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Domain-warped noise texture fill

Source: R/fill.R
fill_flow.Rd

fill_flow() is a swirlier variant of fill_noise(): before sampling the final noise field, the tile's own (theta_u, theta_v) angles (see fill_noise() details for why angles, not raw (u, v)) are displaced by a second, independent torus-periodic noise field – the "fBm of fBm" domain-warping recipe popularized for flowing, curl-noise-like textures, adapted here so the warp field is itself torus-periodic rather than sampled directly, keeping the whole result seamless.

Usage

fill_flow(
  color = "black",
  spacing = 0.5,
  aspect = NULL,
  resolution = 32L,
  alpha = 1,
  warp = 2,
  warp_frequency = 1,
  warp_octaves = 1L,
  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.

warp

Warp amplitude, in radians of angular displacement. Must be a non-negative number. Default 2.

warp_frequency

Frequency of the two warp-displacement noise fields. Must be non-negative. Default 1.

warp_octaves

Number of octaves for the warp-displacement noise fields. Must be a positive integer. Default 1L.

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

The warp field needs to be decorrelated from the final field and from itself along each axis, but ambient::gen_simplex()'s 4 input dimensions are already fully spent on the (theta_u, theta_v) torus trick, leaving no spare dimension to offset. fill_flow() decorrelates by seed instead: the u- and v-displacement fields are sampled at seed + 104729L and seed + 200003L respectively (arbitrary large primes, chosen only to make collisions with a user's own nearby seed choices unlikely), before the final field is sampled at seed itself.

Displacing a periodic field's own periodic coordinates by another periodic field preserves periodicity: shifting u from 0 to 1 still advances theta_u by exactly 2 * pi (a full turn), and the warp added at each end is identical since it's sampled from a field that's periodic in u itself – so the warped angle wraps around exactly as the unwarped one did, with no seam.

As with fill_noise(), a faint tile-boundary rasterization seam can still be visible on some devices despite the field being exactly periodic (see its details); larger warp values tend to make this more noticeable, for the same reason described at fill_marble().

See also

Other fill helpers: fill(), fill_charcoal(), fill_checker(), fill_crosshatch(), fill_gradient(), fill_halftone(), fill_hatch(), 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_flow(warp = 3, seed = 9350L)))


# a larger warp gives a swirlier, more curl-noise-like look; warp = 0
# reduces to plain fill_noise()
draw(shape_circle(fill = fill_flow(warp = 0, seed = 9350L)))

draw(shape_circle(fill = fill_flow(warp = 6, seed = 9350L)))


# two or more colours blend across the field, as in fill_noise()
draw(shape_circle(
  fill = fill_flow(color = c("steelblue", "white", "tomato"), seed = 9350L)
))