svg_loader: handle embedded fonts

It is possible to embed fonts directly into an SVG file.
Support for parsing and loading embedded fonts has been added.

@Issue: https://github.com/thorvg/thorvg/issues/1897

src/loaders/svg/tvgSvgLoader.cpp

@@ -375,6 +375,27 @@ static char* _idFromUrl(const char* url)
 }
 
 
+static size_t _srcFromUrl(const char* url, char*& src)
+{
+    src = (char*)strchr(url, '(');
+    auto close = strchr(url, ')');
+    if (!src || !close || src >= close) return 0;
+
+    src = strchr(src, '\'');
+    if (!src || src >= close) return 0;
+    ++src;
+
+    close = strchr(src, '\'');
+    if (!close || close == src) return 0;
+    --close;
+
+    while (src < close && *src == ' ') ++src;
+    while (src < close && *close == ' ') --close;
+
+    return close - src + 1;
+}
+
+
 static unsigned char _parseColor(const char* value, char** end)
 {
     float r;
@@ -2082,6 +2103,42 @@ static SvgNode* _createImageNode(SvgLoaderData* loader, SvgNode* parent, const c
 }
 
 
+static char* _unquote(const char* str)
+{
+    auto len = str ? strlen(str) : 0;
+    if (len >= 2 && str[0] == '\'' && str[len - 1] == '\'') return duplicate(str + 1, len - 2);
+    return strdup(str);
+}
+
+
+static bool _attrParseFontFace(void* data, const char* key, const char* value)
+{
+    if (!key || !value) return false;
+
+    key = _skipSpace(key, nullptr);
+    value = _skipSpace(value, nullptr);
+
+    auto loader = (SvgLoaderData*)data;
+    auto& font = loader->fonts.last();
+
+    if (STR_AS(key, "font-family")) {
+        if (font.name) tvg::free(font.name);
+        font.name = _unquote(value);
+    } else if (STR_AS(key, "src")) {
+        font.srcLen = _srcFromUrl(value, font.src);
+    }
+
+    return true;
+}
+
+
+static void _createFontFace(SvgLoaderData* loader, const char* buf, unsigned bufLength, parseAttributes func)
+{
+    loader->fonts.push(FontFace());
+    func(buf, bufLength, _attrParseFontFace, loader);
+}
+
+
 static SvgNode* _getDefsNode(SvgNode* node)
 {
     if (!node) return nullptr;
@@ -3518,6 +3575,8 @@ static void _svgLoaderParserXmlCssStyle(SvgLoaderData* loader, const char* conte
             TVGLOG("SVG", "Unsupported elements used in the internal CSS style sheets [Elements: %s]", tag);
         } else if (STR_AS(tag, "all")) {
             if ((node = _createCssStyleNode(loader, loader->cssStyle, attrs, attrsLength, simpleXmlParseW3CAttribute))) node->id = _copyId(name);
+        } else if (STR_AS(tag, "@font-face")) { //css at-rule specifying font
+            _createFontFace(loader, attrs, attrsLength, simpleXmlParseW3CAttribute);
         } else if (!isIgnoreUnsupportedLogElements(tag)) {
             TVGLOG("SVG", "Unsupported elements used in the internal CSS style sheets [Elements: %s]", tag);
         }
@@ -3871,6 +3930,13 @@ void SvgLoader::clear(bool all)
     ARRAY_FOREACH(p, loaderData.images) tvg::free(*p);
     loaderData.images.reset();
 
+    ARRAY_FOREACH(p, loaderData.fonts) {
+        Text::unload(p->name);
+        tvg::free(p->decoded);
+        tvg::free(p->name);
+    }
+    loaderData.fonts.reset();
+
     if (copy) tvg::free((char*)content);
 
     delete(root);

src/loaders/svg/tvgSvgLoaderCommon.h

@@ -568,6 +568,14 @@ struct SvgNodeIdPair
     char *id;
 };
 
+struct FontFace
+{
+    char* name = nullptr;
+    char* src = nullptr;
+    size_t srcLen = 0;
+    char* decoded = nullptr;
+};
+
 enum class OpenedTagType : uint8_t
 {
     Other = 0,
@@ -587,6 +595,7 @@ struct SvgLoaderData
     Array<SvgNodeIdPair> cloneNodes;
     Array<SvgNodeIdPair> nodesToStyle;
     Array<char*> images;        //embedded images
+    Array<FontFace> fonts;
     int level = 0;
     bool result = false;
     OpenedTagType openedTag = OpenedTagType::Other;

src/loaders/svg/tvgSvgSceneBuilder.cpp

@@ -947,6 +947,43 @@ static void _updateInvalidViewSize(Scene* scene, Box& vBox, float& w, float& h,
     if (!validHeight) h *= vBox.h;
 }
 
+
+static void _loadFonts(Array<FontFace>& fonts)
+{
+    if (fonts.empty()) return;
+
+    static constexpr struct {
+        const char* prefix;
+        size_t len;
+    } prefixes[] = {
+        {"data:font/ttf;base64,", sizeof("data:font/ttf;base64,") - 1},
+        {"data:application/font-ttf;base64,", sizeof("data:application/font-ttf;base64,") - 1}
+    };
+
+
+    ARRAY_FOREACH(p, fonts) {
+        if (!p->name) continue;
+
+        size_t shift = 0;
+        for (const auto& prefix : prefixes) {
+            if (p->srcLen > prefix.len && !memcmp(p->src, prefix.prefix, prefix.len)) {
+                shift = prefix.len;
+                break;
+            }
+        }
+        if (shift == 0) {
+            TVGLOG("SVG", "The embedded font \"%s\" data not loaded properly.", p->name);
+            continue;
+        }
+
+        auto size = b64Decode(p->src + shift, p->srcLen - shift, &p->decoded);
+
+        TaskScheduler::async(false);
+        if (Text::load(p->name, p->decoded, size) != Result::Success) TVGERR("SVG", "Error while loading the ttf font named \"%s\".", p->name);
+        TaskScheduler::async(true);
+    }
+}
+
 /************************************************************************/
 /* External Class Implementation                                        */
 /************************************************************************/
@@ -957,6 +994,8 @@ Scene* svgSceneBuild(SvgLoaderData& loaderData, Box vBox, float w, float h, Aspe
 
     if (!loaderData.doc || (loaderData.doc->type != SvgNodeType::Doc)) return nullptr;
 
+    _loadFonts(loaderData.fonts);
+
     auto docNode = _sceneBuildHelper(loaderData, loaderData.doc, vBox, svgPath, false, 0);
 
     if (!(viewFlag & SvgViewFlag::Viewbox)) _updateInvalidViewSize(docNode, vBox, w, h, viewFlag);

src/loaders/svg/tvgXmlParser.cpp

@@ -473,6 +473,14 @@ bool simpleXmlParseW3CAttribute(const char* buf, unsigned bufLength, simpleXMLAt
     do {
         char* sep = (char*)strchr(buf, ':');
         next = (char*)strchr(buf, ';');
+
+        if (auto src = strstr(buf, "src")) {//src tag from css font-face contains extra semicolon
+            if (src < sep) {
+                if (next + 1 < end) next = (char*)strchr(next + 1, ';');
+                else return true;
+            }
+        }
+
         if (sep >= end) {
             next = nullptr;
             sep = nullptr;