We can set all the four settings mentioned under Display Resolution box in Options.
Before setting them through API, we will understand what each variable does.
VIEWRES: Arc and circle smoothness, this sets the resolution for objects in the viewport.
SPLINESEGS: Segments in a polyline curve, this sets number of line segments to be generated for each spline-fit polyline generated by the spline objects of the PEDIT command.
FACETRES: Rendered object smoothness, adjusts the smoothness of shaded and rendered objects and objects with hidden lines removed.
ISOLINES: Contour lines per surface, specifies the number of contour lines displayed on the curved surface of 3D solids.
void changeDispRes()
{
AcDbDatabase *pDb = acdbHostApplicationServices()->workingDatabase();
acutPrintf(_T("\n current SPLINESEGS value %d"),pDb->splinesegs());
acutPrintf(_T("\n current FACETRES value %d"),pDb->facetres());
acutPrintf(_T("\n current ISOLINES value %d"),pDb->isolines());
pDb->setSplinesegs(8);pDb->setFacetres(0.75);pDb->setIsolines(6);
AcDbObjectId curVportId = AcDbObjectId::kNull;
curVportId = acedActiveViewportId();
AcDbObjectPointer<AcDbViewportTableRecord> curVTR (curVportId,AcDb::kForWrite);
if(curVTR.openStatus() == Acad::eOk)
{
acutPrintf(_T("\n current VIEWRES value %d"),curVTR->circleSides());
curVTR->setCircleSides(100);
}
}