//////////////////////////////////////////////////////////////////////
// LibFile: affine.scad
//   Matrix math and affine transformation matrices.
// Includes:
//   include <BOSL2/std.scad>
//////////////////////////////////////////////////////////////////////


// Section: Matrix Manipulation

// Function: ident()
// Usage:
//   mat = ident(n);
// Topics: Affine, Matrices
// Description:
//   Create an `n` by `n` square identity matrix.
// Arguments:
//   n = The size of the identity matrix square, `n` by `n`.
// Example:
//   mat = ident(3);
//   // Returns:
//   //   [
//   //     [1, 0, 0],
//   //     [0, 1, 0],
//   //     [0, 0, 1]
//   //   ]
// Example:
//   mat = ident(4);
//   // Returns:
//   //   [
//   //     [1, 0, 0, 0],
//   //     [0, 1, 0, 0],
//   //     [0, 0, 1, 0],
//   //     [0, 0, 0, 1]
//   //   ]
function ident(n) = [
    for (i = [0:1:n-1]) [
        for (j = [0:1:n-1]) (i==j)? 1 : 0
    ]
];


// Function: is_affine()
// Usage:
//   bool = is_affine(x,<dim>);
// Topics: Affine, Matrices, Transforms, Type Checking
// See Also: is_matrix()
//   fleegul()
// Description:
//   Tests if the given value is an affine matrix, possibly also checking it's dimenstion.
// Arguments:
//   x = The value to test for being an affine matrix.
//   dim = The number of dimensions the given affine is required to be for.  Generally 2 for 2D or 3 for 3D.  If given as a list of integers, allows any of the given dimensions.  Default: `[2,3]`
// Examples:
//   bool = is_affine(affine2d_scale([2,3]));  // Returns true
//   bool = is_affine(affine3d_scale([2,3,4]));  // Returns true
//   bool = is_affine(affine3d_scale([2,3,4]),2);  // Returns false
//   bool = is_affine(affine3d_scale([2,3]),2);  // Returns true
//   bool = is_affine(affine3d_scale([2,3,4]),3);  // Returns true
//   bool = is_affine(affine3d_scale([2,3]),3);  // Returns false
function is_affine(x,dim=[2,3]) =
    is_finite(dim)? is_affine(x,[dim]) :
    let( ll = len(x) )
    is_list(x) && in_list(ll-1,dim) &&
    [for (r=x) if(!is_list(r) || len(r)!=ll) 1] == [];


// Function: is_2d_transform()
// Usage:
//   x = is_2d_transform(t);
// Topics: Affine, Matrices, Transforms, Type Checking
// See Also: is_affine(), is_matrix()
// Description:
//   Checks if the input is a 3D transform that does not act on the z coordinate, except possibly
//   for a simple scaling of z.  Note that an input which is only a zscale returns false.
// Arguments:
//   t = The transformation matrix to check.
// Examples:
//   b = is_2d_transform(zrot(45));  // Returns: true
//   b = is_2d_transform(yrot(45));  // Returns: false
//   b = is_2d_transform(xrot(45));  // Returns: false
//   b = is_2d_transform(move([10,20,0]));  // Returns: true
//   b = is_2d_transform(move([10,20,30]));  // Returns: false
//   b = is_2d_transform(scale([2,3,4]));  // Returns: true
function is_2d_transform(t) =    // z-parameters are zero, except we allow t[2][2]!=1 so scale() works
  t[2][0]==0 && t[2][1]==0 && t[2][3]==0 && t[0][2] == 0 && t[1][2]==0 &&
  (t[2][2]==1 || !(t[0][0]==1 && t[0][1]==0 && t[1][0]==0 && t[1][1]==1));   // But rule out zscale()


// Function: affine2d_to_3d()
// Usage:
//   mat = affine2d_to_3d(m);
// Topics: Affine, Matrices, Transforms
// See Also: affine3d_to_2d()
// Description:
//   Takes a 3x3 affine2d matrix and returns its 4x4 affine3d equivalent.
// Example:
//   mat = affine2d_to_3d(affine2d_translate([10,20]));
//   // Returns:
//   //   [
//   //     [1, 0, 0, 10],
//   //     [0, 1, 0, 20],
//   //     [0, 0, 1,  0],
//   //     [0, 0, 0,  1],
//   //   ]
function affine2d_to_3d(m) = [
    [ m[0][0], m[0][1], 0, m[0][2] ],
    [ m[1][0], m[1][1], 0, m[1][2] ],
    [       0,       0, 1,       0 ],
    [ m[2][0], m[2][1], 0, m[2][2] ]
];


