Entrevista com um dos desenvolvedores do HL2
Pessoal, dêem uma olhada nessa entrevista (em inglês) com um dos desenvolvedores do HL2, Bill Van Buren, da VALVE. Embora ela seja anterior ao lançamento do game, ela trata sobre HDR, stencil shadow volume, shadow mapping, displacement mapping, física Havok e até, pasmem, DOOM3:
Texto de Zenji Nishikawa (ZEN)
Entrevistado: Bill Van Buren, da VALVE (BVB) - Lembra a sigla do Borussia Dortmund, hehehe...
"Half-Life 2 Developer Interview
ZEN:
Please tell me about the circumference of facial expression in "Half-Life2".
There was an explanation on "eyeball shader" in today's presentation. You said "eyeball shader is reproducing the refrection of the scene to eyeballs", then, how does it specifically process? I suppose whether the environmental map is prepared or it may be the technique of a multipass rendering system.
BVB:
In fact, that is a kind of fake. The blightness is projected as if he sees the light source in the scene "from his eyeballs" at the time of seeing. Although there is no technique like an environmental map, it is equally effective when we glance his eyeballs.
ZEN:
I see. Probably, that is the cost-effective technique. Since the light in eyeballs also moved when the character and the light source moved, they were seen like lively eyes. How about eyelids?
BVB:
The trick is realized by changing the outer skin of eyelids.
ZEN:
40 control points are used in the character's facial expression in "Half-Life2", and I heard that displacement of the points was carried out for the expression. Could you tell me the system?
BVB:
There are 34 vertex for controlling expression in the character's face, and the expression is made by such displacement. Since performance falls greatly, we have not used bones inside of a face.
ZEN:
How is the animation of facial expression made?
BVB:
This is the so-called key frame animation. If there is information on the displacement of the vertex in the beginning and the end of expression, changing expression is reproduced by arithmetic vertex coordinates change.
ZEN:
Although the skin of a face model looked very real, is it because special shader is used? It seems that so-called "skin shader"(*) began to be used in the ATI or NVIDIA GPU demonstration.
BVB:
We don't use the so-called skin shader, in order that we may express the textures of the skin. We take care so that it may not become the vinyl textured skin,like old games.
The speculer mask is applied to parts such as a cheek and a nose, in order to express the glisten or sweating skin.
ZEN:
I heard that holes of a nose and ears and the hollows of eyes are carrying out shade processing using a parameter like self-cover degree....
BVB:
At this point, we are working carefully and it has become a texture based expression now.
ZEN:
That is, to say, a dark part of a face is covered by the texture, and is made dark.
BVB:
That's right. Since we took considerable time for designing faces, please check them well. Some 2500 polygons are used only for modeling one face.
ZEN:
How is the hair? I think it is like the "feathered hair" using the anisotropic lighting.
BVB:
Absolutely. When the hair needs to be expressed, we use the technique.
(*) skin shader : Blood and flesh are covered by skin and the translucent skin reflects light intricately. The shader reproducing the textures of skin is especially called skin shader.
The brilliance in eyeballs is expressed by reflecting the light source position in a scene. That is the secret of lively eyes. The control engine of expression was inspired by Dr. Paul Ekman's cooperation who is the professor of psychiatry of the California medical school, and is prominent in the field of psychology.
Generation of the shadow in "Half-Life2" was made possible by projection texture mapping
ZEN:
Please let me know about shadow expression in "Half-Life2". There are techniques like stencil shadow volume or shadow mapping (shadow buffer) in generating a shadow. What technology is used in "Half-Life2"?
BVB:
We used the so-called projection texture shadow. It is the method of making a light source into a viewpoint, rendering a low detail model to a texture, and sticking projection texture mapping.
ZEN:
I see. The technique has high compatibility.
You can use this technique regardless of which card we use, GeForce or RADEON. The technique can be used also for a console game machine, and is advantageous. However, by this system, it is difficult to express the self shadow projected on an own shadow. Again, how is the object's shadow of a background processed?
BVB:
The game doesn't have a feature of self shadow.
The light source which casts a shadow in "Half-Life2" is limited to one area at one piece. The shadow projected on a scene is based on the light source. And a common light map is used for the static shadow of the background.
