Speed Shark Classroom 72: Ray Tracing, Fine Classification, Which Is Not Useful?

Raytrace from RTX Series Graphics card Since its launch, NVIDIA and the major media have been focusing on the promotion of function points. For most players, the effect of light pursuit does not seem to be so great, and the contrast is not so obvious. This time, the author uses the latest domestic game Bright Memory: Unlimited benchmark Software Let's take a look at the detailed effects of various ray tracing special effects.

In addition, in our understanding, ray tracing can only be divided into three effects: reflection, shadow, and ambient light masking. However, with the maturity of software technology and the rapid development of hardware performance, more realistic ray tracing effects have been added to the game. Let's give a simple example.

1. Ray traced caustics

2. Ray traced refractions

3. Ray traced reflections on transparent&opaque surface

4. Ray traced shadows

5. Ray traced ambient occlusion

6. Ray traced order independent transparency (OIT)

Let's first look at the application of each light pursuit effect in the game, and then classify these effects into "difficulty" categories:

01 Light chasing caustics

Caustic effect refers to the convergence or divergence of light reflected/refracted by the surface of smooth metal or transparent objects to form a new light source to illuminate other objects around.

(All pictures in this article can be zoomed in)

Caustics generated by glass (left)/no caustics (right)

Caustics is a more realistic light chasing effect. In the broken glass above, the glass bottle will produce caustics because the light shines on the glass bottle, which can make the water below project.

Caustics generated by glass fragments (left)/no caustics (right)

The armor surface shown in the figure is made of reflective metal, and the caustics are reflected by the projection of other objects on the face shield and shoulder armor, especially on the back shield.

Caustics refers to the phenomenon that when light passes through a transparent object, due to the unevenness of the object surface, light refraction does not occur in parallel, but diffuse refraction occurs, and photon dispersion occurs on the projection surface, commonly known as water light and sparkling.

02 Light tracing refraction

Compared with the common reflection effect, the refraction effect is more difficult to simulate. When light passes through a transparent object, multiple refractions and total reflections will occur. Therefore, multiple ray tracing is required to obtain a complete effect.

3 refractions (left) and 6 refractions (right)

The above figure shows the refraction effect of the glass bottle: the refraction with three light bounces turned on cannot show the texture of transparent glass; When the bounce is increased to 6 times, the complete refraction effect can be observed.

03 Light tracing reflection

Reflections on transparent surfaces: It is difficult to find suitable materials for large area glass without light tracing the reflection of transparent surface. In reality, we often see glass because of reflection.

Transparent reflections on glass windows

In the above figure, you can see the effect of light tracing on the transparent surface. The reflection of light is also the most widely used phenomenon of ray tracing effect in current games. The contrast of this effect is strong, and it is also the easiest to reflect ray tracing.

Multiple reflections: In many cases, a single reflection can not produce a complete effect, and it needs two or more reflections to complete it. It is commonly found in car reflectors or near mirrors.

Single reflection (left) and multiple reflection (right) on automobile rear-view mirror

As shown in the above figure, the reflector of the car is used as the foreground. Once it is reflected as the character image in the scene, and many times it is reflected as the vehicle body reflecting the environment light source. Therefore, it needs to conduct more than two ray tracing to complete the reflection.

04 Shadows and ambient occlusion

After light tracing is added, we usually talk about shadow and ambient light masking together, because penumbra involving light tracing effect will also add ambient light masking effect. The rasterized shadow can only produce the true image, and it is determined by the experience of the game developers, which greatly reduces the authenticity.

Rasterized clear umbra (left) Light follows soft penumbra (right)

High precision ambient light masking effect is an important part of character rendering. In fact, in many games, even though the character modeling is refined, we feel at first sight that it is inconsistent. This is because the light is too different from the real scene, resulting in the character being too "acting".

Ambient occlusion effect: off (left) on (right)

The above figure shows the soft effect of light chasing ambient light masking for skin rendering. The light and shadow of the character's neck use the ambient light masking effect to make the character look more realistic and natural, approaching the light effect in reality.

05 Light tracing multi-layer transparency

The multi-layer transparency effect of ray tracing is not common in previous games, mainly because the effect does not clearly and intuitively show that ray tracing is mostly used in corners and also consumes resources. In short, there is no difference.

Light tracing multi-layer transparency

For example, on the glass of the station behind the character, each glass is transparent, so you can see the scene behind. But its role in the game is not obvious, so it also uses less light pursuit effect.

06 Light chasing effect ranking

Now let's classify and summarize these light chasing effects. In current games, reflection, shadow and ambient light masking are used most frequently. The reason is simple. These light chasing effects are the most obvious.

However, light tracing refraction is not as obvious as direct reflection due to its small scope of application, so few games will use refraction.

The application scope of light tracking caustics is smaller. In addition, the picture area where caustics are commonly used is not large, just the effect of details. If you don't look carefully, you won't find it. Therefore, increasing this effect will only increase the burden of GPU most of the time, so few games will use it.

The light tracing multi-layer transparent effect is similar to the previous one, and it also needs to add a word "change" to the caustics. Who cares about the scenery behind several layers of glass?

Therefore, in view of the summary of the above light pursuit effects, reflection, shadow and ambient light masking are the effects that can obviously feel the difference between the pictures at present. Refraction, caustics and multi-layer transparency are the icing on the cake. Adding them to the 20 series graphics cards will only make players doubt the performance of their own graphics cards. In the 30 series graphics cards with doubled performance, we believe that these effects will be applied to more games and make more players feel that the games are approaching the real light and shadow.

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