// Function: affine3d_to_2d()
// Usage:
//   mat = affine3d_to_2d(m);
// Topics: Affine, Matrices
// See Also: affine2d_to_3d()
// Description:
//   Takes a 4x4 affine3d matrix and returns its 3x3 affine2d equivalent.  3D transforms that would alter the Z coordinate are disallowed.
// Example:
//   mat = affine2d_to_3d(affine3d_translate([10,20,0]));
//   // Returns:
//   //   [
//   //     [1, 0, 10],
//   //     [0, 1, 20],
//   //     [0, 0,  1],
//   //   ]
function affine3d_to_2d(m) =
    assert(is_2d_transform(m))
    [
        for (r=[0:3]) if (r!=2) [
            for (c=[0:3]) if (c!=2) m[r][c]
        ]
    ];


// Function: apply()
// Usage:
//   pts = apply(transform, points);
// Topics: Affine, Matrices, Transforms
// Description:
//   Applies the specified transformation matrix to a point, pointlist, bezier patch or VNF.
//   Both inputs can be 2D or 3D, and it is also allowed to supply 3D transformations with 2D
//   data as long as the the only action on the z coordinate is a simple scaling.
// Arguments:
//   transform = The 2D or 3D transformation matrix to apply to the point/points.
//   points = The point, pointlist, bezier patch, or VNF to apply the transformation to.
// Example(3D):
//   path1 = path3d(circle(r=40));
//   tmat = xrot(45);
//   path2 = apply(tmat, path1);
//   #stroke(path1,closed=true);
//   stroke(path2,closed=true);
// Example(2D):
//   path1 = circle(r=40);
//   tmat = translate([10,5]);
//   path2 = apply(tmat, path1);
//   #stroke(path1,closed=true);
//   stroke(path2,closed=true);
// Example(2D):
//   path1 = circle(r=40);
//   tmat = rot(30) * back(15) * scale([1.5,0.5,1]);
//   path2 = apply(tmat, path1);
//   #stroke(path1,closed=true);
//   stroke(path2,closed=true);
function apply(transform,points) =
    points==[] ? [] :
    is_vector(points)
      ? /* Point */ apply(transform, [points])[0] :
    is_list(points) && len(points)==2 && is_path(points[0],3) && is_list(points[1]) && is_vector(points[1][0])
      ? /* VNF */ [apply(transform, points[0]), points[1]] :
    is_list(points) && is_list(points[0]) && is_vector(points[0][0])
      ? /* BezPatch */ [for (x=points) apply(transform,x)] :
    let(
        tdim = len(transform[0])-1,
        datadim = len(points[0])
    )
    tdim == 3 && datadim == 3 ? [for(p=points) point3d(transform*concat(p,[1]))] :
    tdim == 2 && datadim == 2 ? [for(p=points) point2d(transform*concat(p,[1]))] :
    tdim == 3 && datadim == 2 ?
        assert(is_2d_transform(transform), str("Transforms is 3d but points are 2d"))
        [for(p=points) point2d(transform*concat(p,[0,1]))] :
        assert(false, str("Unsupported combination: transform with dimension ",tdim,", data of dimension ",datadim));


