Add support for expression-style metric override. The old [metric-override.multiplies] and [metric-override.adds] are no longer supported (#1181).

README.md

@@ -3014,23 +3014,47 @@ Subsection `metric-override` provides ability to override certain metric values,
 | `powerlineShiftX`, `powerlineShiftY` | emu | 0 | X and Y shift of Powerline glyphs. |
 | `onumZeroHeightRatio` | (*ratio*) | 1.145 | Ratio of height of `0` under `onum` feature, to the height of `x`. |
 
-Sub-subsection `metric-override.multiplies` and `metric-override.adds` could be used to override the value by multiplying a scale to the default value, then add a shift to it further. The following configuration
+The values of each item could be either a number, or a string representing an expression so that it could be different for different instance fonts, or depending on default values. The syntax of valid expressions are:
+
+```
+Expression -> Term (('+' | '-') Term)*
+Term       -> Factor (('*' | '/') Factor)*
+Factor     -> ('+' | '-')* Primitive
+Primitive  -> Literal
+            | Call
+            | Binding
+            | Group
+            | List
+Literal    -> ['0'..'9']+ ('.' ['0'..'9']+)?
+Identifier -> ['A'..'Z', 'a'..'z', '_']+
+Call       -> Identifier '(' Expression (',' Expression)* ')'
+List       -> Identifier '[' Expression (',' Expression)* ']'
+Binding    -> Identifier
+```
+
+Valid identifiers include:
+ * `weight`: being the weight grade;
+ * `width`: being the characters' unit width, measured in em-units;
+ * `slopeAngle`: being the slope angle in degrees;
+ * Default value of all overridable metrics, prefixed with `default_`, i.e., default `cap` value will be accessable thorugh `default_cap`.
+
+Valid functions include:
+ * `blend`(_x_, \[_x1_, _y1_\], \[_x2_, _y2_\], ...): Perform a smooth interpolation through data pairs \[_x1_, _y1_\], \[_x2_, _y2_\], ..., against parameter _x_.
+
+For example, the following configuration:
 
 ```toml
 [buildPlans.iosevka-custom.metric-override]
 leading = 1500
-
+sb = 'default_sb * 1.0625 + 15'
-[buildPlans.iosevka-custom.metric-override.multiplies]
+dotSize = 'blend(weight, [100, 50], [400, 125], [900, 180])'
-sb = 1.0625
-
-[buildPlans.iosevka-custom.metric-override.adds]
-sb = 15
 ```
 
 will:
 
-* Override line height to `1500` em-unit;
+ * Override line height to `1500` em-unit;
-* Override the sidebearing value by its value multiplied by `1.0625` then added with `15`.
+ * Override the sidebearing value by its value multiplied by `1.0625` then added with `15`.
+ * Override the dot size by a interpolation against weight: at thin (`100`) being `50`, at regular (`400`) being `125`, and at heavy (`900`) being `180`.
 
 #### Sample Configuration
 

changes/9.0.0.md

@@ -1,3 +1,4 @@
+ * \[**Breaking**\]: Add support for expression-style metric override. The old `[metric-override.multiplies]` and `[metric-override.adds]` are no longer supported (#1181).
  * Fix motion-serifed N's broken shape (#1170).
  * Fix bar-serif overlapping in Latin Small H-bar (`U+0127`) and Cyrillic Small Dje (`U+0452`) in Sans subfamily's with-serif variants (#1171).
  * Add flat-boundary brace shape (#1172).

font-src/index.js

@@ -10,6 +10,7 @@ const Toml = require("@iarna/toml");
 
 const { buildFont } = require("./gen/build-font.js");
 const Parameters = require("./support/parameters");
+const { applyMetricOverride } = require("./support/metric-override");
 const VariantData = require("./support/variant-data");
 const { applyLigationData } = require("./support/ligation-data");
 const { createGrDisplaySheet } = require("./support/gr");
@@ -49,7 +50,7 @@ async function getParameters() {
 
 		if (argv.excludedCharRanges) para.excludedCharRanges = argv.excludedCharRanges;
 		if (argv.compatibilityLigatures) para.compLig = argv.compatibilityLigatures;
-		if (argv.metricOverride) Parameters.applyMetricOverride(para, argv.metricOverride);
+		if (argv.metricOverride) applyMetricOverride(para, argv.metricOverride, argv);
 
