Basics of 3D models 2) - The 3DCG World is a Collection of Polygons

Basics of 3D models 2) - The 3DCG World is a Collection of Polygons

Before you start making 3D models, there is something you should know.

It is about polygons.

If you think you know exactly what I'm talking about, you don't have to read this article. But...

"polygon is that thing - the square thing. (I know, but I've never really thought about it.)"

If you think so, read this article.
You may discover an unexpected aspect of polygon that you did not know before.

Polygons are the basic, fundamental element needed to create a 3D model.
You cannot make a good 3D model without knowing a lot about polygons.

I hope you will take this opportunity to deepen your understanding of polygons.

 

Natsu no Lopo-san, free float until 8/31

 
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3D Model is Made Up of a Collection of Polygons

Whether it is a photo-realistic 3D model that looks like live-action or a cel-look 3D model that looks like animation, the reality is a collection of polygons.

In the world of 3DCG, everything you see is polygonal.

In this way, 3DCG can be viewed a little simpler.

Especially in 3DCG that moves in real-time, such as games, it is safe to assume that water, clouds, hair, effects, and everything else are polygonal.

 

For example, the expression of hair.

A very cartoonish-looking game, NARUTIMATE STORM's hair polygons are low poly solid hair.

A fairly realistic-looking game, Final Fantasy 15's hair polygons are high-poly with curved, banded polygons.

In the PC version of Tomb Raider, which has even more realistic hair, each strand of hair is represented with ultra-fine plate polygons.

 

However, the polygons are all the same.

Some 3DCG software such as Maya and Blender have functions to create "hair" such as Hair/Fur.

However, it is impossible to use them as they are in a real-time rendering game, and they still need to be converted to polygons in the end.

As an example, I mentioned the polygonal representation of hair. Even water & effects that do not look like polygons at first glance are made of polygons when you get right down to them.

Let me explain a little more about polygons, such a basic element of 3DCG.

 

  • photo-real
    ...Photorealistic. Refers to a photorealistic representation of the image as if it had been taken in a photograph.
  • cel-look
    ...A representation similar to cel-shaded animation. Also called toon rendering.
  • low-poly
    ...low polygon count. Models for smartphone games are low-poly if classified
  • as high polyethylene terephthalate
    ...a high polygon count. There is no clear definition of the boundary between low poly and
  • rendering
    ...3DCG data is computationally processed & drawn by a computer for display.
  • real-time rendering
    ... rendering immediately on the spot as opposed to pre-rendering
  • pre-rendering
    ...almost all 3DCG movies etc. are done this way.

 

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The smallest element is a triangular polygon, and if two are gathered, a square polygon

A polygon in 3DCG is a single plane surrounded by three vertices and three edges.

This triangular plane is called a triangular polygon. This is the smallest visible 3DCG element.

Two of these triangular polygons attached together and surrounded by four vertices and four edges are square polygons.

Triangular and square polygons

A triangular polygon is a perfect plane that cannot be bent or twisted no matter how hard you try.

In contrast, a square polygon can be bent and twisted. Bent or twisted square polygons are not planar.

 

However, a non-planar square polygon can also be divided into two completely planar triangular polygons.

Triangular polygons that do not bend, square polygons that bend

In the game 3D models, you often hear the term "polygon count," which refers to the number of triangular polygons. The number of polygons in a square polygon is "2" because it is 2 triangular polygons x 2.

 

Incidentally, the polygon count is displayed in the lower right corner of the screen in Blender 2.8 and the upper left corner in Blender 2.9.

In Japanese display, face = square polygon, triangle face = triangle polygon.

Blender 2.8 shows polygon count in the lower right corner of the screen.
Blender 2.93 Display of vertex and polygon count information is On/Off in the Statistics viewport overlay

 

Polygons are planar, you can't create a "curved surface" by collecting polygons

Triangular polygons, the smallest elements that makeup 3DCG, are completely flat.

No matter how many planes you join together, you cannot create a "curved surface. This is an important point.

3D models made of polygons cannot represent perfectly curved surfaces.

 

Let's take a look at a 3D model of a sphere made in Blender for a moment.

Sphere made in Blender

At first glance, it appears to be a perfectly round sphere, but closer inspection reveals that the outline of the sphere is crisscrossed.

The identity of this sphere looks like this.

