## Presentation Device Driver Reference for OS/2

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### Simulated Functions

These functions are simulated by handling routines in the graphics engine and are called through pointers in the default dispatch table. Any simulated functions can be "hooked" to improve performance or to exploit special features of the device. Hooking is performed by overwriting the pointer in the presentation driver's copy of the dispatch table with a pointer to the presentation driver's handling routine. If this is done, the original pointer must be saved in order to pass calls to the engine's handling routine.

When the presentation driver has hooked a function, all calls to that function are passed through the dispatch table directly to the driver's handling routine. If the presentation driver cannot completely handle a hooked function, it can pass the call to the engine's routine for completion.

The functions in this section are grouped according to the conditional include sections of the header file:

Arc functions (INCL_GRE_ARCS)
Area and Path functions (INCL_GRE_PATHS)
Clip functions (INCL_GRE_CLIP)
Line functions (INCL_GRE_LINE)
Palette Manager functions (INCL_GRE_PALETTE)
Region functions (INCL_GRE_REGIONS)
Transform functions (INCL_GRE_XFORMS)

Each description defines what the handling routine is expected to do, the parameters passed to the routine, and the values that the routine returns.