strokes to make the fur point in the desired direc- tion. Combing the fur requires some patience and practice. It’s helpful to increase the U and V samples on the FurFeedback node so that you can see more fur as you are painting. It can be difficult to maintain a consistent direction across UV seams. The fewer seams you have in your UV texture coordinates, the easier it will be to paint the direction of the fur. The Direction attribute responds to the direction in which you move the cursor over the surface. 8. Save the scene as hound_v04.ma. To see a version of the scene to this point, open the hound_v04.ma scene from the chapter15\ scenes directory. addIng Fur to CharaCters | 813 Figure 15.10 Observe the direc- tion of the fur in this photo of an Ameri- can foxhound. Figure 15.11 Paint the direc- tion of the fur on the surface of the hound. Increase the U and V Samples in the fur feedback node to 256 to make it easier to see details in the fur direction. 814 | Chapter 15 Fur, haIr, and ClothIng painting across UV texture Borders As you paint across UV borders on the model, you’ll see the hair suddenly flip around. Since fur relies on UV texture coordinates to determine how the Polar attribute affects direction, as you move from one part of the texture space to another, the polarity of the fur can suddenly change (a good example of this occurs on the back of the hound’s head). This may drive you crazy. To help deal with these problems, select the model, and choose Display  Polygons  Texture Border Edges. This makes the border edges of the UV coordinates visible as bold lines on the surface of the model. You can also reduce the size of the brush so that you can more easily paint specific areas along the border. With some patience and work, you’ll be able to make the direction of the fur consistent across the UV texture border. Editing the Fur Description: Length You can edit the Length attribute using the Paint Attributes tool as well. When editing lengths, you need to pay attention to the values used in the options for the Artisan Brush. For the hound, the fur is shorter near the end of the nose, is medium length on the face, and is long on the back of the head and neck. 1. Continue with the scene from the previous section, or open the hound_v04.ma scene from the chapter15\scenes directory. 2. In the houndHead_furFeedbackShape tab, set U and V Samples to 128. 3. Select the houndHead object, and choose Fur  Paint Fur Attributes Tool. addIng Fur to CharaCters | 815 4. In the pop-up menu for the Paint Fur Attributes Tool settings, set Fur Attribute to Length. Make sure Fur Description is set to houndFur and Attribute Map Width and Height are set to 1024. 5. In the options for the Artisan Brush, set Paint Operation to Replace and Value to 0.5. 6. Paint around the area of the neck. You’ll see the fur become longer as you paint (Figure 15.12). 7. Set Value to 0.25, and paint on the ears, under the ears, the top of the head, and the upper part of the throat. 8. Set Value to 0.1, and paint the area near the nose and the front of the snout near the lips. 9. To even out the transition between the fur lengths, set Paint Operation to Smooth, and paint the areas on the border between the different lengths of fur. 10. Save the scene as hound_v05.ma. To see a version of the scene to this point, open the hound_v05.ma scene from the chapter15\ scenes directory. After painting fur lengths you may decide to touch up the Direction attribute of the fur as well. You can change the paint operation mode (from Length to Direction, for example) in the Paint Fur Attributes Tool Settings pop-up whenever you need to, but remember that Maya may pause for a few moments to update the maps when you change attributes. Figure 15.12 Edit the length of the hair by paint- ing on areas of the houndHead surface. 816 | Chapter 15 Fur, haIr, and ClothIng Baking textures into Maps You can use a procedural texture node (such as a ramp, fractal, or checker) as a starting place for a fur attribute map, as shown here. This works well when you are painting fur applied to a NURBS surface, since the UV texture coordinates are based on the parameterization of the surface itself. The following steps demonstrate how to do this. 1. Create a new scene in Maya. 2. Create a NURBS sphere. 3. Select the sphere, and choose Fur Attach  Fur Description  New. 4. Open the Attribute Editor for the FurDescription1 node. 5. Right-click the field next to Baldness, and choose Create New Texture. 6. From the Create Texture Node window, choose the ramp texture. The fur on the sphere disappears. 7. Open the Attribute Editor for the ramp texture. Change the colors of the ramp so that the top is black and the bottom is white. Delete the color marker in the center. The fur display returns. If you move the markers on the ramp up and down, you’ll notice that the fur display does not change. In order to use the ramp values to affect the Baldness setting, you need to bake the ramp. 8. Move the black marker halfway down the ramp, and set Interpolation to None. 9. In the Attribute Editor for the FurDescription node, set Bake Attribute to Baldness, and leave Map Width and Height set to 256. Click the Bake button. The fur becomes sparse on part of the sphere. This sparse area corresponds to the black part of the ramp. You can select the ramp texture in the Hypershade and connect it to the Color channel of the sphere’s shader if you’d like to see a visual representation of the placement of the ramp on the sphere. addIng Fur to CharaCters | 817 10. Move the Black color marker down. The fur on the sphere will not update until you bake the texture again. 