Function findSegment

plugin/seq/plotPDF.cpp:2759–2801

bool isSegment( const std::vector<double> &cx, const std::vector<double> &cy, const int i )
{
    // examine a part of cubic Bezier curve (i--i+1--i+2--i+3) is a segment or not.
    return (cx[i] == cx[i+1]) && (cy[i] == cy[i+1]) && (cx[i+2] == cx[i+3]) && (cy[i+2] == cy[i+3]);
}

int findSegment( const double x, const double y,
		 const std::vector<double> &cx, const std::vector<double> &cy )
{
    const double EPS = 1e-10;

    // cx and cy are control points of cubic Bezier curve.
    // (cx[0],cy[0]) -- (cx[1],cy[1]) -- (cx[2],cy[2]) -- (cx[3],cy[3])  : 0
    //               -- ...
    //               -- (cx[3i+1],cy[3i+1]) -- (cx[3i+2],cy[3i+2]) -- (cx[3i+3],cy[3i+3]) : 3i

    for(size_t i = 0; i+3 < cx.size(); i += 3){

	if( !isSegment( cx, cy, i ) )
	    continue;

	const double &x0 = cx[i];   const double &y0 = cy[i];
	const double &x1 = cx[i+3]; const double &y1 = cy[i+3];
	
	// if (x,y) \in (x0,y0) -- (x1,y1), then
	// x = (1-t)*x0 + t*x1 and y = (1-t)*y0 + t*y1, 0 <= t <= 1
	// <=> x = x0 - t*x0 + t*x1, y = y0 - t*y0 + t*y1
	// <=> t = (x-x0) / (x1-x0) = (y-y0) / (y1-y0)

	if( fabs( (x-x0)*(y1-y0) - (x1-x0)*(y-y0) ) > EPS )
	    continue;

	if( fabs( x1-x0 ) > EPS ){
	    const double t = (x-x0) / (x1-x0);

	    if( (-EPS < t) && (t < 1+EPS) )
		return i;
	}

	if( fabs( y1-y0 ) > EPS ){
	    const double t = (y-y0) / (y1-y0);
	    
	    if( (-EPS < t) && (t < 1+EPS) )
		return i;
	}
    }