text: allow the unnamed font

If the font name is not specified,
ThorVG will select any available font candidate.

This could be useful for font fallback mechanism.

examples/Text.cpp

@@ -72,7 +72,7 @@ struct UserExample : tvgexam::Example
         canvas->push(text2);
 
         auto text3 = tvg::Text::gen();
-        text3->font("Arial", 40);
+        text3->font(nullptr, 40);  //Use any font
         text3->text("Kerning Test: VA, AV, TJ, JT");
         text3->fill(255, 255, 255);
         text3->translate(0, 225);

inc/thorvg.h

@@ -1528,6 +1528,7 @@ public:
      *
      * @retval Result::InsufficientCondition when the specified @p name cannot be found.
      *
+     * @note If the @p name is not specified, ThorVG will select any available font candidate.
      * @note Experimental API
      */
     Result font(const char* name, float size, const char* style = nullptr) noexcept;

src/bindings/capi/thorvg_capi.h

@@ -2021,6 +2021,7 @@ TVG_API Tvg_Paint* tvg_text_new(void);
 * @retval TVG_RESULT_INVALID_ARGUMENT A @c nullptr passed as the @p paint argument.
 * @retval TVG_RESULT_INSUFFICIENT_CONDITION  The specified @p name cannot be found.
 *
+* @note If the @p name is not specified, ThorVG will select any available font candidate.
 * @note Experimental API
 */
 TVG_API Tvg_Result tvg_text_set_font(Tvg_Paint* paint, const char* name, float size, const char* style);

src/renderer/tvgLoader.cpp

@@ -341,6 +341,18 @@ LoadModule* LoaderMgr::loader(const char* key)
 }
 
 
+LoadModule* LoaderMgr::anyfont()
+{
+    INLIST_FOREACH(_activeLoaders, loader) {
+        if ((loader->type == FileType::Ttf) && loader->pathcache) {
+            ++loader->sharing;
+            return loader;
+        }
+    }
+    return nullptr;
+}
+
+
 LoadModule* LoaderMgr::loader(const char* data, uint32_t size, const char* mimeType, const char* rpath, bool copy)
 {
     //Note that users could use the same data pointer with the different content.

src/renderer/tvgLoader.h

@@ -34,6 +34,7 @@ struct LoaderMgr
     static LoadModule* loader(const uint32_t* data, uint32_t w, uint32_t h, ColorSpace cs, bool copy);
     static LoadModule* loader(const char* name, const char* data, uint32_t size, const char* mimeType, bool copy);
     static LoadModule* loader(const char* key);
+    static LoadModule* anyfont();
     static bool retrieve(const char* filename);
     static bool retrieve(LoadModule* loader);
 };

src/renderer/tvgText.h

@@ -62,7 +62,7 @@ struct Text::Impl : Paint::Impl
 
     Result font(const char* name, float size, const char* style)
     {
-        auto loader = LoaderMgr::loader(name);
+        auto loader = name ? LoaderMgr::loader(name) : LoaderMgr::anyfont();
         if (!loader) return Result::InsufficientCondition;
 
         if (style && strstr(style, "italic")) italic = true;

test/testText.cpp

@@ -108,6 +108,7 @@ TEST_CASE("Text Font", "[tvgText]")
     REQUIRE(text->font("Arial", 80) == tvg::Result::Success);
     REQUIRE(text->font("Arial", 1) == tvg::Result::Success);
     REQUIRE(text->font("Arial", 50) == tvg::Result::Success);
+    REQUIRE(text->font(nullptr, 50) == tvg::Result::Success);
     REQUIRE(text->font("InvalidFont", 80) == tvg::Result::InsufficientCondition);
 
     Initializer::term();