'General'

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"Completing the Human Figure, chapter 7" by Peter Ratner


Creating Hair
There are many approaches to modeling hair. In fact, it becomes even more confusing when one considers all the different hair styles that people wear.
Normally, your choices are dictated by the type of software that you are using. If it implements pixel shaders that render fur and hair then you can make a more realistic hairdo. Pixel shaders are programs which process pixels. These generators can be used to perform mathematical operations that render fur and hair.
If your software does not have this ability then you will most likely have to do some creative texturing and/or model a hair object(s). Transparency mapping makes the hair object appear as if it is made up of many hair strands. The first set of instructions explain how to make hair from objects rather than a hair generator.
Hair Object(s) Steps
Fig. 7-27 Object hair step 1. Creating the hair model from long flattened cylindrical shapes.
Fig. 7-28 Step 2. Painting a UV color hair map and an alpha map for transparency mapping.
Fig. 7-29 Step 3. Specifying the UV map for the hair object.
Step 1 (Figure 7-27). Make long flattened cylindrical objects and place them on the head as if they were really fat hair strands. Be sure to overlap them. Give the object one texture name.
Step 2 (Figure 7-28). Create a color image map that has thin vertical lines. Make another transparency map image from the original that is white where the color strands are and black in the spaces between them.
Step 3 (Figure 7-29). Make a UV map of the hair object and apply both the transparency and color map as the UV hair texture.
Figure 7-30 shows a rendering of the same female wearing a hair object with transparency mapping and hair made from a pixel shader.
Fig. 7-30 Two different methods for creating hair. The female on the left has hair made from an object that is transparency mapped while the one on the right is wearing a wig made with a hair generator.
Hair Generator Guide Steps
If your software has a hair generator or plug-ins available then you can use the following instructions to make long hair guides. Your hair generator can then use these guides to create more hairs. Even though this tutorial shows how to make ponytail hairstyle, you might still be able to utilize the information to create whatever hairdo you want.
Fig. 7-31 Pixel shader hair step 1. Making the first three strands for the bangs.
Fig. 7-32 Step 2. Duplicating and distributing the hair groups across the forehead.
Step 1 (Figure 7-31). Create a spline that sticks into the scalp a little bit and whose end sticks out and hangs down over the forehead. This short strand of hair has approximately 7 vertices. Make 2 duplicates of the hair strand and arrange them similarly to the illustration.
Step 2 (Figure 7-32). Duplicate the 3 hair splines and place them next to the first set. Continue copying, pasting, and placing the set of 3 hairs until they are arranged around the forehead. It is important to always have the first point of each spline inside the scalp.
Step 3 (Figure 7-33). Hide all the hair splines except for the top ones that run across the forehead. Start on one end, select each corresponding point and create a spline that connects across these vertices. Do the same for all the other points until you have a mesh of vertical and horizontal splines.
Step 4 (Figure 7-34). Hide this mesh and connect the middle vertical splines. Finally connect the splines that are closest to the head. You should now have 3 sets of connected splines.


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Fig. 7-34 Step 4. The 3 groups of hair meshes after connecting each set of splines.
Fig. 7-35 Step 5. Deleting the vertical splines except for those at the beginning of the forehead. These are rail cloned across the horizontal splines.
Fig. 7-36 Step 6. Rail cloned guides for the bangs.
Fig. 7-37 Step 7. The guides are jittered and brought together at the ends.
Fig. 7-33 Step 3. Connecting the corresponding hair splines.
Step 5 (Figure 7-35). The horizontal splines that were the result of connecting the vertical ones will now be used as the rails when performing a rail clone. A rail clone is an operation that duplicates splines and polygons across a given path such as a spline(s). Delete all the original vertical splines except for the ones at the side and beginning of the forehead. Place the horizontal splines (the rails) in a background layer.
Step 6 (Figure 7-36). Rail clone the 3 vertical splines. For segments pick length, make the clone uniform, type 80 for the amount of strands, and turn off oriented and scaling. If 80 yields too many hair strands, you can always cut back on the amount.
Step 7 (Figure 7-37). Right now the hair strands are too even so they need to be jittered a little bit. Bring the ends of the hair together so that groups appear to bunch up.
Step 8 (Figure 7-38). Now it is time to make the hair that runs across the scalp toward the back. The beginning overlaps into the bangs and ends where the ponytail will begin. Create 3 sets of splines that run the length of the head. The 3rd spline is the one that is furthest from the scalp. Duplicate the set of 3 splines and distribute each group around the head. Make sure the beginning of each spline is inside the scalp.
Fig. 7-38 Step 8. New sets, each consisting of 3 hair guides, are created across the scalp. These lead toward the ponytail.
 
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