cube environment
English translation: 3D Mapping Technologies
| 01:19 Jan 12, 2002 |
| English language (monolingual) [PRO] Tech/Engineering / Computers -> Hardware | |||||||
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|  Selected response from: EngIndonesian Australia Local time: 16:58 | ||||||
Grading comment
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| SUMMARY OF ALL EXPLANATIONS PROVIDED | ||||
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| 3 +2 | 3D Mapping Technologies |
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| 4 +1 | 3D technology |
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Answers
29 mins confidence: 
peer agreement (net): +2
peer agreement (net): +23D Mapping Technologies Explanation: "A third parameterization of environment mapping uses six cube face views directly as an environment map instead of requiring a re-warping of the cube views into a sphere map or dual-paraboloid map. To support cube mapping, the OpenGL implementation's texturing hardware is expected to directly fetch texels from the six cube face views loaded into texture memory. Existing OpenGL implementations do not support such a mode. This approach is described by Voorhies and Foran [98]. Voorhies and Foran make two important observations. First, the expensive divider required in perspective-correct texture mapping hardware can be used by cube map texturing hardware to pre-construct the per-fragment divide necessary to project an unnormalized reflection vector to a particular cube face. Second, an efficient hardware block is proposed to compute the reflection vector per-pixel using linearly interpolated eye-space normal and eye-space position vectors. Unfortunately, efficient cube mapping requires special hardware support that is not available at the time of this writing." See: http://www.opengl.org/developers/code/sig99/advanced99/notes... Multiple texture support in Direct3D allows the use of environment maps for lighting and reflections. However, single-map 360-degree solutions like circular or spherical maps aren't robust enough to be widely used in real time. The most suitable solution for real-time generation and addressing of a 360-degree environment is a cubical map, composed of six textures (faces). Each face can be generated by pointing a camera with a 90-degree field-of-view in the appropriate direction. Per-vertex vectors (normal, reflection, or refraction) are provided to the rasterization hardware that then iterates them across the polygon and calculates the intersections of the interpolated vectors with the faces of the cube map. If the application or API generates the cube environment map, the driver does not require the information about the transformation matrix or coordinate space in which the per-vertex vectors are defined. This is because the vectors are used only to address the environment map, which is logically in the same coordinate space. Addressing of a circular map involves vector normalization; addressing of a spherical map requires the use of trigonometric functions. All types of single-map environments are nonlinear: a circular map is extremely distorted and anisotropic near its periphery, while a spherical map has large distortions near its poles. This makes it necessary to re-create the environment map every time the viewpoint changes in such a way that the central view area becomes distorted. Cubical environment maps, formed by pointing a real or simulated camera with 90-degree field-of-view in six different directions, are free of these disadvantages. They can be generated faster but need to be updated less frequently, have fewer distortions, and can be addressed by using equations similar to the ones already used for perspective-correct texture mapping. See: http://www.osr.com/ddk/d3d_8l2f.htm Reference: http://www.3dconcept.ch/artikel/environment/3.htm |
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Grading comment
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9 hrs confidence: peer agreement (net): +1
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