## Presentation Device Driver Reference for OS/2

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### Bounds, Correlation, and Clipping

All presentation drivers must support bounds computation for both GPI bounds (COM_BOUND) and user bounds (COM_ALT_BOUND). Bounds are calculated on unclipped primitives for all operations that draw to the device, including AVIO functions. GPI bounds are passed in model space coordinates. User bounds are calculated in device-coordinate space. To prevent inaccuracies from occurring when the transform changes, the typical presentation driver maintains bounds in both coordinate sets in its instance data structure. It then accumulates the transforms as they occur.

Correlation is performed in page-coordinate space on the output of primitives that have been clipped only to the viewing limits and graphics field. Correlation is also performed on all operations that draw to the device, except the AVIO function. Note that hardcopy drivers are not required to perform correlation.