DG Kernel (ActiveX) Documentation

This interface allows modification of the meshed surface, which implements it. Note that these modifications are low- level ones. Special care has to be taken to ensure that normals are setup and directed correctly. IMeshMods can be queried from IMesh interface.

Note that in case of a parametric surfaces (See Generic 3D Object) any modifications of the surface parameters (for example via IElement ) and subsequent call to UpdateSurface method of DG Kernel control or call for Update method of IModel interface will remove any modifications performed directly.

Methods of this interface requires a call to IModel.Update() or DG Kernel.UpdateSurface() for changes to appear in 3D view

See more at Meshed Surface Modifications

HRESULT SetVertexCoord(POSN vertex, double x, double y, double z )

Parameters

vertex - [in] position of the vertex in vertex list of the mesh.

x, y, z - [in] - New coordinates of the vertex.

Returns

S_OK in case of success.


Remarks:

This method allows direct manipulation of vertices in the mesh.

HRESULT SetNormal(POSN vertex, double vx, double vy, double vz )

Parameters

vertex - [in] position of the vertex in vertex list of the mesh.

vx, vy, vz- [in] - New coordinates of the normal.

Returns

S_OK in case of success.


Remarks:

This method allows direct manipulation or normals in the mesh. Note that when there is a singularity at the point, the surface can have several normals. In this case the modification is applied to the first normal. To modify other normals use IVertex interface, which can be obtained via path: IMesh->IMeshEx->IMeshEx.GetVertex->IVertex

HRESULT FixupNormals(double creaseDegrees, double tolerDegrees)

Parameters

creaseDegrees - [in] Crease angle in degrees.

tolerDegrees- [in] - Tolerance Angle in degrees.

Returns

S_OK in case of success.


Remarks:

This method recalculates all normals in the mesh. It is useful in Mesh Entities, which are normally created on import of objects from external formats. In this case normals are created directly by reading from the file without relating them to the geometry of the surface. FixupNormals allows correcting possible problems with supplied normals.

Note that the method should be used judiciously because sometimes problems with normals are caused by incorrect underlying mesh, in which case the result may be undesirable or there where some other reasons for supplying that sort of normals.

The Crease Angle is the angle used to determine whether two adjoin simplexes form a sharp edge. All neighbor simplexes with angle between their planes under creaseDegrees will be considered as a part of smooth surface.

If angle between the old normal and newly recalculated normal is less than the Tolerance Angle, the normal will be left unchanged. Set tolerDegrees to a negative or zero to skip performing this test.

Note: for singular vertexes (vertexes with several normals) the method may change numbering of the normals. See also IVertex.

HRESULT Offset(double dist)

Parameters

dist - [in] Offset distance. Can be negative


Remarks:

This method translates every vertex in the mesh along its normal by the specified distance. When a vertex has several normals (edge or corner) an average direction is used instead. dist can be negative, in which case the object will appear shrunk, otherwise the surface will appear expanded.

Note that generally offsetting a surface by large distance can create self interentitys and sharp edges.

HRESULT Clear()


Remarks:

Deletes all elements form the mesh. As the result the object will not have a visible surface

HRESULT ClearList(int dim)

Parameters

dim -[in] Identifies type of elements to delete: 0 - verticies, 1 - segments, 2 - simplexes


Remarks:

Deletes relevant elements from the list. Notice often as the result the mesh will be an invalid state. When mesh is not empty either new elements of dim type have to be added of elements of the other dimention need to be removed before rendering or otherwise using the object

HRESULT Begin()


Remarks:

Call this method to notify the software about series of mesh modification calls. See remarks for the End() method below. Call for this method should be followed by call to the End() method in the end of the series. This method affects only performance of mesh manipulation.

HRESULT End(int action)

Parameters

action - [in] Specifies method of updating normals to to be performed. Valid values are enumerated in EMeshModsAction. See remarks


Remarks:

Mesh modifications performed via calls to IMeshTopol.AddSimplex and IVertex.SetVertexCoord automatically recalculate normals at adjacent vertices or modify some internal data. This slows down execution when a large mesh is being built up or massively modified. To improve perfomance in this situation call IMeshMods.Begin() before the series of modification calls and call IMeshMods.End() in the end of the series. See more at Meshed Surface Modifications

Valid values for the action parameter are enumerated in EMeshModsAction:

eMeshActionNone - End the modification series without any additional calculations. Use this option when vertex normals are recalculated and set using IVertex.SetNormal() or other method by the application itself

eMeshActionNormalsFastApprox - Recalculate adjacent normals using approximate but fast method. Use this option for very dense mesh when precise normals are less important

eMeshActionNormalsMedium - Recalculate adjacent normals using method which is not completely accurate but gives good performance

eMeshActionNormalsFull - Recalculate adjacent normals using the most accurate calculation. This option is the slowest for large meshes

eMeshActionNormalsAuto - Automatically select one of the above methods depending on size of the mesh and performance of the computer. In this case the software estimates time to execute the calculation. If the estimated time is less than MeshModsAutoUpdateLimit0 eMeshActionNormalsFull algorithm is used. Otherwise if If the estimated time is less than MeshModsAutoUpdateLimit1 eMeshActionNormalsMedium algorithm is used. Otherwise eMeshActionNormalsFastApprox method is executed. Notice that MeshModsAutoUpdateLimit* parameters can be tuned in using the component context

The Begin()/End() sequence is not required and does not improve performance of a single isolated mesh modification call.

HRESULT SwapSide()

Changes positive side of the mesh. Re-orders vertices of every simplex to keep it in Counter Clock Wise order and changes direction of all normals to the opposite

HRESULT ToLocal(IFrame* frame)

Makes cordinates of all elements in this mesh relative to frame

HRESULT ToGlobal(IFrame* frame)

Assuming this mesh is relative to frame converts all elements to global axes