 		para.naming = {
 			...para.naming,

font-src/support/metric-override.js

@@ -0,0 +1,246 @@
+"use strict";
+
+const { monotonicInterpolate } = require("./util/monotonic-interpolate");
+
+exports.applyMetricOverride = applyMetricOverride;
+function applyMetricOverride(para, mo, argv) {
+	const bindings = initBindings(para, argv);
+	for (const [field, expr] of Object.entries(mo)) {
+		if (!validMetricOverrideFields.has(field)) {
+			console.error(`Field ${field} cannot be get overridden.`);
+			continue;
+		}
+		if (typeof expr === "number") {
+			para[field] = expr;
+		} else if (typeof expr === "string") {
+			const e = RootExpression(new State(expr), bindings);
+			if (typeof e !== "number")
+				throw new TypeError(`Expression ${e} do not evaluate to a number`);
+			para[field] = e;
+		} else {
+			throw new SyntaxError(`Invalid expression ${JSON.stringify(expr)}`);
+		}
+	}
+}
+
+const validMetricOverrideFields = new Set([
+	"cap",
+	"xheight",
+	"sb",
+	"accentWidth",
+	"accentClearance",
+	"accentHeight",
+	"accentStackOffset",
+	"dotSize",
+	"periodSize",
+	"leading",
+	"winMetricAscenderPad",
+	"winMetricDescenderPad",
+	"symbolMid",
+	"parenSize",
+	"powerlineScaleY",
+	"powerlineScaleX",
+	"powerlineShiftY",
+	"powerlineShiftX",
+	"onumZeroHeightRatio"
+]);
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+// Function bindings
+
+function initBindings(para, argv) {
+	const valueBindings = new Map();
+	for (const k of validMetricOverrideFields) {
+		valueBindings.set("default_" + k, para[k]);
+	}
+	valueBindings.set("weight", argv.shape.weight);
+	valueBindings.set("width", argv.shape.width);
+	valueBindings.set("slopeAngle", argv.shape.slopeAngle);
+
+	const functionBindings = new Map();
+	functionBindings.set("blend", blend);
+	return { val: valueBindings, functions: functionBindings };
+}
+
+function blend(against, ...pairs) {
+	const xs = [],
+		ys = [];
+	for (const [x, y] of pairs) {
+		xs.push(x), ys.push(y);
+	}
+	return monotonicInterpolate(xs, ys)(against);
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+// Simple expression parser
+class State {
+	constructor(input) {
+		this.input = input;
+		this.cp = 0;
+	}
+	fetch(ch) {
+		return this.input[this.cp];
+	}
+	test(ch) {
+		return this.input[this.cp] === ch;
+	}
+	testCk(f) {
+		return f(this.input[this.cp]);
+	}
+	advance() {
+		return this.input[this.cp++];
+	}
+	expectAndAdvance(ch) {
+		if (!this.test(ch)) this.fail();
+		this.advance();
+	}
+	expectEnd() {
+		if (this.cp < this.input.length) this.fail();
+	}
+	fail() {
+		throw new SyntaxError("Failed to parse expression: " + this.input + "@" + this.cp);
+	}
+}
+
+function RootExpression(state, bindings) {
+	const e = Expression(state, bindings);
+	state.expectEnd();
+	return e;
+}
+function Expression(state, bindings) {
+	skipSpaces(state);
+	const e = Sum(state, bindings);
+	skipSpaces(state);
+	return e;
+}
+
+function Sum(state, bindings) {
+	let f = Term(state, bindings);
+	skipSpaces(state);
+	while (state.test("+") || state.test("-")) {
+		let op = state.advance();
+		skipSpaces(state);
+		const g = Term(state, bindings);
+		skipSpaces(state);
+		switch (op) {
+			case "+":
+				f = f + g;
+				break;
+			case "-":
+				f = f - g;
+				break;
+		}
+	}
+	return f;
+}
+function Term(state, bindings) {
+	let f = Factor(state, bindings);
+	skipSpaces(state);
+	while (state.test("*") || state.test("/")) {
+		let op = state.advance();
+		skipSpaces(state);
+		const g = Factor(state, bindings);
+		skipSpaces(state);
+		switch (op) {
+			case "*":
+				f = f * g;
+				break;
+			case "/":
+				f = f / g;
+				break;
+		}
+	}
+	return f;
+}
+
+function Factor(state, bindings) {
+	if (state.test("+")) {
+		state.advance();
+		skipSpaces(state);
+		return Factor(state, bindings);
+	} else if (state.test("-")) {
+		state.advance();
+		skipSpaces(state);
+		return -Factor(state, bindings);
+	} else {
+		return Primitive(state, bindings);
+	}
+}
+
+function Primitive(state, bindings) {
+	if (state.testCk(isDigit)) return Lit(state, bindings);
+	if (state.testCk(isAlpha)) return BindingOrCall(state, bindings);
+	if (state.test("(")) return Group(state, bindings);
+	if (state.test("[")) return List("[", "]", state, bindings);
+	state.fail();
+}
+
+function Lit(state, bindings) {
+	let integerPart = 0;
+	let fractionPart = 0;
+	let fractionScale = 1;
+	while (state.testCk(isDigit)) {
+		const digit = state.advance().codePointAt(0) - "0".codePointAt(0);
+		integerPart = integerPart * 10 + digit;
+	}
+	if (state.test(".")) {
+		state.advance();
+		while (state.testCk(isDigit)) {
+			fractionScale /= 10;
+			const digit = state.advance().codePointAt(0) - "0".codePointAt(0);
+			fractionPart += digit * fractionScale;
+		}
+	}
+	return integerPart + fractionPart;
+}
+
+function BindingOrCall(state, bindings) {
+	let symbolName = "";
+	while (state.testCk(isAlpha)) symbolName += state.advance();
+	if (state.test("(")) {
+		const args = List("(", ")", state, bindings);
+		if (bindings.functions.has(symbolName)) return bindings.functions.get(symbolName)(...args);
+		else throw new TypeError(`Unknown function ${symbolName}.`);
+	} else {
+		if (bindings.val.has(symbolName)) return bindings.val.get(symbolName);
+		else throw new TypeError(`Unknown identifier ${symbolName}.`);
+	}
+}
+
+function Group(state, bindings) {
+	state.expectAndAdvance("(");
+	skipSpaces(state);
+	const e = Expression(state, bindings);
+	skipSpaces(state);
+	state.expectAndAdvance(")");
+	return e;
+}
+function List(start, end, state, bindings) {
+	let results = [];
+	state.expectAndAdvance(start);
+	skipSpaces(state);
+	results.push(Expression(state, bindings));
+	skipSpaces(state);
+	while (state.test(",")) {
+		state.expectAndAdvance(",");
+		skipSpaces(state);
+		results.push(Expression(state, bindings));
+		skipSpaces(state);
+	}
+	state.expectAndAdvance(end);
+	return results;
+}
+
+function skipSpaces(state) {
+	while (state.testCk(isSpace)) state.advance();
+}
+
+function isSpace(ch) {
+	return ch === " " || ch === "\t";
+}
+function isDigit(ch) {
+	return ch >= "0" && ch <= "9";
+}
+function isAlpha(ch) {
+	return (ch >= "A" && ch <= "Z") || (ch >= "a" && ch <= "z") || ch === "_";
+}