// Function: rot_decode()
// Usage:
//   info = rot_decode(rotation); // Returns: [angle,axis,cp,translation]
// Topics: Affine, Matrices, Transforms
// Description:
//   Given an input 3D rigid transformation operator (one composed of just rotations and translations) represented
//   as a 4x4 matrix, compute the rotation and translation parameters of the operator.  Returns a list of the
//   four parameters, the angle, in the interval [0,180], the rotation axis as a unit vector, a centerpoint for
//   the rotation, and a translation.  If you set `parms = rot_decode(rotation)` then the transformation can be
//   reconstructed from parms as `move(parms[3]) * rot(a=parms[0],v=parms[1],cp=parms[2])`.  This decomposition
//   makes it possible to perform interpolation.  If you construct a transformation using `rot` the decoding
//   may flip the axis (if you gave an angle outside of [0,180]).  The returned axis will be a unit vector, and
//   the centerpoint lies on the plane through the origin that is perpendicular to the axis.  It may be different
//   than the centerpoint you used to construct the transformation.
// Example:
//   info = rot_decode(rot(45));
//   // Returns: [45, [0,0,1], [0,0,0], [0,0,0]]
// Example:
//   info = rot_decode(rot(a=37, v=[1,2,3], cp=[4,3,-7])));
//   // Returns: [37, [0.26, 0.53, 0.80], [4.8, 4.6, -4.6], [0,0,0]]
// Example:
//   info = rot_decode(left(12)*xrot(-33));
//   // Returns: [33, [-1,0,0], [0,0,0], [-12,0,0]]
// Example:
//   info = rot_decode(translate([3,4,5]));
//   // Returns: [0, [0,0,1], [0,0,0], [3,4,5]]
function rot_decode(M) =
    assert(is_matrix(M,4,4) && approx(M[3],[0,0,0,1]), "Input matrix must be a 4x4 matrix representing a 3d transformation")
    let(R = submatrix(M,[0:2],[0:2]))
    assert(approx(det3(R),1) && approx(norm_fro(R * transpose(R)-ident(3)),0),"Input matrix is not a rotation")
    let(
        translation = [for(row=[0:2]) M[row][3]],   // translation vector
        largest  = max_index([R[0][0], R[1][1], R[2][2]]),
        axis_matrix = R + transpose(R) - (matrix_trace(R)-1)*ident(3),   // Each row is on the rotational axis
            // Construct quaternion q = c * [x sin(theta/2), y sin(theta/2), z sin(theta/2), cos(theta/2)]
        q_im = axis_matrix[largest],
        q_re = R[(largest+2)%3][(largest+1)%3] - R[(largest+1)%3][(largest+2)%3],
        c_sin = norm(q_im),              // c * sin(theta/2) for some c
        c_cos = abs(q_re)                // c * cos(theta/2)
    )
    approx(c_sin,0) ? [0,[0,0,1],[0,0,0],translation] :
    let(
        angle = 2*atan2(c_sin, c_cos),    // This is supposed to be more accurate than acos or asin
        axis  = (q_re>=0 ? 1:-1)*q_im/c_sin,
        tproj = translation - (translation*axis)*axis,    // Translation perpendicular to axis determines centerpoint
        cp    = (tproj + cross(axis,tproj)*c_cos/c_sin)/2
    )
    [angle, axis, cp, (translation*axis)*axis];




// Section: Affine2d 3x3 Transformation Matrices


// Function: affine2d_identity()
// Usage:
//   mat = affine2d_identify();
// Topics: Affine, Matrices, Transforms
// Description:
//   Create a 3x3 affine2d identity matrix.
// Example:
//   mat = affine2d_identity();
//   // Returns:
//   //   [
//   //     [1, 0, 0],
//   //     [0, 1, 0],
//   //     [0, 0, 1]
//   //   ]
function affine2d_identity() = ident(3);


// Function: affine2d_translate()
// Usage:
//   mat = affine2d_translate(v);
// Topics: Affine, Matrices, Transforms, Translation
// See Also: move(), affine3d_translate()
// Description:
//   Returns the 3x3 affine2d matrix to perform a 2D translation.
// Arguments:
//   v = 2D Offset to translate by.  [X,Y]
// Example:
//   mat = affine2d_translate([30,40]);
//   // Returns:
//   //   [
//   //     [1, 0, 30],
//   //     [0, 1, 40],
//   //     [0, 0,  1]
//   //   ]
function affine2d_translate(v=[0,0]) =
    assert(is_vector(v),2)
    [
        [1, 0, v.x],
        [0, 1, v.y],
        [0 ,0,   1]
    ];


