Retained Mode Versus Immediate Mode-优快云博客

本文探讨了图形API的两种主要模式：保留模式API和即时模式API。保留模式API以声明方式构建场景，并由库维护场景模型；而即时模式API则直接在每一帧中发出绘制命令，应用程序自身跟踪场景状态。两种模式各有优缺点，保留模式API更易于使用但灵活性较低，即时模式API则提供更多的定制优化空间。

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ref: https://msdn.microsoft.com/en-us/library/windows/desktop/ff684178(v=vs.85).aspx

Graphics APIs can be divided into retained-mode APIs and immediate-mode APIs. Direct2D is an immediate-mode API. Windows Presentation Foundation (WPF) is an example of a retained-mode API.

A retained-mode API is declarative. The application constructs a scene from graphics primitives, such as shapes and lines. The graphics library stores a model of the scene in memory. To draw a frame, the graphics library transforms the scene into a set of drawing commands. Between frames, the graphics library keeps the scene in memory. To change what is rendered, the application issues a command to update the scene — for example, to add or remove a shape. The library is then responsible for redrawing the scene.

An immediate-mode API is procedural. Each time a new frame is drawn, the application directly issues the drawing commands. The graphics library does not store a scene model between frames. Instead, the application keeps track of the scene.

Retained-mode APIs can be simpler to use, because the API does more of the work for you, such as initialization, state maintenance, and cleanup. On the other hand, they are often less flexible, because the API imposes its own scene model. Also, a retained-mode API can have higher memory requirements, because it needs to provide a general-purpose scene model. With an immediate-mode API, you can implement targeted optimizations.

转载于:https://www.cnblogs.com/Searchor/p/6955555.html