EPUB: Rewrite absolute font sizes

https://forums.zotero.org/discussion/comment/461514/#Comment_461514
zotero · Apr 25, 2024 · 250935a · 250935a
1 parent 224b64e
commit 250935a
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Showing 2 changed files with 67 additions and 9 deletions.
diff --git a/src/dom/epub/lib/sanitize-and-render.ts b/src/dom/epub/lib/sanitize-and-render.ts
@@ -99,7 +99,7 @@ export class StyleScoper {
 		let scopeClass = `__scope_${this._sheets.size}`;
 		this._sheets.set(css, { scopeClass });
 
-		let cssModified = this._rewriteEPUBProperties(css);
+		let cssModified = rewriteEPUBProperties(css);
 
 		let sheet;
 		let added = false;
@@ -197,6 +197,11 @@ export class StyleScoper {
 			if (styleRule.style.fontFamily && /\bmono(space)?\b/i.test(styleRule.style.fontFamily)) {
 				styleRule.style.setProperty('font-family', styleRule.style.fontFamily, 'important');
 			}
+
+			// If this rule sets a font-size, rewrite it to be relative
+			if (styleRule.style.fontSize) {
+				styleRule.style.fontSize = rewriteFontSize(styleRule.style.fontSize);
+			}
 		}
 		else if (rule.constructor.name === 'CSSImportRule') {
 			let importRule = rule as CSSImportRule;
@@ -210,13 +215,6 @@ export class StyleScoper {
 			}
 		}
 	}
-
-	private _rewriteEPUBProperties(css: string): string {
-		for (let [re, replacement] of EPUB_CSS_REPLACEMENTS) {
-			css = css.replace(re, replacement);
-		}
-		return css;
-	}
 }
 
 // Mappings based on https://github.com/JayPanoz/postcss-epub-interceptor/blob/1aca86e1f4f996f9ec3a8735bd70e673f3e0f504/index.js
@@ -260,6 +258,65 @@ const EPUB_CSS_REPLACEMENTS: [RegExp, string][] = Object.entries({
 	return [[ruleRe, ruleReplacement], ...valueReplacements];
 });
 
+function rewriteEPUBProperties(css: string): string {
+	for (let [re, replacement] of EPUB_CSS_REPLACEMENTS) {
+		css = css.replace(re, replacement);
+	}
+	return css;
+}
+
+// Mappings and routine based on
+// https://github.com/kovidgoyal/calibre/blob/d1bbe63eb10cbf0abbe56a06fce92ad220de03b0/src/calibre/srv/fast_css_transform.cpp#L191-L210
+// Copyright (C) 2008-2024 Kovid Goyal (GPLv3)
+
+/* eslint-disable quote-props */
+const BASE_FONT_SIZE = 13;
+const DPI = 96;
+const PT_TO_PX = DPI / 72;
+const PT_TO_REM = PT_TO_PX / BASE_FONT_SIZE;
+
+const FONT_SIZE_REPLACEMENTS: Record<string, string> = {
+	'xx-small': '0.5rem',
+	'x-small': '0.625rem',
+	'small': '0.75rem',
+	'medium': '1rem',
+	'large': '1.125rem',
+	'x-large': '1.5rem',
+	'xx-large': '2rem',
+	'xxx-large': '2.55rem',
+};
+
+const FONT_SIZE_UNITS: Record<string, number> = {
+	'mm': 2.8346456693,
+	'cm': 28.346456693,
+	'in': 72,
+	'pc': 12,
+	'q': 0.708661417325,
+	'pt': 1,
+};
+/* eslint-enable quote-props */
+
+function rewriteFontSize(fontSize: string): string {
+	if (fontSize.toLowerCase() in FONT_SIZE_REPLACEMENTS) {
+		return FONT_SIZE_REPLACEMENTS[fontSize.toLowerCase()];
+	}
+
+	let match = fontSize.match(/^([0-9.]+)([a-zA-Z]+)$/);
+	if (match) {
+		let value = parseFloat(match[1]);
+		let unit = match[2].toLowerCase();
+		if (unit === 'px') {
+			return value / BASE_FONT_SIZE + 'rem';
+		}
+		else if (unit in FONT_SIZE_UNITS) {
+			let factor = FONT_SIZE_UNITS[unit];
+			return value * factor * PT_TO_REM + 'rem';
+		}
+	}
+
+	return fontSize;
+}
+
 type SheetMetadata = {
 	sheet?: CSSStyleSheet;
 	scopeClass: string;

diff --git a/src/dom/epub/stylesheets/_content.scss b/src/dom/epub/stylesheets/_content.scss
@@ -56,6 +56,7 @@
 }
 
 :root {
+	font-size: calc(var(--content-scale) * 13pt) !important;
 	background-color: var(--background-color) !important;
 	color: var(--text-color) !important;
 }
@@ -80,7 +81,7 @@ replaced-body {
 	color: inherit !important;
 
 	font-family: var(--content-font-family, "Georgia"), serif;
-	font-size: calc(var(--content-scale) * 13pt) !important;
+	font-size: inherit !important;
 	line-height: var(--content-line-height);
 	text-align: justify;
 	text-rendering: optimizeLegibility;