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The Optimization-Based Method

The Optimization-based approach is a more complex method that actually spawns another background process to work on the model, allowing you to get back to work on other parts of the scene, while the poly mesh slowly cooks down. The Optimization method uses a point cloud representation to retain the form of the original mesh and can do a great job, with adequate practice.

The secret to it is to select the Start radio button, then click the Apply button to kick off the calculation, and spawn the new process. Then you use the Query radio button and Apply to check on the progress of the model. Use the Stop radio button with the Apply button to stop the process before your model cooks down into a crumpled ball.

The Filter Method

The Filter method cleans up models, closes holes left when bad polygons are collapsed, and removes redundant collinear edges. Just make selections as to the function you want applied to the model, and use the Apply button to perform the filter. Unlike the other portions of the POlygon Reduction toolset, it does not reduce the number of polygons in the active model.

Converting Patches to Polygons

When you have a model that has already been created as a patch surface, it is simple to convert it down into polygons.

First check the level of detail that will be created by checking the Info->Selection command’s dialog box for the selected object. The dialog shows you how many polygons and triangles are required to tessellate the patch surface to the current level of detail (see Figure 7.48).

Figure 7.48 Set the detail needed in the Patch Info dialog box.

Reducing the step of the U or V parameterization reduces the polygons required. When you have set a reasonable degree of subdivision for the model, close the Info Selection dialog and choose the Effect->Convert command in the Model module (see Figure 7.49).

Figure 7.49 The Effect->Convert menu cell.

Effect->Convert first converts the patch into polygons. If you recall the command with the middle mouse button, it then converts the quad polygons into triangles. You can also use Effect->Convert to change patches into NURBS, NURBS into polygons, and change the degree of curves.

Making Terrain with Polygon Effects

There are two different ways to use polygonal geometry to form more complex terrain models for animation and games geometry. The first, Polygon->Fractalize, creates imaginary landscapes based on fractal algorithms. The second, Deformation->BumpMap, uses an image you paint to create a topography (see Figure 7.50).

Figure 7.50 The Fractalize and BumpMap menu cells.

The Fractalize Method

Polygon->Fractalize is a simple tool that creates sufficient results for many uses. It can take a long time to run and can generate a great many polygons if you are too liberal in your settings, because it includes some recursive functionality. The Fractalize command looks at each vertex in a triangulated grid and moves it according to a fractal calculation, either in positive Y or in the normal direction. The grid can be automatically subdivided by the command to generate finer detail, and the changes can be applied interactively to amplify the effects.

To design a landscape, start by creating a polygon grid and converting it to triangles with the Effect->Convert command (see Figure 7.51). You can use Proportional modeling at this point to add some major features to the land if you wish.

Figure 7.51 The starting mesh, triangulated.

Execute the Polygon->Fractalize command. The Fractalize dialog (see Figure 7.52) appears, where you may set a number of parameters, then after you dismiss the dialog, pick the grid to complete the command.

Figure 7.52 The Fractalize dialog box.

Positive Offset makes sure that the vertices are always moved in a positive direction, never negative. Best results occur with this option on.

Normal Offset uses the normals of the grid to determine the direction that the vertices are pushed. If you start with a completely flat grid, leave this off. If you bump up your surface a bit and want your work considered by the fractal algorithm, check this on.

Additive forces the changes to accumulate as you run more iterations. This generates bigger changes in your terrain-peaks and valleys instead of random noise on the floor of a jungle.

Subdivide divides each triangle into four triangles every iteration when it is checked on. This creates smoother geometry, but beware of setting iterations too high for your machine memory and processor. When the setting is too high, the command takes an extremely long time. Imagine that if you start with a 10 by 10 grid, convert it to 200 triangles, and then run five iterations, you create 200 x 4^5 triangles, or 204,800 triangles. Seven iterations give you just over three million triangles, which brings your machine to a halt.

Seed is a Randomization value that makes sure the fractalization algorithm comes up with different results given different seed values. Experiment to see what happens at different seeds.

Iterations sets the number of times to subdivide the model and repeat the offset process. As mentioned earlier, keep it under 6 unless you have a long lunch break coming up.

Magnitude is a value, expressed in Softimage units, that sets the range for each possible offset. Increasing it gives you more treacherous terrain, while low numbers give you grasslands.

TIP:

Being able to stop Softimage is often useful if a calculation seems to be running away from you, or if the software has become non-responsive and you suspect that it has crashed. In IRIX, if you start from a command shell with the Soft command, you can close the shell to terminate the programs that started from it.

If you did not start from a command shell, open a new shell window and examine the running processes with the PS -E command. Look for the soft process, and note the process ID number printed with it. Then give the command "Kill 1234," where 1234 is the process number you noted. The command "Killall Soft" will do it as well.

Jagginess determines the scale of the fractal and can be used to set the sharpness of the average angles between polygons. Low numbers (under 0.4) give you gradual rolling changes, and higher numbers give you cliffy craggs, eagles nests, and so on.

Set the parameters to your liking, and complete the command by picking the mesh to be fractalized. Softimage then creates a new object in the Schematic, showing you the results of your choices.

 

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