The shadow of the static object is generated by the traditional light map and the moving character's shadow is by the projection texture. The techniques are often seen recently. When we look into the shadow of a game, we often make sure whether the graphics ofthe PC game casts self shadow. Unexpectedly, "Half-Life2" does not employ the technique.
High Dynamic Range rendering technique (HDR) is employed
ZEN:
When I see "Half-Life2" graphics, expressions like HDR rendering(*1) will be seen in some places. May I think that "Half-Life2" engine has employed HDR rendering technique?
BVB:
Yes. About the HDR rendering, it was implemented by the cooperation of a certain GPU vender, although I can't tell the vender's name. That's why HDR rendering-expression will be seen here and there when you play "Half-Life2".
ZEN:
By what technique does the rendering specifically carry out? When we use ATI RADEON 9500 or greater, the HDR rendering using the floating decimal point real number buffer will also be possible.
BVB:
HDR rendering expression of "Half-Life2" is the system which gives the luminosity intensity of light to an alpha channel and finally casts the glare effect with programmable pixel shader.
ZEN:
The technique is often used in DirectX 8 based 3D games like "Splinter Cell" and began to appear recently. Further more, when I see "Half-Life2", there are scenes which look like volume rendering. Could you tell us the name of the technique?
BVB:
We use the particle system for most volume expression. On scenes such as underwater, it seems that particle system is used together with the so-called usual fog function.
The glare effect, which is popular HDR expression, is used for the very bright place like a skylight. By expression called the glare effect and the light breeding effect, the light of an electric bulb shines beyond a pillar. When the traditional fog function with near/far parameter is used, a long distance scene will fade and that is called air distance expression.
About the employment of displacement mapping of "Half-Life2"
Zen:
There was an explanation that the geographical feature data of "Half-Life2" engine had the attribute of displacement map data.
BVB:
Yes. Geographical feature upheaves or caves by interference of a player, and displacement mapping(*) technology is used for the expression.
In "Half-Life2", the software-based displacement mapping technology has realized upheaval or cave of the ground, and modification expression of some objects.
ZEN:
Displacement mapping means that the so-called Sub-Division Surface technology which carries out arithmetic division of the polygon is implemented.
BVB:
That's right.
ZEN:
Although the displacement mapping can be accelerated by ATI RADEON 9500 or greater using TRUFROM 2.0, does the game utilize this function?
BVB:
No. The function is processed by the software.
(*) Simply speaking, a technology of sticking unevenness on a polygon at a geometry level. Unlike the bump mapping which performs shade processing, unevenness is geometrically stuck as if the surface was actually irregular.
About physical engine
ZEN:
Speaking of physical engine, it is heard that "Half-Life2" is using HAVOK physical engine, carrying out the license.
BVB:
HAVOK offered us the basic set of very powerful physical engine.
A hit judging, a kinetics simulation, a pressure simulation, spring dynamics, and a simulation of actuator etc. is main, I think.
Since each function could not be used separately in a game like "Half-Life2", we rebuild the game physics engine which works well in "Half-Life2" world combining basic physics engine which includes interference of objects and the relation of a reaction.
Although the three leg huge arms swings and strolls heavily owing to the high center of gravity, such action also follows the physical law in the game world.
ZEN:
All the physical engine of upper layer the game uses is originally made to "Half-Life2", after all.
BVB:
Absolutely. And we also developed "Physics AI" technology newly for "Half-Life2". The technology is incorporated in the vehicle or the machine appears in "Half-Life2", and in our game design tool.
ZEN:
How does the system act on a game concretely?
BVB:
For example, there is a "substance system" in "Half-Life2", and the system enables high level work of game designers or artists.
When we utilize this system, the physical property of a character is calculated automatically and the action comes to follow the physical law in the game world, only by giving a substance parameter to the part which constitutes the character.
ZEN:
That is, if a character is designed with heavy material, he walks heavily even if you don't attach heavy action.... The system is interesting.
About the adaptability to programmable shader
ZEN:
After all, is DirectX-9 GPU required to play "Half-Life2"?
