oxedyne/fe2o3/fe2o3_graphics/src/stroke.rs
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| 1 | //! Stroking: the ink a pen leaves as it travels a path. |
| 2 | //! |
| 3 | //! # A stroke is a fill |
| 4 | //! |
| 5 | //! Stroking is not a second kind of painting that needs a second rasteriser. The ink a pen leaves |
| 6 | //! is a region of the plane like any other, so the whole job here is to build that region as a |
| 7 | //! [`Path`], hand it to the filler, and add no code at all to the rasteriser. Everything the |
| 8 | //! rasteriser already knows -- the analytic anti-aliasing, the clipping, the compositing -- comes |
| 9 | //! for nothing. |
| 10 | //! |
| 11 | //! # How the region is built |
| 12 | //! |
| 13 | //! The tempting way is to offset the path to one side, offset it to the other, and sew the two |
| 14 | //! offsets into a single outline. That way lies grief. On the inside of a turn tighter than the pen |
| 15 | //! is wide the two offsets cross, and the outline ties itself into knots that only a |
| 16 | //! boolean-geometry engine can untie. |
| 17 | //! |
| 18 | //! So the region is built instead as a heap of convex pieces: a quadrilateral for each straight run |
| 19 | //! of the pen, a wedge or a triangle at each corner it turns, a cap at each loose end. Every piece |
| 20 | //! is wound the same way, by [`piece`], and that is the whole trick. Wound alike they add and never |
| 21 | //! cancel, so under the non-zero rule their union is exactly the ink -- knots, overlaps, hairpins |
| 22 | //! and all. It is also why the path [`Path::stroke`] returns must be filled with |
| 23 | //! [`crate::raster::FillRule::NonZero`]: fill it even-odd and every place two pieces overlap would |
| 24 | //! come out as a hole. |
| 25 | //! |
| 26 | //! # Why the pieces meet rather than overlap |
| 27 | //! |
| 28 | //! Where two pieces can be cut to share an edge, they are. A bevel or a miter join meets the two |
| 29 | //! runs it joins along the pen's end edge; a round join is a wedge of a disc rather than the whole |
| 30 | //! disc, and a round cap a half disc rather than a whole one. |
| 31 | //! |
| 32 | //! This is not tidiness. Because the rasteriser accumulates area rather than compositing coverage, |
| 33 | //! two pieces that meet edge to edge sum to exactly one across the seam, and the seam cannot be |
| 34 | //! seen. Two pieces that lie over each other along the union's own boundary would sum to two there, |
| 35 | //! and a pixel half covered would come out fully inked: a bright bead at every join. Cutting the |
| 36 | //! pieces to meet is what buys clean edges, and it costs nothing. |
| 37 | //! |
| 38 | //! [Written with AI entirely](https://need2know.ai/entirely-ai/code)\ |
| 39 | //! Anthropic Claude |
| 40 | |
| 41 | use crate::path::{ |
| 42 | Path, |
| 43 | PathBuilder, |
| 44 | Polyline, |
| 45 | Pt, |
| 46 | TOLERANCE, |
| 47 | }; |
| 48 | use crate::transform::Transform; |
| 49 | |
| 50 | use oxedyne_fe2o3_core::prelude::*; |
| 51 | |
| 52 | const MAX_ARC_STEPS: usize = 256; // however large the pen |
| 53 | |
| 54 | // The most dashes one contour may be cut into: a ceiling against a pattern so fine, on a path so |
| 55 | // long, that the outline would swallow the memory of the machine. |
| 56 | pub const MAX_DASHES: usize = 1 << 16; |
| 57 | |
| 58 | // Below this a cross product counts as zero and two directions as parallel. Both are unit vectors, |
| 59 | // so this is the sine of the angle between them, and an angle this small bends nothing a pixel can |
| 60 | // show. |
| 61 | const EPS_TURN: f32 = 1e-5; |
| 62 | |
| 63 | // Below this two points count as one, and a run of pen between them as having no length and so no |
| 64 | // direction to be offset along. |
| 65 | const EPS_LEN: f32 = 1e-6; |
| 66 | |
| 67 | // The default miter limit, as SVG and PostScript both have it: a corner whose miter would reach |
| 68 | // more than four line widths past it is bevelled instead. |
| 69 | pub const MITER_LIMIT: f32 = 4.0; |
| 70 | |
| 71 | /// How a stroke finishes at the loose end of an open contour. |
| 72 | #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)] |
| 73 | pub enum Cap { |
| 74 | #[default] |
| 75 | Butt, // stops dead on the end point, so a contour with no length is left undrawn |
| 76 | Round, // a half disc past the end point, so a contour with no length comes out as a dot |
| 77 | Square, // a half square past the end point, reaching out by half the line width |
| 78 | } |
| 79 | |
| 80 | /// How a stroke turns a corner. |
| 81 | #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)] |
| 82 | pub enum Join { |
| 83 | #[default] |
| 84 | Miter, // the outer edges carry on until they meet, or bevel where the limit is passed |
| 85 | Round, // a wedge of a disc, rounding the corner off |
| 86 | Bevel, // a straight cut across the corner, from one outer edge to the other |
| 87 | } |
| 88 | |
| 89 | /// A dash pattern: alternating lengths of ink and gap, walked round and round along the contour. |
| 90 | #[derive(Clone, Debug, Default, PartialEq)] |
| 91 | pub struct Dash { |
| 92 | // A pattern of odd length is walked twice over, so that ink and gap trade places on the second |
| 93 | // pass and the pattern only truly repeats after both, which is the rule SVG and PostScript |
| 94 | // share. |
| 95 | pub pattern: Vec<f32>, // lengths of ink and gap in turn, beginning with ink |
| 96 | pub offset: f32, // how far into the pattern the contour's first point stands |
| 97 | } |
| 98 | |
| 99 | impl Dash { |
| 100 | |
| 101 | /// Creates a pattern that begins at the start of its first length of ink. |
| 102 | pub fn new(pattern: Vec<f32>) -> Self { |
| 103 | Self { pattern, offset: 0.0 } |
| 104 | } |
| 105 | |
| 106 | pub fn with_offset(mut self, offset: f32) -> Self { |
| 107 | self.offset = offset; |
| 108 | self |
| 109 | } |
| 110 | } |
| 111 | |
