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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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