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Plot a pdfium_bitmap

Source: R/render.R
plot.pdfium_bitmap.Rd

Draws the bitmap into the active graphics device at its source pixel resolution. Internally the bitmap is converted to a 3-D numeric array (the format png::writePNG() and the R graphics engine both consume cleanly) and drawn with grid::grid.raster() on a fresh grid page.

Usage

# S3 method for class 'pdfium_bitmap'
plot(x, interpolate = TRUE, ...)

Arguments

x

A pdfium_bitmap from pdf_render_page() or pdf_image_bitmap() / pdf_image_rendered().

interpolate

Passed through to grid::grid.raster(). Default TRUE; set FALSE for pixel-exact (nearest-neighbour) display of small bitmaps.

...

Further arguments passed to grid::grid.raster().

Value

Invisibly returns x. Called for the plotting side effect.

Details

We go through as.array(x) rather than handing the integer matrix directly to graphics::rasterImage() for two reasons that compound:

  1. Per the documented raster contract (see ?grDevices::as.raster, "Raster images are internally represented row-first"), "raster" and nativeRaster objects must have row-major memory layout. R's as.raster.matrix() transposes its input precisely to satisfy that. Our integer matrix comes out of C++ as a standard R column-major matrix, so feeding it directly is non-conformant and shows diagonal stripe artifacts on detailed content.

  2. rasterImage with plot.window uses the user-coordinate system, which defaults (xaxs = "r", yaxs = "r") to padding the interval by 4% on each side — silently compressing the raster into ~92% of the device and forcing sub-pixel resampling. grid::grid.raster() uses npc coordinates and isn't subject to this.

Going through as.array(x) to a 3-D c(H, W, 4) numeric array and rendering with grid::grid.raster() sidesteps both: the array path uses positional channel storage (no row-vs-column convention), and grid coordinates are 0..1 npc without padding.

Examples

fixture <- system.file("extdata", "fixtures", "shapes.pdf",
  package = "pdfium"
)
if (nzchar(fixture) && interactive()) {
  bmp <- pdf_render_page(pdf_doc_open(fixture), dpi = 96)
  plot(bmp)
}