| 112 | /// The pen: everything that decides what ink a path leaves. |
| 113 | #[derive(Clone, Debug, PartialEq)] |
| 114 | pub struct Stroke { |
| 115 | pub width: f32, // in the coordinates the path is expressed in; must be positive |
| 116 | pub cap: Cap, // only an open contour has loose ends to finish |
| 117 | pub join: Join, |
| 118 | // The furthest a miter may reach past a corner, as a multiple of the line width. A corner |
| 119 | // sharper than this is bevelled instead, which is what stops a path that nearly doubles back |
| 120 | // from throwing a spike clear across the page. Must be at least one, since even a right angle |
| 121 | // mitres to more than one line width. |
| 122 | pub miter_limit: f32, |
| 123 | pub dash: Option<Dash>, // set where the line is to be broken |
| 124 | // The flattening tolerance, in the coordinates the path is expressed in: the furthest a |
| 125 | // straight segment may stray from the curve or the arc it stands in for. A caller who will |
| 126 | // then scale the stroked path up tenfold should divide this by ten, as Path::flatten does with |
| 127 | // its own tolerance, and as Pixmap::stroke_path does on the caller's behalf. |
| 128 | pub tol: f32, |
| 129 | } |
| 130 | |
| 131 | impl Default for Stroke { |
| 132 | fn default() -> Self { |
| 133 | Self { |
| 134 | width: 1.0, |
| 135 | cap: Cap::default(), |
| 136 | join: Join::default(), |
| 137 | miter_limit: MITER_LIMIT, |
| 138 | dash: None, |
| 139 | tol: TOLERANCE, |
| 140 | } |
| 141 | } |
| 142 | } |
| 143 | |
| 144 | impl Stroke { |
| 145 | |
| 146 | /// Creates a pen, refusing a width that cannot draw. |
| 147 | pub fn new(width: f32) -> Outcome<Self> { |
| 148 | let s = Self { width, ..Self::default() }; |
| 149 | res!(s.check()); |
| 150 | Ok(s) |
| 151 | } |
| 152 | |
| 153 | pub fn with_cap(mut self, cap: Cap) -> Self { |
| 154 | self.cap = cap; |
| 155 | self |
| 156 | } |
| 157 | |
| 158 | pub fn with_join(mut self, join: Join) -> Self { |
| 159 | self.join = join; |
| 160 | self |
| 161 | } |
| 162 | |
| 163 | /// The limit is a multiple of the line width. |
| 164 | pub fn with_miter_limit(mut self, limit: f32) -> Self { |
| 165 | self.miter_limit = limit; |
| 166 | self |
| 167 | } |
| 168 | |
| 169 | pub fn with_dash(mut self, dash: Dash) -> Self { |
| 170 | self.dash = Some(dash); |
| 171 | self |
| 172 | } |
| 173 | |
| 174 | pub fn with_tolerance(mut self, tol: f32) -> Self { |
| 175 | self.tol = tol; |
| 176 | self |
| 177 | } |
| 178 | |
| 179 | /// Refuses a pen that cannot draw. |
| 180 | /// |
| 181 | /// The fields are public, so a pen can be assembled without passing through [`Stroke::new`]. |
| 182 | /// This is where every pen is checked all the same, once, at the moment it is asked to draw. |
| 183 | pub fn check(&self) -> Outcome<()> { |
| 184 | if !self.width.is_finite() || self.width <= 0.0 { |
| 185 | return Err(err!( |
| 186 | "A stroke width must be positive and finite, but {} was given.", self.width; |
| 187 | Invalid, Input)); |
| 188 | } |
| 189 | if !self.miter_limit.is_finite() || self.miter_limit < 1.0 { |
| 190 | return Err(err!( |
| 191 | "A miter limit must be at least one, since a miter reaches at least one line width \ |
| 192 | past even a right angle, but {} was given.", self.miter_limit; |
| 193 | Invalid, Input, Range)); |
| 194 | } |
| 195 | if !self.tol.is_finite() || self.tol <= 0.0 { |
| 196 | return Err(err!( |
| 197 | "A flattening tolerance must be positive and finite, but {} was given.", self.tol; |
| 198 | Invalid, Input)); |
| 199 | } |
| 200 | if let Some(d) = &self.dash { |
| 201 | if d.pattern.is_empty() { |
| 202 | return Err(err!( |
| 203 | "A dash pattern must name at least one length of ink."; |
| 204 | Invalid, Input, Missing)); |
| 205 | } |
| 206 | if !d.offset.is_finite() { |
| 207 | return Err(err!( |
| 208 | "A dash offset must be finite, but {} was given.", d.offset; |
| 209 | Invalid, Input)); |
| 210 | } |
| 211 | let mut total = 0.0f32; |
| 212 | for (i, len) in d.pattern.iter().enumerate() { |
| 213 | if !len.is_finite() || *len < 0.0 { |
| 214 | return Err(err!( |
| 215 | "A dash length must be finite and no less than zero, but the one at {} is \ |
| 216 | {}.", i, len; |
| 217 | Invalid, Input)); |
| 218 | } |
| 219 | total += *len; |
| 220 | } |
| 221 | if total <= 0.0 { |
| 222 | return Err(err!( |
| 223 | "A dash pattern of {} lengths that are all zero never turns the ink on.", |
| 224 | d.pattern.len(); |
| 225 | Invalid, Input)); |
| 226 | } |
| 227 | } |
| 228 | Ok(()) |
| 229 | } |
| 230 | } |
| 231 | |
| 232 | impl Path { |
| 233 | |
| 234 | /// The ink the pen leaves, as a new path. |
| 235 | /// |
| 236 | /// The result is a union of convex pieces all wound the same way, so it must be filled under |
| 237 | /// [`crate::raster::FillRule::NonZero`] -- which is the default, and what |
| 238 | /// [`crate::pixmap::Pixmap::fill_path`] uses. Filling it even-odd would open a hole wherever two |
| 239 | /// pieces overlap. |
| 240 | pub fn stroke(&self, pen: &Stroke) -> Outcome<Self> { |
| 241 | res!(pen.check()); |
| 242 | let r = 0.5 * pen.width; // Half the width: how far the pen reaches to either side. |
| 243 | let mut pb = PathBuilder::new(); |
| 244 | for pl in self.flatten_contours(&Transform::IDENTITY, pen.tol) { |
| 245 | match &pen.dash { |
| 246 | None => stroke_contour(&mut pb, &pl, pen, r), |
| 247 | Some(d) => { |
| 248 | for run in res!(dash(&pl, d)) { |
| 249 | stroke_contour(&mut pb, &run, pen, r); |
| 250 | } |
| 251 | }, |
| 252 | } |
| 253 | } |
| 254 | pb.finish() |
| 255 | } |
| 256 | } |
| 257 | |
| 258 | fn stroke_contour(pb: &mut PathBuilder, pl: &Polyline, pen: &Stroke, r: f32) { |
| 259 | let pts = dedup(&pl.pts, pl.closed); |
| 260 | if pts.is_empty() { |
| 261 | return; |
| 262 | } |
| 263 | if pts.len() == 1 { |
| 264 | // A contour with no length. It still leaves a mark, if the cap reaches anywhere. |
