public Camera(Vector pos, Vector lookAt)
{
var down = new Vector(0.0, -1.0, 0.0);
forward = Help.norm(lookAt - pos);
right = 1.5 * Help.norm(Vector.CrossProduct(forward, down));
up = 1.5 * Help.norm(Vector.CrossProduct(forward, right));
}
//
// Processes a ray-line intersection to see if it's a valid hit.
//
// Shares some code with ValidateRayHit
//
private void ValidateLineHit(
RayHitTestParameters rayParams,
FaceType facesToHit,
int i0,
int i1,
int i2,
ref Point3D v0,
ref Point3D v1,
ref Point3D v2,
ref Point barycentric
)
{
Matrix3D worldTransformMatrix = rayParams.HasWorldTransformMatrix ? rayParams.WorldTransformMatrix : Matrix3D.Identity;
// OK, we have an intersection with the LINE but that could be wrong on three
// accounts:
// 1. We could have hit the line on the wrong side of the ray's origin.
// 2. We may need to cull the intersection if it's beyond the far clipping
// plane (only if the hit test originated from a Viewport3DVisual.)
// 3. We could have hit a back-facing triangle
// We will transform the hit point back into world space to check these
// things & compute the correct distance from the origin to the hit point.
// Hit point in model space
Point3D pointHit = M3DUtil.Interpolate(ref v0, ref v1, ref v2, ref barycentric);
Point3D worldPointHit = pointHit;
worldTransformMatrix.MultiplyPoint(ref worldPointHit);
// Vector from origin to hit point
Vector3D hitVector = worldPointHit - rayParams.Origin;
Vector3D originalDirection = rayParams.Direction;
double rayDistanceUnnormalized = Vector3D.DotProduct(originalDirection, hitVector);
if (rayDistanceUnnormalized > 0)
{
// If we have a HitTestProjectionMatrix than this hit test originated
// at a Viewport3DVisual.
if (rayParams.HasHitTestProjectionMatrix)
{
// To test if we are in front of the far clipping plane what we
// do conceptually is project our hit point in world space into
// homogenous space and verify that it is on the correct side of
// the Z=1 plane.
//
// To save some cycles we only bother computing Z and W of the
// projected point and use a simple Z/W > 1 test to see if we
// are past the far plane.
//
// NOTE: HitTestProjectionMatrix is not just the camera matrices.
// It has an additional translation to move the ray to the
// origin. This extra translation does not effect this test.
Matrix3D m = rayParams.HitTestProjectionMatrix;
// We directly substitute 1 for p.W below:
double pz = worldPointHit.X * m.M13 + worldPointHit.Y * m.M23 + worldPointHit.Z * m.M33 + m.OffsetZ;
double pw = worldPointHit.X * m.M14 + worldPointHit.Y * m.M24 + worldPointHit.Z * m.M34 + m.M44;
// Early exit if pz/pw > 1. The negated logic is to reject NaNs.
if (!(pz / pw <= 1))
{
return;
}
Debug.Assert(!double.IsInfinity(pz / pw) && !double.IsNaN(pz / pw),
"Expected near/far tests to cull -Inf/+Inf and NaN.");
}
Point3D a = v0, b = v1, c = v2;
worldTransformMatrix.MultiplyPoint(ref a);
worldTransformMatrix.MultiplyPoint(ref b);
worldTransformMatrix.MultiplyPoint(ref c);
Vector3D normal = Vector3D.CrossProduct(b - a, c - a);
double cullSign = -Vector3D.DotProduct(normal, hitVector);
double det = worldTransformMatrix.Determinant;
bool frontFace = (cullSign > 0) == (det >= 0);
if (((facesToHit & FaceType.Front) == FaceType.Front && frontFace) || ((facesToHit & FaceType.Back) == FaceType.Back && !frontFace))
{
double dist = hitVector.Length;
if (rayParams.HasModelTransformMatrix)
{
rayParams.ModelTransformMatrix.MultiplyPoint(ref pointHit);
}
rayParams.ReportResult(this, pointHit, dist, i0, i1, i2, barycentric);
}
}
}
