"Sonic World Adventure" Graphics Course for Zenji Nishikawa's 3D Game Fans -GAME Watch

■ Graphic specs of "Sonic World Adventure" -Sonic is now a 18,000 polygon character!

Mr. Hashimoto "I haven't done almost anything about LOD, because in the case of" Sonic WA ", the load on the geometry side was hardly a problem. We prepared multi-polygon and low-polygon models for LOD. I was only preparing to do it, but considering cost effectiveness, I decided not to implement it because it would be unnecessary. It is LOD-like and only the texture mipmap was implemented in "Sonic WA" Is it? "

Mr. Ogino "Since the PS3 version also used Playstation Edge, I was not worried about the geomery performance. In the case of PS3, the main memory capacity is tight, so it was possible that the low polygon model would occupy the memory with the introduction of LOD. So I'm glad I didn't have to introduce it as a result (laughs). "

■ Pixar CG movie ambient feeling into game graphics

Mr. Hashimoto "I think that the game graphics of this generation have become very shader-rich, but if parallel light sources (light sources that fall on the entire scene such as sunlight) and point light sources (light sources that locally illuminate all directions) hit directly. I started to think that the fact that the shadows of the missing parts were omitted might be "unsatisfactory". After that, the work of Pixar, who is famous as a feature-length CG movie production studio. We set out to develop real-time GI with the goal of reproducing the atmosphere of the group. "

■ "Sonic WA" GI Technique (1) -GI for Static Objects

Mr. Iwasaki "The calculation unit of the GI texture can be set variable, but it's about 2 cm to 3 cm on each side. The daytime scene is not so noticeable, but the nighttime scene is the GI that the lighting such as street lights exerts. However, I was careful about the adjustment because it came out in an easy-to-understand manner. "

Mr. Hashimoto "It took two days to calculate for a terrain of 500m x 500m with one PC. The completed GI texture is about 100MB. There are places where there is about 15km per stage, so a simple estimate I found that the GI texture size increased from several hundred MB to about 1 GB, and the calculation time was several months (laughs). This is not good, so the tool for generating GI textures is used for distributed computing. I made it correspond. "

Mr. Hashimoto: "We expanded dozens of PCs in the department for this distributed computing for GI texture calculation. Then we ran out of power, and when we turned on some equipment, we had a breaker at work. Has come to fall (laughs). In the end, I ended up having to do power boosting work. "

Mr. Iwasaki "Instead, the BGM and sounds in the game are on-memory. I have given a capacity limit to the sound, but I still allocated about 40MB, so the BGM and sounds used in one stage That's enough. Sonic runs at speeds of 100m / s or more, so I was worried whether it would be possible to read the GI texture in time, but when I designed the streaming reading of the GI texture so that it would be in time for the calculation on the desk, the result was There was no problem. "

■ GI technique of "Sonic WA" (2) -GI for dynamic characters

Mr. Hashimoto "We have considered various things, but we decided to introduce a concept that is one step ahead of hemispherical writing. We used a technique called" light field "in the team to create a two-way environment for hemispherical writing. Ambient light from more directions than light is automatically calculated and placed in space. "

Mr. Hashimoto "In" Sonic WA ", each point in the light field has eight directions of ambient light as data, but due to the constant specifications of the pixel shader, there are six orthogonal directions of x, y, and z. In the case of straddling eight light field ambient lights, we sample multiple light fields in the immediate vicinity and calculate the weighted average for the subsequent lighting. "

Mr. Iwasaki "After generating a GI texture for a background or prop / prop object, the light field value is also calculated based on the scene to which the GI texture is applied. The light field spacing also depends on the scene. However, it is basically 2m to 3m, and there may be a little more detail if it is near a building with many objects. However, if there is little change between adjacent light fields, combine them into one. The distance between each light field is actually variable because it has been processed. "

Mr. Hashimoto "Actually, depending on the material, the light field refers not only to the light field in the normal direction but also to the light field in the reflection vector direction opposite to the line-of-sight vector. By doing this, the ambient light on the other side penetrates. You can create a subtle shade effect that seems to be overflowing here as well. "

Mr. Iwasaki "I also considered a plan to implement this light field using spherical harmonics (SH), but it doesn't make much sense when considering the balance between the memory capacity used and the effect obtained. I understand that I haven't adopted it. It seems that an implementation with 8-direction ambient light like our implementation can obtain sufficient quality without using SH. "

■ HDR rendering technique in "Sonic WA"

