Retained mode

Retained mode in computer graphics is a major pattern of API design in graphics libraries, 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.[1] It does not preclude the use of double-buffering.

Immediate mode is an alternative approach. Historically, retained mode has been the dominant style in GUI libraries[2]; however, both can coexist in the same library and are not necessarily exclusionary in practice.

Overview

Schematic explanation of a retained mode graphics API

In retained mode the client calls do not directly cause actual rendering, but instead updates 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.[1]

Some techniques to optimize rendering include:

• managing double buffering[3][4]
• treatment of hidden surfaces by backface culling[5]/occlusion culling (Z-buffering)[6]
• 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.[7] 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.

Examples of retained mode rendering systems include Windows Presentation Foundation,[1] SceneKit on macOS,[8] and PHIGS.

Schematic explanation of an immediate mode graphics API in contrast

There is another major pattern of API design in graphics libraries – the Immediate mode.

See also

• Compositing window manager
• Scene graph
• Immediate mode

References

1. Quinn Radich (May 30, 2018). "Retained Mode Versus Immediate Mode". Win32 apps. Microsoft. Retrieved 21 December 2019.
2. Feldmeier, Alex (October 12, 2013). "GUI Programming". UWP Computer Science and Software Engineering Technical Report. Retrieved 22 December 2019. Retained mode has been the standard for years. Just about every GUI is in retained mode.
3. "OpenGL double buffering". Retrieved 7 May 2020.
4. "DirectX double buffering". Retrieved 7 May 2020.
5. "OpenGL face culling". Retrieved 7 May 2020.
6. "DirectX occlusion culling". Retrieved 7 May 2020.
7. "OpenGL". Retrieved 4 May 2020.
8. Weiher, Marcel (Feb 24, 2017). iOS and macOS Performance Tuning: Cocoa, Cocoa Touch, Objective-C, and Swift. Addison-Wesley Professional. ISBN 9780133085532. Retrieved 22 December 2019. SceneKit and SpriteKit on the other hand are retained-mode APIs