Convert a Direction3d to a Vec3.

Direction3d.toVec3 Direction3d.y
--> vec3 0 1 0

Convert a Direction3d to a Vec4. The resulting Vec4 will have a W component of 0 so that it is not affected by translation when performing matrix transformations.

Direction3d.toVec4 Direction3d.y
--> vec4 0 1 0 0