MatrixSkew

procedure MatrixSkew(var matrix: TMatrixD; angleX, angleY: double);

Adds an affine skew to the supplied matrix.
dx is the horizontal skew angle (in radians).
And likewise, dy is the vertical skew angle.

For example, if dx = 0.3927 (~22.5 degrees), dy = 0 and the matrix is applied to the coordinate [20,10], then the transformed coordinate will become roughly [20 + 5, 10] or [25, 10].

uses Img32, Img32.Fmt.PNG, 
  Img32.Vector, Img32.Transform;
...
var
  img: TImage32;
  m: TMatrixD;
begin
  img := TImage32.Create;
  img.LoadFromFile('beetle.png');
    
  m := IdentityMatrix;
  //vertical skew
  MatrixSkew(m, 0,-0.5);
  //and rotate about the image center
  MatrixRotate(m, PointD(128,128), angle45);
  //apply the matrix to the image
  AffineTransformImage(img, m);

  img.SaveToFile('beetle_affine.png');
  img.Free;
end;