| 265 | point_cap(pb, pts[0], pen.cap, r, pen.tol); |
| 266 | return; |
| 267 | } |
| 268 | let n = pts.len(); |
| 269 | // The runs of pen: one for each edge, and for a closed contour the edge back to the start too. |
| 270 | let edges = if pl.closed { n } else { n - 1 }; |
| 271 | let mut dirs: Vec<Pt> = Vec::with_capacity(edges); |
| 272 | for i in 0..edges { |
| 273 | match dir(pts[i], pts[(i + 1) % n]) { |
| 274 | Some(d) => dirs.push(d), |
| 275 | // Unreachable after `dedup`, but no offset here may ever divide by a zero length. |
| 276 | None => return, |
| 277 | } |
| 278 | } |
| 279 | |
| 280 | // Each straight run of the pen, as a quadrilateral. |
| 281 | for i in 0..edges { |
| 282 | let (a, b) = (pts[i], pts[(i + 1) % n]); |
| 283 | let nv = mul(left(dirs[i]), r); |
| 284 | piece(pb, &[add(a, nv), add(b, nv), sub(b, nv), sub(a, nv)]); |
| 285 | } |
| 286 | |
| 287 | if pl.closed { |
| 288 | // A closed contour turns a corner at every point, its first included, and has no ends. |
| 289 | for i in 0..edges { |
| 290 | let prev = (i + edges - 1) % edges; |
| 291 | join(pb, pts[i], dirs[prev], dirs[i], pen, r); |
| 292 | } |
| 293 | } else { |
| 294 | for i in 1..(n - 1) { |
| 295 | join(pb, pts[i], dirs[i - 1], dirs[i], pen, r); |
| 296 | } |
| 297 | // The two loose ends. The pen leaves the first one travelling backwards. |
| 298 | end_cap(pb, pts[0], mul(dirs[0], -1.0), pen.cap, r, pen.tol); |
| 299 | end_cap(pb, pts[n - 1], dirs[edges - 1], pen.cap, r, pen.tol); |
| 300 | } |
| 301 | } |
| 302 | |
| 303 | /// Adds the piece that fills the corner at `v`, where the pen turns from direction `d0` to `d1`. |
| 304 | fn join(pb: &mut PathBuilder, v: Pt, d0: Pt, d1: Pt, pen: &Stroke, r: f32) { |
| 305 | let cross = d0.x * d1.y - d0.y * d1.x; |
| 306 | let dot = d0.x * d1.x + d0.y * d1.y; |
| 307 | |
| 308 | if cross.abs() < EPS_TURN { |
| 309 | if dot > 0.0 { |
| 310 | return; // Straight on. There is no corner here to fill. |
| 311 | } |
| 312 | // A hairpin: the pen doubles back along itself, and the corner is the whole half disc past |
| 313 | // `v`. A miter here would reach to infinity and so is always over its limit, and the bevel |
| 314 | // it falls back to is a triangle with no area, so only a round join leaves anything at all. |
| 315 | if let Join::Round = pen.join { |
| 316 | piece(pb, &round_cap(v, d0, r, pen.tol)); |
| 317 | } |
| 318 | return; |
| 319 | } |
| 320 | |
| 321 | // The outside of the turn is the side the pen sweeps the long way round: the right hand turning |
| 322 | // one way, the left hand turning the other. |
| 323 | let outer = if cross > 0.0 { right } else { left }; |
| 324 | let n0 = mul(outer(d0), r); |
| 325 | let n1 = mul(outer(d1), r); |
| 326 | // The signed angle the pen turns through, which is also the angle from `n0` to `n1`, a normal |
| 327 | // being nothing but its direction under a quarter turn. |
| 328 | // |
| 329 | // Taken at double width and brought back. See [`arc_steps`] for why: the single-width form of this |
| 330 | // function is what ties a binary to the C library it was built against. |
| 331 | let phi = (cross as f64).atan2(dot as f64) as f32; |
| 332 | |
| 333 | match pen.join { |
| 334 | Join::Bevel => piece(pb, &[v, add(v, n0), add(v, n1)]), |
| 335 | Join::Round => { |
| 336 | // A wedge of the disc, not the disc: its two straight edges are the end edges of the |
| 337 | // two runs of pen it sits between, so it meets them instead of lying over them. |
| 338 | let steps = arc_steps(r, phi, pen.tol); |
| 339 | let step = phi / (steps as f32); |
| 340 | let mut pts = Vec::with_capacity(steps + 2); |
| 341 | pts.push(v); |
| 342 | for k in 0..=steps { |
| 343 | pts.push(add(v, rot(n0, (k as f32) * step))); |
| 344 | } |
| 345 | piece(pb, &pts); |
| 346 | }, |
| 347 | Join::Miter => { |
| 348 | // The miter reaches 1 / cos(phi / 2) line widths past the corner, which runs away to |
| 349 | // nothing as the corner sharpens towards a hairpin. The limit is what keeps a needle |
| 350 | // from becoming a spear. |
| 351 | let c = (0.5 * phi).cos(); |
| 352 | let reach = if c > f32::EPSILON { 1.0 / c } else { f32::INFINITY }; |
| 353 | let bisect = add(n0, n1); // Two normals of a length bisect the angle between them. |
| 354 | let len = (bisect.x * bisect.x + bisect.y * bisect.y).sqrt(); |
| 355 | if !reach.is_finite() || reach > pen.miter_limit || len <= EPS_LEN { |
| 356 | piece(pb, &[v, add(v, n0), add(v, n1)]); // Over the limit: bevel it instead. |
| 357 | } else { |
| 358 | let m = add(v, mul(bisect, r * reach / len)); |
| 359 | piece(pb, &[v, add(v, n0), m, add(v, n1)]); |
| 360 | } |
| 361 | }, |
| 362 | } |
| 363 | } |
| 364 | |
| 365 | /// Adds the piece that finishes a loose end at `e`, which the pen reached travelling in `d`. |
| 366 | fn end_cap(pb: &mut PathBuilder, e: Pt, d: Pt, cap: Cap, r: f32, tol: f32) { |
| 367 | match cap { |
| 368 | Cap::Butt => (), |
| 369 | Cap::Round => piece(pb, &round_cap(e, d, r, tol)), |
| 370 | Cap::Square => piece(pb, &square_cap(e, d, r)), |
| 371 | } |
| 372 | } |
| 373 | |
| 374 | /// Adds the mark a contour with no length leaves: a dot under a round cap, a square under a square |
| 375 | /// cap, and nothing at all under a butt cap, which reaches nowhere. |
| 376 | fn point_cap(pb: &mut PathBuilder, e: Pt, cap: Cap, r: f32, tol: f32) { |
| 377 | match cap { |
| 378 | Cap::Butt => (), |
| 379 | Cap::Round => { |
| 380 | // A whole disc, since there is no direction here to take half of. |
| 381 | let steps = arc_steps(r, std::f32::consts::TAU, tol).max(3); |
| 382 | let step = std::f32::consts::TAU / (steps as f32); |
| 383 | let pts: Vec<Pt> = (0..steps) |
| 384 | .map(|k| add(e, rot(Pt::new(r, 0.0), (k as f32) * step))) |
| 385 | .collect(); |
| 386 | piece(pb, &pts); |
| 387 | }, |
| 388 | Cap::Square => piece(pb, &[ |
| 389 | Pt::new(e.x - r, e.y - r), |
| 390 | Pt::new(e.x + r, e.y - r), |
| 391 | Pt::new(e.x + r, e.y + r), |
