A subset of Softimage’s
Modeling tools, the Polygonal Modeling tools enable you to
manipulate objects made of polygons, as well as individual
polygons themselves. Sometimes using the Polygon Modeling
tools is just the easiest way to make the objects you need
for your rendered scenes, but other times Polygonal Modeling
is the only way to precisely control what you get. Using the
Polygon Modeling tools you can draw each polygon precisely
where you want it, control the exact location of every vertex,
and keep total control over the number of polygons in each
model (see Figure 7.1).
Figure 7.1
Several models with different levels of polygonal detail.
Every polygon
in Softimage can be transformed separately, colored and textured
individually, and even animated individually. The POL mode
restricts all the Transformation menus to work only on polygons,
and the Polygon menu cells add even more polygon-specific
functionality.
In this chapter,
you will
- Create and
edit polygons, point by point and edge by edge
- Model from
poly primitives
- Copy, duplicate,
and transform polygons
- Extrude polygons
- Make polygonal
terrain models
- Round and
bevel poly objects
- Perform Polygon
reduction
Making an entire
scene by drawing and connecting individual polygons is like
building yourself a house out of toothpicks, or knitting a
car out of steel wool. Sometimes that's what it takes!
Polygon Modeling
for Games
For real-time
3D scenarios, however, all this possible detail can be too
much of a good thing. Polygonal modeling has become increasingly
important over the last few years with the popularity of real-time
3D games and VRML (Virtual Reality Markup Language). When
a game or VR simulator needs to display a 3D environment interactively
to the user, so the user can move freely about the 3D space,
the computer rendering the scene must be able to redraw the
scene very rapidly, typically 24 to 30 times each second.
Because the computer must evaluate and perhaps draw each polygon
in the scene every single time the scene is refreshed, keeping
the polygon count low is critical to smooth gameplay and good
computer performance (see Figure 7.2).
Figure
7.2 A real-time image and the geometry behind it.
In game development,
the programmers who build the code engine typically perform
tests to determine exactly how many polygons the engine can
draw per second, on a reference machine that the game players
are likely to have. Then the game designer sets the frame
rate at which the game must refresh for smooth action, and
the total engine performance number is divided by that frame
rate to deliver the polygon budget. The Polygon budget is
how many polygons can be on screen in each frame, before the
game engine begins to choke and can’t draw them all in
time. After the polygon budget has been determined, the game
designers list all the elements that need to be onscreen at
one time, and divide the polygon budget up into a budget for
each element.
For example,
if my game engine can draw 90,000 lit, textured triangles
per second, and I want the game to play at 30 frames per second,
the polygon budget is 3000 triangles per each frame. If I
assign 1000 triangles to the terrain, 200 to the backdrop,
and decide that five enemies can be onscreen at once, each
with 200 triangles for the enemy and 100 triangles for weapons,
shots, and so on, that leaves me with 300 triangles for the
main character.
Modeling an attractive,
convincing main character in less than 300 triangles isn't
easy, but it can be done by creating your character from scratch
with the Polygon Modeling tools.
| NOTE:
For
those of you interested in video game technology,
there is usually a texture budget as well. A typical
game engine can draw a polygon without a texture
in about 10% of the processor cycles required for
the same polygon with a texture, so reducing texture
usage can help performance.
Also,
as the textures get larger, the time required to
map them onto polygons and the memory used to store
them increases. Texture maps in video games are
often very small, ranging from 32 pixels wide by
32 pixels tall to 128 pixels square for really big
ones (See Figures 7.4 and 7.5). Some game engines
even store multiple sizes of each texture to assist
in drawing the textures at different scales, called
MIP mapping (see Figure 7.3).
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Figure 7.3
A real-time texture library with many textures in a single
file.
