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Polygon Reduction Tools

Sometimes it is easier to model with patch or MetaClay tools, even when you need to end up with low poly models. Sometimes you will be given large, heavy models that need to lose weight for use in your current project. In both cases, you need to take models with lots of detail and a lot of polygons, and reduce the polygon weight while striving to retain detail and model quality.

Softimage has a complete complement of world-class Polygon Reduction tools to remove polygons from models while maintaining quality, using a variety of different methods. In general, as you reduce the number of polygons in the model, the detail in the model begins to degrade. The smaller the model gets, the worse it looks. Polygon reduction, like so many operations in Softimage, is not a science but an art[md]the art of finding the perfect balance between detail, shape, and number of polygons (see Figure 7.44).

Figure 7.44 The same model, in several stages of polygonal reduction.

It must be said, however, that the Softimage Polygon Reduction toolset is not very popular, perhaps because it looks so darn complicated. In reality, it is simple to operate once you know the tricks. Here I'll show the basic functionality of the toolset in a way that will enable you to explore the features more fully. Check the Softimage documentation for a complete explanation of all the features.

The Effect->PolygonReduction command brings up a large dialog box, divided into four different areas (see Figure 7.45). The top area contains the options used to operate the Polygon Reduction command itself. The three lower areas are all different toolsets in their own right, and each operates independently of the others. Only one can be active at a time, set by clicking the radio button next to the section names, Rule-Based, Optimization-Based, and Filter.

Figure 7.45 The Polygon Reduction dialog box

The Rule-Based Method

The trick that usually stops users cold is that the effect must first be attached to an object, and then iteratively adjusted for optimal results. After the first application, a new cone icon appears in the scene, representing the Polygon Reduction tool. You can then select that icon and edit the parameters of the command with the Effect->Custom->Edit Parameters menu cell. This two-part method allows you to make a great many small changes to the model very rapidly, trying things out, undoing the changes, trying different things, and trying combinations of things to get exactly the right balance for each different model. It works like this:

1. Tessellate the model.

Select the model and tessellate it into triangles with the Effect]Convert command.

2. Adjust the radio buttons.

Use the Effect->PolygonReduction menu cell to call up the Polygon Reduction dialog. Check the top of the box in the Processing options. Set the All radio button to apply the effect to the entire object, and the Standard radio button to start the default operation. The other options in this area are special cases for hierarchies of objects and objects with materials. You can ignore the other options, because they won't operate yet. Click the OK button to start the effect, dismiss the dialog, and then pick the target mesh you want to reduce.

3. Modify the effect.

An icon appears in the scene, representing the effect. Select this cone icon and begin to modify the Effect commands with the Effect->Edit->CustomParameters menu cell (see Figure 7.46).

Figure 7.46 The Edit->Custom->Effects menu cell.

The dialog comes back. Move it on the screen so that you can see your original model in the Perspective view while you modify the effect, so that you can observe changes in the model (see Figure 7.47).

Figure 7.47 The interface, with the Polygon Reduction tools up.

4.Make the rule.

Choose the method of Polygon Reduction and start in. The first tool to try is the Rule-Based method, which allows you to reduce the polygons in an object either by a percentage or until a target number of polygons is reached, based on a number of different factors.

In general, the effect looks at each polygon in the model and ranks it according to the value of a factor. It then places all the polygons in a list sorted by that value, and begins to remove them one at a time from the smallest to the largest, stopping when it reaches the number you set:

Radius examines each polygon to see how big a circle can be placed within each one. Those polygons with the smallest circles are removed first, on the theory that they are smaller and less important.

Length ranks the polys by the length of the longest edge, again removing smaller polys first.

Area calculates surface area, and again removes smaller polys first.

Height examines each vertex and looks at it's height above the plane formed by the neighboring vertices. The Remove button must be on for this option to work. When polygons are removed by Height, small bumps in the surface detail go away first, leaving larger, flatter areas on the model.

Angle examines the angle along edges between polygons, just like the Effect->Cleanup command. This is a simple, fairly fool proof method.

Choose one of these methods and set the slider for % Face Count to the percentage of polygons you want removed. Start small, like 20%, and work slowly.

5. Reduce the model.

Click the Apply button to reduce the model. The effect runs and the model onscreen changes. The dialog remains up, allowing you to change the % Face Count, choose a different method, and run the effect again. Continue this method of stepwise enhancement until you are satisfied with the results. If you go too far and the model is hashed into a small crumpled ball, you can change the Processing Option from Standard to Undo Last, and click Apply again to undo the last command. You can then change back to Standard to try another setting.

When you are happy with the results, click Ok to dismiss the dialog. Remember you can always go back and do it some more.


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