| 392 | Pt::new(e.x - r, e.y + r), |
| 393 | ]), |
| 394 | } |
| 395 | } |
| 396 | |
| 397 | /// The points of a round cap: a half disc past `e`, bulging the way `d` points. |
| 398 | /// |
| 399 | /// The straight edge of the half disc runs from one side of the line to the other, which is exactly |
| 400 | /// the end edge of the run of pen reaching `e`, so cap and run meet rather than overlap. |
| 401 | fn round_cap(e: Pt, d: Pt, r: f32, tol: f32) -> Vec<Pt> { |
| 402 | let n = mul(left(d), r); |
| 403 | // The left normal leads the direction by a quarter turn, so sweeping back by half a turn from |
| 404 | // it passes through the direction itself, which is the way the cap must bulge. Sweeping forward |
| 405 | // would put the cap behind the pen, inside the ink, where it would do nothing. |
| 406 | let steps = arc_steps(r, std::f32::consts::PI, tol); |
| 407 | let step = -std::f32::consts::PI / (steps as f32); |
| 408 | (0..=steps).map(|k| add(e, rot(n, (k as f32) * step))).collect() |
| 409 | } |
| 410 | |
| 411 | /// The points of a square cap: a half square past `e`, reaching out by `r` the way `d` points. |
| 412 | fn square_cap(e: Pt, d: Pt, r: f32) -> Vec<Pt> { |
| 413 | let n = mul(left(d), r); |
| 414 | let out = mul(d, r); |
| 415 | let (a, b) = (add(e, n), sub(e, n)); |
| 416 | vec![a, add(a, out), add(b, out), b] |
| 417 | } |
| 418 | |
| 419 | /// Adds one convex piece of the outline, wound the same way as every other piece. |
| 420 | /// |
| 421 | /// The winding is settled here, by the sign of the shoelace area, and nowhere else. The union only |
| 422 | /// holds if nothing cancels: two pieces wound against each other would subtract where they overlap |
| 423 | /// and eat a hole out of the middle of a perfectly good stroke. |
| 424 | fn piece(pb: &mut PathBuilder, pts: &[Pt]) { |
| 425 | if pts.len() < 3 { |
| 426 | return; // Nothing with an interior. |
| 427 | } |
| 428 | let mut area = 0.0f32; |
| 429 | for i in 0..pts.len() { |
| 430 | let (a, b) = (pts[i], pts[(i + 1) % pts.len()]); |
| 431 | area += a.x * b.y - b.x * a.y; |
| 432 | } |
| 433 | if area >= 0.0 { |
| 434 | pb.move_to(pts[0]); |
| 435 | for p in &pts[1..] { |
| 436 | pb.line_to(*p); |
| 437 | } |
| 438 | } else { |
| 439 | pb.move_to(pts[pts.len() - 1]); |
| 440 | for p in pts[..pts.len() - 1].iter().rev() { |
| 441 | pb.line_to(*p); |
| 442 | } |
| 443 | } |
| 444 | pb.close(); |
| 445 | } |
| 446 | |
| 447 | /// Cuts a contour into the runs of ink a dash pattern leaves along it. |
| 448 | fn dash(pl: &Polyline, d: &Dash) -> Outcome<Vec<Polyline>> { |
| 449 | // An odd pattern is walked twice, so that ink and gap trade places on the second pass. |
| 450 | let mut pat = d.pattern.clone(); |
| 451 | if pat.len() % 2 == 1 { |
| 452 | pat.extend_from_within(..); |
| 453 | } |
| 454 | let total: f32 = pat.iter().sum(); |
| 455 | let pts = &pl.pts; |
| 456 | if pts.len() < 2 || total <= 0.0 { |
| 457 | return Ok(vec![pl.clone()]); |
| 458 | } |
| 459 | |
| 460 | // Where in the pattern the contour's first point already stands. |
| 461 | let mut phase = d.offset % total; |
| 462 | if phase < 0.0 { |
| 463 | phase += total; |
| 464 | } |
| 465 | let mut i = 0usize; |
| 466 | // The phase is less than the total, so it is spent before the pattern runs out. |
| 467 | for _ in 0..pat.len() { |
| 468 | if phase < pat[i] { |
| 469 | break; |
| 470 | } |
| 471 | phase -= pat[i]; |
| 472 | i = (i + 1) % pat.len(); |
| 473 | } |
| 474 | let mut on = i % 2 == 0; // Even lengths are ink, odd ones gap. |
| 475 | let mut rest = pat[i] - phase; // How much of the current length has yet to run. |
| 476 | |
| 477 | let began_on = on; |
| 478 | let n = pts.len(); |
| 479 | let edges = if pl.closed { n } else { n - 1 }; |
| 480 | let mut out: Vec<Polyline> = Vec::new(); |
| 481 | let mut cur: Vec<Pt> = if on { vec![pts[0]] } else { Vec::new() }; |
| 482 | |
| 483 | for e in 0..edges { |
| 484 | let (a, b) = (pts[e], pts[(e + 1) % n]); |
| 485 | let len = a.distance(b); |
| 486 | if !len.is_finite() || len <= EPS_LEN { |
| 487 | continue; // Nothing to walk along, and nothing to divide by. |
| 488 | } |
| 489 | let mut t = 0.0f32; // How far along this edge the walk has come. |
| 490 | while rest < len - t { |
| 491 | t += rest; |
| 492 | let p = lerp(a, b, t / len); |
| 493 | if on { |
| 494 | cur.push(p); |
| 495 | out.push(Polyline { pts: std::mem::take(&mut cur), closed: false }); |
| 496 | if out.len() > MAX_DASHES { |
| 497 | return Err(err!( |
| 498 | "A dash pattern of total length {} cuts this contour into more than {} \ |
| 499 | runs of ink.", total, MAX_DASHES; |
| 500 | Invalid, Input, Excessive)); |
| 501 | } |
| 502 | } else { |
| 503 | cur.clear(); |
| 504 | cur.push(p); |
| 505 | } |
| 506 | on = !on; |
| 507 | i = (i + 1) % pat.len(); |
| 508 | rest = pat[i]; |
| 509 | } |
| 510 | rest -= len - t; |
| 511 | if on { |
| 512 | cur.push(b); |
| 513 | } |
| 514 | } |
| 515 | |
| 516 | // Whatever the walk was still laying down when it ran out of contour. |
| 517 | if on && !cur.is_empty() { |
| 518 | if out.is_empty() { |
| 519 | // The pattern never turned off, so the contour survives whole, and closed if it began |
| 520 | // so: a dash long enough to swallow a ring leaves a ring, not a ring cut open. |
| 521 | out.push(Polyline { pts: cur, closed: pl.closed }); |
| 522 | } else if pl.closed && began_on { |
| 523 | // The walk began and ended inside the same length of ink, on either side of the |
| 524 | // contour's first point. They are one run, and must be sewn back into one, or the |
| 525 | // corner there would come out capped twice over instead of joined. |
| 526 | let head = std::mem::take(&mut out[0].pts); |
| 527 | let mut sewn = cur; |
| 528 | sewn.extend_from_slice(&head[1..]); |
| 529 | out[0].pts = sewn; |
| 530 | } else { |
| 531 | out.push(Polyline { pts: cur, closed: false }); |
| 532 | } |
| 533 | } |
| 534 | Ok(out) |
