silk.text.vertical_text.

When to use#

Use orientations to lay out vertical text, such as vertical Japanese: it splits the text into runs that stand upright and runs that are rotated.

Details#

The orientation belongs to a whole extended grapheme cluster, so combining marks and emoji sequences never split. An enclosing mark makes its cluster upright. The runs are byte ranges of the text, appended to a caller-owned list.

Gotchas#

The result is the fallback orientation, without font data. A character with Vertical_Orientation Tu or Tr needs its vertical alternate glyph when the font has one. Read VerticalOrientation.of in silk.text.unicode_properties for that.

Examples#

Find the rotated part of vertical text#

import silk.collections.list { List }
import silk.core.effect { Effect }
import silk.mem.allocator { Allocator, OutOfMemoryError }
import silk.text.vertical_text
import silk.text.vertical_text { Orientation, OrientationRun }

pub effect fn main() -> i32
  ! OutOfMemoryError {
  let mut allocator = Allocator.systemAllocatorProvider()
  let mut runs = List<OrientationRun>.make()
  // Two kanji, then Latin letters.
  run vertical_text.orientations("\u{65e5}\u{672c}abc", &mut runs)
    |> Effect.provideMut<Allocator>(&mut allocator)
  let items = runs.asSlice()
  if items.length != 2 || items[0].orientation != Orientation.Upright || items[1].start != 6
    || items[1].orientation != Orientation.Rotated {
    return 1
  }
  return 0
}

Import as vertical_text with import silk.text.vertical_text as vertical_text.

Public declarations: 3.

Orientation#

pub enum Orientation

The fallback orientation of a character in vertical text.

Upright#

Upright

The glyph stands upright, as in the code charts.

Rotated#

Rotated

The glyph is rotated 90 degrees clockwise.

OrientationRun#

pub struct OrientationRun

A maximal range of a text with one fallback orientation, as orientations gives it.

Field start#

pub start: usize

The byte offset where the run starts.

Field end#

pub end: usize

The byte offset where the run ends.

Field orientation#

pub orientation: Orientation

The fallback orientation of the run.

Implementation Copy for OrientationRun#

impl Copy for OrientationRun

orientations#

pub effect fn orientations(text: string, output: &mut List<OrientationRun>) -> ()
  ! OutOfMemoryError
  ? &mut Allocator

Appends the runs of fallback orientation of text for vertical layout to output.

Details#

The orientation follows UAX #50 for whole extended grapheme clusters: the first scalar of a cluster decides, but an enclosing mark (General_Category Me) makes the cluster upright. Vertical_Orientation U and Tu give Orientation.Upright, and R and Tr give Orientation.Rotated. The runs are not empty, they cover the text in order without gaps, and empty text gives none. The function does not clear output, so clear it first to reuse its storage.

Errors#

• OutOfMemoryError if the Allocator cannot grow output.

Gotchas#

Tu and Tr characters need a vertical alternate glyph when the font has one; the fallback orientation applies only without it. Read VerticalOrientation.of in silk.text.unicode_properties to tell them apart from U and R.

Category: Text.

Profiles: aarch64-apple-darwin, aarch64-unknown-linux-gnu, aarch64-unknown-linux-gnu-no-libc, x86_64-unknown-linux-gnu, x86_64-unknown-linux-gnu-no-libc, wasm32-unknown-unknown, wasm32-wasip1, wasm32-wasip2, x86_64-pc-windows-msvc, wasm64-unknown-unknown.