feat: the defaultFontFamily is not found in the OS and needs to be fa…

…llback

Previously, resvg-js would not match any fonts in SVG text, even if there were fonts in the OS that could render them. This commit makes it possible to fallback properly.

```js
const resvg = new Resvg(svg, {
    font: {
      loadSystemFonts: true,
      defaultFontFamily: 'this-is-a-non-existent-font-family',
    },
  })
```

__test__/index.spec.ts

@@ -270,6 +270,29 @@ test('should be load custom fontDirs(no defaultFontFamily option)', (t) => {
   t.is(originPixels.join(',').match(/0,0,255/g)?.length, 1726)
 })
 
+test('The defaultFontFamily is not found in the OS and needs to be fallback', (t) => {
+  const svg = `
+<svg xmlns="http://www.w3.org/2000/svg" width="300" height="200" viewBox="0 0 300 200">
+  <text fill="blue" font-family="" font-size="100">
+    <tspan x="10" y="60%">Abc</tspan>
+  </text>
+</svg>
+  `
+  const resvg = new Resvg(svg, {
+    font: {
+      loadSystemFonts: true,
+      defaultFontFamily: 'this-is-a-non-existent-font-family',
+    },
+  })
+  const pngData = resvg.render()
+  const originPixels = pngData.pixels.toJSON().data
+  // Find the number of blue `rgb(0,255,255)`pixels
+  const matchPixels = originPixels.join(',').match(/0,0,255/g)
+  console.info('✅ matchPixels length =', matchPixels?.length)
+  t.true(matchPixels !== null) // If the font is not matched, there are no blue pixels.
+  t.true((matchPixels?.length ?? 0) > 1500)
+})
+
 test('Async rendering', async (t) => {
   const filePath = '../example/text.svg'
   const svg = await fs.readFile(join(__dirname, filePath))

src/fonts.rs

@@ -172,16 +172,16 @@ fn set_wasm_font_families(
     fontdb.set_monospace_family(&default_font_family);
 }
 
+/// 查询指定 font family 的字体是否存在，如果不存在则使用 fallback_font_family 代替。
 #[cfg(not(target_arch = "wasm32"))]
 fn find_and_debug_font_path(fontdb: &mut Database, font_family: &str) {
-    // 查找指定字体的路径
     let query = Query {
         families: &[Family::Name(font_family)],
         ..Query::default()
     };
 
     let now = std::time::Instant::now();
-    // 当前使用的字体是否存在
+    // 查询当前使用的字体是否存在
     match fontdb.query(&query) {
         Some(id) => {
             let (src, index) = fontdb.face_source(id).unwrap();
@@ -195,6 +195,13 @@ fn find_and_debug_font_path(fontdb: &mut Database, font_family: &str) {
             }
         }
         None => {
+            let fallback_font_family = "Arial".to_string();
+            fontdb.set_serif_family(&fallback_font_family);
+            fontdb.set_sans_serif_family(&fallback_font_family);
+            fontdb.set_cursive_family(&fallback_font_family);
+            fontdb.set_fantasy_family(&fallback_font_family);
+            fontdb.set_monospace_family(&fallback_font_family);
+
             warn!(
                 "Warning: The default font-family '{}' not found.",
                 font_family