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/// Pattern fill for filled areas, bars, and other solid regions.
///
/// The default is [`FillPattern::Solid`] (no pattern, plain color fill).
///
/// Patterns are fully independent of the fill color — the hatch lines are
/// always black and render as an overlay on top of whatever color fill is
/// applied. This means every combination of color and pattern is valid, and
/// patterns remain useful even after converting a figure to greyscale.
///
/// When used with [`crate::render::Layout::with_bw_mode()`], patterns and grey
/// shades are assigned automatically to maximise distinguishability without
/// relying on color.
#[derive(Debug, Clone, Copy, PartialEq, Default)]
pub enum FillPattern {
/// No pattern — plain solid fill (default).
#[default]
Solid,
/// Horizontal parallel lines (═══).
Horizontal,
/// Vertical parallel lines (|||).
Vertical,
/// Forward-diagonal lines (///).
DiagonalForward,
/// Back-diagonal lines (\\\).
DiagonalBack,
/// Horizontal + vertical grid (+++).
Crosshatch,
/// Forward + back diagonal grid (×××).
DiagonalCrosshatch,
/// Scattered filled dots (···).
Dots,
}
impl FillPattern {
/// The SVG `id` used to reference this pattern via `fill="url(#id)"`.
///
/// Returns an empty string for [`FillPattern::Solid`].
pub fn id(self) -> &'static str {
match self {
FillPattern::Solid => "",
FillPattern::Horizontal => "kuva-fp-horiz",
FillPattern::Vertical => "kuva-fp-vert",
FillPattern::DiagonalForward => "kuva-fp-diag-fwd",
FillPattern::DiagonalBack => "kuva-fp-diag-back",
FillPattern::Crosshatch => "kuva-fp-crosshatch",
FillPattern::DiagonalCrosshatch => "kuva-fp-diag-cross",
FillPattern::Dots => "kuva-fp-dots",
}
}
/// The complete SVG `<pattern>…</pattern>` element to place in `<defs>`.
///
/// The pattern has a transparent background so the base fill color shows
/// through. Hatch lines are black and sized for readability at typical plot
/// resolutions and at 300 DPI print output.
///
/// Returns an empty string for [`FillPattern::Solid`].
pub fn svg_def(self) -> &'static str {
match self {
FillPattern::Solid => "",
FillPattern::Horizontal => concat!(
r#"<pattern id="kuva-fp-horiz" patternUnits="userSpaceOnUse" width="8" height="6">"#,
r#"<line x1="0" y1="3" x2="8" y2="3" stroke="black" stroke-width="0.6"/>"#,
r#"</pattern>"#,
),
FillPattern::Vertical => concat!(
r#"<pattern id="kuva-fp-vert" patternUnits="userSpaceOnUse" width="6" height="8">"#,
r#"<line x1="3" y1="0" x2="3" y2="8" stroke="black" stroke-width="0.6"/>"#,
r#"</pattern>"#,
),
// Three path segments tile a continuous diagonal line across any
// shape without gaps: top-left corner, main stripe, bottom-right corner.
FillPattern::DiagonalForward => concat!(
r#"<pattern id="kuva-fp-diag-fwd" patternUnits="userSpaceOnUse" width="6" height="6">"#,
r#"<path d="M-1,1 l2,-2 M0,6 l6,-6 M5,7 l2,-2" stroke="black" stroke-width="0.6" fill="none"/>"#,
r#"</pattern>"#,
),
FillPattern::DiagonalBack => concat!(
r#"<pattern id="kuva-fp-diag-back" patternUnits="userSpaceOnUse" width="6" height="6">"#,
r#"<path d="M-1,5 l2,2 M0,0 l6,6 M5,-1 l2,2" stroke="black" stroke-width="0.6" fill="none"/>"#,
r#"</pattern>"#,
),
FillPattern::Crosshatch => concat!(
r#"<pattern id="kuva-fp-crosshatch" patternUnits="userSpaceOnUse" width="8" height="8">"#,
r#"<path d="M0,4 H8 M4,0 V8" stroke="black" stroke-width="0.6" fill="none"/>"#,
r#"</pattern>"#,
),
FillPattern::DiagonalCrosshatch => concat!(
r#"<pattern id="kuva-fp-diag-cross" patternUnits="userSpaceOnUse" width="6" height="6">"#,
r#"<path d="M-1,1 l2,-2 M0,6 l6,-6 M5,7 l2,-2 M-1,5 l2,2 M0,0 l6,6 M5,-1 l2,2" stroke="black" stroke-width="0.6" fill="none"/>"#,
r#"</pattern>"#,
),
FillPattern::Dots => concat!(
r#"<pattern id="kuva-fp-dots" patternUnits="userSpaceOnUse" width="8" height="8">"#,
r#"<circle cx="4" cy="4" r="0.9" fill="black"/>"#,
r#"</pattern>"#,
),
}
}
/// Returns `true` for any variant other than [`FillPattern::Solid`].
