Computer graphics lighting: Difference between revisions

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{{short description|Simulation of light in computer graphics}}

'''Computer graphics lighting''' isencompasses the collectionrange of techniques used to simulate light inwithin [[computer graphics]] scenes. WhileThese lightingmethods techniques offer flexibilityvary in the[[computational level of detail and functionality availablecomplexity]], theyoffering alsoartists operateflexibility atin differentboth levelsvisual of computational demanddetail and [[Computational complexity|complexity]]performance. Graphics artistsprofessionals can chooseselect from a varietywide array of [[light sourcessource]]s, models[[lighting model]]s, [[shading]] techniques, and effects to suitmeet the needsspecific requirements of each applicationproject.

== Light sources ==

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=== Point ===

Point sources emit light from a single point in all directions, with the intensity of the light decreasing with distance.<ref name=":72">{{Cite web|url=https://www.cs.uic.edu/~jbell/CourseNotes/ComputerGraphics/LightingAndShading.html|title=Intro to Computer Graphics: Lighting and Shading|website=www.cs.uic.edu|access-date=2019-11-05}}</ref> An example of a point source is a standalone light bulb.<ref name=":8">{{Cite web|url=http://www.bcchang.com/immersive/ygbasics/lighting.html|title=Lighting in 3D Graphics|website=www.bcchang.com|access-date=2019-11-05}}</ref>

[[File:Real-time Raymarched Terrain.png|thumb|309x309px|A directional light source illuminating a terrain.]]

=== Directional ===

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=== Lightwarp ===

A lightwarp is a technique of which an object in the geometrical world [[refracts]] light based on the [[Unit vector|direction]] and [[Intensity (physics)|intensity]] of the light. The light is then [[Wave function|warped]] using an ambient diffuse term with a range of the [[color spectrum]]. The light then may be [[reflectively]] scattered to produce a higher [[depth of field]], and [[refracted]]. The technique is used to produce a [[Style_(visual_arts)#Stylization|unique rendering style]] and can be used to limit [[overexposure]] of objects. Games such as [[Team Fortress 2]] use the rendering technique to create a [[cartoon]] [[cel shaded]] stylized look.<ref>{{Cite book|chapter-url=https://hal.inria.fr/inria-00449828|chapter=Radiance Scaling for Versatile Surface Enhancement|first1=Romain|last1=Vergne|first2=Romain|last2=Pacanowski|first3=Pascal|last3=Barla|first4=Xavier|last4=Granier|first5=Christophe|last5=Schlick|title=Proceedings of the 2010 ACM SIGGRAPH symposium on Interactive 3D Graphics and Games |date=February 19, 2010|pages=143–150 |publisher=ACM|via=hal.inria.fr|doi=10.1145/1730804.1730827|isbn=9781605589398 |s2cid=18291692 }}</ref>

===HDRI===

HDRI stands for High dynamic range image and is a 360° image that is wrapped around a [[3D modeling|3D model]] as an outdoor setting and uses the sun typically as a light source in the sky. The [[Texture mapping|textures]] from the model can reflect the direct and [[Shading#Ambient lighting|ambient light]] and colors from the HDRI.<ref>{{cite web | url=https://visao.ca/what-is-hdri/#:~:text=High%20dynamic%20range%20images%20are,look%20cartoonish%20and%20less%20professional. | title=What are HDRI images? | date=13 January 2021 }}</ref>

== Lighting interactions ==

In computer graphics, the overall effect of a light source on an object is determined by the combination of the object's interactions with it usually described by at least three main components.<ref name=":82">{{Cite web|url=http://www.bcchang.com/immersive/ygbasics/lighting.html|title=Lighting in 3D Graphics|website=www.bcchang.com|access-date=2019-11-05}}</ref> The three primary lighting components (and subsequent interaction types) are diffuse, ambient, and specular.<ref name=":82" />

[[File:Phong components revised.png|thumb|544x544px|Decomposition of lighting interactions.]]

=== Diffuse ===

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Polygonal [[shading]] is part of the [[Rasterisation|rasterization]] process where [[3D computer graphics|3D]] models are drawn as [[2D computer graphics|2D]] pixel images.<ref name=":4">{{Cite web|url=https://cglearn.codelight.eu/pub/computer-graphics/shading-and-lighting|title=Computer Graphics: Shading and Lighting|website=cglearn.codelight.eu|access-date=2019-10-30}}</ref> Shading applies a lighting model, in conjunction with the geometric attributes of the 3D model, to determine how lighting should be represented at each [[Fragment (computer graphics)|fragment]] (or pixel) of the resulting image.<ref name=":4" /> The [[Polygon mesh|polygons]] of the 3D model store the geometric values needed for the shading process.<ref name=":11">{{Cite web|url=http://math.hws.edu/graphicsbook/c4/s1.html|title=Introduction to Computer Graphics, Section 4.1 -- Introduction to Lighting|website=math.hws.edu}}</ref> This information includes [[Vertex (geometry)|vertex]] positional values and [[Normal (geometry)|surface normals]], but can contain optional data, such as [[Texture mapping|texture]] and [[Bump mapping|bump]] maps.<ref>{{Cite web|url=https://www.khronos.org/opengl/wiki/Vertex_Specification#Primitives|title=Vertex Specification - OpenGL Wiki|website=www.khronos.org|access-date=2019-11-06}}</ref>

[[File:Flatshading00.png|alt=|thumb|165x165px|An example of flat shading.]]

[[File:Gouraudshading01.png|alt=|thumb|165x165px|An example of Gouraud shading.]]

[[File:Phongshading00.png|alt=|thumb|165x165px|An example of Phong shading.]]

=== Flat shading ===

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== Lighting effects ==

[[File:Miroir-cercle.jpg|thumb|A reflective material demonstrating caustics.]]

=== Caustics ===