Suggestion
ObjectARX and .NET applications
AcEdInputPointFilter::processInputPoint() is the "last change" callout. It can be used to implement sophisticated "snapping" behavior by modifying the point value processed by the current point clients. This callback is made for points input by a "live user" (that is, eNotInteractive is not set in the pointHistory flags) as well as by various forms of program and script input. AutoCAD's OSNAP facility can be made to skip its processing on scripted input points by setting the $OSNAPCOORD system variable to 1 or 2, as documented in the AutoCAD product Help.
When a point filter is used for optional snapping purposes (that is, to guide the user to a more desirable point), you should disable this behavior when OSNAPCOORD is set to 1 or 2. However, if leaving an input point alone can cause corruption or error in an application, then ignore this variable setting.