// Function: affine2d_scale()
// Usage:
//   mat = affine2d_scale(v);
// Topics: Affine, Matrices, Transforms, Scaling
// See Also: scale(), xscale(), yscale(), zscale(), affine3d_scale()
// Description:
//   Returns the 3x3 affine2d matrix to perform a 2D scaling transformation.
// Arguments:
//   v = 2D vector of scaling factors.  [X,Y]
// Example:
//   mat = affine2d_scale([3,4]);
//   // Returns:
//   //   [
//   //     [3, 0, 0],
//   //     [0, 4, 0],
//   //     [0, 0, 1]
//   //   ]
function affine2d_scale(v=[1,1]) =
    assert(is_vector(v,2))
    [
        [v.x,   0, 0],
        [  0, v.y, 0],
        [  0,   0, 1]
    ];


// Function: affine2d_zrot()
// Usage:
//   mat = affine2d_zrot(ang);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine3d_zrot()
// Description:
//   Returns the 3x3 affine2d matrix to perform a rotation of a 2D vector around the Z axis.
// Arguments:
//   ang = Number of degrees to rotate.
// Example:
//   mat = affine2d_zrot(90);
//   // Returns:
//   //   [
//   //     [0,-1, 0],
//   //     [1, 0, 0],
//   //     [0, 0, 1]
//   //   ]
function affine2d_zrot(ang=0) =
    assert(is_finite(ang))
    [
        [cos(ang), -sin(ang), 0],
        [sin(ang),  cos(ang), 0],
        [       0,         0, 1]
    ];


// Function: affine2d_mirror()
// Usage:
//   mat = affine2d_mirror(v);
// Topics: Affine, Matrices, Transforms, Reflection, Mirroring
// See Also: mirror(), xflip(), yflip(), zflip(), affine3d_mirror()
// Description:
//   Returns the 3x3 affine2d matrix to perform a reflection of a 2D vector across the line given by its normal vector.
// Arguments:
//   v = The normal vector of the line to reflect across.
// Example:
//   mat = affine2d_mirror([0,1]);
//   // Returns:
//   //   [
//   //     [ 1, 0, 0],
//   //     [ 0,-1, 0],
//   //     [ 0, 0, 1]
//   //   ]
// Example:
//   mat = affine2d_mirror([1,0]);
//   // Returns:
//   //   [
//   //     [-1, 0, 0],
//   //     [ 0, 1, 0],
//   //     [ 0, 0, 1]
//   //   ]
// Example:
//   mat = affine2d_mirror([1,1]);
//   // Returns approximately:
//   //   [
//   //     [ 0,-1, 0],
//   //     [-1, 0, 0],
//   //     [ 0, 0, 1]
//   //   ]
function affine2d_mirror(v) =
    assert(is_vector(v,2))
    let(v=unit(point2d(v)), a=v.x, b=v.y)
    [
        [1-2*a*a, 0-2*a*b, 0],
        [0-2*a*b, 1-2*b*b, 0],
        [      0,       0, 1]
    ];


// Function: affine2d_skew()
// Usage:
//   mat = affine2d_skew(xa);
//   mat = affine2d_skew(ya=);
//   mat = affine2d_skew(xa, ya);
// Topics: Affine, Matrices, Transforms, Skewing
// See Also: skew(), affine3d_skew()
// Description:
//   Returns the 3x3 affine2d matrix to skew a 2D vector along the XY plane.
// Arguments:
//   xa = Skew angle, in degrees, in the direction of the X axis. Default: 0
//   ya = Skew angle, in degrees, in the direction of the Y axis. Default: 0
// Example:
//   mat = affine2d_skew(xa=45,ya=-45);
//   // Returns approximately:
//   //   [
//   //     [ 1, 1, 0],
//   //     [-1, 1, 0],
//   //     [ 0, 0, 1]
//   //   ]
function affine2d_skew(xa=0, ya=0) =
    assert(is_finite(xa))
    assert(is_finite(ya))
    [
        [1,       tan(xa), 0],
        [tan(ya), 1,       0],
        [0,       0,       1]
    ];



// Section: Affine3d 4x4 Transformation Matrices


// Function: affine3d_identity()
// Usage:
//   mat = affine3d_identity();
// Topics: Affine, Matrices, Transforms
// Description:
//   Create a 4x4 affine3d identity matrix.
// Example:
//   mat = affine2d_identity();
//   // Returns:
//   //   [
//   //     [1, 0, 0, 0],
//   //     [0, 1, 0, 0],
//   //     [0, 0, 1, 0],
//   //     [0, 0, 0, 1]
//   //   ]
function affine3d_identity() = ident(4);


