## Presentation Device Driver Reference for OS/2

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### Programming Considerations

Typical cursors are an arrow or a cross with an action point called the hot spot at the point of the arrow or the center of the cross. When the presentation driver draws a cursor, the origin of the image must be offset to place the action point at the required (X,Y) position. The required offset is specified in the call to GreSetCursor. Because the cursor entry point can be called at various times from many different places, the cursor routine uses semaphores to protect itself (protection is the responsibility of the presentation driver). Similarly, because cursor drawing can be a time-consuming operation, the display driver must also protect itself against re-entrance.

The display driver must resolve all interactions between cursor drawing at interrupt time and access to video hardware. While in the background, the display driver does not draw any cursor image.

Caution should be used when the display is a buffered device and the cursor is drawn into a bit map in the buffer. In this case, the display driver deletes the cursor and excludes it when a draw operation occurs at the cursor location. To do this, the driver does a "hit test" for each output operation to see if the cursor location is in the drawing area and to set a protection rectangle that is used to exclude the cursor.