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.
