Render a grid or base drawing to PNG bytes

The raster counterpart to draw_to_svg(), for the same job: letting a module whose output is not a plotly graph supply its own artwork to an export. Where draw_to_svg() yields markup to splice, this yields the bytes of a finished file.

Usage

draw_to_png(draw_fn, width, height, res = 72, scale = 2, bg = "white")

Arguments

draw_fn

A function of no arguments that draws onto the active device.

width, height

Size in pixels.

res

Pixels per inch used to size the drawing. The default matches shiny::renderPlot()'s own res, so the result is laid out on a canvas the same physical size as the one the plot was rendered at on screen – which matters for anything sized in absolute points; see the note on res in draw_to_svg().

scale

Pixel density multiplier. The drawing is laid out at the same physical size (res scales with the pixel count) but rasterised at scale times the resolution, so the result is a crisp image rather than a screenshot. Matches the scale plotly's own image export defaults to.

bg

Background color.

Value

A raw vector holding a PNG file, or NULL if the requested size is not usable or the R build has no PNG support. An error raised by draw_fn itself propagates to the caller; the device is closed either way.

See also

draw_to_svg() for the vector counterpart.

Author

Jared Andrews

Examples

png_bytes <- draw_to_png(function() plot(1:10), width = 480, height = 360)
head(png_bytes, 4)
#> [1] 89 50 4e 47