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发表于 2011-4-23 01:57 · 福建
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Video footage Information
The goal of the demo is to "Keep material consistency under indirect illumination using Physically-based Rendering."
Technical facts:
Rendered in real-time on Xbox 360 / PlayStation 3
Runs at 30Hz with 720p and is directly captured from the video output on the devkit
Real-time lighting and shadowing used (no baked light maps)
Key features are physically-based shading models, physically-based lighting and image-based global illumination
Overview
In typical previous real-time rendering implementations materials are diffi*** to work with. To achieve a photo-realistic material with ad-hoc shading models, you would need physically plausible albedo, normal, specular and shininess (gloss) maps. However, physically-based shading models can help us to more easily achieve a photo-realistic look. We presented reasonable physically-based shading models in past conferences and they are one of the solutions to improve material appearance. However, it is diffi*** to produce realistic lighting condition results, even with physically-based shading models and traditional light models that include existing deferred techniques. This is because all light sources have "size" and there are no punctual (zero-size) lights in the real world.
We also presented physically-based lighting and improved ambient lighting BRDF models in 2010. Since then we are continuing to improve our own physically-based rendering engine, including physically-based shading models and lighting. With our latest engine, we doesn't have to use a "Shininess Hack" to achieve soft-looking specular highlights caused by an area light source. (Shininess Hack: If you set a physically plausible shininess parameter with punctual lights, specular highlights look smaller than they should in the real world. Thus, artists set smaller shininess parameters to increase the highlight size and avoid the problem.)
Physically-based Shading Models
All the objects in the demo use physically-based shading models with physically plausible BRDF model parameters based on their materials. (Actually, the parameters are a little exaggerated for the ease of understanding the difference between materials.) In the video, you may recognize what the objects are made from and see the consistency of materials in different lighting conditions. In typical real-time rendering, ambient lighting doesn't have a physically-based shading model and results in unrealistic materials. Our engine can handle physically-based shading models for all types of light sources such as punctual lights, ambient lights including deferred-based lights.
True HDR
Using physically-based rendering (shading models and lighting), the rendering result looks as if it contains "High Dynamic Range" signals, even with moderate glare effects. In the demo, each light source (sun light, sky light, inter-reflections) has physically correct quantities; the reflected light from the surfaces continues to be physically correct. This rendering pipeline creates a "true dynamic range" which is carried to the film simulation pass. Our camera and film simulation system use a true F number, Time Value and ISO speed. The result is a beautiful blur (bokeh) effect, resembling a photograph, as well as a high dynamic range that is not based on "glare effects."
Physically-based Lighting
As you can see in the indoor scene, the sun light only illuminates a few objects through the window and the objects in the room are mostly dominated by indirect illumination. However, each object still seems to have "consistent materials." As mentioned in the “video facts” section, all the objects don't use pre-computed light maps.
To that end, our rendering engine implements physically-based lighting as mentioned previously. Light sources have physical quantities which are correctly handled in the rendering pipeline. For example, a "Line Light Source" would be implemented in a general rendering engine but it wouldn't be handled as an "Area Line Light." At each shading pixel, the distance from the pixel to the light source is computed as the nearest distance from a point to a line. The line light is just a single point light changing its distance along with the line. A true line light source must be handled as an area light, similar to a collection of point light sources. In our rendering system, a point light source can handle its size and ambient lights are handled as area light sources. As mentioned before, all types of light sources are evaluated with physically-based shading models. This allows us to achieve "consistent visuals under any kind of lighting condition and any kind of materials." For one material example in the demo, we don't use a special material for the character’s eyes (traditionally an environmental mapping material node is used). The eyes simply reflect the surrounded lighting environment.
Diffi*** Lighting Conditions
Recently, global illumination is becoming popular in real-time rendering. However, it typically handles only the diffuse component. That is one of the reasons why materials look flat under indirect illumination. Why do objects come to have only the diffuse component when they are illuminated indirectly? Objects must be rendered with the same rules under any kind of lighting conditions. As you can see in the demo, our rendering engine succeeds in achieving good results under the diffi*** lighting conditions previously mentioned.
If you want to see how specular components for indirect illumination are important, see more comparisons!
貌似找到一个类似解说的东西。 |
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