Create a sketchy engraving grob (tonal cross-hatch by line density)

Fills a region with engrave_fill(): a ladder of hatch layers whose accumulated density follows a tone field, so the region shades continuously from blank paper (light) to dense cross-hatch (dark) the way an etching does. The hatch geometry is computed in device inches (so angles and wobble are device-consistent); the field is supplied in npc [0,1] and sampled through an inch-to-npc affine at draw time.

Usage

sketch_engrave_grob(
  rings,
  field,
  ladder = NULL,
  ladder_levels = 5L,
  ladder_base_gap = 0.08,
  ladder_gap_ratio = 0.62,
  ladder_base_angle = 45,
  ladder_cross_after = 3L,
  roughness = 0.5,
  bowing = 0.3,
  seed = NULL,
  min_gap_in = 0.012,
  gp = gpar(),
  name = NULL,
  vp = NULL
)

Arguments

rings

A list of rings, each a list with npc [0,1] x and y vertex vectors bounding the region to engrave (even-odd holes honoured).

field

A vectorised tone function function(x, y) taking npc [0,1] coordinates and returning tone in [0, 1] (0 = paper, 1 = darkest).

ladder

A ladder from engrave_ladder(); NULL builds a default from the ladder_* parameters.

ladder_levels, ladder_base_gap, ladder_gap_ratio, ladder_base_angle, ladder_cross_after

Ladder controls used when ladder is NULL. ladder_base_gap is an npc-x fraction (converted to inches at draw time).

roughness, bowing, seed

Sketch parameters for the engraving strokes.

min_gap_in

Hard pitch floor in inches: ladder layers finer than this are dropped, so the darkest tones cannot explode into a runaway number of strokes. Default 0.012.

gp

gpar() for the engraving strokes (col, lwd).

name, vp

Passed to grid::gTree().

Value

A SketchEngraveGrob grob subclass.

See also

Other grob-layer: sketch_arrow_grob(), sketch_band_grob(), sketch_callout_grob(), sketch_dotplot_grob(), sketch_ellipse_grob(), sketch_path_grob(), sketch_polygon_grob(), sketch_repel_grob(), sketch_spray_grob(), sketch_stroke_grob(), sketch_wedge_grob()