Editing Real-time computer graphics (section)

== Principles of real-time 3D computer graphics ==
{{Main|3D computer graphics}}
The goal of computer graphics is to generate [[Computer-generated imagery|computer-generated images]], or [[Film frame|frame]]s, using certain desired metrics. One such metric is the number of [[Image-based modeling and rendering|frames generated]] in a given second. Real-time computer graphics systems differ from traditional (i.e., non-real-time) rendering systems in that non-real-time graphics typically rely on [[Ray tracing (graphics)|ray tracing]]. In this process, millions or billions of rays are traced from the [[Virtual camera system|camera]] to the [[Virtual world|world]] for detailed rendering—this expensive operation can take hours or days to render a single frame.
[[File:Real-time Raymarched Terrain.png|thumb|[[Terrain rendering]] made in 2014]]
Real-time graphics systems must render each image in less than 1/30th of a second. Ray tracing is far too slow for these systems; instead, they employ the technique of [[Z-buffering|z-buffer]] [[triangle rasterization]]. In this technique, every object is decomposed into individual primitives, usually triangles. Each triangle gets [[Shader#Vertex shaders|positioned, rotated and scaled]] on the screen, and [[Rasterisation|rasterizer]] hardware (or a software emulator) generates pixels inside each triangle. These triangles are then decomposed into atomic units called [[Fragment (computer graphics)|fragments]] that are suitable for displaying on a [[Computer monitor|display screen]]. The fragments are drawn on the screen using a color that is computed in several steps. For example, a [[Texture mapping|texture]] can be used to "paint" a triangle based on a stored image, and then [[shadow mapping]] can alter that triangle's colors based on line-of-sight to light sources.
{{See also|Level of detail (computer graphics)}}

===Video game graphics===
Real-time graphics optimizes image quality subject to time and hardware constraints. GPUs and other advances increased the image quality that real-time graphics can produce. GPUs are capable of handling millions of triangles per frame, and modern [[DirectX]]/[[OpenGL]] class hardware is capable of generating complex effects, such as [[shadow volume]]s, [[motion blur]]ring, and [[Shader#Geometry shaders|triangle generation]], in real-time. The advancement of real-time graphics is evidenced in the progressive improvements between actual [[gameplay]] graphics and the pre-rendered [[cutscenes]] traditionally found in video games.<ref name="hoso">{{cite book|url={{google books |plainurl=y |id=fvSbCgAAQBAJ|page=86}}|title=How Software Works: The Magic Behind Encryption, CGI, Search Engines and Other Everyday Technologies.|last=Spraul|first=V. Anton|publisher=No Starch Press|year=2013|isbn=978-1593276669|page=86|access-date=24 September 2017}}</ref> Cutscenes are typically rendered in real-time—and may be [[interactivity|interactive]].<ref name="tvge">{{cite book|url={{google books |plainurl=y |id=XiM0ntMybNwC|page=86}}|title=The Video Game Explosion: A History from PONG to Playstation and Beyond|last=Wolf|first=Mark J. P.|publisher=ABC-CLIO|year=2008|isbn=9780313338687|page=86|access-date=24 September 2017}}</ref> Although the gap in quality between real-time graphics and traditional off-line graphics is narrowing, offline rendering remains much more accurate.

=== Advantages ===
[[File:FaceRig with full body.png|thumb|Real-time full body and [[face tracking]]]]

Real-time graphics are typically employed when interactivity (e.g., player feedback) is crucial. When real-time graphics are used in films, the director has complete control of what has to be drawn on each frame, which can sometimes involve lengthy decision-making. Teams of people are typically involved in the making of these decisions.

In real-time computer graphics, the user typically operates an input device to influence what is about to be drawn on the display. For example, when the user wants to move a character on the screen, the system updates the character's position before drawing the next frame. Usually, the display's response-time is far slower than the input device—this is justified by the immense difference between the (fast) response time of a human being's motion and the (slow) [[Persistence of vision|perspective speed of the human visual system]]. This difference has other effects too: because input devices must be very fast to keep up with human motion response, advancements in input devices (e.g., the current{{when|date=August 2019}} Wii remote) typically take much longer to achieve than comparable advancements in display devices.

Another important factor controlling real-time computer graphics is the combination of [[Game physics|physics]] and [[Computer animation|animation]]. These techniques largely dictate what is to be drawn on the screen—especially ''where'' to draw objects in the scene. These techniques help realistically imitate real world behavior (the [[Dimension#Time|temporal dimension]], not the [[Dimension|spatial dimensions]]), adding to the computer graphics' degree of realism.

Real-time previewing with [[graphics software]], especially when adjusting [[computer graphics lighting|lighting effects]], can increase work speed.<ref name="dili">{{cite book|url={{google books |plainurl=y |id=IRrsAQAAQBAJ|page=442}}|title=Digital Lighting and Rendering: Edition 3|last=Birn|first=Jeremy|publisher=New Riders|year=2013|isbn=9780133439175|page=442|access-date=24 September 2017}}</ref> Some parameter adjustments in [[fractal generating software]] may be made while viewing changes to the image in real time.