API reference

Use case 1: height only

import { prepare, layout } from '@chenglou/pretext'

const prepared = prepare('Hello', '16px Inter')
const { height, lineCount } = layout(prepared, 280, 24)

• prepare(text, font, options?): font matches CanvasRenderingContext2D.font; optional { whiteSpace: 'pre-wrap' }.
• layout(prepared, maxWidth, lineHeight): returns height and line count.

Use case 2: line strings or varying widths

import {
  prepareWithSegments,
  layoutWithLines,
  walkLineRanges,
  layoutNextLine,
} from '@chenglou/pretext'

const p = prepareWithSegments(text, font)
const { lines, height, lineCount } = layoutWithLines(p, maxWidth, lineHeight)

walkLineRanges(p, maxWidth, (line) => {
  // line.width, line.start, line.end
})

let cursor = { segmentIndex: 0, graphemeIndex: 0 }
for (;;) {
  const line = layoutNextLine(p, cursor, widthForThisLine)
  if (line === null) break
  cursor = line.end
}

Main types (conceptual)

• LayoutLine: text, width, start, end.
• LayoutCursor: segmentIndex, graphemeIndex.

Other helpers

• clearCache(): drop internal measurement caches (e.g. when swapping many fonts).
• setLocale(locale?): affects future prepare calls and clears cache.
• profilePrepare(...): timing breakdown for profiling.