bool CalculateIsAboveHorizonToCamera(DoubleVector3 cameraLocation, DoubleVector3 planetLocation, DoubleVector3 closestVertex)
{
// Taken from http://www.crappycoding.com/2009/04/
// TODO: This algorithm is poor. Implement this algorithm instead:
// http://www.gamedev.net/community/forums/mod/journal/journal.asp?jn=263350&reply_id=3173799
// TODO: sometimes the mesh is so large and we're so close the surface that none of the sampled
// vertices are above the horizon. That causes problems when we want to do early termination
// when we do a draw walk on the QuadNode tree (see comments there). Can we add a test here to
// see if we're inside the mesh's bounding box?
var planetToCamera = DoubleVector3.Normalize(cameraLocation - planetLocation);
var planetToMesh = DoubleVector3.Normalize(closestVertex - planetLocation);
var horizonAngle = Math.Acos(_planetRadius * 0.99 / DoubleVector3.Distance(planetLocation, cameraLocation));
var angleToMesh = Math.Acos(DoubleVector3.Dot(planetToCamera, planetToMesh));
return(horizonAngle > angleToMesh);
}
void UpdateStatistics(DoubleVector3 cameraLocation)
{
_statistics.CameraAltitude = DoubleVector3.Distance(_location, cameraLocation) - _radius;
}
