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IBoolSectionEx Interface

IBoolSectionEx interface is an enhanced version of IBoolSection, which returns information about the intersection curve of the two objects.

See also Cross View sample and BoolOp Sample

• Execute
• Execute2
• CreateExtendedContext
• Execute3
• Clip
• Clip2

HRESULT Execute( EBooleanOperation operation, ISection* object, VARIANT_BOOL createIntersLine, IArray** edges )

Parameters

operation - [in] member of EBooleanOperation enumeration indicating the operation to perform

object - [in] reference to the second object for the operation. (The first object is the section which implements this IBoolSectionEx interface)

createIntersLine - [in] If true a set of Line Strip objects representing intersection line will be created and added as child of the first section (the section where this interface was queried form). See remarks for more details

edges - [out, retval] Array of isolated intersection loops. Each element has type IArray, elements in the later array have type IVertex. See remarks

Remarks

Performs operation indicated by operation on the section where this IBoolSectionEx was queried from and object. This method also allows performing subtraction of a programmatically defined plane from the object. See details in Planar Subtract.

If createIntersLine parameter is true a new empty object will be created and added as new child of the first section. The object will act as a group (container for its children). The objects will have one or more child objects of Line Strip type one per linked piece of intersection. For example, subtraction of a long and thin cylinder from a sphere will have two closed isolated intersection loops. In that case the newly added object will have two children one per each intersection loop. Coordinates of points in the lines and other information can be obtained via ISectionPointSet and ISectionLineStrip queried form the relevant child. See BoolOp Sample for an example.

The returned edges array contains information abut the isolated linked intersection loops. Each loop is an array (IArray) of IVertex elements, which can be used to obtain coordinates and normals to the surface at the intersection points.  See Cross View sample for an example. This calculation is not performed and NULL will be returned if createIntersLine is false.

IVertex obtained above contains all normals to the resulting surface. The most frequent case when two surfaces are smooth around the intersection curve the vertex contains two normals on the left (side of surface of the first object, where this interface was queried form) and right hand side of the intersection curve. Often there are several normals on each side, for example when intersection curve crosses an edge of either surface. In some cases (planar subtract or case when the second object is not a closed surface and edges do not intersect) the intersection curve becomes an edge of the resulting surface, so the vertex can have only single normal, the one which belongs to the first surface.

To find out which normals in the vertex belong to which side of the curve query IUserData from the IVertex and call IUserData.GetData. The returned cnt number is count of normals which belong to the first surface (normals on the left). Normals 0 to cnt-1 in the vertex belong to the first surface, the rest belong to the second surface.