Retained mode

Retained mode in computer graphics is a major pattern of API design in graphics libraries,^[1] in which

• the graphics library, instead of the client, retains the scene (complete object model of the rendering primitives) to be rendered and
• the client calls into the graphics library do not directly cause actual rendering, but make use of extensive indirection to resources, managed – thus retained – by the graphics library.^[2] It does not preclude the use of double-buffering.^[3]

Immediate mode is an alternative approach. Historically, retained mode has been the dominant style in GUI libraries;^[4] however, both can coexist in the same library and are not necessarily exclusionary in practice.^[5]

Overview

Schematic explanation of a retained mode graphics API

In retained mode the client calls do not directly cause actual rendering, but instead update an abstract internal model (typically a list of objects) which is maintained within the library's data space. This allows the library to optimize when actual rendering takes place along with the processing of related objects.^[2]

Some techniques to optimize rendering include:

• managing double buffering^[6][7]
• treatment of hidden surfaces by backface culling^[8]/occlusion culling (Z-buffering)^[9]
• only transferring data that has changed from one frame to the next from the application to the library

Example of coexistence with immediate mode in the same library is OpenGL.^{[dubious – discuss][failed verification][10]} OpenGL has immediate mode functions that can use previously defined server side objects (textures, vertex buffers and index buffers, shaders, etc.) without resending unchanged data.^[11][12]

Examples of retained mode rendering systems include Windows Presentation Foundation,^[2] SceneKit on macOS,^[13] and PHIGS.

Schematic explanation of an immediate mode graphics API in contrast

See also

• Compositing window manager
• Scene graph