| 535 | } |
| 536 | |
| 537 | /// Drops each point that repeats the one before it, and the closing point of a closed contour that |
| 538 | /// names its first point twice. |
| 539 | /// |
| 540 | /// A run of pen with no length has no direction, and a direction is what every offset, every join |
| 541 | /// and every cap here is built from. |
| 542 | fn dedup(pts: &[Pt], closed: bool) -> Vec<Pt> { |
| 543 | let mut out: Vec<Pt> = Vec::with_capacity(pts.len()); |
| 544 | for p in pts { |
| 545 | match out.last() { |
| 546 | Some(q) if q.distance(*p) < EPS_LEN => (), |
| 547 | _ => out.push(*p), |
| 548 | } |
| 549 | } |
| 550 | if closed && out.len() > 1 { |
| 551 | let (first, last) = (out[0], out[out.len() - 1]); |
| 552 | if first.distance(last) < EPS_LEN { |
| 553 | out.pop(); |
| 554 | } |
| 555 | } |
| 556 | out |
| 557 | } |
| 558 | |
| 559 | /// How many straight segments an arc needs to stay within the tolerance. |
| 560 | /// |
| 561 | /// A chord subtending an angle `a` on a circle of radius `r` bulges away from it by `r(1 - |
| 562 | /// cos(a/2))`, so holding that below the tolerance fixes the angle, and the angle fixes the count. |
| 563 | fn arc_steps(r: f32, sweep: f32, tol: f32) -> usize { |
| 564 | let sweep = sweep.abs(); |
| 565 | if !sweep.is_finite() || sweep <= 0.0 { |
| 566 | return 1; |
| 567 | } |
| 568 | let cos = (1.0 - tol / r).clamp(-1.0, 1.0); |
| 569 | // The widest angle one chord may span. Taken at DOUBLE width and brought back, rather than in single |
| 570 | // width directly. |
| 571 | // |
| 572 | // This is a portability matter, not a numerical one. The single-width transcendentals -- `acosf`, |
| 573 | // `atan2f` and their kin -- gained fresh symbol versions in glibc 2.43, so a binary built against it |
| 574 | // asks for `acosf@GLIBC_2.43` and will not load on a machine whose C library is older, however little |
| 575 | // of it the program actually uses. The double-width forms have carried the same version since |
| 576 | // glibc 2.2.5 and are on every machine that will ever run this. A binary built on the newest |
| 577 | // distribution therefore still runs on the ones beside it -- which for a library whose whole point is |
| 578 | // to be self-contained is the behaviour to want. The double-width answer is also the more accurate of |
| 579 | // the two; nothing is given up. |
| 580 | let a = 2.0 * (cos as f64).acos() as f32; |
| 581 | if !a.is_finite() || a <= 0.0 { |
| 582 | return MAX_ARC_STEPS; |
| 583 | } |
| 584 | ((sweep / a).ceil().max(1.0) as usize).min(MAX_ARC_STEPS) |
| 585 | } |
| 586 | |
| 587 | /// The unit direction from `a` to `b`, or `None` where there is none because they are one point. |
| 588 | fn dir(a: Pt, b: Pt) -> Option<Pt> { |
| 589 | let d = sub(b, a); |
| 590 | let len = (d.x * d.x + d.y * d.y).sqrt(); |
| 591 | if !len.is_finite() || len < EPS_LEN { |
| 592 | return None; |
| 593 | } |
| 594 | Some(mul(d, 1.0 / len)) |
| 595 | } |
| 596 | |
| 597 | fn add(a: Pt, b: Pt) -> Pt { |
| 598 | Pt::new(a.x + b.x, a.y + b.y) |
| 599 | } |
| 600 | |
| 601 | fn sub(a: Pt, b: Pt) -> Pt { |
| 602 | Pt::new(a.x - b.x, a.y - b.y) |
| 603 | } |
| 604 | |
| 605 | fn mul(a: Pt, s: f32) -> Pt { |
| 606 | Pt::new(a.x * s, a.y * s) |
| 607 | } |
| 608 | |
| 609 | fn lerp(a: Pt, b: Pt, s: f32) -> Pt { |
| 610 | Pt::new(a.x + (b.x - a.x) * s, a.y + (b.y - a.y) * s) |
| 611 | } |
| 612 | |
| 613 | /// The left normal of a direction: the direction under a quarter turn. |
| 614 | fn left(d: Pt) -> Pt { |
| 615 | Pt::new(-d.y, d.x) |
| 616 | } |
| 617 | |
| 618 | /// The right normal of a direction: the direction under a quarter turn the other way. |
| 619 | fn right(d: Pt) -> Pt { |
| 620 | Pt::new(d.y, -d.x) |
| 621 | } |
| 622 | |
| 623 | fn rot(v: Pt, a: f32) -> Pt { |
| 624 | let (s, c) = a.sin_cos(); |
| 625 | Pt::new(v.x * c - v.y * s, v.x * s + v.y * c) |
| 626 | } |
| 627 | |
| 628 | #[cfg(test)] |
| 629 | mod tests { |
| 630 | use super::*; |
| 631 | |
| 632 | use crate::{ |
| 633 | colour::Rgba, |
| 634 | pixmap::Pixmap, |
| 635 | }; |
| 636 | |
| 637 | /// Renders a stroke, black on white, so that a test can read the ink back pixel by pixel. |
| 638 | fn ink(path: &Path, pen: &Stroke, w: usize, h: usize) -> Outcome<Pixmap> { |
| 639 | let mut pm = res!(Pixmap::filled(w, h, Rgba::WHITE)); |
| 640 | res!(pm.stroke_path(path, &Transform::IDENTITY, Rgba::BLACK, None, pen)); |
| 641 | Ok(pm) |
| 642 | } |
| 643 | |
| 644 | /// How dark a pixel came out, from 0 for untouched to 1 for solid. |
| 645 | fn dark(pm: &Pixmap, x: usize, y: usize) -> f32 { |
| 646 | match pm.pixel(x, y) { |
| 647 | Some(c) => 1.0 - (c.r as f32) / 255.0, |
| 648 | None => 0.0, |
| 649 | } |
| 650 | } |
| 651 | |
| 652 | /// The topmost row holding any real ink, which is how far a corner reaches. |
| 653 | fn top_row(pm: &Pixmap) -> Option<usize> { |
| 654 | for y in 0..pm.height() { |
| 655 | for x in 0..pm.width() { |
| 656 | if dark(pm, x, y) > 0.5 { |
| 657 | return Some(y); |
| 658 | } |
| 659 | } |
| 660 | } |
| 661 | None |
| 662 | } |
| 663 | |
| 664 | fn line(a: Pt, b: Pt) -> Outcome<Path> { |
| 665 | let mut pb = PathBuilder::new(); |
| 666 | pb.move_to(a); |
| 667 | pb.line_to(b); |
| 668 | pb.finish() |
| 669 | } |
| 670 | |
| 671 | fn square(x0: f32, y0: f32, x1: f32, y1: f32, closed: bool) -> Outcome<Path> { |
| 672 | let mut pb = PathBuilder::new(); |
| 673 | pb.move_to(Pt::new(x0, y0)); |
| 674 | pb.line_to(Pt::new(x1, y0)); |
| 675 | pb.line_to(Pt::new(x1, y1)); |
| 676 | pb.line_to(Pt::new(x0, y1)); |
| 677 | if closed { |
| 678 | pb.close(); |
| 679 | } |
| 680 | pb.finish() |
| 681 | } |
| 682 | |
| 683 | /// A narrow V, whose apex is sharp enough to mitre past the default limit. |
| 684 | /// |
| 685 | /// The arms meet at about 28 degrees, so the miter reaches about 4.1 line widths past the apex: |
| 686 | /// over the default limit of 4, and under a limit of 6. |
