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and other polyhedron mappings address the severe distortion of sphere maps. If cube maps are made and filtered correctly, they have no visible seams, and can be used independent of the viewpoint of the often-virtual camera acquiring the map. Cube and other polyhedron maps have since superseded sphere
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Environment mapping is generally the fastest method of rendering a reflective surface. To further increase the speed of rendering, the renderer may calculate the position of the reflected ray at each vertex. Then, the position is interpolated across polygons to which the vertex is attached. This
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A diagram depicting an apparent reflection being provided by cube-mapped reflection. The map is actually projected onto the surface from the point of view of the observer. Highlights which in raytracing would be provided by tracing the ray and determining the angle made with the normal, can be
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is used, each polygon has many face normals (the direction a given point on a polygon is facing), which can be used in tandem with an environment map to produce a more realistic reflection. In this case, the angle of reflection at a given point on a polygon will take the normal map into
205:" effect) is visible in the reflection on the object where texel colors at or near the edge of the map are distorted due to inadequate resolution to represent the points accurately. The spherical mapping also wastes pixels that are in the square but not in the sphere.
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environment mapping is similar to the other polyhedron mappings, but can be hierarchical, thus providing a unified framework for generating polyhedra that better approximate the sphere. This allows lower distortion at the cost of increased computation.
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in the environment map. This technique often produces results that are superficially similar to those generated by raytracing, but is less computationally expensive since the radiance value of the reflection comes from calculating the angles of
221:"fudged", if they are manually painted into the texture field (or if they already appear there depending on how the texture map was obtained), from where they will be projected onto the mapped object along with the rest of the texture detail.
319:, who developed environment mapping in 1976; these developments which refined Catmull's original algorithms led them to conclude that "these generalizations result in improved techniques for generating patterns and texture".
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created an algorithm for "rendering images of bivariate surface patches" which worked directly with their mathematical definition. Further refinements were researched and documented by
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Catmull, E.A. Computer display of curved surfaces. Proc. Conf. on Comptr. Graphics, Pattern
Recognition, and Data Structure, May 1975, pp. 11-17 (IEEE Cat. No. 75CH0981-1C).
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However, in most circumstances a mapped reflection is only an approximation of the real reflection. Environment mapping relies on two assumptions that are seldom satisfied:
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comes from an infinite distance. When this is not the case the reflection of nearby geometry appears in the wrong place on the reflected object. When this is the case, no
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and reflection, followed by a texture lookup, rather than followed by tracing a ray against the scene geometry and computing the radiance of the ray, simplifying the
145:, such that it contains no self-interreflections. When this is not the case the object does not appear in the reflection; only the environment does.
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The artifacts of the spherical mapping are so severe that it is effective only for viewpoints near that of the virtual orthographic camera.
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into six square regions of a single texture. Other projections that have some superior mathematical or computational properties include the
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The spherical mapping suffers from limitations that detract from the realism of resulting renderings. Because spherical maps are stored as
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Heidrich, W., and H.-P. Seidel. "View-Independent
Environment Maps". Eurographics Workshop on Graphics Hardware 1998, pp. 39–45.
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which provides the radiance value used in the lighting calculation. This creates the effect that the object is reflective.
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Emil Praun and Hugues Hoppe. "Spherical parametrization and remeshing". ACM Transactions on
Graphics, 22(3):340–349, 2003.
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consideration. This technique is used to make an otherwise flat surface appear textured, for example corrugated metal, or
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of incident illumination as though it were seen in the reflection of a reflective sphere through an
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is determined by calculating the reflection vector at the point on the object and mapping it to the
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Mauro
Steigleder. "Pencil Light Transport". A thesis presented to the University of Waterloo, 2005.
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Several ways of storing the surrounding environment have been employed. The first technique was
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camera. The texture image can be created by approximating this ideal setup, or using a
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that is used in outdoor renderings. Cube-mapped reflection is done by determining the
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which computes the exact reflection by tracing a ray of light and following its
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maps in most computer graphics applications, with the exception of acquiring
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Approximation of reflective and transparent objects with environmental maps
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http://web.cse.ohio-state.edu/~whmin/courses/cse5542-2013-spring/17-env.pdf
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eliminates the need for recalculating every pixel's reflection direction.
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Real-time
Environment Mapping with Equal Solid-Angle Spherical Quad-Map
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Gene Miller experimented with spherical environment mapping in 1982 at
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of the environments they represent, an abrupt point of singularity (a "
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of where the camera vector intersects the object. This results in the
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429:, Shader X4: Lighting & Rendering, Charles River Media, 2006.
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Example of a three-dimensional model using cube-mapped reflection
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An image used in early reflection mapping, created in 1976 by
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Tien-Tsin Wong, Liang Wan, Chi-Sing Leung, and Ping-Man Lam.
106:. The reflection color used in the shading computation at a
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of the distant environment surrounding the rendered object.
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Wolfgang
Heidrich introduced Paraboloid Mapping in 1998.
444:"Texture and reflection in computer generated images"
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http://www.ics.uci.edu/~majumder/VC/classes/BEmap.pdf
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Mauro
Steigleder introduced Pyramid Mapping in 2005.
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442:Blinn, James F.; Newell, Martin E. (October 1976).
90:Reflection mapping is one of several approaches to
332:Emil Praun introduced Octahedron Mapping in 2003.
40:technique for approximating the appearance of a
338:Tien-Tsin Wong, et al. introduced the existing
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130:All radiance incident upon the object being
63:. It has been almost entirely surpassed by
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263:that the object is being viewed at. This
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255:Generally, cube mapping uses the same
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48:. The texture is used to store the
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44:surface by means of a precomputed
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371:"Higher Education | Pearson"
20:An example of reflection mapping
548:The Story of Reflection mapping
342:mapping for rendering in 2006.
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505:"Reflection Mapping History"
275:which is then passed to the
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599:Texture mapping techniques
138:is seen in the reflection.
448:Communications of the ACM
559:Cube Environment Mapping
96:screen space reflections
267:is reflected about the
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460:10.1145/360349.360353
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199:azimuthal projections
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613:Displacement mapping
412:. 29 September 2012.
352:Skybox (video games)
250:image-based lighting
92:reflection rendering
38:image-based lighting
684:Environment mapping
491:"Computer Graphics"
311:in 1975, and later
34:environment mapping
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30:reflection mapping
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653:Occlusion mapping
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65:cube mapping
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667:Environment
633:UVW mapping
313:James Blinn
279:to get the
162:aluminium.
100:ray tracing
699:Categories
628:UV mapping
358:References
265:camera ray
203:black hole
123:workload.
81:octahedron
73:paraboloid
42:reflective
468:0001-0782
303:In 1974,
117:incidence
87:mapping.
346:See also
277:cube map
136:parallax
69:unfolded
340:HEALPix
299:History
292:HEALPix
190:or via
160:brushed
85:HEALPix
77:pyramid
46:texture
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261:vector
257:skybox
180:sphere
143:convex
132:shaded
606:Local
374:(PDF)
281:texel
166:Types
112:texel
108:pixel
50:image
464:ISSN
324:MAGI
315:and
550:by
456:doi
153:If
121:GPU
98:or
32:or
24:In
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434:^
418:^
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28:,
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