Function trackP1isoline

plugin/seq/plotPDF.cpp:1306–1358

//---------------------------------------------------------------------------
// P1 Finite Element (also used in P1nc : Non-Conforming Finite Element)
//---------------------------------------------------------------------------

void trackP1isoline( std::vector<double> &px, std::vector<double> &py,
		     const double *const vx, const double *const vy,
		     const double value, const double *const vf )
{
    const double TOLERANCE = 1e-12;

    const int nVertices_in_each_Element = 3;

    for(int i = 0; i < nVertices_in_each_Element; i++){

	const double &x0 = vx[i];
	const double &y0 = vy[i];
	const double &f0 = vf[i];
		    
	const double &x1 = vx[(i+1)%3];
	const double &y1 = vy[(i+1)%3];
	const double &f1 = vf[(i+1)%3];

	if( (value < f0) && (value < f1) ) // no cossing point
	    continue;
		
	if( (f0 < value) && (f1 < value) ) // no crossing point
	    continue;

	if( (fabs(f0-f1) < TOLERANCE) && (fabs(f0-value) < TOLERANCE) ){ // coinside: edge is isoline
	    px.push_back( x0 );
	    py.push_back( y0 );
	    px.push_back( x1 );
	    py.push_back( y1 );
	    continue;
	}

	const double t = (value-f0)/(f1-f0); // (1-t)*f0 + t*f1 = value
	const double x = (1-t)*x0 + t*x1;
	const double y = (1-t)*y0 + t*y1;

	px.push_back( x );
	py.push_back( y );
    }

    if( px.size() == 3 ){   // if f(x,y)==value on either vertex

	if( (px[0] == px[1]) && (py[0] == py[1]) ){
	    px[1] = px[2];
	    py[1] = py[2];
	}

	//if( (px[1] == px[2]) && (py[1] == py[2]) ) // node 0 is differ from node 1
	//if( (px[2] == px[0]) && (py[2] == py[0]) ) // node 0 is differ from node 1
    }

    return;
}