Editing Ray tracing (graphics) (section)

==History==
[[File:Albrecht durer ray tracing enhanced.png|thumb|"Draughtsman Making a Perspective Drawing of a Reclining Woman" by Albrecht Dürer, possibly from 1532, shows a man using a grid layout to create an image. The German Renaissance artist is credited with first describing the technique.]]
[[File:Perspective-projection-albrecht-drer-science-source.jpg|thumb|Dürer woodcut of Jacob de Keyser's invention. With de Keyser's device, the artist's viewpoint was fixed by an eye hook inserted in the wall. This was joined by a silk string to a gun-sight style instrument, with a pointed vertical element at the front and a peephole at the back. The artist aimed at the object and traced its outline on the glass, keeping the eyepiece aligned with the string to maintain the correct angle of vision.]]

The idea of ray tracing comes from as early as the 16th century when it was described by [[Albrecht Dürer]], who is credited for its invention.<ref name="raytracing">{{Cite journal|title=Who invented ray tracing?|author=Georg Rainer Hofmann|journal=The Visual Computer|volume=6|issue=3|pages=120–124|year=1990|doi=10.1007/BF01911003|s2cid=26348610}}.</ref> 
Dürer described multiple techniques for projecting 3-D scenes onto an image plane. Some of these project chosen geometry onto the image plane, as is done with [[rasterization]] today. Others determine what geometry is visible along a given ray, as is done with ray tracing.<ref>{{Cite web|title=Dürer, drawing, and digital thinking - 2013 FATE Conference|url=http://www.brian-curtis.com/text/conferpape_steveluecking.html|author=Steve Luecking|date=2013|website=brian-curtis.com|access-date=2020-08-13}}</ref><ref>{{Cite web|title=Stephen J Luecking|url=https://www.academia.edu/34722794|author=Steve Luecking|access-date=2020-08-13}}</ref>

Using a computer for ray tracing to generate shaded pictures was first accomplished by [[Arthur Appel]] in 1968.<ref>{{Cite book| last = Appel | first = Arthur
  | title = Proceedings of the April 30--May 2, 1968, spring joint computer conference on - AFIPS '68 (Spring)
 | chapter = Some techniques for shading machine renderings of solids
 | date = April 30, 1968
  | pages = 37–45
  | doi = 10.1145/1468075.1468082
  | s2cid = 207171023
 | url = http://graphics.stanford.edu/courses/Appel.pdf
 }}</ref> Appel used ray tracing for primary visibility (determining the closest surface to the camera at each image point) by tracing a ray through each point to be shaded into the scene to identify the visible surface. The closest surface intersected by the ray was the visible one. This non-recursive ray tracing-based rendering algorithm is today called "[[ray casting]]". His algorithm then traced secondary rays to the light source from each point being shaded to determine whether the point was in shadow or not.

Later, in 1971, Goldstein and Nagel of [[Mathematical Applications Group|MAGI (Mathematical Applications Group, Inc.)]]<ref>{{Citation
  | last1 = Goldstein | first1 = Robert
  | last2 = Nagel | first2 = Roger
  | title = 3-D Visual simulation
  | journal = Simulation
  | volume = 16
  | date = January 1971
  | pages = 25–31
  | issue = 1| doi = 10.1177/003754977101600104
 | s2cid = 122824395
 }}</ref> published "3-D Visual Simulation", wherein ray tracing was used to make shaded pictures of solids. At the ray-surface intersection point found, they computed the surface normal and, knowing the position of the light source, computed the brightness of the pixel on the screen. Their publication describes a short (30 second) film “made using the University of Maryland’s display hardware outfitted with a 16mm camera. The film showed the helicopter and a simple ground level gun emplacement. The helicopter was programmed to undergo a series of maneuvers including turns, take-offs, and landings, etc., until it eventually is shot down and crashed.” A ''[[CDC 6600]]'' computer was used. MAGI produced an animation video called ''MAGI/SynthaVision Sampler'' in 1974.<ref>{{cite AV media |url=https://archive.org/details/synthavisionsampler |title=Syntha Vision Sampler |date=1974 |via=[[Internet Archive]]}}</ref>

[[File:Flip Book Movie v2.gif|thumb|right|Flip book created in 1976 at Caltech]]Another early instance of ray casting came in 1976, when Scott Roth created a flip book animation in [[Bob Sproull]]'s computer graphics course at [[California Institute of Technology|Caltech]]. The scanned pages are shown as a video in the accompanying image. Roth's computer program noted an edge point at a pixel location if the ray intersected a bounded plane different from that of its neighbors. Of course, a ray could intersect multiple planes in space, but only the surface point closest to the camera was noted as visible. The platform was a DEC [[PDP-10]], a [[Tektronix]] storage-tube display, and a printer which would create an image of the display on rolling thermal paper. Roth extended the framework, introduced the term ''[[ray casting]]'' in the context of [[computer graphics]] and [[solid modeling]], and in 1982 published his work while at GM Research Labs.<ref>{{Citation
  | last1 = Roth | first1 = Scott D.
  | title = Ray Casting for Modeling Solids
  | journal = Computer Graphics and Image Processing
  | volume = 18
  | date = February 1982
  | pages = 109–144
  | doi = 10.1016/0146-664X(82)90169-1
  | issue = 2}}</ref>

[[J. Turner Whitted|Turner Whitted]] was the first to show recursive ray tracing for mirror reflection and for refraction through translucent objects, with an angle determined by the solid's index of refraction, and to use ray tracing for [[anti-aliasing]].<ref>Whitted T. (1979) ''[http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.156.1534 An Improved Illumination Model for Shaded Display]''. Proceedings of the 6th annual conference on Computer graphics and interactive techniques</ref> Whitted also showed ray traced shadows. He produced a recursive ray-traced film called ''The Compleat Angler''<ref>{{cite AV media|url=https://archive.org/details/thecompleatangler1978 |title=The Compleat Angler |date=1978 |publisher=Bell Laboratories |via=[[Internet Archive]]}}</ref> in 1979 while an engineer at Bell Labs. Whitted's deeply recursive ray tracing algorithm reframed rendering from being primarily a matter of surface visibility determination to being a matter of light transport. His paper inspired a series of subsequent work by others that included [[Distributed ray tracing|distribution ray tracing]] and finally [[Unbiased rendering|unbiased]] [[path tracing]], which provides the ''[[rendering equation]]'' framework that has allowed computer generated imagery to be faithful to reality.

For decades, [[global illumination]] in major films using [[computer-generated imagery]] was approximated with additional lights. Ray tracing-based rendering eventually changed that by enabling physically-based light transport. Early feature films rendered entirely using path tracing include ''[[Monster House (film)|Monster House]]'' (2006), ''[[Cloudy with a Chance of Meatballs (film)|Cloudy with a Chance of Meatballs]]'' (2009),<ref>{{Cite web
|title=Food for Laughs
|url=https://www.cgw.com/Publications/CGW/2009/Volume-32-Issue-9-Sep-2009-/Food-for-Laughs.aspx
|website=Computer Graphics World
}}</ref> and ''[[Monsters University]]'' (2013).<ref>{{Cite web|title=This Animated Life: Pixar's Lightspeed Brings New Light to Monsters University|url=https://thisanimatedlife.blogspot.com/2013/05/pixars-chris-horne-sheds-new-light-on.html|last=M.s|date=2013-05-28|website=This Animated Life|access-date=2020-05-26}}</ref>