font-src/support/parameters.js

@@ -115,51 +115,3 @@ function hiveBlend(hive, value) {
 	}
 	return generatedHive;
 }
-
-exports.applyMetricOverride = applyMetricOverride;
-function applyMetricOverride(para, mo) {
-	const overrideObj = { metricOverride: {} };
-	createMetricDataSet(overrideObj.metricOverride, mo);
-	apply(para, overrideObj, ["metricOverride"]);
-}
-
-function createMetricDataSet(sink, mo) {
-	for (const key in mo) {
-		if (metricOverrideHandlers[key]) {
-			metricOverrideHandlers[key](sink, key, mo[key]);
-		} else {
-			console.error(`Metric override key ${key} is not supported. Skipping it.`);
-		}
-	}
-}
-
-function numericFieldHandler(sink, key, x) {
-	if (x != null && isFinite(x)) sink[key] = x;
-}
-function subObjectHandler(sink, key, obj) {
-	sink[key] = {};
-	createMetricDataSet(sink[key], obj);
-}
-const metricOverrideHandlers = {
-	cap: numericFieldHandler,
-	xheight: numericFieldHandler,
-	sb: numericFieldHandler,
-	accentWidth: numericFieldHandler,
-	accentClearance: numericFieldHandler,
-	accentHeight: numericFieldHandler,
-	accentStackOffset: numericFieldHandler,
-	dotSize: numericFieldHandler,
-	periodSize: numericFieldHandler,
-	leading: numericFieldHandler,
-	winMetricAscenderPad: numericFieldHandler,
-	winMetricDescenderPad: numericFieldHandler,
-	symbolMid: numericFieldHandler,
-	parenSize: numericFieldHandler,
-	powerlineScaleY: numericFieldHandler,
-	powerlineScaleX: numericFieldHandler,
-	powerlineShiftY: numericFieldHandler,
-	powerlineShiftX: numericFieldHandler,
-	onumZeroHeightRatio: numericFieldHandler,
-	multiplies: subObjectHandler,
-	adds: subObjectHandler
-};