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Dynamically spread a raster grob to a target density

Source: R/spread.R
dynspread.Rd

datashader's dynspread: pick the smallest spread radius (up to max_px) at which the shaded pixels become "connected enough" — the fraction of non-empty pixels with a non-empty neighbour reaches threshold — then spread() by it. Denser images spread less, sparse ones more, so a mix of dense and sparse regions all stay legible.

Usage

dynspread(
  grob,
  max_px = 3L,
  threshold = 0.5,
  shape = c("circle", "square"),
  how = c("over", "add")
)

Arguments

grob

A raster grob (e.g. from datashade()). Other grob kinds are returned unchanged.

max_px

Largest spread radius to consider (non-negative integer).

threshold

Target fraction in (0, 1] of non-empty pixels that should have a non-empty neighbour; growth stops once it is reached.

shape

Neighbourhood shape: "circle" (default, Euclidean radius) or "square" (Chebyshev radius).

how

How overlapping spread pixels combine: "over" (default) keeps the colour of the most-opaque contributor; "add" accumulates opacity (clamped) so overlaps darken.

Value

A raster grob with the chosen spread applied.

See also

spread(), datashade(), datashade_lines().

Examples

set.seed(1)
g <- datashade_segments(rnorm(2000), rnorm(2000), rnorm(2000), rnorm(2000))
g2 <- dynspread(g)