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Simplex/fractal noise texture fill

Source: R/fill.R
fill_noise.Rd

fill_noise() builds a grid::pattern() fill value from a rasterised simplex/fractal noise field, using the same noise machinery as shape_blob()'s wobbly outline (ambient::fracture() / ambient::gen_simplex() / ambient::fbm(), with matching frequency, octaves, and seed arguments), so a noise-filled shape and a noise-wobbled outline share one visual vocabulary.

Usage

fill_noise(
  color = "black",
  spacing = 0.5,
  aspect = NULL,
  resolution = 32L,
  alpha = 1,
  frequency = 1,
  octaves = 2L,
  seed = 1L,
  extend = "repeat"
)

Arguments

color

One or more fill colours. A single colour (the default) fades in opacity from fully transparent to alpha, exactly as before this argument accepted a vector. Two or more colours instead blend across a grDevices::colorRamp() built from them, driven by the noise value, with alpha applied as a flat opacity across the whole fill (see the internal noise_to_pixels() helper). Default "black".

spacing

Baseline tile size, as a fraction of the target's bounding box. Must be a positive number. Default 0.5.

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.

resolution

Raster resolution (pixels per tile edge). Must be a positive integer of at least 2L. Default 32L.

alpha

Opacity. For a single color, the maximum opacity at the noise field's peak; for two or more, a flat opacity applied uniformly. Must be a number in (0, 1]. Default 1.

frequency

Noise frequency, as in shape_blob(). Must be non-negative. Default 1.

octaves

Number of noise octaves, as in shape_blob(). Must be a positive integer. Default 2L.

seed

Integer seed for the noise field, as in shape_blob(). Default 1L.

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

Noise is rendered as varying opacity of a single color, from fully transparent at the noise field's minimum to alpha at its maximum – a mottled, cloud-like texture rather than a hard-edged one.

A raster tile has no baked-in direction the way a hatch line does, so fill_hatch()'s tile-edge "dashing" problem doesn't apply directly, but an ordinary noise field still isn't periodic, and grid::pattern()'s extend = "repeat" will visibly seam wherever one tile edge fails to match the next. fill_noise() avoids this by sampling the noise on a torus: each raster pixel's (u, v) tile coordinate is mapped onto a pair of circles (ambient::gen_simplex()'s 4 dimensions, x/y for u and z/t for v) rather than sampled directly, so the field is mathematically periodic in both directions and tiles with no visible seam, at the cost of the noise "wrapping around" within each tile rather than varying smoothly across a larger area.

In practice, a very faint seam can still be visible at tile boundaries on some devices, even though the underlying field is exactly periodic; this appears to be an artifact of how the graphics device samples a repeated raster tile (it persists regardless of interpolate and doesn't improve with higher resolution), not a flaw in the noise field itself, and is far subtler than the tile-edge mismatch fill_hatch() has to actively avoid.

See also

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

Examples

draw(shape_circle(fill = fill_noise(seed = 8843L)))


# higher frequency/octaves give finer-grained texture
draw(shape_circle(
  fill = fill_noise(frequency = 4, octaves = 4L, seed = 8843L)
))


# a lower alpha lets the shape's own outline/background show through more
draw(shape_circle(
  fill = fill_noise(color = "steelblue", alpha = 0.5, seed = 8843L)
))


# two or more colours blend across the field instead of fading to transparent
draw(shape_circle(
  fill = fill_noise(color = c("steelblue", "white", "tomato"), seed = 8843L)
))