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Render a PDF page with an arbitrary affine transformation

Source: R/render.R
pdf_render_page_with_matrix.Rd

Power-user counterpart to pdf_render_page(). Instead of choosing a DPI + rotation, the caller supplies a 3x2 affine transformation matrix and the destination bitmap's pixel dimensions, plus an optional clipping rectangle in PDF user-space points. Useful for:

Usage

pdf_render_page_with_matrix(
  page,
  matrix,
  pixel_width,
  pixel_height,
  clip_rect = NULL,
  page_num = 1L,
  background = "white",
  annotations = FALSE
)

Arguments

page

A pdfium_page from pdf_page_load(), or a pdfium_doc (the page given by page_num will be loaded and closed internally).

matrix

Length-6 numeric vector (or 3x2 / 2x3 matrix coerced to length-6).

pixel_width, pixel_height

Output bitmap dimensions in pixels (positive integers).

clip_rect

Length-4 numeric c(left, bottom, right, top) in PDF user-space points, or NULL to skip clipping.

page_num

One-based page index. Only used when page is a pdfium_doc. Ignored otherwise.

background

Background color drawn behind the page content before rendering. Accepts any string grDevices::col2rgb() understands (named color, "#RRGGBB", "#RRGGBBAA"), or NA for a fully transparent background. Defaults to "white".

annotations

Logical; render annotation appearance streams on top of the page content. Defaults to FALSE.

Value

A pdfium_bitmap.

Details

  • Rendering a cropped region of a page (set the matrix to scale

    • translate the desired region into the bitmap, plus a matching clip_rect to discard everything outside).

  • Implementing zoom / pan in interactive viewers.

  • Pre-warping for non-rectilinear projections (the matrix can include shear).

Wraps FPDF_RenderPageBitmapWithMatrix.

Matrix layout

matrix is a 3x2 numeric matrix (or a length-6 numeric vector) representing the PDFium-order affine transformation (a, b, c, d, e, f), applied as:

$$x' = a\cdot x + c\cdot y + e$$ $$y' = b\cdot x + d\cdot y + f$$

For a simple scale, use matrix(c(s, 0, 0, s, 0, 0), 3, 2, byrow = TRUE). To crop to (x0, y0) -> (x1, y1) at scale s, use matrix(c(s, 0, 0, s, -s*x0, -s*y0), 3, 2, byrow = TRUE) plus clip_rect = c(x0, y0, x1, y1).

See also

pdf_render_page() for the simpler dpi+rotation API.