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# OpenSolid.LinearAlgebra.Vector3d

Conversion and transformation functions for `Vector3d`.

toVec3 : Vector3d -> Vec3

Convert a `Vector3d` to a `Vec3`.

``````Vector3d.toVec3 (Vector3d ( 2, 1, 3 ))
--> Vector3.vec3 2 1 3
``````
fromVec3 : Vec3 -> Vector3d

Convert a `Vec3` to a `Vector3d`.

``````Vector3d.fromVec3 (Vector3.vec3 2 1 3)
--> Vector3d ( 2, 1, 3 )
``````
transformBy : Mat4 -> Vector3d -> Vector3d

Transform a `Vector3d` by a `Mat4`; note that

``````Vector3d.transformBy matrix vector
``````

is similar to but not in general equivalent to

``````Vector3d.fromVec3 (Matrix4.transform matrix (Vector3d.toVec3 vector))
``````

since `Matrix4.transform` implicitly assumes that the given argument represents a point, not a vector, and therefore applies translation to it. Transforming a vector by a 4x4 matrix should in fact ignore any translation component of the matrix, which this function does. For example:

``````vector =
Vector3d ( 2, 1, 3 )

-- 90 degree rotation around the Z axis, followed by a translation
matrix =
Matrix4.makeTranslate3 5 5 5
|> Matrix4.rotate (degrees 90) Vector3.k

Vector3d.transformBy matrix vector
--> Vector3d ( -1, 2, 3 )
``````
``````module OpenSolid.LinearAlgebra.Vector3d
exposing
( toVec3
, fromVec3
, transformBy
)

{-| Conversion and transformation functions for `Vector3d`.

@docs toVec3, fromVec3, transformBy

-}

import OpenSolid.Geometry.Types exposing (..)
import OpenSolid.Vector3d as Vector3d
import Math.Vector3 exposing (Vec3)
import Math.Matrix4 exposing (Mat4)

{-| Convert a `Vector3d` to a `Vec3`.

Vector3d.toVec3 (Vector3d ( 2, 1, 3 ))
--> Vector3.vec3 2 1 3

-}
toVec3 : Vector3d -> Vec3
toVec3 vector =
Math.Vector3.fromTuple (Vector3d.components vector)

{-| Convert a `Vec3` to a `Vector3d`.

Vector3d.fromVec3 (Vector3.vec3 2 1 3)
--> Vector3d ( 2, 1, 3 )

-}
fromVec3 : Vec3 -> Vector3d
fromVec3 vec =
Vector3d (Math.Vector3.toTuple vec)

{-| Transform a `Vector3d` by a `Mat4`; note that

Vector3d.transformBy matrix vector

is similar to but *not* in general equivalent to

Vector3d.fromVec3 (Matrix4.transform matrix (Vector3d.toVec3 vector))

since `Matrix4.transform` implicitly assumes that the given argument represents
a point, not a vector, and therefore applies translation to it. Transforming a
vector by a 4x4 matrix should in fact ignore any translation component of the
matrix, which this function does. For example:

vector =
Vector3d ( 2, 1, 3 )

-- 90 degree rotation around the Z axis, followed by a translation
matrix =
Matrix4.makeTranslate3 5 5 5
|> Matrix4.rotate (degrees 90) Vector3.k

Vector3d.transformBy matrix vector
--> Vector3d ( -1, 2, 3 )

-}
transformBy : Mat4 -> Vector3d -> Vector3d
transformBy matrix vector =
let
{ m11, m12, m13, m14, m21, m22, m23, m24, m31, m32, m33, m34, m41, m42, m43, m44 } =
Math.Matrix4.toRecord matrix

( x, y, z ) =
Vector3d.components vector
in
Vector3d
( m11 * x + m12 * y + m13 * z
, m21 * x + m22 * y + m23 * z
, m31 * x + m32 * y + m33 * z
)
```
```