11. In the Attribute Editor for Fur Description, click the Bake button. The fur on the sphere updates. To see this example, open the rampBaldness.ma scene from the chapter15\scenes directory on the DVD. A good use for this technique would be for applying fur as grass to a NURBS plane. You can use a frac- tal texture to create procedural variation in baldness or length to make the grass appear patchy. Test Render Fur Now that you have the basic fur description created for the houndHead, you may want to see what it looks like when rendered. You can render the scene using either mental ray or Maya Software. The results should be fairly similar. In this example, you’ll use mental ray. 1. Continue using the scene from the previous section, or open the hound_v05.ma scene from the chapter15\scenes folder. 2. Open the Render Settings window, and set the Render Using menu to mental ray. 3. On the Quality tab, set Quality Presets to Production: Rapid Fur (see Figure 15.13). This preset uses the Rasterizer as the primary renderer instead of raytracing. For more infor- mation on rendering with mental ray, consult Chapter 12. Figure 15.13 Choose the Rapid Fur preset on the Quality tab of the Render Settings window. 818 | Chapter 15 Fur, haIr, and ClothIng 4. Open the Render View window, and create a test render using the perspective camera. You’ll notice immediately that the fur does not look very realistic (see the upper-left image in Figure 15.14). It is very sparse and bright red. You need to increase the Density setting of the fur so that enough hair covers the surface of the model. 5. Set Density in the houndFur tab to 100,000, and create another test render (see the upper- right image in Figure 5.14). The fur is much denser without adding too much to the render time. To improve the look of the fur, you can edit the base and tip widths as well as the basic color. 6. In the houndFur tab in the Attribute Editor, click the color swatch next to Base Color, and use the Color Chooser to set the color to a dark brown. 7. Set Tip Color to a light brown. 8. Make sure Base Opacity is set to 1, and use the following settings: Tip Opacity: 0.1 Base Width: 0.01 Tip Width: 0.005 9. Create another test render (see the lower-left image in Figure 5.14). Figure 15.14 Create test renders of the fur as you adjust the settings. addIng Fur to CharaCters | 819 10. Raise Density to 500,000, and create another test render (see the lower-right image in Figure 5.14). 11. Save the scene as hound_v06.ma. To see a version of the scene, open the hound_v06.ma scene from the chapter15\scenes directory. The fur should cover the model completely; however, you will notice that some attributes, such as the baldness map and the direction, may require further editing. Applying a Color Map Adding a texture map to the color greatly helps the realism of the fur. You can increase the effi- ciency of the render by applying the same file texture to the fur color and the shader as applied to the model. This technique should work as long as the model does not get extremely close to the camera. A texture map that has been carefully painted in Photoshop or in a 3D texturing program works better than a map created by painting color on the fur. In this case, ZBrush was used to create the color texture map for the hound model. 1. Continue with the scene from the previous section, or open the hound_v06.ma scene from the chapter15\scenes directory on the DVD. 2. Open the Hypershade, select the houndShader material, and open its Attribute Editor. 3. Click the checkered button next to the Color channel to open the Create Texture Node window. 4. Click the File button to create a file texture node. 5. In the Attribute Editor for the file node, click the folder icon next to File Name. 6. Use the browser to select the houndBaseColor file texture from the chapter15\ sourceimages directory on the DVD. 7. Press the 6 key to switch to textured view so you can see how the color is placed on the model. 8. Keep the Hypershade window open. In the Outliner, expand the FurFeedback group, and select the houndHead_FurFeedback node. 9. In the Attribute Editor, select the houndFur tab. 10. In the Hypershade, switch to the Textures tab. MMB-drag the file1 texture onto the Base Color swatch in the Attribute Editor for houndFur (see Figure 15.15). 11. In the Hypershade, create a second file texture node (Create 2D Texture  File). 12. In the Attribute Editor for file2, load the houndTipColor texture. This is a lighter, less- saturated version of the base color. 13. Attach this file to the Tip Color channel in the houndFur node. 820 | Chapter 15 Fur, haIr, and ClothIng 14. Lower Specular Color to a dark gray, and set Specular Sharpness to 80. This makes the specular highlight on the fur smaller and less reflective. 15. Set the Density value of the fur to 250,000 in the houndFur tab, and create a test render (see the left image in Figure 15.16). 16. To increase the realism of the fur, turn on shadows for the scene lights: a. Select the spotlight1 object, and open its Attribute Editor. b. Under Shadows, turn on Use Depth Map Shadows. c. Set Resolution to 1024, and turn off Use Auto Focus. d. Create another test render (see the right image in Figure 15.16). 