Mr. Iwasaki "HDR rendering of" Sonic WA "is an 8-bit integer 32-bit buffer specification of integer 8888, which is common to Xbox 360 and PS3. It is a so-called pseudo HDR rendering that assigns 0.0-2.0 to 0-255. I tried using FP16-64 bit at the beginning, but it was so tight in terms of performance that I made it to the current specifications. "

Mr. Hashimoto "In the case of" Sonic WA ", the maximum brightness of 2.0 was sufficient because there were no scenes that were shaken with such high brightness. The reason why the Mach band is not noticeable is that there are few objects with a very flat surface expression. Is it because of it? "

Mr. Hashimoto "There are various reasons for this to make it easier to play, and for directing to show the scene firmly, but adjustments are still necessary. In the first place, the texture drawn by the designer is at the time of design. It is colored with an appropriate color, but it may not be the appropriate color under certain circumstances in terms of gradation level. "

■ The secret of the fur of Sonic "Wearhog" at night

Mr. Iwasaki "The number of layers of fur is about 15 layers. At the time of development, the designer was able to adjust the number of layers and the density of hair. Shell polygons for applying fur are dynamically generated on the engine side. Since it is a mechanism, the character in the modeling stage does not have a multi-layered outer skin polygon. The number of layers is changed between the event scene and the game, and in the event scene it is often an up shot of the character, so the number of layers is increased. increase"

Mr. Iwasaki "We also tried putting hair fins in the development stage, but the wear hog of" Sonic WA "has not so much lack of hair density due to the large number of layers of shell type fur. So I stopped hiring. "

Mr. Hashimoto "In addition to this, we are doing shading treatment so that specular appears in the direction of the hair tips, and by saying that the inner lower shell is shielded around, the hair tips are bright and the roots are darker. I think that the fur of "Sonic WA" went well, but there was a problem and when I was blurred with the expression of depth of field, my hair was blurred. It's a bit unnatural, isn't it? This is the weakness of the shell-type fur shader, or the future issue to be solved. "

■ Shadow generation in "Sonic WA"

Mr. Iwasaki "Even if all the shadows of static objects are drawn, they will match the shadows on the GI texture, but they will not match. However, for example, the shadow of a tree falling on the ground Players will not care if the shadows of the trees projected on the sonic match, and the shadow map generation of static objects is also narrow to the extent that dynamic characters will intersect. I'm done. "

Mr. Hashimoto "By the way, the shadow around the root of Sonic's pointed back hair is a correction of the shadow burned in 3ds MAX. The shadow that is very local and clear is also burned with an emphasis on appearance. There is. "

■ Other highlights of "Sonic WA" graphics

Mr. Iwasaki "At the beginning of development, we used parallax mapping for the ripple expression, and realized a fairly three-dimensional ripple expression. However, due to the GPU load problem, we settled on the ripple expression by the current normal map. rice field"

■ Bonus-The story of the development difficulties of PS3 version and Xbox 360 version

Mr. Ogino "Development of the PS3 version was quite difficult. Functions and functions equivalent to the library provided on Xbox 360 were ported to PS3 considerably. It was also difficult to handle the main memory. DMA convenience in PS3 Above, performance will not come out unless the data is aligned with a 128-byte border. Moreover, unlike the 512MB of Xbox 360 that can be used freely, the PS3 is divided into 256MB of main memory and 256MB of graphics memory according to usage. I will ... "

Mr. Ogino "In the development of this PS3 version, the library provided by SCE, Playstation Edge, helped me a lot. The edge geometry that utilizes the SPE (Synergistic Processor Element) in the CELL processor as a vertex shader is active. Of course, the effect of skinning was great, and the performance improved 10 times when it was processed only with RSX of PS3 (laugh). Many data are common with the Xbox 360 version. However, due to the fact that this Edge geometry is utilized, 3D model data etc. are optimized exclusively for PS3. "

■ 3D game graphics lighting evolves in the direction of GI

Mr. Hashimoto "When it comes to GI, I wish I could handle specular (specular reflection) information. Currently, our GI technique deals only with diffuse reflection systems. Spherical harmonics. I think that if you can use a function to include information such as what kind of light is coming about each surface of the object in the scene, you can get a very beautiful luster. You can manually create a cube map etc. There seems to be a way to arrange it in a large number of spaces, but again, I would like to create a system that generates data fully automatically instead of manually setting it by the artist. There is room for the artist to make adjustments. I think it's best to have.

(C) SEGA