pub fn is_patterned(self) -> bool {
self != FillPattern::Solid
}
/// Reverse of [`FillPattern::id`] — looks up the variant from its SVG
/// pattern `id`. Used by backends that can't resolve an SVG `<pattern>`
/// paint server (e.g. the raster backend) and need to identify which
/// hatch a `fill="url(#id)"` reference names.
pub fn from_id(id: &str) -> Option<Self> {
Some(match id {
"kuva-fp-horiz" => FillPattern::Horizontal,
"kuva-fp-vert" => FillPattern::Vertical,
"kuva-fp-diag-fwd" => FillPattern::DiagonalForward,
"kuva-fp-diag-back" => FillPattern::DiagonalBack,
"kuva-fp-crosshatch" => FillPattern::Crosshatch,
"kuva-fp-diag-cross" => FillPattern::DiagonalCrosshatch,
"kuva-fp-dots" => FillPattern::Dots,
_ => return None,
})
}
/// Ink coverage (`0.0` transparent .. `1.0` solid black) of this pattern's
/// hatch at local point `(x, y)`, in the same coordinate units as
/// [`FillPattern::svg_def`]'s tile (unscaled user-space units, tiled from
/// the origin). For backends that raster shapes directly instead of
/// resolving an SVG `<pattern>` paint server.
pub fn hatch_coverage(self, x: f32, y: f32) -> f32 {
// Matches `stroke-width="0.6"` in `svg_def`.
const HALF_STROKE: f32 = 0.3;
// Antialiasing ramp width, in the same user-space units as the tile.
const AA: f32 = 0.5;
// Distance from `v` to the nearest point where `(v - center)` is a
// multiple of `period` (i.e. distance to the nearest repeat of a
// 1-D line family), folded into `[0, period/2]`.
fn line_dist_1d(v: f32, period: f32, center: f32) -> f32 {
let m = (v - center).rem_euclid(period);
m.min(period - m)
}
// Coverage from a perpendicular distance to a stroked line: full ink
// within HALF_STROKE, ramping to zero over the next AA units.
fn stroke_ramp(dist: f32) -> f32 {
((HALF_STROKE + AA - dist) / AA).clamp(0.0, 1.0)
}
// Coverage from a distance to a filled disk of radius `r`.
fn disk_ramp(dist: f32, r: f32) -> f32 {
((r + AA - dist) / AA).clamp(0.0, 1.0)
}
match self {
FillPattern::Solid => 0.0,
// Line spans the full tile width; only y repeats.
FillPattern::Horizontal => stroke_ramp(line_dist_1d(y, 6.0, 3.0)),
// Line spans the full tile height; only x repeats.
FillPattern::Vertical => stroke_ramp(line_dist_1d(x, 6.0, 3.0)),
// Diagonal line family x + y ≡ 0 (mod 6); perpendicular distance
// divides the (x+y)-distance by sqrt(2).
FillPattern::DiagonalForward => {
stroke_ramp(line_dist_1d(x + y, 6.0, 0.0) / std::f32::consts::SQRT_2)
}
// Diagonal line family x - y ≡ 0 (mod 6).
FillPattern::DiagonalBack => {
stroke_ramp(line_dist_1d(x - y, 6.0, 0.0) / std::f32::consts::SQRT_2)
}
// Horizontal line (period 8, y=4) union vertical line (period 8, x=4).
FillPattern::Crosshatch => {
let h = stroke_ramp(line_dist_1d(y, 8.0, 4.0));
let v = stroke_ramp(line_dist_1d(x, 8.0, 4.0));
h.max(v)
}
// Union of both diagonal families, period 6.
FillPattern::DiagonalCrosshatch => {
let fwd = stroke_ramp(line_dist_1d(x + y, 6.0, 0.0) / std::f32::consts::SQRT_2);
let back = stroke_ramp(line_dist_1d(x - y, 6.0, 0.0) / std::f32::consts::SQRT_2);
fwd.max(back)
}
// Filled disk of radius 0.9 centered in an 8x8 tile.