17. Save the scene as hound_v07.ma. To see a version of the scene, open the hound_v07.ma scene from the chapter15\scenes directory. Figure 15.15 Drag the file1 node from the Textures tab of the Hypershade onto the Base Color channel of the houndFur node. Figure 15.16 Add a color map to the fur description (left image), and render the scene shadows (right image). addIng Fur to CharaCters | 821 Applying Map Offsets and Multipliers In the Details section of the houndFur node, you’ll notice each attribute has Map Offset, Map Multiplier, Noise Amplitude, and Noise Frequency settings. These sliders can apply an addi- tional adjustment to the fur map attributes. The Map Offset and Multiplier attributes are used to change the range of values for any of the attributes. Most of the attributes are limited to a range between 0 and 1, which corresponds to the grayscale values painted on the surface with the Paint Fur Attributes brush. If you would like to change the range so that it can go beyond 1, you can use Map Offset or Map Multiplier. Offset adds a number to the overall range. If you want to offset the range for an attribute so that instead of a range of 0 to 1 the range becomes 2 to 3, set Offset to 2. If you want to expand or diminish the range of values, use Multiplier. For example, if you want the range of a value to be between 0 and 10 instead of 0 to 1, set Multiplier to 10. The Noise Amplitude and Frequency sliders add randomness to the map values. 1. Continue with the scene from the previous section, or open the hound_v07.ma scene from the chapter15\scenes directory. The fur for the hound is a little too long to be appropriate for a typical foxhound. Rather than repaint the Length values, you can simply adjust Multiplier for the Length attribute. 2. Open the Attribute Editor for the houndFur node, and expand the Details  Length roll- out panel. 3. Set Map Multiplier to 0.5. 4. Expand the Tip Ambient Color attribute, and set Noise Amplitude to 0.5 and Noise Frequency to 25. This adds variation to the brightness of the fur tips. 5. Make sure the texture maps are properly connected in the houndFur tab and on the shader. 6. Create a test render from the perspective camera (Figure 15.17). 7. Save the scene as hound_v08.ma. To see a version of the scene, open the hound_v08.ma scene from the chapter15\scenes directory. Figure 15.17 Shorten the overall length of the hair by reducing the Multiplier value for the Length attri- bute. Add variation to the tip color by adding noise to the Tip Ambient Color attribute. 822 | Chapter 15 Fur, haIr, and ClothIng Enhancing the Realism of Fur The basic fur description for the hound has been created, but to make it look realistic, a fair amount of editing still needs to be done. There are many additional attributes you can use to help accomplish this. This section describes how these attributes work. As with the Baldness, Length, Direction, and Color attributes, you can use a single value to determine the overall set- ting for each attribute, paint values for the attribute on selected areas, or use a texture map to determine the strength of the selected values. Inclination, Roll, and Polar are attributes that determine the direction the fur is point- ing along the surface of the model. As noted, Inclination determines whether the hair points straight up from the surface (at values closer to 0) or lies along the surface (at values closer to 1). The Roll setting rotates each hair around the base, and the Polar attribute determines the direc- tion the fur points along the surface. Roll and Polar can be used together to fine-tune the direction of the hair. If you have painted a map for the Direction attribute using the Paint Fur Attributes tool, changing the Polar setting has no effect. After painting a map for the Direction attribute using the Paint Fur Attributes tool, you may want to paint values for the Inclination and Roll attributes. This can help define more exactly the direction in which the fur points along the surface. You may find yourself switching back and forth among Direction, Inclination, and Roll as you edit the fur on the surface. If you need precise control over the styling of the fur, be prepared to spend some time working with these attributes. Base Opacity and Tip Opacity are self-explanatory attributes. The base of the fur is the part of the fur strands closest to the surface; the tip is the part of the fur farthest from the surface. Opacity is applied as a gradient across the length of the fur. To create the look of soft, fine fur, set Base Opacity to 1 and Tip Opacity to a very low setting or even 0. You can experiment with these values to create special effects; try a low Base Opacity and a high Tip Opacity. Base Width and Tip Width establish the shape of the fur strands. A small Tip Width coupled with a large Base Width produces a pointy shape for the fur. A very low Tip Width helps create the look of soft, fine fur. The Base Curl and Tip Curl attributes add curl to the fur strands at the base or tip. A value of 0.5 produces no curling. A value of 1 or 0 produces curling in one direction or the other. The Scraggle, Scraggle Frequency, and Scraggle Correlation attributes add random kinks to the hair to create a messy appearance. The Scraggle setting determines the strength of the scraggle. Scraggle Frequency determines how many kinks appear in each strand of fur. Scraggle Correlation determines how the Scraggle value of one strand affects another. A setting of 0 for Scraggle Correlation creates random kinks throughout the fur strands, and a Scraggle Correlation of 1 means all the fur strands kink the same way, creating a wavy appearance for the fur. The Clumping, Clumping Frequency, and Clump Shape settings cause the fur strands to attract each other into bunches on the surface. This is useful for making a surface appear wet or matted. The Clumping