内核模式GDI

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GDI from the Driver's Perspective

GDI is the intermediary support between a Microsoft Windows NT-based graphics driver and an application. Applications call Microsoft Win32 GDI functions to make graphics output requests. These requests are routed to kernel-mode GDI. Kernel-mode GDI then sends these requests to the appropriate graphics driver, such as a display driver or printer driver. Kernel-mode GDI is a system-supplied module that cannot be replaced.
（app-GDI32-Graph Engine-Graph Driver，见下图）

GDI communicates with the graphics driver through a set of graphics device driver interface (graphics DDI) functions. These functions are identified by their Drv prefix. Information is passed between GDI and the driver through the input/output parameters of these entry points. The driver must support certain DrvXxx functions for GDI to call. The driver supports GDI's requests by performing the appropriate operations on its associated hardware before returning to GDI.
（Graph Engine和Graph Driver使用DDI接口通信，函数前缀 Drv。驱动完成Kernel-mode GDI请求后才能返回）

GDI includes many graphics output capabilities in itself, eliminating the need for the driver to support these capabilities and thereby making it possible to reduce the size of the driver. GDI also exports service functions that the driver can call, further reducing the amount of support the driver must provide. GDI service functions are identified by their Eng prefix, and functions that provide access to GDI-maintained structures have names in the form XxxOBJ_Xxx.

（Graph Engine（GDI）拥有多个图形输出能力集，降低了驱动需要完成的功能及减小驱动的体积。GDI导出一些自身的函数供驱动调用，使用Eng前缀。这些导出函数中由GDI管理的结构体以XxxOBJ_Xxx命名）

The following figure shows this flow of communication.