获取块索引的XCLIP边界（Get the XCLIPped boundary of BlockReferences）
问题：How can I get the XCLIPped boundary of BlockReferences?
解答：
The boundary data is stored in an AcDbSpatialFilter object which in turn is stored in an entry name 'SPATIAL' in the extension dictionary 'ACAD_FILTER' of the XCLIPped block reference. More specifically, AcDbSpatialFilter::getDefinition() does the trick. Please bear one point in mind though. That is, it returns the points list of the XCLIPped boundary with the same coordinate system as the block definition. We need to transform those points by the block definition transform matrix manually. Refer to the ObjectARX Reference Guide for description of AcDbSpatialFilter::getClipSpaceToWCSMatrix() and AcDbSpatialFilter::getOriginalInverseBlockXform(). The full code is appended as follows:
// Draw a red polyline by the given points etc.
//--------------------------------------------------
static BOOL drawAPlineWithPropertiesFromBlockRef(AcGePoint2dArray pts,
AcDbBlockReference* ref, double elevation, AcGeVector3d& normal)
{
AcDbPolyline *pl = new AcDbPolyline;
AcDbObjectId owner;
pl->setDatabaseDefaults();
pl->setClosed(Adesk::kTrue);
pl->setThickness(0.0);
if (ref != NULL) {
owner=ref->ownerId();
pl->setPropertiesFrom(ref);
}
pl->setNormal(normal);
for (int i=0; i < pts.length(); i++)
{
pl->addVertexAt(i, pts);
}
pl->setElevation(elevation);
pl->setColorIndex(1); // Red
AcDbBlockTableRecord *rec=NULL;
acdbOpenObject(rec, owner, AcDb::kForWrite);
if (rec != NULL)
{
AcDbObjectId id;
rec->appendAcDbEntity(id, pl);
pl->close();
rec->close();
}
else
{
delete pl;
return false;
}
return true;
} // End of drawAPlineWithPropertiesFromBlockRef()
// Get the boundary from a Block Reference given by the blk parameter.
// Transform that boundary to the WCS.
//-------------------------------------------------------------------
static BOOL GetBlockClippingPolyline(ads_name blk)
{
BOOL ret = FALSE;
AcDbBlockReference *ref = NULL;
AcDbObjectId insId = AcDbObjectId::kNull;
acdbGetObjectId(insId, blk);
if (acdbOpenObject(ref, insId, AcDb::kForRead) != Acad::eOk)
return ret;
// Find the clipping object (AcDbSpatialFilter) in the ExtDict of the BlockRef
AcDbObjectId extDicId = ref->extensionDictionary();
if( extDicId == AcDbObjectId::kNull )
return ret;
AcDbDictionary *extDict=NULL, *acadFilterDict=NULL;
if (acdbOpenObject(extDict, extDicId, AcDb::kForRead) != Acad::eOk)
return ret;
Acad::ErrorStatus err = extDict->getAt(_T("ACAD_FILTER"), (AcDbObject*&)acadFilterDict, AcDb::kForRead);
extDict->close();
if( err != Acad::eOk )
return ret;
AcDbSpatialFilter *filter=NULL;
err = acadFilterDict->getAt(_T("SPATIAL"), (AcDbObject*&)filter, AcDb::kForRead);
acadFilterDict->close();
if ( err != Acad::eOk)
return ret;
// Get the transform matrix stored in the XClip boundary
AcGeMatrix3d xformInBoundary = filter->getClipSpaceToWCSMatrix( xformInBoundary );
// and the transform of the BlockRef at the time when the Filter was set
AcGeMatrix3d xformRefOrig = filter->getOriginalInverseBlockXform( xformRefOrig );
// Get the transform matrix that the current BlockRef has, so, we can find the difference
// with the xformRefOrig
AcGeMatrix3d refMatrix = ref->blockTransform();
refMatrix = refMatrix.postMultBy(xformRefOrig );
// Calculate the final transform matrix which applies to the points
// returned from filter->getDefinition().
AcGeMatrix3d finalMatrix = refMatrix.postMultBy(xformInBoundary);
AcGePoint2dArray pts;
AcGePoint3dArray pts3d;
AcGeVector3d normal;
double elevation = 0, frontClip = 0, backClip = 0;
Adesk::Boolean enabled= false;
// Get all boundary points
if (filter->getDefinition(pts, normal, elevation, frontClip, backClip, enabled) == Acad::eOk)
{
// Rectanglar boundary
if (pts.length() == 2)
{
AcGePoint2d p1(pts.x, pts.y);
AcGePoint2d p3(pts.x, pts.y);
pts.insertAt(1, p1);
pts.insertAt(3, p3);
}
// Transform all points with the transform matrix we calculated
for(int i=0; i<pts.length(); i++)
{
AcGePoint2d pt2d;
AcGePoint3d pt3d;
pt2d = pts;
pt3d = pt2d; pt3d = pt2d; pt3d = 0;
pt3d.transformBy(finalMatrix);
pts3d.append(pt3d);
}
}
// Get the new normal and new ECS information for the polyline.
AcGeVector3d xfnorm = normal.transformBy(finalMatrix);
AcGeMatrix3d plineECS;
AcDbPolyline* pline = new AcDbPolyline();
pline->setNormal(xfnorm);
pline->getEcs(plineECS);
delete pline; pline = NULL;
AcGeMatrix3d plineECSInv = plineECS.inverse();
double xfelev = 0.0;
for (int i = 0; i < pts.length(); i++)
{
pts.x = pts3d.x;
pts.y = pts3d.y;
if (i == 0)
xfelev = pts3d.z;
// Should be identical to within roundoff
assert(fabs(xfelev - pts3d.z) < 1.0e-10);
}
// Show the boundary
drawAPlineWithPropertiesFromBlockRef(pts, ref, xfelev, xfnorm);
filter->close();
ref->close();
return true;
} // End of GetBlockClippingPolyline()
// "MClip" test command for the GetBlockClippingPolyline() function.
static void MMRCplusplus_MClip(void)
{
ads_name en;
AcGePoint3d pt;
if (acedEntSel(_T("\nSelect an INSERT clipped by XCLIP command: "), en, asDblArray(pt)) != RTNORM)
{
acutPrintf(_T("\nNothing selected"));
return;
}
assert(GetBlockClippingPolyline(en)==TRUE);
}
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