setting sets the strength of the clumping, and Clumping Frequency determines the number of clumps created across the surface. Clumping Frequency ranges between 0 and 100; higher values take longer to render. Clump Shape determines whether the clumps themselves are convex or concave. Settings closer to -10 produce concave clump shapes, while settings closer to 10 produce convex clumps (Figure 15.18). addIng dynaMIC MotIon to Fur | 823 Adding Dynamic Motion to Fur Creating dynamic motion for fur is actually quite easy. A fur description node uses dynamic hair curves to control the movement of the fur. Attaching a Fur Description to Hair Curves In this example, you’ll add a hair system to a simple NURBS sphere that already has fur applied. The hair curves will then be used to add dynamic motion to the fur. 1. Open the furBall_v01.ma scene from the chapter15\scenes directory on the DVD. The Baldness attribute of the fur has been created using a ramp texture that has been baked into the fur description. 2. Right-click the sphere, and choose Surface Point. 3. Hold the Shift key, and select 10 or 12 surface points at the top of the sphere (see Figure 15.19). 4. Switch to the Dynamics menu set, and choose Hair  Create Hair  Options. 5. In the Create Hair Options box, set Output to NURBS Curves, and choose At Selected Points Faces. Leave the other settings at their default values. adding hairs to polygons If fur is applied to a polygon surface, select the faces of the surface before adding the hair curves. If you want to add hair curves all over the surface rather than at specific points/faces, choose the Grid option on the Create Hair Option box. Figure 15.18 Clumping is dem- onstrated on two planes. The plane on the left has a Clump Shape value of -10; the plane on the right has a Clump Shape value of 10. 824 | Chapter 15 Fur, haIr, and ClothIng 6. Click the Create Hairs button to make the hairs. The hair curves appear as longer curves coming out of the surface of the sphere. 7. Open the Outliner, and select the hairSystem1 node. 8. Switch to the Rendering menu set, and choose Fur  Attach Hairsystem To Fur  FurDescription1. 9. Set the timeline to 200, and play the scene. As the hair curves fall, the strands of fur fol- low. Try animating the sphere so that it moves around the scene (see Figure 15.20). 10. Save the scene as furBall_v02.ma. Figure 15.19 Select surface points at the top of the sphere. Figure 15.20 The strands of fur follow the motion of the hair curves. renderIng Fur usIng Mental ray | 825 To see a version of the scene, open the furBall_v02.ma scene from the chapter15\scenes folder on the DVD. To keep the hair from penetrating the NURBS sphere, you need to make the sphere a collision object for the hair curves. This along with other dynamic properties of hair curves is discussed later in the chapter. Essentially, any dynamics added to the hair curves are inherited by the fur. Rendering Fur Using mental ray You can render fur using mental ray or Maya Software. When rendering with Maya Software, you’ll need to add a fur shadowing node to the lights in the scene. In this section, you’ll learn how to render fur with mental ray, which generally produces a more realistic result than Maya Software. If you plan to use depth map shadows, use the Production: Rapid Fur preset. If you plan to use ray trace shadows, use the Production: Fine Trace Render preset. If you need the fur to appear in reflections or refractions, use raytracing. Fur renders use indirect lighting techniques such as Final Gathering. Be aware that the ren- der times for dense fur descriptions when Final Gathering is enabled can be quite long. Rendering Fur Using Raytracing To create a realistic render of the hound using raytracing, follow these steps: 1. Open the hound_v08.ma scene from the chapter15\scenes directory. 2. Open the Hypershade, and select the houndShader material. 3. In the attributes for the material, set the Diffuse attribute to 1. Increasing the Diffuse quality of the shader can sometimes help blend the surface material with the color of the fur. 4. Open the Render Settings window, and select the Quality tab. Set Quality Presets to Production: Fine Trace. 5. In the Outliner, select the spotlight, and open its Attribute Editor. 6. Under Shadows, turn on Use Ray Trace Shadows. The Fur/Shadowing attributes listed below the Use Ray Trace Shadows settings are used specifically when rendering with Maya Software, which requires that the shadow-casting lights be connected to the fur description. This is not necessary when rendering with mental ray. 7. Create a directional light. Rotate the light so that it is shining toward the camera. This creates nice fill lighting as well as a fringe of light along the edge of the fur. 8. In the settings for the directional light, turn off Emit Specular, and set Intensity to 0.8. 9. In the Outliner, expand the FurFeedback group, and select the houndHead_FurFeedback node. In the Attribute Editor, click the houndFur node. 826 | Chapter 15 Fur, haIr, and ClothIng 10. Set Density to 500,000. Scroll down to the list of Attributes. Set Tip Opacity to 0 and Base Opacity to 0.5. This helps soften the look of the fur. 11. Set Base Width to 0.008 and Tip Width to 0.001. 12. Create a test render from the perspective camera. The scene takes between five and eight minutes to render depending on your machine (see Figure 15.21). 