| 687 | fn vee() -> Outcome<Path> { |
| 688 | let mut pb = PathBuilder::new(); |
| 689 | pb.move_to(Pt::new(14.0, 38.0)); |
| 690 | pb.line_to(Pt::new(20.0, 14.0)); |
| 691 | pb.line_to(Pt::new(26.0, 38.0)); |
| 692 | pb.finish() |
| 693 | } |
| 694 | |
| 695 | #[test] |
| 696 | fn test_a_width_that_cannot_draw_is_refused_00() -> Outcome<()> { |
| 697 | let path = res!(line(Pt::new(2.0, 8.0), Pt::new(14.0, 8.0))); |
| 698 | assert!(Stroke::new(0.0).is_err(), "a zero width"); |
| 699 | assert!(Stroke::new(-3.0).is_err(), "a negative width"); |
| 700 | assert!(Stroke::new(f32::NAN).is_err(), "a width that is not a number"); |
| 701 | assert!(Stroke::new(f32::INFINITY).is_err(), "an infinite width"); |
| 702 | // The fields are public, so the check must also bite at the moment of drawing. |
| 703 | let bad = Stroke { width: -1.0, ..Stroke::default() }; |
| 704 | assert!(path.stroke(&bad).is_err(), "a negative width set after construction"); |
| 705 | Ok(()) |
| 706 | } |
| 707 | |
| 708 | #[test] |
| 709 | fn test_a_miter_limit_below_one_is_refused_01() -> Outcome<()> { |
| 710 | let path = res!(vee()); |
| 711 | let pen = res!(Stroke::new(4.0)).with_miter_limit(0.5); |
| 712 | assert!(pen.check().is_err(), "a limit no miter could ever meet"); |
| 713 | assert!(path.stroke(&pen).is_err()); |
| 714 | Ok(()) |
| 715 | } |
| 716 | |
| 717 | #[test] |
| 718 | fn test_a_line_strokes_to_a_band_02() -> Outcome<()> { |
| 719 | // A pen four wide, run from (2, 8) to (14, 8), inks the band x in [2, 14], y in [6, 10]. |
| 720 | let path = res!(line(Pt::new(2.0, 8.0), Pt::new(14.0, 8.0))); |
| 721 | let pen = res!(Stroke::new(4.0)); |
| 722 | let pm = res!(ink(&path, &pen, 16, 16)); |
| 723 | assert!(dark(&pm, 8, 6) > 0.99, "the top row of the band, found {}", dark(&pm, 8, 6)); |
| 724 | assert!(dark(&pm, 8, 9) > 0.99, "the bottom row of the band"); |
| 725 | assert!(dark(&pm, 8, 5) < 0.01, "above the band, found {}", dark(&pm, 8, 5)); |
| 726 | assert!(dark(&pm, 8, 10) < 0.01, "below the band, found {}", dark(&pm, 8, 10)); |
| 727 | assert!(dark(&pm, 2, 8) > 0.99, "the first column of the band"); |
| 728 | assert!(dark(&pm, 13, 8) > 0.99, "the last column of the band"); |
| 729 | Ok(()) |
| 730 | } |
| 731 | |
| 732 | #[test] |
| 733 | fn test_a_butt_cap_reaches_nowhere_but_the_others_reach_out_03() -> Outcome<()> { |
| 734 | let path = res!(line(Pt::new(2.0, 8.0), Pt::new(14.0, 8.0))); |
| 735 | let base = res!(Stroke::new(4.0)); |
| 736 | |
| 737 | let butt = res!(ink(&path, &base.clone().with_cap(Cap::Butt), 16, 16)); |
| 738 | assert!(dark(&butt, 1, 8) < 0.01, "a butt cap stops dead, found {}", dark(&butt, 1, 8)); |
| 739 | |
| 740 | let square = res!(ink(&path, &base.clone().with_cap(Cap::Square), 16, 16)); |
| 741 | assert!(dark(&square, 1, 8) > 0.99, "a square cap reaches out by half the width"); |
| 742 | assert!(dark(&square, 0, 6) > 0.99, "and squarely, right into its corner"); |
| 743 | |
| 744 | let round = res!(ink(&path, &base.with_cap(Cap::Round), 16, 16)); |
| 745 | assert!(dark(&round, 1, 8) > 0.99, "a round cap reaches out too"); |
| 746 | assert!( |
| 747 | dark(&round, 0, 6) < 0.5, |
| 748 | "but roundly, so it does not fill the corner, found {}", dark(&round, 0, 6), |
| 749 | ); |
| 750 | Ok(()) |
| 751 | } |
| 752 | |
| 753 | #[test] |
| 754 | fn test_a_point_is_a_dot_under_a_round_cap_and_nothing_under_a_butt_04() -> Outcome<()> { |
| 755 | // A contour with no length: the pen is set down and lifted in the same place. |
| 756 | let mut pb = PathBuilder::new(); |
| 757 | pb.move_to(Pt::new(8.0, 8.0)); |
| 758 | pb.line_to(Pt::new(8.0, 8.0)); |
| 759 | let path = res!(pb.finish()); |
| 760 | let base = res!(Stroke::new(4.0)); |
| 761 | |
| 762 | let butt = res!(path.stroke(&base.clone().with_cap(Cap::Butt))); |
| 763 | assert!(butt.is_empty(), "a butt cap on a point reaches nowhere, so there is no ink"); |
| 764 | |
| 765 | let round = res!(ink(&path, &base.clone().with_cap(Cap::Round), 16, 16)); |
| 766 | assert!(dark(&round, 8, 8) > 0.99, "a round cap on a point is a dot"); |
| 767 | assert!(dark(&round, 8, 4) < 0.01, "and no larger than the pen"); |
| 768 | assert!( |
| 769 | dark(&round, 6, 6) < 0.5, |
| 770 | "and round, so its corner is bitten off, found {}", dark(&round, 6, 6), |
| 771 | ); |
| 772 | |
| 773 | let sq = res!(ink(&path, &base.with_cap(Cap::Square), 16, 16)); |
| 774 | assert!(dark(&sq, 8, 8) > 0.99, "a square cap on a point is a square"); |
| 775 | assert!(dark(&sq, 6, 6) > 0.99, "with its corner still on, found {}", dark(&sq, 6, 6)); |
| 776 | Ok(()) |
| 777 | } |
| 778 | |
| 779 | #[test] |
| 780 | fn test_a_closed_contour_is_joined_all_the_way_round_05() -> Outcome<()> { |
| 781 | // The corner at the contour's first point is the one that tells the tale. Closed, the pen |
| 782 | // turns it and the miter fills the outer corner. Open, the pen starts and stops there, and |
| 783 | // two butt caps leave the outer corner bare. |
| 784 | let pen = res!(Stroke::new(2.0)); |
| 785 | let shut = res!(ink(&res!(square(4.0, 4.0, 12.0, 12.0, true)), &pen, 16, 16)); |
| 786 | let open = res!(ink(&res!(square(4.0, 4.0, 12.0, 12.0, false)), &pen, 16, 16)); |
| 787 | assert!( |
| 788 | dark(&shut, 3, 3) > 0.99, |
| 789 | "a closed contour joins its first corner, found {}", dark(&shut, 3, 3), |
| 790 | ); |
| 791 | assert!( |
| 792 | dark(&open, 3, 3) < 0.01, |
| 793 | "an open one caps it instead, found {}", dark(&open, 3, 3), |
| 794 | ); |
| 795 | // The other three corners are turned either way, so they must agree. |
| 796 | assert!(dark(&shut, 12, 3) > 0.99, "the far corner, closed"); |
| 797 | assert!(dark(&open, 12, 3) > 0.99, "the far corner, open"); |
| 798 | Ok(()) |
| 799 | } |
| 800 | |
| 801 | #[test] |
| 802 | fn test_a_miter_over_the_limit_falls_back_to_a_bevel_06() -> Outcome<()> { |
| 803 | let path = res!(vee()); |
| 804 | let base = res!(Stroke::new(4.0)); |
| 805 | |
