| // @flow | |
| /** | |
| * This file does conversion between units. In particular, it provides | |
| * calculateSize to convert other units into ems. | |
| */ | |
| import ParseError from "./ParseError"; | |
| import Options from "./Options"; | |
| // This table gives the number of TeX pts in one of each *absolute* TeX unit. | |
| // Thus, multiplying a length by this number converts the length from units | |
| // into pts. Dividing the result by ptPerEm gives the number of ems | |
| // *assuming* a font size of ptPerEm (normal size, normal style). | |
| const ptPerUnit = { | |
| // https://en.wikibooks.org/wiki/LaTeX/Lengths and | |
| // https://tex.stackexchange.com/a/8263 | |
| "pt": 1, // TeX point | |
| "mm": 7227 / 2540, // millimeter | |
| "cm": 7227 / 254, // centimeter | |
| "in": 72.27, // inch | |
| "bp": 803 / 800, // big (PostScript) points | |
| "pc": 12, // pica | |
| "dd": 1238 / 1157, // didot | |
| "cc": 14856 / 1157, // cicero (12 didot) | |
| "nd": 685 / 642, // new didot | |
| "nc": 1370 / 107, // new cicero (12 new didot) | |
| "sp": 1 / 65536, // scaled point (TeX's internal smallest unit) | |
| // https://tex.stackexchange.com/a/41371 | |
| "px": 803 / 800, // \pdfpxdimen defaults to 1 bp in pdfTeX and LuaTeX | |
| }; | |
| // Dictionary of relative units, for fast validity testing. | |
| const relativeUnit = { | |
| "ex": true, | |
| "em": true, | |
| "mu": true, | |
| }; | |
| export type Measurement = {| number: number, unit: string |}; | |
| /** | |
| * Determine whether the specified unit (either a string defining the unit | |
| * or a "size" parse node containing a unit field) is valid. | |
| */ | |
| export const validUnit = function(unit: string | Measurement): boolean { | |
| if (typeof unit !== "string") { | |
| unit = unit.unit; | |
| } | |
| return (unit in ptPerUnit || unit in relativeUnit || unit === "ex"); | |
| }; | |
| /* | |
| * Convert a "size" parse node (with numeric "number" and string "unit" fields, | |
| * as parsed by functions.js argType "size") into a CSS em value for the | |
| * current style/scale. `options` gives the current options. | |
| */ | |
| export const calculateSize = function( | |
| sizeValue: Measurement, options: Options): number { | |
| let scale; | |
| if (sizeValue.unit in ptPerUnit) { | |
| // Absolute units | |
| scale = ptPerUnit[sizeValue.unit] // Convert unit to pt | |
| / options.fontMetrics().ptPerEm // Convert pt to CSS em | |
| / options.sizeMultiplier; // Unscale to make absolute units | |
| } else if (sizeValue.unit === "mu") { | |
| // `mu` units scale with scriptstyle/scriptscriptstyle. | |
| scale = options.fontMetrics().cssEmPerMu; | |
| } else { | |
| // Other relative units always refer to the *textstyle* font | |
| // in the current size. | |
| let unitOptions; | |
| if (options.style.isTight()) { | |
| // isTight() means current style is script/scriptscript. | |
| unitOptions = options.havingStyle(options.style.text()); | |
| } else { | |
| unitOptions = options; | |
| } | |
| // TODO: In TeX these units are relative to the quad of the current | |
| // *text* font, e.g. cmr10. KaTeX instead uses values from the | |
| // comparably-sized *Computer Modern symbol* font. At 10pt, these | |
| // match. At 7pt and 5pt, they differ: cmr7=1.138894, cmsy7=1.170641; | |
| // cmr5=1.361133, cmsy5=1.472241. Consider $\scriptsize a\kern1emb$. | |
| // TeX \showlists shows a kern of 1.13889 * fontsize; | |
| // KaTeX shows a kern of 1.171 * fontsize. | |
| if (sizeValue.unit === "ex") { | |
| scale = unitOptions.fontMetrics().xHeight; | |
| } else if (sizeValue.unit === "em") { | |
| scale = unitOptions.fontMetrics().quad; | |
| } else { | |
| throw new ParseError("Invalid unit: '" + sizeValue.unit + "'"); | |
| } | |
| if (unitOptions !== options) { | |
| scale *= unitOptions.sizeMultiplier / options.sizeMultiplier; | |
| } | |
| } | |
| return Math.min(sizeValue.number * scale, options.maxSize); | |
| }; | |
| /** | |
| * Round `n` to 4 decimal places, or to the nearest 1/10,000th em. See | |
| * https://github.com/KaTeX/KaTeX/pull/2460. | |
| */ | |
| export const makeEm = function(n: number): string { | |
| return +n.toFixed(4) + "em"; | |
| }; | |