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 Features
GDC
2002: Incredibly Dense Meshes
This paper
proposes a general solution for a problem that will probably arise in
the near future, perhaps with the launch of PlayStation 3 and its counterparts.
Presupposed is the exacerbation of a current trend in console hardware,
where hardware transformation, lighting, and triangle drawing outpace
the hardware's capacity to store and move data. In other words, in the
future, transforming vertices and drawing triangles will be virtually
free in comparison with storing model data and reading it from main RAM.
For brevity the paper focuses on a solution for character models. On the
one hand, character models pose more problems than fixed environment geometry
in regard to controlling the animation of vertices with bones. On the
other hand, culling and view-dependent level-of-detail need not be considered.
The summary of the problem we propose to solve is as follows: render a
very dense animated skinned character mesh in "the future,"
when transforming vertices and drawing triangles will be cheap, and when
loading from RAM will be expensive. (For programmers of the PS2, this
"future" will sound more like the present!)
The contribution of this paper is to collect together several already-published
conceptions and propose their application to the problem at hand. Some
details are given here, but the reader is encouraged to consult the academic
papers in the References for more detail.
Later sections discusse the details of the problem, outline several techniques
whose integration yields a potential solution, and briefly discuss a possible
future without textures.
The Future
of Character Models
With the onset of the next "new thing" in game hardware, consumer
expectation could very well be an amount of detail equivalent to one triangle
per pixel. If screen resolution continues to double with each generation,
1024x768 will be the typical screen size. If, when close to the view,
a character model occupies roughly 50% of the screen pixels, and given
that the model has half its triangles facing away from the view, then
the total triangle count will be nearly 800,000 triangles per character
model.
Will transformation and drawing performance really be up to this task?
To answer that question, let's look at the advance we saw from PS1 to
PS2. The best PS1 character engines seen by the author could render about
20 400-triangle characters at 30Hz, with only single-bone control and
no dynamic lighting. The author has seen character engines on PS2 with
performance of 31 3400-triangle characters at 60Hz, with up to 3 bones
per vertex and with dynamic lighting on all vertices. Even ignoring the
added bone control and the dynamic lighting, we have an increase by a
factor of more than 25.
So let's assume that transformation and drawing performance will increase
again by a factor of 25. In terms of total capacity for a character renderer,
PS3 will then have the ability to transform, light, and draw 31*3400*25
> 2.6 million triangles per frame at 60Hz.
If we have a system incorporated LOD control, if we assume the 800,000-triangle
density above, and if on average each character occupies only 25% of its
near-view screen space, then we would have to render an average of 200,000
triangles per character. This means that in games like team sports, where
most of the rendering horsepower is devoted to character rendering, it
is perfectly reasonable that we'll be seeing 10 characters in a scene
where at maximum detail, each character is 800,000 triangles.
Make the following assumptions about storage technique:
- Indexed
triangle strips. Each strip vertex has a 32-bit index and 32-bit texture
coordinates (16-bits for U and for V).
- Each
vertex is 32-bit floating-point.
- The mesh
has a 2-to-1 triangle-to-vertex ratio.
- Stripping
performance is 8 strip vertices per strip.
With these
assumptions, current techniques will result in the following storage needs
for each character:
|
Data
|
Count
|
Size
|
| Vertices |
400,000 |
1,600,000
bytes |
| Strip
Vertices |
900,000
(100,000 restarts) |
7,200,000
bytes |
| Total |
|
8,800,000
bytes!! |
So for the
characters in our 10-character scene, we would need to store 83MB of data
and mess with it each frame.
While predicting the future is dangerous, it is the author's opinion that
future hardware will be able to easily transform and draw meshes of the
above size but that it will not be able to store and access that much
data. The predicted implications are that rendering techniques that store
and move only small amounts of data will be necessary in order to meet
consumer expectations of visual quality. Those rendering techniques will
have to include smooth LOD control.
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The
Future of Character Models
