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User input validation for Arc/Line splines

Programmatically geometry of an 3DS object is modified via call to SetParam() or SetNamedParam() mathods of IElement. Quite often the new value of the parameter makes geometry of the model invalid. For example when radius of an arc is too small to connect its ends.  In this case above methods return without changing anything in the geometry. In C++ this situation can be detected from the returned HRESULT, which will be equal to DI_E_INVALIDGEOMETRY (defined in <Install dir>\Samples\VC\IncludeDIInterface.h). Higher level development environments like Visual Basic and .NET can use IElem interface instead.

IElem interface is analogous to IElement. The only difference is that SetParam and SetNamedParam methods have additional parameter, which acts as the return value for  This return value notifies the caller if the new value was accepted, rejected or did not have any effect on the model.  

If IElem is implemented it can be queried from the correspondent IElement interface. Note that some simple objects (IElement implemented by an axial point) always accept its modification, and hence do not implement IElem interface.

After successful call to SetParam method and before any other modification of  the same parameter, there should be a call to UpdateSurface method of the KernelCAD control or call to Update method of the IModel interface. Normally you would make all requested modifications for the user input (one modification per parameter) and call UpdateSurface methods to recalculates the surface and display the result for viewing in 3D. 

 

Note that successful return from SetParam and SetNamedParam means that only a simple validation succeeded. The geometry of the model may still be invalid and can be rejected later during the call to UpdateSurface() method of the control. In the later case all modifications since the previous call to UpdateSurface() will be discarded.

All angles in the software are internally represented in radians, so when the parameter is an angle, new value should be in range (-PI, PI] otherwise the methods returns DI_E_INVALIDGEOMETRY and the parameter will remain unchanged.

See also Parameters, Interface List