static void _makeWalls( const QgsCurve &ring, bool ccw, float extrusionHeight, QVector<float> &data, bool addNormals, double originX, double originY )
{
// we need to find out orientation of the ring so that the triangles we generate
// face the right direction
// (for exterior we want clockwise order, for holes we want counter-clockwise order)
bool is_counter_clockwise = _isRingCounterClockWise( ring );
QgsVertexId::VertexType vt;
QgsPoint pt;
QgsPoint ptPrev;
ring.pointAt( is_counter_clockwise == ccw ? 0 : ring.numPoints() - 1, ptPrev, vt );
for ( int i = 1; i < ring.numPoints(); ++i )
{
ring.pointAt( is_counter_clockwise == ccw ? i : ring.numPoints() - i - 1, pt, vt );
float x0 = ptPrev.x() - originX, y0 = ptPrev.y() - originY;
float x1 = pt.x() - originX, y1 = pt.y() - originY;
float z0 = ptPrev.z();
float z1 = pt.z();
// make a quad
make_quad( x0, y0, z0, x1, y1, z1, extrusionHeight, data, addNormals );
ptPrev = pt;
}
}
static bool _isRingCounterClockWise( const QgsCurve &ring )
{
double a = 0;
int count = ring.numPoints();
QgsVertexId::VertexType vt;
QgsPoint pt, ptPrev;
ring.pointAt( 0, ptPrev, vt );
for ( int i = 1; i < count + 1; ++i )
{
ring.pointAt( i % count, pt, vt );
a += ptPrev.x() * pt.y() - ptPrev.y() * pt.x();
ptPrev = pt;
}
return a > 0; // clockwise if a is negative
}