// Function: affine3d_translate()
// Usage:
//   mat = affine3d_translate(v);
// Topics: Affine, Matrices, Transforms, Translation
// See Also: move(), affine2d_translate()
// Description:
//   Returns the 4x4 affine3d matrix to perform a 3D translation.
// Arguments:
//   v = 3D offset to translate by.  [X,Y,Z]
// Example:
//   mat = affine2d_translate([30,40,50]);
//   // Returns:
//   //   [
//   //     [1, 0, 0, 30],
//   //     [0, 1, 0, 40],
//   //     [0, 0, 1, 50]
//   //     [0, 0, 0,  1]
//   //   ]
function affine3d_translate(v=[0,0,0]) =
    assert(is_list(v))
    let( v = [for (i=[0:2]) default(v[i],0)] )
    [
        [1, 0, 0, v.x],
        [0, 1, 0, v.y],
        [0, 0, 1, v.z],
        [0 ,0, 0,   1]
    ];


// Function: affine3d_scale()
// Usage:
//   mat = affine3d_scale(v);
// Topics: Affine, Matrices, Transforms, Scaling
// See Also: scale(), affine2d_scale()
// Description:
//   Returns the 4x4 affine3d matrix to perform a 3D scaling transformation.
// Arguments:
//   v = 3D vector of scaling factors.  [X,Y,Z]
// Example:
//   mat = affine3d_scale([3,4,5]);
//   // Returns:
//   //   [
//   //     [3, 0, 0, 0],
//   //     [0, 4, 0, 0],
//   //     [0, 0, 5, 0],
//   //     [0, 0, 0, 1]
//   //   ]
function affine3d_scale(v=[1,1,1]) =
    assert(is_list(v))
    let( v = [for (i=[0:2]) default(v[i],1)] )
    [
        [v.x,   0,   0, 0],
        [  0, v.y,   0, 0],
        [  0,   0, v.z, 0],
        [  0,   0,   0, 1]
    ];


// Function: affine3d_xrot()
// Usage:
//   mat = affine3d_xrot(ang);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns the 4x4 affine3d matrix to perform a rotation of a 3D vector around the X axis.
// Arguments:
//   ang = number of degrees to rotate.
// Example:
//   mat = affine3d_xrot(90);
//   // Returns:
//   //   [
//   //     [1, 0, 0, 0],
//   //     [0, 0,-1, 0],
//   //     [0, 1, 0, 0],
//   //     [0, 0, 0, 1]
//   //   ]
function affine3d_xrot(ang=0) =
    assert(is_finite(ang))
    [
        [1,        0,         0,   0],
        [0, cos(ang), -sin(ang),   0],
        [0, sin(ang),  cos(ang),   0],
        [0,        0,         0,   1]
    ];


// Function: affine3d_yrot()
// Usage:
//   mat = affine3d_yrot(ang);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns the 4x4 affine3d matrix to perform a rotation of a 3D vector around the Y axis.
// Arguments:
//   ang = Number of degrees to rotate.
// Example:
//   mat = affine3d_yrot(90);
//   // Returns:
//   //   [
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 1, 0, 0],
//   //     [-1, 0, 0, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_yrot(ang=0) =
    assert(is_finite(ang))
    [
        [ cos(ang), 0, sin(ang),   0],
        [        0, 1,        0,   0],
        [-sin(ang), 0, cos(ang),   0],
        [        0, 0,        0,   1]
    ];


// Function: affine3d_zrot()
// Usage:
//   mat = affine3d_zrot(ang);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns the 4x4 affine3d matrix to perform a rotation of a 3D vector around the Z axis.
// Arguments:
//   ang = number of degrees to rotate.
// Example:
//   mat = affine3d_zrot(90);
//   // Returns:
//   //   [
//   //     [ 0,-1, 0, 0],
//   //     [ 1, 0, 0, 0],
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_zrot(ang=0) =
    assert(is_finite(ang))
    [
        [cos(ang), -sin(ang), 0, 0],
        [sin(ang),  cos(ang), 0, 0],
        [       0,         0, 1, 0],
        [       0,         0, 0, 1]
    ];