| 806 | // Under a limit of six the apex mitres, throwing the ink well above the apex at y = 14. |
| 807 | let long = res!(ink(&path, &base.clone().with_miter_limit(6.0), 40, 40)); |
| 808 | let far = match top_row(&long) { |
| 809 | Some(y) => y, |
| 810 | None => return Err(err!("The stroke of a V must leave some ink."; Bug)), |
| 811 | }; |
| 812 | assert!(far < 9, "a miter should reach far past the apex, but stopped at row {}", far); |
| 813 | |
| 814 | // Under the default limit of four the same apex is over the limit, and is bevelled: the ink |
| 815 | // stops within half a line width of the apex. |
| 816 | let cut = res!(ink(&path, &base.clone(), 40, 40)); |
| 817 | let near = match top_row(&cut) { |
| 818 | Some(y) => y, |
| 819 | None => return Err(err!("The stroke of a V must leave some ink."; Bug)), |
| 820 | }; |
| 821 | assert!( |
| 822 | near >= 12, |
| 823 | "a miter over its limit should be bevelled back, but reached row {}", near, |
| 824 | ); |
| 825 | |
| 826 | // A bevel asked for outright must land in the same place as the miter that fell back to one. |
| 827 | let bevel = res!(ink(&path, &base.with_join(Join::Bevel), 40, 40)); |
| 828 | assert_eq!(cut, bevel, "a miter over its limit must be exactly a bevel"); |
| 829 | Ok(()) |
| 830 | } |
| 831 | |
| 832 | #[test] |
| 833 | fn test_a_round_join_stays_within_half_a_width_of_the_corner_07() -> Outcome<()> { |
| 834 | // A round join is a wedge of a disc of half the line width, so however sharp the corner, it |
| 835 | // can never reach further than that. The apex is at y = 14 and the pen is 4 wide. |
| 836 | let path = res!(vee()); |
| 837 | let pen = res!(Stroke::new(4.0)).with_join(Join::Round); |
| 838 | let pm = res!(ink(&path, &pen, 40, 40)); |
| 839 | let top = match top_row(&pm) { |
| 840 | Some(y) => y, |
| 841 | None => return Err(err!("The stroke of a V must leave some ink."; Bug)), |
| 842 | }; |
| 843 | assert!(top >= 11, "a round join cannot reach past row 12, but reached row {}", top); |
| 844 | assert!(top <= 13, "nor should it fall short of the corner, found row {}", top); |
| 845 | Ok(()) |
| 846 | } |
| 847 | |
| 848 | #[test] |
| 849 | fn test_a_hairpin_is_rounded_off_but_not_mitred_08() -> Outcome<()> { |
| 850 | // The pen runs out to (20, 8) and doubles straight back. A round join must put a half disc |
| 851 | // past the turn, bulging the way the pen was going, not the way it came. A miter there |
| 852 | // would reach to infinity, so it must fall back to a bevel, which at a hairpin is nothing. |
| 853 | let mut pb = PathBuilder::new(); |
| 854 | pb.move_to(Pt::new(4.0, 8.0)); |
| 855 | pb.line_to(Pt::new(20.0, 8.0)); |
| 856 | pb.line_to(Pt::new(4.0, 8.0)); |
| 857 | let path = res!(pb.finish()); |
| 858 | let base = res!(Stroke::new(4.0)); |
| 859 | |
| 860 | // The pen is 4 wide, so the half disc has a radius of 2. The pixel at (20, 8) lies wholly |
| 861 | // inside it, and the one at (21, 8) hangs over its rim. |
| 862 | let round = res!(ink(&path, &base.clone().with_join(Join::Round), 24, 16)); |
| 863 | assert!( |
| 864 | dark(&round, 20, 8) > 0.99, |
| 865 | "a round join must bulge past the turn, found {}", dark(&round, 20, 8), |
| 866 | ); |
| 867 | assert!( |
| 868 | dark(&round, 21, 8) > 0.8, |
| 869 | "and reach nearly a full radius past it, found {}", dark(&round, 21, 8), |
| 870 | ); |
| 871 | |
| 872 | let mitre = res!(ink(&path, &base.with_join(Join::Miter), 24, 16)); |
| 873 | assert!( |
| 874 | dark(&mitre, 20, 8) < 0.01, |
| 875 | "a miter at a hairpin must fall back to a bevel, and so to nothing, found {}", |
| 876 | dark(&mitre, 20, 8), |
| 877 | ); |
| 878 | Ok(()) |
| 879 | } |
| 880 | |
| 881 | #[test] |
| 882 | fn test_the_seams_between_the_pieces_do_not_show_09() -> Outcome<()> { |
| 883 | // The outline is a heap of pieces, and the joins between them run right through the ink. If |
| 884 | // the pieces were composited the seams would show as light or dark lines; because the |
| 885 | // rasteriser adds areas, they cannot. Every pixel well inside the band must be solid. |
| 886 | let mut pb = PathBuilder::new(); |
| 887 | pb.move_to(Pt::new(4.0, 8.0)); |
| 888 | pb.line_to(Pt::new(20.0, 8.0)); |
| 889 | pb.line_to(Pt::new(20.0, 24.0)); |
| 890 | let path = res!(pb.finish()); |
| 891 | let pen = res!(Stroke::new(6.0)).with_join(Join::Round); |
| 892 | let pm = res!(ink(&path, &pen, 32, 32)); |
| 893 | for x in 5..19 { |
| 894 | assert!(dark(&pm, x, 8) > 0.99, "a seam shows at ({}, 8): {}", x, dark(&pm, x, 8)); |
| 895 | } |
| 896 | for y in 10..22 { |
| 897 | assert!(dark(&pm, 20, y) > 0.99, "a seam shows at (20, {}): {}", y, dark(&pm, 20, y)); |
| 898 | } |
| 899 | // And the corner itself, which is where three pieces meet. |
| 900 | assert!(dark(&pm, 19, 9) > 0.99, "the corner is not solid: {}", dark(&pm, 19, 9)); |
| 901 | Ok(()) |
| 902 | } |
| 903 | |
| 904 | #[test] |
| 905 | fn test_a_curve_is_stroked_10() -> Outcome<()> { |
| 906 | // The pen follows the flattened curve, so the ink must be a band about it and nothing more. |
| 907 | let mut pb = PathBuilder::new(); |
| 908 | pb.move_to(Pt::new(4.0, 28.0)); |
| 909 | pb.quad_to(Pt::new(16.0, 0.0), Pt::new(28.0, 28.0)); |
| 910 | let path = res!(pb.finish()); |
| 911 | let pen = res!(Stroke::new(3.0)).with_cap(Cap::Round); |
| 912 | let pm = res!(ink(&path, &pen, 32, 32)); |
| 913 | assert!(dark(&pm, 16, 14) > 0.9, "the crown of the arc, found {}", dark(&pm, 16, 14)); |
| 914 | assert!(dark(&pm, 16, 26) < 0.01, "under the arc, found {}", dark(&pm, 16, 26)); |
| 915 | assert!(dark(&pm, 16, 8) < 0.01, "over the arc, found {}", dark(&pm, 16, 8)); |
| 916 | Ok(()) |
| 917 | } |
| 918 | |
| 919 | #[test] |
| 920 | fn test_a_dash_breaks_the_line_11() -> Outcome<()> { |
| 921 | // Four on, four off, from x = 0. |
| 922 | let path = res!(line(Pt::new(0.0, 8.0), Pt::new(32.0, 8.0))); |
| 923 | let pen = res!(Stroke::new(4.0)).with_dash(Dash::new(vec![4.0, 4.0])); |
