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Concept
Reflection (computer graphics)
Résumé
Reflection in computer graphics is used to render reflective objects like mirrors and shiny surfaces.
Accurate reflections are commonly computed using ray tracing whereas approximate reflections can usually be computed faster by using simpler methods such as environment mapping. Reflections on shiny surfaces like wood or tile can add to the photorealistic effects of a 3D rendering.
For rendering environment reflections there exist many techniques that differ in precision, computational and implementation complexity. Combination of these techniques are also possible.
algorithms based on tracing rays of light, such as ray tracing or path tracing, typically compute accurate reflections on general surfaces, including multiple reflections and self reflections. However these algorithms are generally still too computationally expensive for real time rendering (even though specialized HW exists, such as Nvidia RTX) and require a different rendering approach from typically used rasterization.
Reflections on planar surfaces, such as planar mirrors or water surfaces, can be computed simply and accurately in real time with two pass rendering — one for the viewer, one for the view in the mirror, usually with the help of stencil buffer. Some older video games used a trick to achieve this effect with one pass rendering by putting the whole mirrored scene behind a transparent plane representing the mirror.
Reflections on non-planar (curved) surfaces are more challenging for real time rendering. Main approaches that are used include:
Environment mapping (e.g. cube mapping): a technique that has been widely used e.g. in video games, offering reflection approximation that's mostly sufficient to the eye, but lacking self-reflections and requiring prerendering of the environment map. The precision can be increased by using a spatial array of environment maps instead of just one.
Screen space reflections (SSR): a more expensive technique that traces reflection rays in screen space (as opposed to world space in e.g. ray tracing).
Source officielle
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