Reflection (computer graphics): Difference between revisions

Revision as of 01:13, 27 July 2022

Revision as of 13:26, 8 November 2022

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{{short description|Simulation of reflective surfaces}}

{{FullMore citations needed|date=AprilNovember 20202022}}

[[Image:Refl sample.jpg|frame|right|Ray traced model demonstrating specular reflection.]]

'''Reflection''' in [[computer graphics]] is used to emulate [[reflection (physics)|reflective]] objects like [[mirror]]s and shiny surfaces.

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[[Image and object order rendering|Image order rendering]] algorithms based on tracing rays of light, such as [[Ray tracing (graphics)|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]].<ref>{{cite journal |last1=Kligard |first1=Mark |title=Improving Shadows and Reflections via the Stencil Buffer |date=1999 |pages=7 |url=https://www.researchgate.net/publication/238248138 |journal=[[ResearchGate]]|accessdate=25 April 2020}}</ref> 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.<ref>{{cite AV media video| title =Off Camera Secrets, Metal Gear Solid: Twin Snakes - Boundary Break|url =https://www.youtube.com/channel/UCHTnEwQKNwm49CQeCVZogMwwatch?pagev=1&sort_by=popularfas0zJ8C7GU|time =4:32|date=2016-11-28|access-date =25 April 2020}}</ref>

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.<ref name="randima">{{cite book |last1=Fernando |first1=Randima |last2=Kilgard |first2=Mark |title=The Cg tutorial. The definitive guide to programmable real-time graphics |date=2003 |publisher=Addison-Wesley Professional |isbn=9780321194961}}</ref>{{rp|174}} 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). This is done for each rendered pixel of the reflected surface, using the surface normal and scene depth. The disadvantage is that objects not captured in the rendered frame cannot appear in the reflections, which results in unresolved intersections and incomplete reflection image.<ref>{{cite web |title=Unity-Technologies: Screen space Reflections |website=[[GitHub]] |url=https://github.com/Unity-Technologies/PostProcessing/wiki/Screen-space-Reflections |accessdate=25 April 2020}}</ref>{{better source needed}}

==Types of reflection==

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===Wet floor reflections===

{{anchor|Wet floor effect}}

The ''wet floor effect''<ref>[{{cite web|url=http://twinsparc.com/a/wetfloor/|title=WetFloor|author=Nate|archive-url=https://web.archive.org/web/20080531144057/http://twinsparc.com:80/a/wetfloor/ Twinsparc] Article in which the term is coined|archive-date=2008-05-31}}</ref>{{better source needed}}

is a [[Computer graphics|graphic]] [[Special effect|effect]]s technique popular in conjunction with [[Web 2.0]] style pages, particularly in [[logo]]s. The effect can be done manually or created with an auxiliary tool which can be installed to create the effect automatically. Unlike a standard computer reflection (and the [[Java (programming language)|Java]] water effect popular in first-generation web [[Digital image|graphics]]), the wet floor effect involves a [[gradient]] and often a slant in the reflection, so that the mirrored image appears to be [[Levitation|hovering]] over or resting on a wet floor.