13. Save the scene as hound_v09.ma. To see a finished version of the scene, open the hound_v09.ma scene from the chapter15\ scenes directory on the DVD. You can continue to improve the look of the fur by improving the texture maps applied to the fur description as well as by improving the lighting in the scene. Maya Fur does a pretty good job creating fur effects for many typical situations. For truly stunning fur and hair effects, you may want to consider using the Shave and a Haircut plug-in developed for Maya by Joe Alter. This plug-in has been used for many feature films and televi- sion shows. For more information, visit www.joealter.com. Animating Using Dynamic Curves Dynamic curves are NURBS curves that have dynamic properties. The primary use of dynamic curves is to drive the dynamics of hair systems applied to characters. However, the usefulness of dynamic curves goes far beyond creating hair motion. Curves used to loft or extrude surfaces, curves used for Paint Effects strokes, curves projected on NURBS surfaces, curves used as IK splines, curves used as particle emitters, and so on, can be made dynamic, thus opening up a large number of possibilities for creating additional dynamic effects in Maya. Furthermore, Figure 15.21 Render the hound using ray trace shadows. anIMatIng usIng dynaMIC CurVes | 827 dynamic curves calculate fairly quickly compared to nCloth, making surfaces created from lofted dynamic curves a useful alternative to nCloth for some situations. While working through the scenes in this chapter, you may want to set the timeline prefer- ences to loop so that you can see the hair update continuously as you adjust its settings. To do this, follow these steps: 1. Choose Window  Settings/Preferences  Preferences. 2. Choose the Time Slider category in the Preferences box. 3. Set Looping to Continuous. Dynamic Curves vs. Nucleus As you learn about dynamic curves, you’ll immediately notice many similarities between the interfaces for dynamic curves and Nucleus, yet dynamic curves are not part of nDynamics. This is because the introduction of dynamic curves predates the introduction of nDynamics and the Nucleus solver. Using Dynamic Curves with iK Splines In Chapter 7, you learned about the IK Spline tool, which uses a curve to control the Inverse Kinematics (IK) of a joint chain. The curve itself can be converted into a dynamic curve that can be used to drive the IK Spline tool. This is a great way to add dynamic motion to a rig used for tails or tentacles. In this example, you’ll use a dynamic curve to control a segmented armored tail. The armored tail consists of polygon pieces, each of which has been parent-constrained to a joint in a chain. The first step is to create a curve (see Figure 15.22). 1. Open the armoredTail_v01.ma scene from the chapter15\scenes folder on the DVD. 2. Switch to a side view, and turn on Point Snapping. Figure 15.22 The armored tail consists of polygon pieces constrained to a joint chain. 828 | Chapter 15 Fur, haIr, and ClothIng 3. In the viewport’s Show menu, turn off the visibility of polygons so only the joints are visible. 4. Choose Create  EP Curve Tool. Click the first joint in the chain on the far left and the last joint in the chain on the far right. 5. Press the Enter key to complete the curve. The EP Curve tool creates a curve that has four CVs. Using the EP Curve tool is an easy way to create a straight curve. If you want to add more vertices, you can use the Edit Curves  Rebuild Curve command. In the options, specify how many spans you want to add to the curve. In this example, the curve should work fine with only four CVs. 6. Switch to the perspective view. Turn off the visibility of Joints in the Show menu so only the curve is visible. 7. Switch to the Dynamics menu set. Select curve1, and choose Hair  Make Selected Curves Dynamic. In the Outliner, a new hairSystem1 node is created as well as two groups: hairSystem1Follicles and hairSystem1OutputCurves (see Figure 15.23). Understanding Dynamic hair Curve Nodes The hairSystem1 node controls the dynamics of the curve; it is similar to the Nucleus solver when using nDynamics. The hairSystem1Follicles group contains the follicle1 node and the original curve1. The follicle node contains settings to control the dynamics of the individual follicles. Some of these settings can override the hairSystem settings. If you selected a number of curves before issuing the Make Selected Curves Dynamic command, the hairSystem1Follicles group would contain a follicle node for each curve. This is explored later on when creating hair for a character. The hairSystem1OutputCurves group creates a duplicate curve named curve2. This curve is a dupli- cate of the original curve. The output curve is the dynamic curve; the curve in the follicle group is the original, nondynamic curve. The purpose of the nondynamic curve is to serve as an attractor for the dynamic curve if needed. The dynamic curve gets its shape from the follicle curve. 8. Set the timeline to 200, and click the Play button. You’ll see the dynamic curve move a little (it can be a little hard to see; this will be more obvious in the next step). 9. Stop the playback, and switch to the hairSystem1 tab. 10. In the Dynamics rollout panel, set the Stiffness value to 0, and play the scene. You’ll see the dynamic curve droop a little. As the scene is playing, increase Length Flex. Figure 15.23 A number of nodes are added to the scene when a curve is made dynamic. anIMatIng usIng dynaMIC CurVes | 829 The Stiffness setting controls the rigidity of the curve. A higher Stiffness setting makes the curve less flexible. Lowering the Stiffness value makes the curve bend easily. As you increase the Length Flex value, the curve stretches as much as it needs to in order to accommodate the dynamic forces applied to the curve. You’ll notice the curve droop downward, indicating that it has weight. The hairSystem1 shape has a Gravity setting built in, much like the Nucleus solver discussed in Chapter 13. You’ll notice that both ends of the curve appear to be attached to the original curve (Figure 15.24). 