Today, most computer games are characterized by detailed 3D characters, created to astonish with their realism and beauty. But designers and creators of models during the process of working out objects do not limit themselves and let their imagination run free. It often happens that the result of their creativity is a well-developed, recognizable and interesting character, worked out to the smallest detail, who simply cannot be transferred to the computer game world. The reason is the huge number of polys.

The history or retopology

Poly is a rectangle that has a long-range distortion. You can make a polyhedron of almost any shape using such elements. If there are many polys, it is easy to cover with them, for example, a model of a human face. On flatter surfaces, a minimum number of quadrangles will be used, and convex, texture details (eyes, nose, lips) will be covered with dozens of primitive shapes. The more polys are used, the more realistic, detailed the result looks.

Sample of retopology

All 3D models can be roughly divided into 3 categories:

● Hi-poly. They are the most detailed and contain 1-3 million polys. They are used to create AAA game projects for consoles and PCs. They are distinguished by a detailed drawing and heaviness.
● Mid-poly. Medium detail objects. The best option for console games and PC projects.
● Low-poly. They contain only 5-10 thousand polys. Their use saves resources, so games with such models are mostly intended for mobile devices, as well as augmented and virtual reality.

Mobile developers strive to create models with as few polys as possible, but do not want to refuse of their beautiful, detailed look. Therefore, a method called “retopology” is used.

Why retopology is needed

Modeling is a complex process, at the beginning of which we rarely pay attention to how the polys of the developed object will be located. Therefore, its creation is followed by a retopology. The word literally means “reproduced topology”.

Having a ready-made model, the developer can animate it in Maya, 3ds Max or Blender. But if there are about 5-20 million polys, it is almost impossible to make them react quickly. The hi-poly mesh simply cannot be integrated into a computer game in its original form. But you can reduce their number by building a new topology based on the existing one.

3D artists use a number of programs to do it:

● 3D Coat,
● Maya,
● Blender,
● 3ds Max;
● Modo,
● ZBrush,
● Topogun.

By placing ready hi-poly model in one of them, it is easy to redevelop a mesh with a small number of polys. It is more convenient and easier to animate, but there is a question: is it possible to maintain high quality graphics? Yes. Let’s consider an example.

An example of retopology in modeling

This model was created in one of the 3D editors for a game that will be released on a smartphone. The detailed character figure is distinguished not only by the high-quality design of small elements, but also by realistic textures. It is not advisable to lose them in the process of transferring the model to the game.

Low poly 3D model

We applied a mesh over the already complex figure, simplifying it before animating. If the object has symmetry, the process can be speed up. In other cases, polys are applied manually, and this is a rather diligent work. You can see how their number has decreased from 3-5 million to 40-50 thousand. This is far from the ideal, but at the initial stage, the achieved result can already be considered good.

High and low poly 3D model

However, without using different textures and materials, the model looks too primitive. And we would like to get the result as close as possible to the concept. Details from the hi-poly version to the low-poly version can be transferred by baking a normal map. To do this, you need to select a detailed hi-poly model as a source of baking and specify a low-poly model as its follower. Having provided the name and size of the texture (or several), you need to select the “bake” button in the editor, and the original version details will be transferred to the low-poly model. There are other ways, but this one is quite simple and convenient.

Normal map in retopology

The model obtained in this way is easy to work with when animating, but in the game it will not look simplified. The use of retopology allows you to create beautiful and realistic characters and other objects with detailed textures, without overestimating the performance requirements of PC or console. This is a great opportunity to realize a complex idea on any platform, from a powerful modern PC to a regular smartphone. By placing a simplified topology on the existing one, 3D artists can apply all their creativity.

One more sample of retopology

Retopology in action