BVB:
When you want to enjoy image expression on the level of an official announcement at SIGGRAPH, DirectX-9 GPU is required.
However, although some expression is simplified, you can enjoy "Half-Life2" by DirectX-8 GPU. Moreover, when you use DirectX-6 or 7 GPU, "Half-Life2" can still be playable, although it will be simplified further more.
Since "Half-Life2" is a PC game, it is programmed with flexibility.
ZEN:
We think of "Half-Life2" as is suitable to DirectX-9 GPU. Then, we can say that "Half-Life2" utilizes the programmable shader 2.0 which is special-feature of DirectX-9?
BVB:
Sure. "Half-Life2" is using both programmable shader 2.0 and 2.0+.
ZEN:
For what expression is the shaders specifically utilized?
BVB:
Though regrettable, I can not answer about it.
Zen:
For example, does "Halfe-Life2" engine perform such things as changing the rendering path or switching moving shader, according to the video cards like GeForce FXs or RADEON 9500 and faster?
BVB:
I can't answer about it, either.
ZEN:
It is often with the case with our readers, they tried to perform 3D benchmark only even if they have DirectX video cards. When we show how DirectX can be used for "Half-Life2"'s expression, it will become useful information for them.
BVB:
Although I am sorry, I can't give shader-related information beyond this up to now. At present, only information I can tell is that, as for "Half-Life2", programmable shader 2.0 or 2.0+ also works really well.
As a matter of fact, authoring to high-end GPU is under advance now.
The water surface is rendered by the dynamic environmental bump mapping, by which the circumference moves with the effect of ripples. By the relation between positions of a light source and a viewpoint, the fresnel effect that changes the transparency under the water surface is also supported. The effect is produced by programmable shader, indeed.
Last Words
ZEN:
Although maps and maps are connected seamlessly, loading occured in the first "Half-Life" on the area boundary. How is "Half-Life2"?
BVB:
Loading occurs like "Half-Life". The flaw is not fixed yet.
The hero is, same as the previous game, Gordon Freeman. When I asked "Is the mystery of the previous game solved?" he answered "Secret!"
ZEN:
Most 3D game fans consider "Half-Life2" and "DOOM III" as the platform because each of the games can be a basement of new games. It seems that there are many fans who consider a rival relation between the two games since they are "the new platform of the same PC game."
BVB:
I have not considered "Half-Life2" and "DOOM III" are rival <g>. The purpose of the each games is different and the directivity of the contents is also different. I think what they are doing is wonderful and it is also very excellent what we are doing.
ZEN:
We can roughly say that "Half-Life2" is open field type, and "DOOM III" indoor one.
BVB:
Indeed. Each of us developed the optimal technic for what we are going to do, and thinks that it can be done. Even if we think of one technique of lighting, both differ.
ZEN:
I agree.
While "Half-Life2" puts emphasis on expression of reality, "DOOM III" gives us the atmosphere of Gothic horror movie inside of the reality.
BVB:
I don't think that every game developer is so mutually conscious. When I see a excellent game in the other company, I applaud the game immediately "Great!", "Fantastic!".
Owing to the top-level graphics and contents, "ICO" on PS2 have the completeness. Although Japanese regard the game as average work, in the European and American game developer, "ICO" has the greatest popularity.
ZEN:
I have somewhat trivial question; are you going to implement bench mark mode on "Half-Life2"? Again, do you have a plan to port "Half-Life2" to another platform?
BVB:
We have not implemented benchmark mode on the game yet, but are going to add the feature anyway. Talk about porting, Xbox is leading and others are undecided.
ZEN:
The last question; what is your favorite game?
BVB:
Since our work of shipment is the last scene, I hardly play games now <g>. I play "Medal of Honor" or "Battlefield 1942" recently. When I talk to console games, I play "ICO" on PS2. "ICO" entertains me because both graphics and the contents were wonderful.
ZEN:
Thank you for today. We are looking forward to see "Half-Life2".
"Normal map" is mostly used for rendering textures of rocks. A concavo-convex expression of geographical feature is rendered by bump mapping. To see the technics, we have to install more than 128MB of VRAM."
Fonte:
http://www.4gamer.net
Abraços.
