Read a rendered scene back as pixels

scene_raster() renders scene and returns its pixels as an integer array with dimensions c(channel, x, y) — RGBA channels in 0:255, top-left origin, y increasing downward. This is the form most convenient for probing or testing (e.g. scene_raster(s)[1, x, y] is the red value at pixel (x, y)).

Usage

scene_raster(scene, cvd = "none")

Arguments

scene

A vl_scene() (or anything with an as_vellum_scene() method).

cvd

Simulate a colour-vision deficiency: "none" (default), "protanopia" (red-blind), "deuteranopia" (green-blind, the common one that breaks red/green encodings), "tritanopia" (blue-blind), or "achromatopsia" (total, and a fair proxy for greyscale printing). The simulation is a post-pass over the finished raster using the Machado et al. (2009) matrices applied in linear light, so it turns an accessibility check into a one-line change instead of an export-and-upload round trip. Raster output only — a vector format has no pixels to transform, and render() warns if you ask for one.

Value

scene_raster(): an integer array of dimension c(4, width, height). The as.raster() method: a raster (character matrix, c(height, width)).

Details

An grDevices::as.raster() method returns the same image as a raster object (a character matrix of hex colours), drawable with graphics::plot() or grid::rasterGrob().

Examples

s <- vl_scene(2, 1, bg = "white") |>
  draw(circle_grob(r = 0.3, gp = vl_gpar(fill = "red", col = NA)))
dim(scene_raster(s)) # c(4, width_px, height_px)
#> [1]   4 192  96