FillPattern::Dots => {
let xm = x.rem_euclid(8.0) - 4.0;
let ym = y.rem_euclid(8.0) - 4.0;
disk_ramp((xm * xm + ym * ym).sqrt(), 0.9)
}
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn from_id_round_trips_with_id() {
for p in [
FillPattern::Horizontal,
FillPattern::Vertical,
FillPattern::DiagonalForward,
FillPattern::DiagonalBack,
FillPattern::Crosshatch,
FillPattern::DiagonalCrosshatch,
FillPattern::Dots,
] {
assert_eq!(
FillPattern::from_id(p.id()),
Some(p),
"{p:?} should round-trip through its id"
);
}
}
#[test]
fn from_id_rejects_unknown_and_solid() {
assert_eq!(FillPattern::from_id("not-a-pattern"), None);
// Solid has an empty id and is never referenced via url(#...), so it
// must not be reachable through from_id.
assert_eq!(FillPattern::from_id(""), None);
}
#[test]
fn solid_has_zero_coverage_everywhere() {
for (x, y) in [(0.0, 0.0), (3.0, 3.0), (100.0, -50.0)] {
assert_eq!(FillPattern::Solid.hatch_coverage(x, y), 0.0);
}
}
#[test]
fn horizontal_hatch_peaks_on_line_and_fades_between() {
// svg_def: line at y=3, tile height 6 — on-line at y=3, off-line
// (farthest from any line) at y=6 (equidistant between y=3 and y=9).
assert_eq!(FillPattern::Horizontal.hatch_coverage(0.0, 3.0), 1.0);
assert_eq!(FillPattern::Horizontal.hatch_coverage(0.0, 6.0), 0.0);
// Periodic: y=3 and y=9 (one tile over) are both on-line.
assert_eq!(FillPattern::Horizontal.hatch_coverage(0.0, 9.0), 1.0);
// x doesn't matter for a full-width horizontal line.
assert_eq!(
FillPattern::Horizontal.hatch_coverage(0.0, 3.0),
FillPattern::Horizontal.hatch_coverage(1000.0, 3.0),
);
}
#[test]
fn vertical_hatch_peaks_on_line_and_fades_between() {
assert_eq!(FillPattern::Vertical.hatch_coverage(3.0, 0.0), 1.0);
assert_eq!(FillPattern::Vertical.hatch_coverage(6.0, 0.0), 0.0);
}
#[test]
fn diagonal_forward_and_back_are_distinct() {
// At (0,0): forward's line family is x+y=0 (on-line, full coverage);
// back's line family is x-y=0 (also on-line here) — pick a point
// where they diverge: (1, 0). Forward: x+y=1, dist to nearest
// multiple of 6 is 1 (not on-line). Back: x-y=1, same. Use (3, -3):
// forward x+y=0 -> on-line; back x-y=6 -> on-line too. Use (1, 2):
// forward x+y=3 -> off-line (dist 3, max off); back x-y=-1 -> dist 1.
let fwd = FillPattern::DiagonalForward.hatch_coverage(1.0, 2.0);
let back = FillPattern::DiagonalBack.hatch_coverage(1.0, 2.0);
assert!(
fwd < back,
"forward ({fwd}) should be farther off-line than back ({back}) at (1,2)"
);
}
#[test]
fn crosshatch_covers_both_diagonal_and_horizontal_lines() {
// Crosshatch tile is 8x8 with lines at x=4 and y=4.
assert_eq!(FillPattern::Crosshatch.hatch_coverage(4.0, 0.0), 1.0);
assert_eq!(FillPattern::Crosshatch.hatch_coverage(0.0, 4.0), 1.0);
// Off both lines and far from either (corner of the tile).
assert_eq!(FillPattern::Crosshatch.hatch_coverage(0.0, 0.0), 0.0);
}
#[test]
fn dots_peak_at_tile_center_and_fade_at_tile_corner() {
// Dots tile is 8x8 with a disk at (4,4), r=0.9.
assert_eq!(FillPattern::Dots.hatch_coverage(4.0, 4.0), 1.0);
assert_eq!(FillPattern::Dots.hatch_coverage(0.0, 0.0), 0.0);
// Periodic: (12, 12) is the same tile-local point as (4, 4).
assert_eq!(FillPattern::Dots.hatch_coverage(12.0, 12.0), 1.0);
}
}