事實(shí)上，并不需要直接對(duì)采用api_curve_spline生成的曲線進(jìn)行離散。ACIS提供了
bs2_curve/bs3_curve（bs指的是B-Spline)，你可以利用bs curve的插值函數(shù)（如
bs3_curve_interp）得到近似曲線bs3_curve，然后按一定間隔取該近似曲線上的
點(diǎn)，用這些點(diǎn)來構(gòu)造橡皮筋。
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以下代碼僅供參考：
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//----------------------------------------------------------------------
// Purpose---
//??? draw to a new SPAposition
//
//----------------------------------------------------------------------
void
ah_rubberband_spline::draw(
??? HEventInfo event
??? )
{
??? ENTER_FUNCTION("ah_rubberband_spline::draw");
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????? ah_rb_start_creation(LastView);
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????? //draw rubberband here
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????? if( m_numPoints == 2)
????? {
??????????? Display_Points[0] = (float)m_points[0].x();
??????????? Display_Points[1] = (float)m_points[0].y();
??????????? Display_Points[2] = (float)m_points[0].z();
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??????????? float* pt = Display_Points + 3;
??????????? *(pt++) = (float)m_points[1].x();
??????????? *(pt++) = (float)m_points[1].y();
??????????? *pt = (float)m_points[1].z();
??????????? m_numDisplayPoints = 2;
????? }
????? else if(m_numPoints > 2)
????? {
??????????? // Compute the spline
??????????? double fitol = 0.0;
??????????? bs3_curve bs = bs3_curve_interp(m_numPoints,m_points,
????????????????? *(SPAunit_vector *)NULL_REF,*(SPAunit_vector *)NULL_REF,
????????????????? fitol);
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??????????? // Get the number of positions to use for the display
??????????? m_numDisplayPoints = (m_numPoints ) * m_numPosPerSeg;
??????????? if( m_numDisplayPoints > MAX_DISPLAY_POSITIONS ) {
????????????????? m_numDisplayPoints = MAX_DISPLAY_POSITIONS;
??????????? } else if( m_numDisplayPoints < MIN_DISPLAY_POSITIONS ) {
????????????????? m_numDisplayPoints = MIN_DISPLAY_POSITIONS;
??????????? }
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??????????? // Get the SPAparameter range of the curve
??????????? SPAinterval range = bs3_curve_range(bs);
??????????? double t0 = range.start_pt();
??????????? double t1 = range.end_pt();
??????????? double dt = (t1-t0)/(m_numDisplayPoints - 1);
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??????????? // Evaluate to get the display positions
??????????? float* pt = Display_Points + 3;
??????????? for(int j=1; j<m_numDisplayPoints; j++) {
????????????????? double t = t0 + j*dt;
????????????????? SPAposition pos = bs3_curve_position(t, bs);
????????????????? *(pt++) = (float)(pos.x());
????????????????? *(pt++) = (float)(pos.y());
????????????????? *(pt++) = (float)(pos.z());
??????????? }
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??????????? // We are done with the curve so we can delete it
??????????? bs3_curve_delete(bs);
????? }
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????? if(m_numDisplayPoints>1)
????? {
??????????? HC_Insert_Polyline(m_numDisplayPoints,Display_Points);
????? }
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????? ah_rb_end_creation();
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}