Diagonal hatch pattern fill

fill_hatch() builds a grid::pattern() fill value that renders a repeating diagonal hatch line. It's meant to be used as the fill argument to grid::gpar() (and eventually style()'s fill property), in place of a plain colour.

Usage

fill_hatch(
  color = "black",
  angle = 45,
  spacing = 0.1,
  aspect = NULL,
  linewidth = 1,
  extend = "repeat"
)

Arguments

color

Line colour. Default "black".

angle

Hatch angle in degrees, measured counterclockwise from the positive x-axis. Default 45.

spacing

Baseline tile size, as a fraction of the target's bounding box. Must be a positive number. Default 0.1.

aspect

Width-to-height ratio of the target polygon's bounding box. Must be a positive number, or NULL (the default) to resolve it automatically from the real target's own bounding-box aspect ratio at draw() time – see the fill class. Passing a fixed number instead computes the pattern once, immediately, against that value only.

linewidth

Line width. Must be a positive number. Default 1.

extend

Passed to grid::pattern(). Default "repeat".

Value

A pattern object as returned by grid::pattern(), suitable for use as the fill argument to grid::gpar().

Details

grid::pattern() tiles are sized as a fraction of the target polygon's own bounding box, not a fixed physical square, so a tile that looks square in that relative sense can be a stretched rectangle in absolute terms whenever the target's bounding box isn't square itself – which distorts any angle baked directly into the pattern content. This is corrected automatically: aspect defaults to NULL, resolved against the real target's own bounding-box aspect ratio (width / height) at draw() time (see the fill class); pass a fixed number instead to compute the pattern once, immediately, against that value only.

Internally, the hatch line is always drawn as a plain diagonal from one tile corner to the opposite corner (or the mirror image, for a negative-sloped angle) – never at an arbitrary slope baked into the segment's own coordinates. A corner-to-corner diagonal is the only slope that tiles seamlessly under grid::pattern()'s extend = "repeat", which translates tile copies by whole tile-widths/heights only; any other local slope leaves a visible mismatch ("dashing") at every tile edge. The desired angle is instead achieved entirely by choosing the tile's width/height ratio. Exactly horizontal/vertical angles are handled as a special case, since a straight (non-diagonal) line tiles seamlessly at any tile aspect ratio.

See also

Other fill helpers: fill(), fill_charcoal(), fill_checker(), fill_crosshatch(), fill_flow(), fill_gradient(), fill_halftone(), fill_image(), fill_marble(), fill_noise(), fill_none(), fill_scatter(), fill_scribble(), fill_solid(), fill_stipple(), fill_stripe(), fill_vignette()

Examples

draw(shape_circle(fill = fill_hatch(angle = 30, spacing = 0.15)))


# a steeper angle and finer spacing
draw(shape_circle(fill = fill_hatch(angle = 75, spacing = 0.06)))


# exactly horizontal/vertical are handled as a special case (no
# diagonal-tile trick needed)
draw(shape_circle(fill = fill_hatch(angle = 0, spacing = 0.1)))


# aspect corrects the rendered angle for a non-square bounding box --
# without it, a 45 degree hatch looks skewed on a wide rectangle
draw(shape_rectangle(width = 3, height = 1, fill = fill_hatch(angle = 45)))

draw(shape_rectangle(
  width = 3,
  height = 1,
  fill = fill_hatch(angle = 45, aspect = 3)
))