Tessellation (surface subdivision) displacement Mapping (map displacement)

DirectX one-tessellation (surface subdivision)-What is tessellation (surface subdivision)? Why does it play such an important role?

With the recent buzz about DirectX 11, you've probably heard a lot about the most new features of DirectX 11 tessellation (surface subdivision). As a concept, tessellation (surface subdivision) is very straightforward, that is, processing a polygon into many small fragments. But why is this way of handling so much attention? How does it help to improve the quality of the game? In this article, we will analyze the reasons why tessellation (surface subdivision) can bring profound changes to PC 3D graphics, and explain NVIDIA®GEFORCE®GTX 400 How the series GPU delivers breakthrough tessellation (surface subdivision) performance.

Essentially, tessellation (surface subdivision) is a method of decomposing polygons into finer fragments to enhance geometric fidelity. For example, if you work with a square and cut it diagonally, you are actually subdividing the square "surface" into two triangles. In itself, tessellation (surface subdivision) does not increase the slightest fidelity. For example, in a game, it doesn't matter whether a square is rendered as two triangles or 2000 triangles. Tessellation (surface subdivision) can increase fidelity only when new triangles are used to describe the new information.

When a displacement map (left) is applied to a plane, the resulting surface (right) displays the height information encoded in the displacement map.

The simplest and most popular way to use a new triangle is the technology called Displacement Mapping (map replacement). A map of displacement is a texture that stores height information. When applied to a surface, the map allows the vertices of the surface to be increased or lowered according to the height information. For example, using a piece of marble, a graphic artist can create a carving effect by means of a "displacement" vertex. Another popular technique is to apply displacement maps to the terrain to carve out craters, canyons, and peaks.

Just like tessellation (surface subdivision), displacement Mapping (map displacement) has been around for a long time. But until recently, it was really popular. The reason for this is that because you want to make displacement Mapping (map replacement) effective, the surface must consist of a large number of vertices. In the case of marble carving, if the marble block is made up of eight vertices, there is no relative displacement between them that can generate a dragon-shaped relief. A detailed emboss can only be generated if enough vertices are available in the underlying mesh to depict the new shape. Essentially, displacement Mapping (map Displacement) requires tessellation (surface subdivision) and vice versa.

With the advent of DirectX 11, tessellation (curved subdivision) and displacement Mapping (map replacement) finally achieved a perfect match, the vast number of developers have joined the camp. Popular games like "Alien vs. Predator" and "Metro 2033" use the tessellation (curved subdivision) to create a smooth-looking model, while developer valve and id Software have done some promising work, Apply these techniques to their existing game characters.

When a rough model (left) is processed by tessellation (surface subdivision), a smooth model (middle) is generated. When the map substitution is applied (right), the game characters are close to the cinematic realism. ©kenneth Scott, id Software All rights reserved. 2008

Because DirectX one-tessellation (surface subdivision) pipelining is programmable, it can be used to solve a large number of graphics problems. Let's take a look at four examples.

Perfect Bump Map

Essentially, displacement Mapping (map substitution) can be used as a temporary alternative to existing bump mapping techniques. Current technologies, such as normal maps, can create an illusion of concave and convex surfaces through better pixel rendering. All of these techniques are only valid in certain situations and are not all that realistic when they are in effect. The following is an example of a more advanced parallax masking map in bump mapping. Although it can generate overlapping geometric artifacts, it can only work on the plane and inside the object (see). True displacement Mapping (map substitution) does not have these problems and can produce accurate results from all perspectives.

More smooth characters

Without the artist's manual input, pn-triangles can achieve automatic smoothing of game characters. Both geometry and illumination fidelity can be improved.

The refinement algorithm is another natural partner of the tessellation (surface subdivision). The refinement algorithm can handle rough models, and with the help of tessellation (surface subdivision), the algorithm creates a smoother-looking model. Pn-triangles (also known as N-patches) is a popular example. The Pn-triangles algorithm transforms a low-resolution model into a curved surface that can then be redrawn into a mesh of triangles that are subdivided by high-precision surfaces. In today's game, we take it for granted that a large number of visual artifacts can be eliminated with this kind of algorithm. These visual artifacts include a blocky pattern in the character's joints, a polygonal appearance on the car's wheels, and rough facial features. For example, in Stalker:call of Pripyat, Pn-triangles is used to create a smoother, more natural figure.

Seamless fine-grained

In a game with a large, open environment, users may notice that objects in the distance often appear and sometimes disappear. This is because the game engine is switching between different degrees of refinement (LOD) to limit the geometry workload. Because there is a need to save multiple versions of data for the same model or environment, there is no simple way to change the granularity continuously until that time. Dynamic tessellation (surface subdivision) solves this problem by changing the fineness instantly. For example, when a distant building is first greeted, it may be rendered using only 10 triangles. As the user's horizons narrowed, the building's salient features began to emerge, and more triangles were used to depict details such as windows and roofs. When you finally arrive at the door, the old brass Door knob alone uses 1000 triangles for rendering; displacement Mapping (map replacement) finely carved each groove. The game environment can now extend to virtually unlimited geometric granularity because of the elimination of the tessellation of dynamic (surface subdivision) objects.

The Art of Retractable freedom

For developers, tessellation (curved subdivision) greatly improves the efficiency of its content authoring pipeline. Describing its motives for using tessellation (curved subdivision), Valve's Jason Mitchell said: "We are interested in being able to edit the content of the game because it allows us to scale." That is, we want to make a model only once, and then we can promote it to movie quality ... Instead, we want to be able to naturally reduce the quality of the game content to meet the need for real-time rendering on a particular system. "This ability to create a model for use on a variety of platforms means that development time is shortened. For PC gamers, this means the highest image quality can be achieved on their GPU.

Geforce®gtx how the GPU (graphics processor) handles tessellation (surface subdivision)

The traditional GPU (graphics processor) design uses a single geometry engine to perform tessellation (surface subdivision) tasks. This approach is similar to the earlier GPU design, which uses a single pixel pipeline to perform pixel coloring. We designed our own parallel tessellation (surface subdivision) architecture from the outset, recognizing how pixel pipelining evolved from one unit to multiple parallel units and how this progress was made in 3D fidelity.

The GEFORCE®GTX-x GPU (graphics processor) has up to 15 tessellation (surface subdivision) units, each with dedicated hardware for vertex pickup, tessellation (surface subdivision), and coordinate transformations. They use 4 parallel raster engines to perform operations that convert the triangles of a recent surface subdivision into fine pixel streams for coloring. In this way, the performance of the tessellation (surface subdivision) achieves a huge breakthrough, with lasting performance of up to 1,600,000,003 corners per second. The GEFORCE®GTX 480 is up to 7.8 times times faster than the fastest comparable product. This data was measured by bjorn3d, an independent website.

Conclusion

After years of repeated experimentation, tessellation (curved subdivision) finally succeeded on the PC. "Metro 2033" and other excellent games have shown the potential of tessellation (curved subdivision). Finally, tessellation (surface subdivision) becomes as critical and essential as pixel coloring. Aware of the importance of tessellation (surface subdivision), NVIDIA® company has created a parallel tessellation (surface subdivision) architecture from the outset to drive this process. The result is a real breakthrough in the GEFORCE®GTX 400 series GPU (graphics processor)-Geometric fidelity and tessellation (surface subdivision) performance.

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Tessellation (surface subdivision) displacement Mapping (map displacement)