// Function: affine3d_rot_by_axis()
// Usage:
//   mat = affine3d_rot_by_axis(u, ang);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns the 4x4 affine3d matrix to perform a rotation of a 3D vector around an axis.
// Arguments:
//   u = 3D axis vector to rotate around.
//   ang = number of degrees to rotate.
// Example:
//   mat = affine3d_rot_by_axis([1,1,1], 120);
//   // Returns approx:
//   //   [
//   //     [ 0, 0, 1, 0],
//   //     [ 1, 0, 0, 0],
//   //     [ 0, 1, 0, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_rot_by_axis(u=UP, ang=0) =
    assert(is_finite(ang))
    assert(is_vector(u,3))
    approx(ang,0)? affine3d_identity() :
    let(
        u = unit(u),
        c = cos(ang),
        c2 = 1-c,
        s = sin(ang)
    ) [
        [u.x*u.x*c2+c    , u.x*u.y*c2-u.z*s, u.x*u.z*c2+u.y*s, 0],
        [u.y*u.x*c2+u.z*s, u.y*u.y*c2+c    , u.y*u.z*c2-u.x*s, 0],
        [u.z*u.x*c2-u.y*s, u.z*u.y*c2+u.x*s, u.z*u.z*c2+c    , 0],
        [               0,                0,                0, 1]
    ];


// Function: affine3d_rot_from_to()
// Usage:
//   mat = affine3d_rot_from_to(from, to);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns the 4x4 affine3d matrix to perform a rotation of a 3D vector from one vector direction to another.
// Arguments:
//   from = 3D axis vector to rotate from.
//   to = 3D axis vector to rotate to.
// Example:
//   mat = affine3d_rot_from_to(UP, RIGHT);
//   // Returns:
//   //   [
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 1, 0, 0],
//   //     [-1, 0, 0, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_rot_from_to(from, to) =
    assert(is_vector(from))
    assert(is_vector(to))
    assert(len(from)==len(to))
    let(
        from = unit(point3d(from)),
        to = unit(point3d(to))
    ) approx(from,to)? affine3d_identity() :
    let(
        u = vector_axis(from,to),
        ang = vector_angle(from,to),
        c = cos(ang),
        c2 = 1-c,
        s = sin(ang)
    ) [
        [u.x*u.x*c2+c    , u.x*u.y*c2-u.z*s, u.x*u.z*c2+u.y*s, 0],
        [u.y*u.x*c2+u.z*s, u.y*u.y*c2+c    , u.y*u.z*c2-u.x*s, 0],
        [u.z*u.x*c2-u.y*s, u.z*u.y*c2+u.x*s, u.z*u.z*c2+c    , 0],
        [               0,                0,                0, 1]
    ];