11. Stop the playback, and rewind the animation. 12. Set Length Flex to 0.5 and Stiffness to 0.1. 13. Select the follicle1 node in the Outliner, and switch to the Move tool (turn off Grid or Point Snapping if it is still on). 14. Choose Solvers  Interactive Playback. The animation starts playing automatically. As it is playing, move the follicle around in the scene; you’ll see the dynamic curve follow the movements. 15. Stop the animation, and switch to the follicleShape1 tab in the Attribute Editor. 16. Set the Point Lock menu to Base. Turn on Interactive Playback, and move the follicle around again. You’ll see that the dynamic curve is attached at only one end. If you wanted the curve to be attached to the other end, you’d set Point Lock to Tip. To detach the curve entirely, set Point Lock to No Attach. 17. Stop the animation, and rewind the playback. Figure 15.24 The dynamic curve droops as if it is attached at both ends to the original curve. 830 | Chapter 15 Fur, haIr, and ClothIng Keyframe point Lock The Point Lock attribute can be keyframed in the Channel Box for the follicle node. To animate a dynamic curve detaching from one end, follow these steps: 1. Set Point Lock to Both Ends. 2. Create a keyframe by right-clicking the Point Lock channel in the Channel Box and choosing Key Selected. 3. Change the current frame on the timeline. 4. Set Point Lock to Tip or Base (the opposite end will become detached). 5. Set another keyframe. This is a good way to create the effect of a cable or rope snapping. 18. Select the follicle node, and set the Translate channels to 0 to return the curve to its start position. 19. With the follicle selected, turn on Point Snapping. 20. Hold the d key, and use the Move tool to move the pivot point of the follicle to the end of the curve on the side where the dynamic curve is still attached, as shown in Figure 15.25. tips for Moving the pivot point As you move the pivot point, the curve should not move; sometimes it takes a couple of tries to get Maya to properly switch to move pivot mode. An alternative to the d hotkey is to press the Insert key on a PC or the Home key on a Mac on the keyboard while the Move tool is activated—not every keyboard has an Insert key, however. Figure 15.25 Move the pivot point of the follicle to the end of the curve. anIMatIng usIng dynaMIC CurVes | 831 21. When the pivot point is repositioned, Shift+click the Translate and Rotate channels in the Channel Box, right-click, and choose Key Selected from the pop-up menu. 22. Turn on Auto Keyframe; go to various points in the animation, and move and rotate the follicle. While Auto Keyframe is on, a keyframe is placed on all the Translate and Rotate channels as you make changes to the position of the follicle. The dynamic curve may not update correctly as you make changes; don’t worry about that at the moment. You want to create an animation where the curve moves around in the scene like a sword slashing through the air. 23. Rewind and play the animation; you’ll see the dynamic curve follow the movements of the follicle as it moves through the air. 24. Save the scene as armoredTail_v02.ma. To see a version of the scene, open the armoredTail_v02.ma scene from the chapter15\ scenes directory. Creating an iK Spline Handle from the Dynamic Curve In this section, you’ll create an IK spline handle for the armored tail and attach it to the dynamic curve. The dynamics of the curve will be edited to change the behavior of the tail. 1. Continue with the scene from the previous section, or open the armoredTail_v02.ma scene from the chapter15\scenes directory. 2. In the perspective view, turn on the visibility of joints in the Show menu. 3. In the Outliner, select and hide the follicle1 node. This prevents you from selecting the wrong curve when creating the IK spline handle. 4. Switch to the Animation menu set, and choose Skeleton  IK Spline Handle Tool  Options. 5. In the options, make sure Auto Create Curve and Snap Curve To Root are both off. 6. With the IK Spline Handle tool active, select the first joint in the chain and the last joint in the chain. 7. Zoom in closely, and carefully select the blue curve that runs down the center of the chain. If the operation is successful, you’ll see the ikHandle1 node appear in the Outliner. The Dynamic curve (curve2) will move out of the hairSystem1OutputCurves group. That should not affect how the curve behaves. 8. Rewind and play the scene. The joints follow the motion of the curves. 9. In the Show menu of the perspective view, turn the visibility of polygons back on, and play the scene. The armored tail thrashes around when you play the animation. 832 | Chapter 15 Fur, haIr, and ClothIng 10. In the Outliner, select the hairSystem1 node, and open its Attribute Editor to the hairSystem Shape1 tab. 11. Scroll down, and expand the Dynamics section. The Stiffness Scale edit curve changes the stiffness of the curve along the length of the curve. The left side of the curve corresponds to the stiffness at the base; the right side of the curve corresponds to the stiffness at the tip. 12. Add a point to the Stiffness Scale edit curve by clicking the left side of the curve and dragging downward. 