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What exactly is the Immediate Mode?

A question that arises when we look at the two modes available in Direct3D, is that what are the differences between the two modes and why these modes at all?

The major difference between the retained mode and the immediate mode that has lead to this classification is the ability to address the data even after it has been rendered.

If an application has access to the data being displayed, after it is rendered, without change in its basic structure, then the application is said to have the ability to retain the object information and hence an application working in this mode or using such a facility is working in the retained mode. For example, if the application is able to address the data points of a cube even after it has been rendered, then the application is said to retain the data being rendered and hence is working in the retained mode.

As compared to this, if the application cannot access the data that was rendered, after rendering its, then the application is said to be working in the immediate mode. In the immediate mode, once the data is rendered, it is lost for ever to the developer. The rendered data might still be available, but the data is no longer 3D data, but 2D pixels.

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