// Function: affine3d_frame_map()
// Usage:
//   map = affine3d_frame_map(v1, v2, v3, <reverse>);
//   map = affine3d_frame_map(x=VECTOR1, y=VECTOR2, <reverse>);
//   map = affine3d_frame_map(x=VECTOR1, z=VECTOR2, <reverse>);
//   map = affine3d_frame_map(y=VECTOR1, z=VECTOR2, <reverse>);
// Topics: Affine, Matrices, Transforms, Rotation
// See Also: rot(), xrot(), yrot(), zrot(), affine2d_zrot()
// Description:
//   Returns a transformation that maps one coordinate frame to another.  You must specify two or
//   three of `x`, `y`, and `z`.  The specified axes are mapped to the vectors you supplied.  If you
//   give two inputs, the third vector is mapped to the appropriate normal to maintain a right hand
//   coordinate system.  If the vectors you give are orthogonal the result will be a rotation and the
//   `reverse` parameter will supply the inverse map, which enables you to map two arbitrary
//   coordinate systems to each other by using the canonical coordinate system as an intermediary.
//   You cannot use the `reverse` option with non-orthogonal inputs.
// Arguments:
//   x = Destination 3D vector for x axis.
//   y = Destination 3D vector for y axis.
//   z = Destination 3D vector for z axis.
//   reverse = reverse direction of the map for orthogonal inputs.  Default: false
// Example:
//   T = affine3d_frame_map(x=[1,1,0], y=[-1,1,0]);   // This map is just a rotation around the z axis
// Example:
//   T = affine3d_frame_map(x=[1,0,0], y=[1,1,0]);    // This map is not a rotation because x and y aren't orthogonal
// Example:
//   // The next map sends [1,1,0] to [0,1,1] and [-1,1,0] to [0,-1,1]
//   T = affine3d_frame_map(x=[0,1,1], y=[0,-1,1]) * affine3d_frame_map(x=[1,1,0], y=[-1,1,0],reverse=true);
function affine3d_frame_map(x,y,z, reverse=false) =
    assert(num_defined([x,y,z])>=2, "Must define at least two inputs")
    let(
        xvalid = is_undef(x) || (is_vector(x) && len(x)==3),
        yvalid = is_undef(y) || (is_vector(y) && len(y)==3),
        zvalid = is_undef(z) || (is_vector(z) && len(z)==3)
    )
    assert(xvalid,"Input x must be a length 3 vector")
    assert(yvalid,"Input y must be a length 3 vector")
    assert(zvalid,"Input z must be a length 3 vector")
    let(
        x = is_undef(x)? undef : unit(x,RIGHT),
        y = is_undef(y)? undef : unit(y,BACK),
        z = is_undef(z)? undef : unit(z,UP),
        map = is_undef(x)? [cross(y,z), y, z] :
            is_undef(y)? [x, cross(z,x), z] :
            is_undef(z)? [x, y, cross(x,y)] :
            [x, y, z]
    )
    reverse? (
        let(
            ocheck = (
                approx(map[0]*map[1],0) &&
                approx(map[0]*map[2],0) &&
                approx(map[1]*map[2],0)
            )
        )
        assert(ocheck, "Inputs must be orthogonal when reverse==true")
        [for (r=map) [for (c=r) c, 0], [0,0,0,1]]
    ) : [for (r=transpose(map)) [for (c=r) c, 0], [0,0,0,1]];



// Function: affine3d_mirror()
// Usage:
//   mat = affine3d_mirror(v);
// Topics: Affine, Matrices, Transforms, Reflection, Mirroring
// See Also: mirror(), xflip(), yflip(), zflip(), affine2d_mirror()
// Description:
//   Returns the 4x4 affine3d matrix to perform a reflection of a 3D vector across the plane given by its normal vector.
// Arguments:
//   v = The normal vector of the plane to reflect across.
// Example:
//   mat = affine3d_mirror([1,0,0]);
//   // Returns:
//   //   [
//   //     [-1, 0, 0, 0],
//   //     [ 0, 1, 0, 0],
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
// Example:
//   mat = affine3d_mirror([0,1,0]);
//   // Returns:
//   //   [
//   //     [ 1, 0, 0, 0],
//   //     [ 0,-1, 0, 0],
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_mirror(v) =
    assert(is_vector(v))
    let(
        v=unit(point3d(v)),
        a=v.x, b=v.y, c=v.z
    ) [
        [1-2*a*a,  -2*a*b,  -2*a*c, 0],
        [ -2*b*a, 1-2*b*b,  -2*b*c, 0],
        [ -2*c*a,  -2*c*b, 1-2*c*c, 0],
        [      0,       0,       0, 1]
    ];


// Function: affine3d_skew()
// Usage:
//   mat = affine3d_skew(<sxy>, <sxz>, <syx>, <syz>, <szx>, <szy>);
// Topics: Affine, Matrices, Transforms, Skewing
// See Also: skew(), affine3d_skew_xy(), affine3d_skew_xz(), affine3d_skew_yz(), affine2d_skew()
// Description:
//   Returns the 4x4 affine3d matrix to perform a skew transformation.
// Arguments:
//   sxy = Skew factor multiplier for skewing along the X axis as you get farther from the Y axis.  Default: 0
//   sxz = Skew factor multiplier for skewing along the X axis as you get farther from the Z axis.  Default: 0
//   syx = Skew factor multiplier for skewing along the Y axis as you get farther from the X axis.  Default: 0
//   syz = Skew factor multiplier for skewing along the Y axis as you get farther from the Z axis.  Default: 0
//   szx = Skew factor multiplier for skewing along the Z axis as you get farther from the X axis.  Default: 0
//   szy = Skew factor multiplier for skewing along the Z axis as you get farther from the Y axis.  Default: 0
// Example:
//   mat = affine3d_skew(sxy=2,szx=3);
//   // Returns:
//   //   [
//   //     [ 1, 2, 0, 0],
//   //     [ 0, 1, 0, 0],
//   //     [ 0, 0, 1, 0],
//   //     [ 3, 0, 0, 1]
//   //   ]
function affine3d_skew(sxy=0, sxz=0, syx=0, syz=0, szx=0, szy=0) = [
    [  1, sxy, sxz, 0],
    [syx,   1, syz, 0],
    [szx, szy,   1, 0],
    [  0,   0,   0, 1]
];