13. Play the animation, and you’ll see the end of the tail lag behind the motion more than the front of the tail. You should be able to edit the curve while the animation is playing and observe the changes (see Figure 15.26). 14. Save the scene as armoredTail_v03.ma. Figure 15.26 Editing the Stiffness Scale curve changes the stiffness along the length of the dynamic hair. The Stiffness setting creates the overall stiffness value for the dynamic curve. Stiffness Scale modifies that value along the length of the curve. Both settings, like almost all of the dynamic curve settings, can be animated. To see a version of the scene, open the armoredTail_v03.ma file from the chapter15\scenes directory. Using Forces The settings in the Forces section add levels of control for the curve’s motion. Play the animation in the armoredTail_v03.ma scene, and adjust these settings while the scene loops so you can see how they affect the motion of the tail. addIng haIr to a CharaCter | 833 The Iterations setting affects how the hair responds to stiffness and dynamics. Iterations refers to the number of times the hair solver calculates per time step, similar to the Substeps set- ting on the Nucleus node. Increase it to improve the accuracy of the hair motion; higher values slow down Maya’s playback. Drag Creates friction between the dynamic curve and the air. Increasing this is a good way to simulate the motion of hair in thick fluids. Motion Drag Similar to Drag. However, Motion Drag is affected by the Stiffness Scale attribute. In other words, the Drag setting creates a drag in the motion across the length of the dynamic curve, whereas Motion Drag creates a drag along the length of the curve that is influenced by the Stiffness Scale curve. This can be used to fine-tune the motion of the dynamic curve. Damp Used most often to control erratic motion of dynamic curves. Higher Damp values decrease the momentum of the curve as it follows the motion of the follicle. Friction Reduces the motion of dynamic curves when they collide with surfaces. This won’t produce a visible effect unless the curve comes in contact with a collision surface. Collisions are discussed in more detail later in the chapter. Mass Affects the motion of the curve only when additional fields (created from the Dynamics menu set) are applied to the curve, for example, a Turbulence or a Drag field. Mass does not change how the curve responds to forces created in the hairSystem1 shape node. Increasing Mass increases the simulated weight of each CV on the curve as the curve moves through a dynamic field. Dynamics Weight Controls the amount of overall influence external dynamic fields (such as Turbulence and Drag) have over the dynamic curve. It does not affect how the Forces set- tings in the hairSystem node affect the dynamic curve. Start Curve Attract Creates an attraction between the original curve (curve1 in the armoredTail example) and the dynamic curve. This can be used to blend between the dynamic curve and animation created through the use of deformers on the original curve. The Attraction Scale curve can be used to edit the strength of the attraction along the length of the curve, similar to the Stiffness Scale. Adding Hair to a Character Hair is created by attaching follicle nodes to a surface. Each follicle node controls a number of hairs. The follicles themselves are styled using a combination of control curves and forces. Follicles and control curves are connected to a hair system node. A single hair system node can control hair connected to any number of surfaces, and a single surface can be attached to mul- tiple hair systems. When you create hair, you have to consider how you plan to render it. You have the choice of creating Paint Effects strokes for the hair or curves that can be used to render in third-party rendering engines such as Render Man, or you can create both Paint Effects strokes and curves. Even though hair uses Paint Effects, it renders using mental ray without the need to convert the hair to polygons. In this section, you’ll create and style hair for a character. 834 | Chapter 15 Fur, haIr, and ClothIng Applying Hair to a Surface When you want to apply hair to a character, you can either apply the hair uniformly to the entire surface or paint the hair selectively on parts of the surface. It is common practice to create a nonrendering scalp surface that can be parented to a character’s head and then apply the hair to the scalp surface rather than directly to the char- acter’s head. This allows flexibility because scalp surfaces and their attached hair can easily be swapped between characters. It also speeds up playback in the animation because the hair dynamics are not factored into the calculations required to deform the character’s surface if it has been skinned to a skeleton or to other deformers. Some animators like to apply separate hair systems to each part of the scalp to control the var- ious sections of a particular hairstyle. For instance, one hair system may be applied to the bangs that hang over the character’s forehead, while another system is used for the hair on the back of the head. In this exercise, you’ll keep things simple by using a single hair system for the charac- ter’s hairstyle. Both methods are valid, and as you become comfortable working with hair, you may want to experiment with different techniques to see which approach works best for you. The following procedure uses the Nancy Hair scene, which contains the rigged nancy char- acter used in Chapter 6. The head is rigged to a series of joints. You can select and rotate the headCtrl curves above the head to change the position of the head. A scalp surface has been cre- ated by duplicating part of the head geometry. This scalp geometry is parent-constrained to one of the joints in the head rig. You can apply hair to NURBS or polygon surfaces. When using polygon surfaces, the UV texture coordinates must be mapped so that none of the UVs overlap and the coordinates fit within the 0 to 1 range in the UV Texture Editor. As with fur, you’ll get better results from your hair system if the UV coordinates have been carefully mapped. Remember to delete history for the surface once you have created UV texture coordinates to keep the coordinates (and attached hair) from moving unpredictably during animation. 