Path segments of a path page-object

Returns one row per segment of the path. Segments are emitted in the same order they appear in the page's content stream, which is the same order PDFium's rendering pipeline consumes. The result is suitable for plotting the geometry or for downstream coordinate analysis.

Usage

pdf_path_segments(obj)

Arguments

obj

A pdfium_obj of type "path" (from pdf_page_objects()).

Value

A tibble with the columns described above. An empty path returns a 0-row tibble of the same shape.

Details

Each row carries:

• segment_index - 1-based segment index within this path

• segment_type - "moveto", "lineto", "bezierto", or "unknown"

• x, y - the segment's point in PDF points

• close_figure - TRUE if this segment closes the current subpath (PDFium's h operator equivalent)

• cx1, cy1, cx2, cy2 - the two control points of the cubic Bezier curve that ends at this row; NA on every other row

Bezier curves

PDFium stores a cubic Bezier curve (the c, v, and y content operators) as three consecutive "bezierto" rows: the first control point, the second control point, and the curve's endpoint, in that order. The endpoint row additionally carries the curve's control points in cx1/cy1/cx2/cy2 (wraps FPDFPath_GetBezierControlPoints), so subset(segs, !is.na(cx1)) gives one row per curve, with the curve's start point being the previous row's x/y. The control-point rows keep cx1..cy2 as NA, which is how to tell them apart from endpoints. pdf_path_append() consumes the triplet form, so the output round-trips.

See also

pdf_page_objects(), pdf_obj_bounds()

Examples

fixture <- system.file("extdata", "fixtures", "shapes.pdf",
  package = "pdfium"
)
if (nzchar(fixture)) {
  doc <- pdf_doc_open(fixture)
  p <- pdf_page_load(doc, 1)
  path_obj <- Filter(\(o) o$type == "path", pdf_page_objects(p))[[1]]
  pdf_path_segments(path_obj)
  pdf_page_close(p)
  pdf_doc_close(doc)
}