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标题: Topology Chapter 1 [打印本页]

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作者: lut_456    时间: 2013-9-23 14:19
标题: Topology Chapter 1



IntroductionOver four chapters we'll be talking about topology. This is a subject that causes problems to many people and in most cases the problem is purely in simple details that can be easily avoided if we plan our modeling and try to get clean topology.

There are a large number of issues that are recurrent concerning topology, especially when the models are made for animation. This will be our focus: making good topology for animation. Once you can do this you should be able to cope with anything, even high poly models for still images (Fig.01 - 02). We will also look at how to achieve functional topology. We will talk about the theory of edge loops .The tools we use to do this will not be focused on, as what is important is the principles. Once you understand these they can be applied in any package.

Fig. 01

Fig.02

To begin it is important to say that when it comes to modeling there is no single correct way to work. Every modeler should understand the way that works best for him or her and choose their own pipeline and method. In this series I'll be working with a pipeline that works for me in most cases, especially for characters. Nevertheless there is a short list of things that are important to keep in mind. So let's get started.

I'll be demonstrating these points using a character from a personal project (Fig.03). His name is Miranda. We won't focus on the modeling process so we will move straight onto topology.

Fig. 03

Most tutorials start by teaching the box-modeling technique and it's really important to know how to use and understand these tools, but today we have the retopology process. This allows us to separate the art/sculpture process from the technical one. We can focus on the shapes, gesture and design without coming across technical issues all the time (a spiral loop or triangles for example). This means that you can create the model in an artistic way and then clean the topology afterwards.

To do this you would use tools like the Snap tool, which allow us to work freely by changing the direction of loops, and deleting and creating polygons. It's faster to do things this way and means that the result is 100% clean and functional topology. However, this does highlight one of the problems with box modeling. It means there are many loops and polygons that will appear useless.

These days the process no longer needs to be linear. We can come and go easily from one program to another to make adjustments using the Projection tool or the GoZ plugin. In addition, all major 3D programs import .obj extensions. For this tutorial I will use XSI for polygonal modeling, ZBrush for sculpting and Silo for the retopology.

I will be looking at a character that has organic and inorganic forms. We will start the tutorial with a rough base without worrying about the loops as we just need something to work with in ZBrush. Fortunately for us artists new tools are appearing all the time that help us avoid the base mesh process, such as ZSpheres.

So to start with you need a rough base mesh, which in my case was made in XSI. Note that I don't even have loops for the eyes and mouth, etc (Fig.04).

Fig.04

After you have created the base mesh, export the .obj file into ZBrush (Fig.05). The next step is to start the blocking process, which in my opinion is the fun part. As it's not the point of this tutorial I won't talk about the sculpting of my image; you will have to create your own character and then we will look at the topology of it. To make my model I primarily used three tools: the Standard, Clay and Move brushes.

Fig. 05

Fig.06 - 07 show a few of the stages of my modeling process. Work with your character until you have the shape and proportions you are happy with. Don't forget that things can still be adjusted after you have handled the topology, but we will come back to that later.

Fig.06


Fig.07

I worked with stylized characters proportions: a big head, heavy hands and thin arms (Fig.08 - 9). You can see the legs before and after the sculpting process in Fig.10 - 12.

Fig.08


Fig.09

Fig.10

Fig. 11

Fig.12
As I mentioned, the point of this process is not to talk about the sculpting process, so let's start working on our topology. I use Silo because I really like the way the Snap tool works, but the principles can be followed in other software packages as well.

I usually start the process by making the high poly model slightly transparent as I think it helps with viewing the topology. If you are using Silo you can turn on Ghost Shaded mode and hide the wireframes (Fig.13 - 14).


Fig.13


Fig.14

Remember to turn on the Snap tool before starting to retopologize. You can find this tool in all the main software like Maya, 3ds Max, XSI and modo etc. Even ZBrush has great tools to do this (Fig.15).

Fig. 15

It is very important to make the loops follow the flow of the volumes/shapes and avoid triangles and shapes with any other amount of sides than four. You will come across problems if you use shapes with more sides than four when using blend shapes, rigging or even when rendering. Some software doesn't work correctly when rendering displacement maps and using geometry with triangles.

Start by creating a single polygon and extruding the edges from it. In the beginning the most important thing is to set the direction of the loops (Fig.16 - 17). I usually work in separate areas and then try to connect them. You can see this at work in Fig.18 - 21.


Fig.16


Fig.17

Fig. 18

Fig.19


Fig.20


Fig.21


Make the loops follow the general flow of the muscle. Knowledge of anatomy helps at this point. If you don't feel confident doing this, find a reference that will help you to make sure it flows correctly. You will also find that the pieces join together better if you follow this rule.

In Fig.22 you will see a higher density of edge loops at the corner of the mouth. This is quite important because if you were making it for an animation you would need these to make the face smile, speak or kiss. You can see how the polygons flow around the face and around the neck (Fig.23 - 25).


Fig.22




Fig.23


Fig.24



In Fig.26 you can see how the direction of the loop follows the collarbone. At the tip of the collarbone we will need to create a circular shape that allows for the rise in the shape of the shoulder.


Fig.26

Make the shoulder loop flow down the chest. This will allow the geometry to behave in a similar way to muscles after rigging (Fig.27 - 28). If you do this correctly you can get good results using simple blend shapes matching the bone's rotation.


Fig.27


Fig.28



Continue to follow the flow of the muscles and forms for the nose and eyebrows, as I have done in Fig.29 - 30. You will be doing this all over your model, matching the flow in the separate areas and then joining them together when the different areas meet (Fig.31 - 34).


Fig.29


Fig.30




Fig.31




Fig.32


Fig.33




Fig.34


In Fig.35 - 36 you can see how to fix problem areas in the topology. In Fig.35 you can see the unwanted triangle and the adjustments made. Each problem area you come across will require a tailored solution. When you browse for shapes that haven't got four sides in your geometry you will come across a few areas where there are problems. Usually this can be solved quite simply by connecting the problem shape with the polygon next to it. This would usually create a square. Another trick is to cut the geometry and make it a quad.


Fig.35


Fig.36



Try to keep the same distance between the loops as much as is possible. This will prevent many problems when creating the UVs and textures, and will avoid division problems when rigging and animating Fig.37 - 38.


Fig.37


Fig.38

Fig.39 is a snapshot of the final head topology. This topology provides enough loops to help the animator to achieve the creases that would be made when the face is expressing emotions. In a professional environment it would be necessary to speak to the rigging and animation team to make sure that you cater for every sort of animation that they would like to do.


Fig.39

When you have done this you can delete the high poly base and finalize any of the remaining details like the inside of the mouth and around the eyes. In the next chapter we will be looking at creating the rest of the body and the accessories.

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作者: may    时间: 2013-9-29 03:00
max技术文章，请多给新人指导!

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作者: 雅雅    时间: 2013-10-30 02:10
感谢楼主分享新的文章

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