Skip to contents

Transformation matrix of a page object

Source: R/objects.R
pdf_obj_matrix.Rd

Returns the 2D affine transformation matrix attached to obj as a 3-by-3 numeric matrix M in homogeneous form, so that a point (x, y) in the object's local space maps to page-space coordinates via M %*% c(x, y, 1). The PDF convention stores the six scalars a, b, c, d, e, f; this function lifts them into the homogeneous-coordinate matrix

Usage

pdf_obj_matrix(obj)

Arguments

obj

A pdfium_obj from pdf_page_objects() (any type).

Value

A 3-by-3 numeric matrix. Use M %*% c(x, y, 1) to transform a point; the first two elements of the result are the transformed coordinates.

Details

        | a c e |
  M  =  | b d f |
        | 0 0 1 |

so multiplication composes the way users expect (M2 %*% M1 applies M1 first then M2). For paths drawn directly on a page the matrix is usually the identity; text objects typically carry a non-trivial matrix (Cairo for example places text at font-size 1 and uses the matrix to scale and position the glyphs).

See also

pdf_obj_bounds(), pdf_path_segments()

Examples

fixture <- system.file("extdata", "fixtures", "shapes.pdf",
  package = "pdfium"
)
if (nzchar(fixture)) {
  doc <- pdf_doc_open(fixture)
  p <- pdf_page_load(doc, 1)
  M <- pdf_obj_matrix(pdf_page_objects(p)[[1]])
  M %*% c(10, 20, 1)
  pdf_page_close(p)
  pdf_doc_close(doc)
}