The true nature of the crackling of the sphere made in Blender.

It looked around, but it is still a collection of flat polygons.

The reason why the surface looked round earlier is that the computer was processing the polygons to make them "look" like they were smoothly connected.

This apparent processing is called "smoothing processing (or smoothing processing).

However, this process only makes the surface appear smooth, so it is not possible to round out even the cracks in the contours.

A 3D model made of polygons, no matter how smooth & curvy it looks, is clunky when zoomed in. This is the fate of polygon models.

 

So what about models made with sculpting?

Sculpting modeling is a method of creating 3D models by stretching and denting shapes like clay. ZBrush is a typical sculpting software.

It can be shaped freely like clay, and the surface is so smooth that polygons don't seem to matter.

However, if you look at the sculpted model under very high magnification, you can see that it is made up of very small polygons.

Sculpted spheres are also crunched when enlarged.

The polygons are so small that the surface is smooth and can be handled like clay.

Sculpted models have a very small number of polygons, so using them as they are in games is inconvenient in many ways. To use a sculpted model in a game, a process called retopology is required to reduce the polygon count while preserving the shape as much as possible.

Retopology is done to some extent automatically by the computer, but the final polygons are adjusted by hand. Sculptural modeling is also not free from polygons.

 

You cannot create curved surfaces with polygons.

This is an important concept to keep in mind if you are creating 3D models.

Especially for 3D models with a limited number of polygons, such as games, how to make a flat polygon look more like a curved surface is a key.

 

There is a big difference in the number of polygons that can be handled in a 3D game model between a smartphone game and a PC game. The more powerful the hardware, the more high-poly 3D models can be handled, but even with high-poly models, the polygon principle is the same: "Curved surfaces cannot be created.

 

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Polygons have a front and back, "invisible" when viewed from the back

Now, this plane called polygon has a front and back.

When the polygon is viewed from the front, it is properly visible, but when the polygon is viewed from the back, nothing is visible.

Even if there is a polygon there, it is "invisible" from the back, so it is the same as "no polygon".

Polygons are not visible from the back.

If there are areas in the 3D model where the polygons are backed up, only there will the model appear to have holes in it.

 

So what if, for example, we want to create a 3D model of a single sheet of paper with no thickness?

If you make a paper pellet with normal polygons, the back side of the paper = the back side of the polygon, and it will not be visible.

In this case, you can either provide a polygon on the backside of the paper model or use the option "double-sided" polygons.

Since double-sided polygons are sometimes too heavy to be used in games due to heavy processing, smartphone games, for example, often provide a front side and back side polygon in such cases.

Polygons have a front and a back, and are invisible when viewed from the back These are the basics of polygons, so please remember them.

 

Human-friendly square polygons, Game processing-friendly triangular polygons

I said that the smallest element in 3DCG is triangular polygons, but when you are playing with 3DCG software, you are more likely to see square polygons.

The 3D model of a sphere created in Blender earlier was also a collection of square polygons.

But some people say that 3D models should be made with triangular polygons.
On the other hand, some people say, no, it is better to make it with square polygons.

Which is better for 3D models, triangular polygons or square polygons?

 

If Toha were to answer.

Square polygons are better, but in some cases, triangular polygons should be used as well.

Here it is.

 

The reason I say it is better to create 3D models with triangular polygons is that this is less likely to cause problems when processing them in games.

In fact, when computers render 3DCG in games and other applications, all square polygons are automatically converted to triangular polygons.

So "the number of polygons in a game model = the number of triangular polygons".

Triangular polygons, which can be defined with only three vertices, are easy for computers to handle.

In contrast, square polygons are more complicated to handle than triangular polygons. A square polygon is first divided into two triangular polygons, but the appearance of the polygon changes depending on how it is divided.

Square polygons look different from triangular polygons because of the way they are divided.

 

These square polygons should be divided into appropriate triangular polygons in advance by human eyes.

So, is it better to use triangular polygons for everything? Not really.

That is why I say it is better to create 3D models with square polygons.

As an example, let's look at this with a model of a character's face.

Comparison of model appearance between square and triangular polygons

The left model is the original square polygon model, and the right is the model converted entirely to triangular polygons.

...Isn't it kind of hard to see the model with the triangular polygons?

It is difficult to do modeling work if it is simply hard to see. (Individual differences exist.)

