katex/src/fontMetrics.js

/* eslint no-unused-vars:0 */

var Style = require("./Style");

/**
 * This file contains metrics regarding fonts and individual symbols. The sigma
 * and xi variables, as well as the metricMap map contain data extracted from
 * TeX, TeX font metrics, and the TTF files. These data are then exposed via the
 * `metrics` variable and the getCharacterMetrics function.
 */

// These font metrics are extracted from TeX by using
// \font\a=cmmi10
// \showthe\fontdimenX\a
// where X is the corresponding variable number. These correspond to the font
// parameters of the symbol fonts. In TeX, there are actually three sets of
// dimensions, one for each of textstyle, scriptstyle, and scriptscriptstyle,
// but we only use the textstyle ones, and scale certain dimensions accordingly.
// See the TeXbook, page 441.
var sigma1 = 0.025;
var sigma2 = 0;
var sigma3 = 0;
var sigma4 = 0;
var sigma5 = 0.431;
var sigma6 = 1;
var sigma7 = 0;
var sigma8 = 0.677;
var sigma9 = 0.394;
var sigma10 = 0.444;
var sigma11 = 0.686;
var sigma12 = 0.345;
var sigma13 = 0.413;
var sigma14 = 0.363;
var sigma15 = 0.289;
var sigma16 = 0.150;
var sigma17 = 0.247;
var sigma18 = 0.386;
var sigma19 = 0.050;
var sigma20 = 2.390;
var sigma21 = 1.01;
var sigma21Script = 0.81;
var sigma21ScriptScript = 0.71;
var sigma22 = 0.250;

// These font metrics are extracted from TeX by using
// \font\a=cmex10
// \showthe\fontdimenX\a
// where X is the corresponding variable number. These correspond to the font
// parameters of the extension fonts (family 3). See the TeXbook, page 441.
var xi1 = 0;
var xi2 = 0;
var xi3 = 0;
var xi4 = 0;
var xi5 = 0.431;
var xi6 = 1;
var xi7 = 0;
var xi8 = 0.04;
var xi9 = 0.111;
var xi10 = 0.166;
var xi11 = 0.2;
var xi12 = 0.6;
var xi13 = 0.1;

// This value determines how large a pt is, for metrics which are defined in
// terms of pts.
// This value is also used in katex.less; if you change it make sure the values
// match.
var ptPerEm = 10.0;

// The space between adjacent `|` columns in an array definition. From
// `\showthe\doublerulesep` in LaTeX.
var doubleRuleSep = 2.0 / ptPerEm;

/**
 * This is just a mapping from common names to real metrics
 */
var metrics = {
    xHeight: sigma5,
    quad: sigma6,
    num1: sigma8,
    num2: sigma9,
    num3: sigma10,
    denom1: sigma11,
    denom2: sigma12,
    sup1: sigma13,
    sup2: sigma14,
    sup3: sigma15,
    sub1: sigma16,
    sub2: sigma17,
    supDrop: sigma18,
    subDrop: sigma19,
    axisHeight: sigma22,
    defaultRuleThickness: xi8,
    bigOpSpacing1: xi9,
    bigOpSpacing2: xi10,
    bigOpSpacing3: xi11,
    bigOpSpacing4: xi12,
    bigOpSpacing5: xi13,
    ptPerEm: ptPerEm,
    emPerEx: sigma5 / sigma6,
    doubleRuleSep: doubleRuleSep,

    // TODO(alpert): Missing parallel structure here. We should probably add
    // style-specific metrics for all of these.
    delim1: sigma20,
    getDelim2: function(style) {
        if (style.size === Style.TEXT.size) {
            return sigma21;
        } else if (style.size === Style.SCRIPT.size) {
            return sigma21Script;
        } else if (style.size === Style.SCRIPTSCRIPT.size) {
            return sigma21ScriptScript;
        }
        throw new Error("Unexpected style size: " + style.size);
    },
};

// This map contains a mapping from font name and character code to character
// metrics, including height, depth, italic correction, and skew (kern from the
// character to the corresponding \skewchar)
// This map is generated via `make metrics`. It should not be changed manually.
var metricMap = require("./fontMetricsData");

/**
 * This function is a convenience function for looking up information in the
 * metricMap table. It takes a character as a string, and a style.
 *
 * Note: the `width` property may be undefined if fontMetricsData.js wasn't
 * built using `Make extended_metrics`.
 */
var getCharacterMetrics = function(character, style) {
    var metrics = metricMap[style][character.charCodeAt(0)];
    if (metrics) {
        return {
            depth: metrics[0],
            height: metrics[1],
            italic: metrics[2],
            skew: metrics[3],
            width: metrics[4],
        };
    }
};

module.exports = {
    metrics: metrics,
    getCharacterMetrics: getCharacterMetrics,
};