1. Open the nancyHair_v01.ma scene from the chapter15\scenes directory. 2. In the Outliner, select the scalp surface, and open its Attribute Editor. 3. In the scalpShape tab, expand the Render Stats section; then turn off Casts Shadows, Receive Shadows, Motion Blur, and Primary Visibility so the surface will not render or affect any other geometry in the render. adding hair to a Surface You can add hair to a surface in a number of ways. You can paint hair on the surface using the Artisan Brush interface, you can select faces on polygons or surface points on NURBS surfaces and apply hair to the selected components, or you can create a uniform grid of follicles on a surface. Once you attach follicles to a surface, you can add more follicles later to fill in blank areas by painting them on the surface. For the scalp you’ll create a simple grid and then add follicles if needed later. 4. Select the scalp surface, switch to the Dynamics menu set, and choose Hair  Create Hair  Options. addIng haIr to a CharaCter | 835 5. In the Create Hair Options box, choose Edit  Reset to reset the options to the default settings. 6. Set the Output to Paint Effects, and choose the Grid option. Use the following settings: U and V Count: 24 Points Per Hair: 20 Passive Fill: 1 Randomization: 0.1 Understanding Follicle types Follicles can be dynamic, passive, or static: Dynamic follicles Dynamic follicles react to forces and dynamic fields based on the set- tings in the hairSystem node or on any dynamic overrides created in the follicle shape node. Dynamic follicles can collide with surfaces. Passive follicles Passive follicles inherit the dynamic motion of nearby dynamic follicles, which can reduce computational overhead, especially when collisions are involved. Static follicles Static follicles have no dynamic motion but can be used to style parts of the hair. You can change the mode of a follicle after creating the hair system if you decide to make a passive follicle dynamic, make a dynamic follicle static, or use any other of the three modes. The Randomization setting randomizes the arrangement of the grid to make the hair placement look less even. By increasing the Passive Fill option, a number of the follicles created when the hair is attached to the surface will be passive rather than dynamic. If the Passive Fill option is set to 1, every other row and column of the follicles based on the settings for U and V Count will be passive follicles. If the setting is 2, every two rows and every two columns of follicles will be passive. When you first create a hair system, you can create a number of passive follicles using this setting. This speeds up the dynamics as you create the initial hairstyle. Later you can convert the follicles to dynamic or static follicles as needed. 7. Turn on the Edge Bounded and Equalize options. When the Grid method is used, the follicles are placed uniformly on the surface based on the U and V coordinates. If Edge Bounded is on, the follicles are placed up to and including the edge of the UV coordinates. In the case of the example, this means hairs are placed along the edge of the scalp surface. The Equalize option evens out the spacing of the follicle placement to compensate for areas of the U and V coordinates that may be stretched or squashed. 8. Set Points Per Hair to 20 and Length to 5. Hairs that have more points per curve are more flexible and have more detail in their motion as they respond to dynamics; they also slow down the playback speed of Maya in the scene. The Length attribute can be modified after creation. 836 | Chapter 15 Fur, haIr, and ClothIng The Place Hairs Into option should be set to New Hair System. If a hair system exists in the scene already, you can use this option to add the newly created hairs into the existing system by selecting it from the list. Figure 15.27 shows the settings for the new hair. 9. Click Create Hairs to make the hair. The hairs appear as long spikes coming out of the head (see Figure 15.28). 10. Click Play on the scene, and the hairs start to fall. After a few moments, the hairs start to settle. 11. Save the scene as nancyHair_v02.ma. To see a version of the scene, open the nancyHair_v02.ma scene from the chapter15\scenes directory. In the next section, you’ll learn how to style the hair. Figure 15.27 The Create Hair Options area Figure 15.28 The hairs appear as long spikes on the top of the head. When you click the Play button, the hairs fall and settle into a basic hair shape. addIng haIr to a CharaCter | 837 hair transplants You can move an existing hair system from one surface to another surface using the Transplant command. To use this command, follow these steps: 1. Select the hair system you want to move. 2. Ctrl+click the destination surface. 3. From the Dynamics menu set, choose Hair  Transplant Hair. If the surfaces have very similar U

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