gradCoord2D
Computes the dot product of a gradient vector and a distance vector in 2D space.
Return
The dot product of the gradient vector and the distance vector.
Parameters
seed
The seed value used for hashing and determining the gradient vector.
x
The x-coordinate in grid space used for hashing.
y
The y-coordinate in grid space used for hashing.
xd
The x component of the distance vector.
yd
The y component of the distance vector.