Pointer to the current plug-in instance. The area to invalidate, specified in a coordinate system that originates at the top left of the plug-in.
Before a windowless plug-in can repaint or refresh part of its drawing area, the plug-in must first invalidate the area with either NPN_InvalidateRect or NPN_InvalidateRegion.
NPN_InvalidateRegion causes the NPP_HandleEvent method to pass an update event or a paint message to the plug-in. If a plug-in calls this method, it receives a paint message later. The browser redraws invalid areas of the document and windowless plug-ins at regularly timed intervals. To force a paint message, the plug-in can call NPN_ForceRedraw after calling this method.