Zooming functionality is included in the BiDisp.DLL . If you have a display to view an image then you can use these functions for zooming.
You can use these functions for example in the mouse message handling functions:

1, Mouse left button down
Use the BZoomStart function for initialize zooming.

2, Mouse moves
Use the BZoomupdate function for updating selection rectangle on the view.

3, Mouse left button up
Use the BZoomEnd function to recalculate the origo and the scaling factor for the display functions.

Zoom with step functions:
BZoomGetScaleSteps : Returns the current scaling settings.
BZoomSetScaleSteps : You can define scaling factor tables for zooming. This is useful for zooming by specific steps.
BZoomStep : This function should be used for zooming by specific step.

Regards,
Technical Support Team