| 924 | let pm = res!(ink(&path, &pen, 32, 16)); |
| 925 | assert!(dark(&pm, 2, 8) > 0.99, "the first dash"); |
| 926 | assert!(dark(&pm, 6, 8) < 0.01, "the first gap, found {}", dark(&pm, 6, 8)); |
| 927 | assert!(dark(&pm, 10, 8) > 0.99, "the second dash"); |
| 928 | assert!(dark(&pm, 14, 8) < 0.01, "the second gap"); |
| 929 | Ok(()) |
| 930 | } |
| 931 | |
| 932 | #[test] |
| 933 | fn test_an_odd_dash_pattern_is_walked_twice_12() -> Outcome<()> { |
| 934 | // A pattern of one length means four on, four off, as if it had been written out in full. |
| 935 | let path = res!(line(Pt::new(0.0, 8.0), Pt::new(32.0, 8.0))); |
| 936 | let pen = res!(Stroke::new(4.0)); |
| 937 | let odd = res!(ink(&path, &pen.clone().with_dash(Dash::new(vec![4.0])), 32, 16)); |
| 938 | let even = res!(ink(&path, &pen.with_dash(Dash::new(vec![4.0, 4.0])), 32, 16)); |
| 939 | assert_eq!(odd, even, "an odd pattern must be walked twice over"); |
| 940 | Ok(()) |
| 941 | } |
| 942 | |
| 943 | #[test] |
| 944 | fn test_a_dash_offset_shifts_the_pattern_13() -> Outcome<()> { |
| 945 | let path = res!(line(Pt::new(0.0, 8.0), Pt::new(32.0, 8.0))); |
| 946 | let dash = Dash::new(vec![4.0, 4.0]).with_offset(4.0); |
| 947 | let pen = res!(Stroke::new(4.0)).with_dash(dash); |
| 948 | let pm = res!(ink(&path, &pen, 32, 16)); |
| 949 | assert!(dark(&pm, 2, 8) < 0.01, "the pattern begins in a gap, found {}", dark(&pm, 2, 8)); |
| 950 | assert!(dark(&pm, 6, 8) > 0.99, "and the first dash follows it"); |
| 951 | Ok(()) |
| 952 | } |
| 953 | |
| 954 | #[test] |
| 955 | fn test_a_dash_that_spans_a_closed_contour_leaves_it_closed_14() -> Outcome<()> { |
| 956 | // The ring is 32 round and the ink runs for 1000, so the pattern never turns off. The ring |
| 957 | // must come back whole, joined at its first corner and not cut open and capped there. |
| 958 | let path = res!(square(4.0, 4.0, 12.0, 12.0, true)); |
| 959 | let pen = res!(Stroke::new(2.0)).with_dash(Dash::new(vec![1000.0])); |
| 960 | let pm = res!(ink(&path, &pen, 16, 16)); |
| 961 | assert!( |
| 962 | dark(&pm, 3, 3) > 0.99, |
| 963 | "the first corner must still be joined, found {}", dark(&pm, 3, 3), |
| 964 | ); |
| 965 | Ok(()) |
| 966 | } |
| 967 | |
| 968 | #[test] |
| 969 | fn test_a_dash_wrapping_a_closed_contour_is_sewn_back_together_15() -> Outcome<()> { |
| 970 | // The ring is 32 round. Ten on, five off, walked from its first corner, ends with the ink |
| 971 | // still on as the walk comes back round to where it began. That last run and the first are |
| 972 | // one run, on either side of the corner, and must be sewn into one: sewn, the corner is |
| 973 | // joined; unsewn, it comes out as two butt caps with a notch between them. |
| 974 | let path = res!(square(4.0, 4.0, 12.0, 12.0, true)); |
| 975 | let pen = res!(Stroke::new(2.0)).with_dash(Dash::new(vec![10.0, 5.0])); |
| 976 | let pm = res!(ink(&path, &pen, 16, 16)); |
| 977 | assert!( |
| 978 | dark(&pm, 3, 3) > 0.99, |
| 979 | "the wrapping dash must be sewn back into one, found {}", dark(&pm, 3, 3), |
| 980 | ); |
| 981 | Ok(()) |
| 982 | } |
| 983 | |
| 984 | #[test] |
| 985 | fn test_a_dash_pattern_that_never_inks_is_refused_16() -> Outcome<()> { |
| 986 | let path = res!(line(Pt::new(0.0, 8.0), Pt::new(32.0, 8.0))); |
| 987 | let base = res!(Stroke::new(4.0)); |
| 988 | let empty = base.clone().with_dash(Dash::new(vec![])); |
| 989 | assert!(path.stroke(&empty).is_err(), "a pattern of no lengths"); |
| 990 | let zeros = base.clone().with_dash(Dash::new(vec![0.0, 0.0])); |
| 991 | assert!(path.stroke(&zeros).is_err(), "a pattern that is all zeroes"); |
| 992 | let neg = base.clone().with_dash(Dash::new(vec![4.0, -1.0])); |
| 993 | assert!(path.stroke(&neg).is_err(), "a pattern with a negative length"); |
| 994 | let nan = base.with_dash(Dash::new(vec![4.0, 4.0]).with_offset(f32::NAN)); |
| 995 | assert!(path.stroke(&nan).is_err(), "an offset that is not a number"); |
| 996 | Ok(()) |
| 997 | } |
| 998 | |
| 999 | #[test] |
| 1000 | fn test_an_empty_path_strokes_to_nothing_17() -> Outcome<()> { |
| 1001 | let pen = res!(Stroke::new(4.0)).with_cap(Cap::Round); |
| 1002 | let empty = res!(PathBuilder::new().finish()); |
| 1003 | assert!(res!(empty.stroke(&pen)).is_empty()); |
| 1004 | // A move with nothing after it goes nowhere and leaves nothing, where a move closed on |
| 1005 | // itself is a path asking for a dot. |
| 1006 | let mut pb = PathBuilder::new(); |
| 1007 | pb.move_to(Pt::new(8.0, 8.0)); |
| 1008 | let lone = res!(pb.finish()); |
| 1009 | assert!(res!(lone.stroke(&pen)).is_empty(), "a lone move leaves nothing"); |
| 1010 | Ok(()) |
| 1011 | } |
| 1012 | |
| 1013 | #[test] |
| 1014 | fn test_the_outline_is_filled_non_zero_not_even_odd_18() -> Outcome<()> { |
| 1015 | // The pieces overlap, so an even-odd fill of the outline would eat holes out of it. This |
| 1016 | // pins the contract that [`Path::stroke`] documents. |
| 1017 | use crate::raster::FillRule; |
| 1018 | let mut pb = PathBuilder::new(); |
| 1019 | pb.move_to(Pt::new(4.0, 8.0)); |
| 1020 | pb.line_to(Pt::new(20.0, 8.0)); |
| 1021 | pb.line_to(Pt::new(20.0, 24.0)); |
| 1022 | let path = res!(pb.finish()); |
| 1023 | let pen = res!(Stroke::new(6.0)).with_join(Join::Round); |
| 1024 | let outline = res!(path.stroke(&pen)); |
| 1025 | |
| 1026 | let mut nz = res!(Pixmap::filled(32, 32, Rgba::WHITE)); |
| 1027 | res!(nz.fill_path(&outline, &Transform::IDENTITY, Rgba::BLACK, None)); |
| 1028 | let mut eo = res!(Pixmap::filled(32, 32, Rgba::WHITE)); |
| 1029 | res!(eo.fill_path_with( |
| 1030 | &outline, &Transform::IDENTITY, Rgba::BLACK, None, FillRule::EvenOdd, |
| 1031 | )); |
| 1032 | assert!(dark(&nz, 19, 9) > 0.99, "the corner is solid under the non-zero rule"); |
| 1033 | assert!( |
| 1034 | dark(&eo, 19, 9) < 0.5, |
| 1035 | "and eaten away under the even-odd rule, found {}", dark(&eo, 19, 9), |
| 1036 | ); |
| 1037 | Ok(()) |
| 1038 | } |
| 1039 | } |