preload font files into memory to avoid frequent IO.

__test__/index.spec.ts

@@ -5,7 +5,7 @@ import test from 'ava'
 import jimp from 'jimp-compact'
 import fetch from 'node-fetch'
 
-import { Resvg, renderAsync } from '../index'
+import { Resvg, ResvgRenderOptions, renderAsync } from '../index'
 
 import { jimpToRgbaPixels } from './helper'
 
@@ -704,3 +704,39 @@ test('should throw (SVG string is empty)', (t) => {
   t.is(error.code, 'GenericFailure')
   t.is(error.message, 'SVG data parsing failed cause the document does not have a root node')
 })
+
+// issue: https://github.com/thx/resvg-js/issues/367
+test('Load custom font with preload_fonts', async (t) => {
+  const filePath = '../example/text.svg'
+  const svg = await fs.readFile(join(__dirname, filePath))
+  const svgString = svg.toString('utf-8')
+  const options: ResvgRenderOptions = {
+    font: {
+      fontFiles: ['./example/SourceHanSerifCN-Light-subset.ttf'], // Load custom fonts.
+      loadSystemFonts: false, // It will be faster to disable loading system fonts.
+      defaultFontFamily: 'Source Han Serif CN Light',
+      preloadFonts: false,
+    },
+  }
+  const expectResvg = new Resvg(svgString, options)
+  const expectPngData = expectResvg.render()
+  const expectPngBuffer = expectPngData.asPng()
+  const expectedResult = await jimp.read(Buffer.from(expectPngBuffer))
+
+  // enable preloadFonts
+  options.font!.preloadFonts = true
+  const actualResvg = new Resvg(svgString, options)
+  const actualPngData = actualResvg.render()
+  const actualPngBuffer = actualPngData.asPng()
+  const actualPng = await jimp.read(Buffer.from(actualPngBuffer))
+  t.is(jimp.diff(expectedResult, actualPng, 0.01).percent, 0) // 0 means similar, 1 means not similar
+
+  // use fontDirs
+  delete options.font!.fontFiles
+  options.font!.fontDirs = ['./example']
+  const actualResvg2 = new Resvg(svgString, options)
+  const actualPngData2 = actualResvg2.render()
+  const actualPngBuffer2 = actualPngData2.asPng()
+  const actualPng2 = await jimp.read(Buffer.from(actualPngBuffer2))
+  t.is(jimp.diff(expectedResult, actualPng2, 0.01).percent, 0) // 0 means similar, 1 means not similar
+})

index.d.ts

@@ -5,6 +5,7 @@ export type ResvgRenderOptions = {
     loadSystemFonts?: boolean // Default: true, if set to false, it will be faster.
     fontFiles?: string[] // A list of local font file paths to load.
     fontDirs?: string[] // A list of local font directories to load.
+    preloadFonts?: boolean // Default: false. When enabled, font files will be read into memory at once to avoid frequent IO.
     defaultFontSize?: number // Default: 12
     defaultFontFamily?: string // Default: "", if `loadSystemFonts` is enabled, it will be set to the first font in the list of system fonts.
     serifFamily?: string

src/fonts.rs

@@ -17,23 +17,62 @@ use wasm_bindgen::JsCast;
 #[cfg(target_arch = "wasm32")]
 use woff2::decode::{convert_woff2_to_ttf, is_woff2};
 
+#[cfg(not(target_arch = "wasm32"))]
+fn load_font_buffer(path: impl AsRef<std::path::Path>) -> Option<Vec<u8>> {
+    match std::fs::read(path.as_ref()) {
+        Ok(buffer) => Some(buffer),
+        Err(e) => {
+            warn!(
+                "Failed to read font file '{}' cause {}.",
+                path.as_ref().display(),
+                e
+            );
+            None
+        }
+    }
+}
+
 /// Loads fonts.
 #[cfg(not(target_arch = "wasm32"))]
 pub fn load_fonts(font_options: &JsFontOptions) -> Database {
-    // Create a new font database
     let mut fontdb = Database::new();
     let now = std::time::Instant::now();
 
-    // 加载指定路径的字体
-    for path in &font_options.font_files {
-        if let Err(e) = fontdb.load_font_file(path) {
-            warn!("Failed to load '{}' cause {}.", path, e);
+    if font_options.preload_fonts {
+        // 预加载单个字体文件
+        font_options
+            .font_files
+            .iter()
+            .filter_map(load_font_buffer)
+            .for_each(|buffer| {
+                let _ = fontdb.load_font_data(buffer);
+            });
+
+        // 预加载字体目录
+        for dir in &font_options.font_dirs {
+            if let Ok(entries) = std::fs::read_dir(dir) {
+                entries
+                    .filter_map(Result::ok)
+                    .filter_map(|entry| entry.path().canonicalize().ok())
+                    .filter(|path| path.is_file())
+                    .filter_map(load_font_buffer)
+                    .for_each(|buffer| {
+                        let _ = fontdb.load_font_data(buffer);
+                    });
+            }
+        }
+    } else {
+        // 默认模式: 直接传递文件路径
+        for path in &font_options.font_files {
+            if let Err(e) = fontdb.load_font_file(path) {
+                warn!("Failed to load '{}' cause {}.", path, e);
+            }
         }
-    }
 
-    // Load font directories
-    for path in &font_options.font_dirs {
-        fontdb.load_fonts_dir(path);
+        // Load font directories
+        for path in &font_options.font_dirs {
+            fontdb.load_fonts_dir(path);
+        }
     }
 
     // 加载系统字体

src/options.rs

@@ -238,6 +238,12 @@ pub struct JsFontOptions {
     /// A list of local font directories to load.
     pub font_dirs: Vec<String>,
 
+    /// Whether to preload font files into memory to improve performance.
+    /// When enabled, font files will be read into memory at once to avoid frequent IO.
+    ///
+    /// Default: false
+    pub preload_fonts: bool,
+
     /// The default font family.
     ///
     /// Will be used when no `font-family` attribute is set in the SVG.
@@ -284,6 +290,7 @@ impl Default for JsFontOptions {
             load_system_fonts: true,
             font_files: vec![],
             font_dirs: vec![],
+            preload_fonts: false,
             default_font_family: "".to_string(),
             default_font_size: 12.0,
             serif_family: "Times New Roman".to_string(),