【Live2D Explanation】 How to Transform Contours without Failure (X-axis) (Patreon)

*This article is a translation of an article written in FANBOX on April 23, 2022.

Good evening. I thought I was going to flip when I saw the notice.

*This is the FANBOX notification screen

Why such a sudden increase was a mystery to me.

I checked and found that this tweet was reprinted on Bilibili Video, so it seems that the number of new supporters from Chinese-speaking countries has increased!

https://twitter.com/himono_vtuber/status/1516400884787208194?s=20&t=RL8WzhwNm4ipB2p5vwDA5Q

I think we got here because you were kind enough to include various links in the summary section. At any rate, thank you for your support!

So this time, I would like to explain about contour deformation as a way of saying thank you.

Speaking of contours, I wrote the following article in NOTE a year ago as an article officially requested by Live2D, Inc.

https://note.com/himono_vtuber/n/na1eb00fbc3b4

I will be honest.

The content of this NOTE is out of date.

The above NOTE does not contain mistakes, but there are so many parts that are poorly explained or explain methods that are no longer used.

The current contour deformation looks like this.

https://youtu.be/OwePpR2Nlnw

It looks like a crazy way to move things around, but there is a certain amount of law.

In this article, I will explain the deformation of clean contours, comparing how the technique described in the NOTE article is older.

◆Partitioning of contours

I used to explain that the line drawing and the base are separate parts.

That in itself has not changed.

However, the scope of contour parts has changed significantly.

Thus, the skull used to be made in such a way that it covered the entire skull, but now it is only made up to the hairline.

Because, in reality, the hair grows on the outside of the hairline and no skin color is ever visible. So there is no use in making it.

Moreover, once the skull portion is made, it is necessary to consider the three-dimensionality of the ear when it is turned sideways.

When you turn at an angle like this, the ears come to the front of the contour, so you have to think about their wrap-around.

If the part range is stopped at the hairline, such an order swap will not occur, making it easier to create.

By the way, this idea of "making a contour part with the hairline" is not my idea.

but it is the idea of Oruko Amase.

https://twitter.com/Amase_Oruko/status/1491727461100363780?s=20&t=OFlOhex6rdrQC6EEjAwk8w

It is HIMONO's way to incorporate ideas that we think are good!

I hope you will all adopt my ideas and make them your own.

◆Contour mesh

This is the way it used to be divided.

Old

Now

Now it looks like this. The interior dots have been reduced a bit and a row of dots has been added inside the boundary.

The reason can be seen in the line drawing part.

By adding one more row of dots, the line drawing can be neatly enclosed as shown here.

Even if the line drawing is distorted by adding a large range of motion, this can be fine-tuned manually.

(Although so far I've been able to deform it nicely with only a deformer!)

◆Contour deformation (angle X)

I used to give this explanation, but this is very old information now....

This deformation is missing something important.

It is "gills.

*In Japanese, the part of the image below is expressed as gills.↓

The protrusion of this part is not overwhelmingly sufficient.

One more thing.

The eyebrows do not protrude enough.

The previous deformations weren't a huge mistake, either.

If we really want to achieve a deformity without breakdown, we have to be

we have to be aware of the "bone".

If you touch this area circled by the red line and the same area on your own face, you will see that the bones are protruding and hard.

These "protruding bone" areas must be deformed with an awareness that they will appear to protrude when you turn your head to the side.

Furthermore, although it is not actually visible, it is recommended to be aware of the three-dimensionality of the hairline here, as it will increase your understanding of the three-dimensionality at once.

Furthermore, there is one more major change.

In the past, we used to make the deformer so that the horizontal line was straight.

The idea was, "The X-axis is a horizontal movement, so it shouldn't move vertically.

When made in this way, the chin, cheeks, and forehead are at the same height as when facing forward.

At first glance, this movement seems to be correct. Of course, this is not wrong.

In fact, in many cases, the height of the head, chin, and nose are aligned like this in a three-view drawing.

However, this is only a "2D" correct way of thinking.

Now we are making it so that the front side goes down and the back side goes up.

Why do we make it this way? It can be seen by looking at the movement of the 3D model.

We borrowed Nikoni Rittai-chan as a sample.

Let's superimpose these "front-facing" and "diagonal" images

It's hard to understand with just this, so I'll explain with an image with guide lines.

I drew guide lines on the chin, mouth, nose, and eyebrows.

Can you see it? If you look at an angle, the height is slightly raised in the direction you are facing.

Body movements are much easier to understand.

The arm in front appears to move downward while the arm behind appears to move upward.

The reason for this appearance is, roughly speaking, that the horizontal axis is also in perspective in 3D space.

It means that it is structurally correct to the left, but to the actual human eye it looks right.

I had posted this self-made diagram in a previous NOTE, and in fact, you can already find the answer here.

So now, as shown here, when deforming the X-axis, I move the deformer diagonally so that the "front is down and the back is up" and deform it by making it protrude while being aware of the bone.

https://youtu.be/ZLJY5iV5fmE

When you move it, it looks like this

https://youtu.be/UVSYszn687g

By the way, just the outline looks like this. It would be good to make this alone so that you can see the three-dimensional effect.

That is all for this commentary.

As a side note, I said earlier that "3D also applies perspective to the horizontal axis". Actually, this is half right and half wrong. Actually, it is correct to say, "When perspective projection is used, perspective is also applied to the horizontal axis.

Actually, there are two types of 3D: parallel projection and perspective projection.

You can think of the left side of the previous figure as "parallel projection" and the right side as "perspective projection.

The reason why there is a left projection method when the actual view is on the right is because it is easier to create it on the left. You use the left projection method to create it, using the three-plane view, etc., as a guide. (That's right. It is very hard to make it with perspective.)

Live2D models are also commonly created using the parallel projection concept, right?

This is where we introduced the concept of perspective projection in the creation of this model.

...I honestly didn't expect this progress video, which is just outlines and expressions, to get such a good response. (currently 50,000 likes)

https://twitter.com/himono_vtuber/status/1516400884787208194?s=20&t=SB69OqKpLfmKy3w45hjfxg

Of course, this is a work that I am very confident in, and I have put all my skills into it, but it does not have any impactful gimmicks or a huge range of motion, so I wondered why the tweet was so well received.

I wondered if it was because I brought the concept of perspective projection to the Live2D industry, which until now had only been based on the idea of 2D parallel projection.

It looks like an illustration, but it moves in the same way as in the real or 3D world... Perhaps that gap creates some kind of attraction.

Lastly, this perspective-based Live2D production method is seriously unsuitable for beginners.

It is simply too difficult, and unless it is made by someone with some understanding of perspective projection, it can lead to incorrect stereotypes.

Even if you make it in parallel projection, I think you can make it move quite nicely just by being aware of the cheekbones and gills I explained at the beginning, so I recommend using parallel projection if you are not familiar with Live2D!

That's all for this time! The explanation of the X-axis alone has become very long, so I will write more about the Y-axis and diagonals in the near future. See you soon!