// Function: affine3d_skew_xy()
// Usage:
//   mat = affine3d_skew_xy(xa);
//   mat = affine3d_skew_xy(ya=);
//   mat = affine3d_skew_xy(xa, ya);
// Topics: Affine, Matrices, Transforms, Skewing
// See Also: skew(), affine3d_skew(), affine3d_skew_xz(), affine3d_skew_yz(), affine2d_skew()
// Description:
//   Returns the 4x4 affine3d matrix to perform a skew transformation along the XY plane.
// Arguments:
//   xa = Skew angle, in degrees, in the direction of the X axis.  Default: 0
//   ya = Skew angle, in degrees, in the direction of the Y axis.  Default: 0
// Example:
//   mat = affine3d_skew_xy(xa=45,ya=-45);
//   // Returns:
//   //   [
//   //     [ 1, 0, 1, 0],
//   //     [ 0, 1,-1, 0],
//   //     [ 0, 0, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_skew_xy(xa=0, ya=0) =
    assert(is_finite(xa))
    assert(is_finite(ya))
    [
        [1, 0, tan(xa), 0],
        [0, 1, tan(ya), 0],
        [0, 0,       1, 0],
        [0, 0,       0, 1]
    ];


// Function: affine3d_skew_xz()
// Usage:
//   mat = affine3d_skew_xz(xa);
//   mat = affine3d_skew_xz(za=);
//   mat = affine3d_skew_xz(xa, za);
// Topics: Affine, Matrices, Transforms, Skewing
// See Also: skew(), affine3d_skew(), affine3d_skew_xy(), affine3d_skew_yz(), affine2d_skew()
// Description:
//   Returns the 4x4 affine3d matrix to perform a skew transformation along the XZ plane.
// Arguments:
//   xa = Skew angle, in degrees, in the direction of the X axis.  Default: 0
//   za = Skew angle, in degrees, in the direction of the Z axis.  Default: 0
// Example:
//   mat = affine3d_skew_xz(xa=45,za=-45);
//   // Returns:
//   //   [
//   //     [ 1, 1, 0, 0],
//   //     [ 0, 1, 0, 0],
//   //     [ 0,-1, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_skew_xz(xa=0, za=0) =
    assert(is_finite(xa))
    assert(is_finite(za))
    [
        [1, tan(xa), 0, 0],
        [0,       1, 0, 0],
        [0, tan(za), 1, 0],
        [0,       0, 0, 1]
    ];


// Function: affine3d_skew_yz()
// Usage:
//   mat = affine3d_skew_yz(ya);
//   mat = affine3d_skew_yz(za=);
//   mat = affine3d_skew_yz(ya, za);
// Topics: Affine, Matrices, Transforms, Skewing
// See Also: skew(), affine3d_skew(), affine3d_skew_xy(), affine3d_skew_xz(), affine2d_skew()
// Description:
//   Returns the 4x4 affine3d matrix to perform a skew transformation along the YZ plane.
// Arguments:
//   ya = Skew angle, in degrees, in the direction of the Y axis.  Default: 0
//   za = Skew angle, in degrees, in the direction of the Z axis.  Default: 0
// Example:
//   mat = affine3d_skew_yz(ya=45,za=-45);
//   // Returns:
//   //   [
//   //     [ 1, 0, 0, 0],
//   //     [ 1, 1, 0, 0],
//   //     [-1, 0, 1, 0],
//   //     [ 0, 0, 0, 1]
//   //   ]
function affine3d_skew_yz(ya=0, za=0) =
    assert(is_finite(ya))
    assert(is_finite(za))
    [
        [      1, 0, 0, 0],
        [tan(ya), 1, 0, 0],
        [tan(za), 0, 1, 0],
        [      0, 0, 0, 1]
    ];



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