Hi, When it comes to games, is the ratio of polys and faces the same? e.g. does 1500 faces = 1500 polys? If so, why is that various graphic designers claim that number of polys is double the number of faces in any given 3D model. By number of faces, I''m counting the one that appears when you try to look at the properties of a model in 3D Studio Max. I hope someone can clear that up. Thanks in advance

can anyone please answer?
I''m simply asking if the number of polys in a model is the same thing as the number of faces

They''re usually the same. Sometimes, the editor might save concave faces or faces with a large number of edges, in which case it may be broken up into triangles or something.

Technically, a polygon is a face, but when most people talk about polygons, they are referring to triangles - because that''s what most hardware draws (triangles are guaranteed to be planar, if you have more than 3 vertices, then they don''t all necessarily have to be on the same plane).

In 3D Studio and other modeling packages, you can have as many sides as you like per face, so when you want to convert them to triangles in opengl or something, you''ll end up with more triangles than you had faces.

In the end, it depends on what you talk about when you say "polygon". A polygon, by difinition has multiple sides. There''s no mention of the actual number. However, most people are just referring to triangles when they talk about polygons.

Phew, I hope I didn''t confuse things even more

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quote: Original post by Dean Harding
Technically, a polygon is a face, but when most people talk about polygons, they are referring to triangles - because that''s what most hardware draws (triangles are guaranteed to be planar, if you have more than 3 vertices, then they don''t all necessarily have to be on the same plane).

In 3D Studio and other modeling packages, you can have as many sides as you like per face, so when you want to convert them to triangles in opengl or something, you''ll end up with more triangles than you had faces.

In the end, it depends on what you talk about when you say "polygon". A polygon, by difinition has multiple sides. There''s no mention of the actual number. However, most people are just referring to triangles when they talk about polygons.

Phew, I hope I didn''t confuse things even more

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Hi,
Thanks alot for your reply.

So when it comes to games, a poly is a triangle.

So let me see if I understand,
In a given model there can be less polys(traingles) than faces but never less faces than polys right?

How could one count the number of triangles in a Max model? The properties shows the faces and vertices while the polygon count option shows the number of polys. How would I be able to count the # of triangles in a max model?


Once again, thanks alot

quote: Original post by Someone1
So when it comes to games, a poly is a triangle.

Yes, because most cards only draw using triangles. Any other polygon can be made up from triangles, so it made sense to have everything made out of triangles.

quote: So let me see if I understand,
In a given model there can be less polys(traingles) than faces but never less faces than polys right?

No, it''s the other way around. There could never be less polys than faces, because that would mean there was a face that didn''t have a polygon to represent it.

Technically faces == polygons/triangles, but it''s conceivable that a system might have multiple polygons/triangles per face. Imagine a cube: you might think it has 6 faces, but to represent that with 12 triangles: 2 for each ''face'' of the cube.

Many, many programmers split everything into triangles when they program a game engine. Not all do.

Don't get confused... one polygon does indeed equal /two/ faces. If you split a square into two triangles, you have two polygons for a total of /four/ faces.

Each polygon has a 'front' face and a 'back' face. When you have only a front face, your polygon is like a one way mirror: it's only visible from one side!

Some game programmers tend to forget about this because they are nearly always employing a technique called backface culling, which skips drawing all the back faces.

To sum up, every model has twice as many faces as it has polygons. However, most programmers toss out the back faces during drawing, so only 1/2 of the faces actually get drawn. This means your video card will draw a number of faces that equals the number of polygons.

Edited by - cheesegrater on September 5, 2001 3:57:03 PM

quote: Original post by CheeseGrater
Many, many programmers split everything into triangles when they program a game engine. Not all do.

Don't get confused... one polygon does indeed equal /two/ faces. If you split a square into two triangles, you have two polygons for a total of /four/ faces.

Each polygon has a 'front' face and a 'back' face. When you have only a front face, your polygon is like a one way mirror: it's only visible from one side!

Some game programmers tend to forget about this because they are nearly always employing a technique called backface culling, which skips drawing all the back faces.

To sum up, every model has twice as many faces as it has polygons. However, most programmers toss out the back faces during drawing, so only 1/2 of the faces actually get drawn. This means your video card will draw a number of faces that equals the number of polygons.

Edited by - cheesegrater on September 5, 2001 3:57:03 PM

Sorry, now I think I'm very confused. Really sorry for taking everyone's time but could someone tell me if this is right:

Lets say there is a character figure model. In 3D studio max, when checking face count, it states 3000 faces. Does the 3000 mean 1500 on the outside + 1500 on the inside? Obviously no one wants to render the inside so when the model is used in a game, programmers use "backface culling" to not render the inside of the character model. Then only 1500 faces are rendered to the screen and therefore that model is considered to be 1500 polys?

Can someone tell me if I got it? Sorry again.

Thanks in advance


Edited by - Someone1 on September 10, 2001 1:16:58 PM

That sounds about right, but I''ve never used 3D Studio Max so couldn''t confirm the exact terminology it uses.

I just did a little test, and it counts both sides of a face as 1 face. So if it says 3000 faces, then that''s 3000 backface-culled faces.

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