 

Also, the flow of polygons can be somehow seen in the square polygons, while the triangular polygons are cluttered and the flow is difficult to see.

This polygon flow is called topology. In the case of character models in particular, topology is sometimes important, so it is better to be able to see the flow with the human eye.

Also, if there are too many triangular polygons, the modeling convenience functions of 3DCG software may not work.

For example, there is a "loop selection" function that allows you to select a group of edges connected by a loop, but this function can only be used for square polygons.

 

Like this, the easy one for people to handle is the square polygon, and the easy one for game processing, etc. is the triangular polygon.

Therefore,
I think it is best to make the 3D model basically in square polygons, but to make it properly in triangular polygons where necessary.

 

By the way, there are more than four vertices. polygonal polygon is a polygon that is not happy for anyone.

Polygonal polygons are not good to use.

Especially polygons with concave shapes are bad.

Polygonal polygons are also automatically converted to triangular polygons by the computer, but with so many vertices, the computer gets confused and divides the polygons in a strange way. This is not a good result.

Sometimes polygonal polygons are inadvertently created during the process of creating a 3D model. If you find polygonal polygons, it is better to separate them into triangular or square polygons.

 

Summary: Knowing polygons is the first step to creating a 3D model

GOGO

Do you understand a little more about polygons than before?

Since a 3D model is ultimately a collection of polygons, understanding the base polygons themselves is the first step toward creating a 3D model.

Here is a brief summary of the various polygons.

- Polygons in 3D models -
  1. Triangular polygons are the smallest element of a 3D model
  2. A square polygon is made up of two triangular polygons.
  3. Triangular polygons are perfectly flat
  4. Impossible to create curved surfaces with polygons
  5. Polygons have a front and back, and are not visible from the back.
  6. It is important to use triangular polygons and square polygons separately.
  7. Polygonal polygons are bad to use.

Polygons and 3D models are inseparable.

This is a good opportunity to learn more about polygons, which will be useful when creating 3D models in the future.

The great 3D model is also started from a single polygon.

 

There is one more thing about "XYZ coordinates" that you should know before you start making 3D models.

XYZ coordinates are described in Basics of 3D Models 1) - The 3DCG World is Managed by Coordinates. Please take a look at it. Please take a look through it.

List of comments

  1. Jurian Prabhujee says:

    There was a time many years ago when I downloaded Blender and tried to make a blender, but unfortunately I couldn't make a human face, so I gave up and uninstalled it. I downloaded it again to try again this time, but it is still difficult.
    I have been using Photoshop and Illustrator for many years and have mastered a good amount of work with them, but I am too ignorant about 3D software.
    I have used Shade, but blender seems to be a few steps more difficult.

  2. ARI says:

    Good evening, Mr. Toha!
    I have written to you before.

    I found the polygon article very informative, perhaps basic, but I didn't know much about it.

    In particular, I thought I get it, especially the part about - when making paper that is not thick.

    I had previously made a rocket's jet port section.

    Specifically, I made a cylinder with a large base and a hollowed out circle on the top and bottom.
    When we incorporated it into a game, we were very troubled by a phenomenon in which the shapes disappeared and became invisible when viewed from below.

    Upon closer examination, this seems to have been the cause of the shape, which was not thick enough.

    I was surprised to read this article and was surprised to see that that was the solution, so I had to write it down.

    P.S. My job search was halted due to Corona, but I was able to create one game piece using Blender + UE4.
       I am currently working hard on learning 3dsmax as it is required by a company.
       3dsmax is a lot different than Blender, and it's something I struggle with.

    • Toha トハ says:

      ARI, hi, long time no see~!
      Thank you for your comment again ^^^.

      I think it's very valuable to know the basics of polygon, but I thought it might be too basic to talk about, so I decided to write an article about it.
      The rocket's jet, which was not visible when viewed from below, was exactly like looking at a polygon from the backside.
      I'm glad you happened to solve the mystery at that time.

      I know that the new virus has affected you in various ways and that you are in a difficult situation, but we all have our lives to live for, so let's take it easy on each other!
      But you made a whole game! That's amazing! I'll do my best too!
      3dsMax and Blender are similar in some ways and different in others, but I am sure that ARI will be able to use them quickly.

Toha
Toha

Please feel free to comment~!

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