View source for Immediate mode (computer graphics)

{{Short description|Graphics libraries API design pattern}}

'''Immediate mode''' is an [[Application programming interface|API design pattern]] in computer graphics libraries, in which
* the [[Client (computing)|client]] calls directly cause [[Rendering (computer graphics)|rendering]] of graphics objects to the display, or in which
* the data to describe rendering primitives is inserted [[Engineering:Film frame|frame]] by frame directly from the [[Client (computing)|client]] into a command list (in the case of ''immediate mode primitive rendering''),
without the use of extensive indirection – thus'' '''immediate''' ''– to retained resources.<ref name="rm_vs_im">{{Cite web
| title = Retained Mode Versus Immediate Mode
| work = Win32 apps
| author = Quinn Radich
| publisher = Microsoft
| date = May 30, 2018
| access-date = 21 December 2019
| url = https://docs.microsoft.com/en-us/windows/win32/learnwin32/retained-mode-versus-immediate-mode
| quote = 
}}</ref> It does not preclude the use of [[Multiple buffering|double-buffering]].

[[Retained mode]] is an alternative approach. Historically, retained mode has been the dominant style in [[Graphical user interface|GUI]] libraries;<ref name="feldmeier">{{Cite web
| title = GUI Programming
| first = Alex
| last = Feldmeier
| work = UWP Computer Science and Software Engineering Technical Report
| date = October 12, 2013
| access-date = 22 December 2019
| url = http://people.uwplatt.edu/~yangq/CSSE411/csse411-materials/f13/feldmeiera-gui%20_programming.doc
| language = 
| quote = Retained mode has been the standard for years. Just about every GUI is in retained mode.
}} </ref> however, both can coexist in the same library and are not necessarily exclusive in practice.

== Overview ==
[[File:Immediate-mode-graphics-api.png|thumb|right|Schematic explanation of an immediate mode graphics API]]

In immediate mode, the scene (complete [[Object model|object model]] of the rendering primitives) is retained in the [[Computer memory|memory space]] of the [[Client (computing)|client]], instead of the [[Software:Graphics library|graphics library]]. This implies that in an immediate mode application the lists of graphical objects to be [[Rendering (computer graphics)|rendered]] are kept by the [[Client (computing)|client]] and are not saved by the graphics library API. The application must re-issue all drawing commands required to describe the entire scene each time a new [[Engineering:Film frame|frame]] is required, regardless of actual changes. This method provides on the one hand a maximum of control and flexibility to the application program, but on the other hand it also generates continuous work load on the [[Central processing unit|CPU]].

[[File:Retail-mode-graphics-api.png|thumb|right|Schematic explanation of a retained mode graphics API in contrast]]

Examples of immediate mode rendering systems include [[Software:Direct2D|Direct2D]],<ref name="rm_vs_im" /> [[Software:OpenGL|OpenGL]]<ref>{{Cite web
| title = OpenGL
| access-date = 4 May 2020
| url = https://www.opengl.org/
}}</ref> 
and [[Quartz (graphics layer)|Quartz]].<ref name="book_iOS">{{Cite book
| title = iOS and macOS Performance Tuning: Cocoa, Cocoa Touch, Objective-C, and Swift
| first = Marcel
| last = Weiher
| publisher = Addison-Wesley Professional
| date = Feb 24, 2017
| access-date = 22 December 2019
| url = https://books.google.com/books?id=1kY2DgAAQBAJ&q=retained%20mode%20APIs
| language =  
| quote = The primary graphics API Quartz and OpenGL are both immediate-mode APIs
| isbn = 9780133085532
}}</ref> There are some [[Immediate mode GUI|immediate mode GUI]]s that are particularly suitable when used in conjunction with immediate mode rendering systems.

== Immediate mode primitive rendering ==

Primitive vertex attribute data may be inserted [[Engineering:Film frame|frame]] by frame into a command buffer by a rendering API. This involves significant bandwidth and processor time (especially if the [[Graphics processing unit|graphics processing unit]] is on a separate bus), but may be advantageous for data generated dynamically by the CPU. It is less common since the advent of increasingly versatile shaders, with which a [[Graphics processing unit|graphics processing unit]] may generate increasingly complex effects without the need for CPU intervention.

== Immediate mode rendering with vertex buffers ==

Although drawing commands have to be re-issued for each new [[Engineering:Film frame|frame]], modern systems using this method are generally able to avoid the unnecessary duplication of more memory-intensive display data by referring to that unchanging data (via indirection) (e.g. textures and vertex buffers) in the drawing commands.

== See also ==

* [[Immediate mode GUI]]
* [[Display list]]
* [[Retained mode]], usually contrasted with immediate mode
* [[Scene graph]]

== References ==

{{Reflist}}

[[Category:Computer graphics]]

{{Sourceattribution|Immediate mode (computer graphics)}}