Computes the matrix that maps an appearance's form space to default user space so that the appearance fills the annotation rectangle: Algorithm "Appearance streams" of ISO 32000-2 §12.5.5.
public static Matrix? ComputeAppearanceMatrix(PdfRectangle rect, PdfRectangle boundingBox, Matrix matrix)
The annotation rectangle (normalized).
The appearance's BBox, in form space.
The appearance's Matrix.
AA = Matrix × A, where A maps the transformed bounding box onto the rectangle; null
when either has zero width or height (nothing can be drawn).
ISO 32000-2 §12.5.5: the bounding box is transformed by the form matrix and the smallest upright rectangle containing the
result is mapped onto rect (lower-left to lower-left, upper-right to upper-right). The appearance's content
is painted with this matrix concatenated to the page's CTM and clipped to its bounding box in form space; the form matrix
is already part of the result and shall not be applied again.