api: OIIO::getattribute queries for available font families and styles (

#4523)

Add an API to query available fonts based on family and style name. The
API can be used to build a UI where users can select a font from a list.
They consist of new queries for `OIIO::getattribute()`:

- `string font_family_list`

  A semicolon-separated list of all the font family names that
  OpenImageIO can find. 

- `string font_style_list:family`

  A semicolon-separated list of all the font style names that
  belong to the given font family. 

- `string font_filename:family:style`

  The font file (with full path) that defines the given font
  family and style. 

Fixes #4503.


---------

Signed-off-by: peter.horvath <peter.horvath@autodesk.com>

src/include/OpenImageIO/imageio.h

@@ -3039,6 +3039,21 @@ inline bool attribute (string_view name, string_view val) {
 ///   full paths), and all the directories that OpenImageIO will search for
 ///   fonts.  (Added in OpenImageIO 2.5)
 ///
+/// - `string font_family_list`
+///
+///   A semicolon-separated list of all the font family names that
+///   OpenImageIO can find.  (Added in OpenImageIO 3.0)
+///
+/// - `string font_style_list:family`
+///
+///   A semicolon-separated list of all the font style names that
+///   belong to the given font family.  (Added in OpenImageIO 3.0)
+///
+/// - `string font_filename:family:style`
+///
+///   The font file (with full path) that defines the given font
+///   family and style.  (Added in OpenImageIO 3.0)
+///
 /// - `string filter_list`
 ///
 ///   A semicolon-separated list of all built-in 2D filters. (Added in

src/include/imageio_pvt.h

@@ -57,7 +57,12 @@ OIIO_API const std::vector<std::string>&
 font_file_list();
 OIIO_API const std::vector<std::string>&
 font_list();
-
+OIIO_API const std::vector<std::string>&
+font_family_list();
+OIIO_API const std::vector<std::string>
+font_style_list(string_view family);
+OIIO_API const std::string
+font_filename(string_view family, string_view style = "");
 
 
 // Make sure all plugins are inventoried. For internal use only.

src/libOpenImageIO/imagebufalgo_draw.cpp

@@ -1318,4 +1318,54 @@ ImageBufAlgo::render_text(ImageBuf& R, int x, int y, string_view text,
 
 
 
+const std::vector<std::string>&
+pvt::font_family_list()
+{
+#ifdef USE_FREETYPE
+    lock_guard ft_lock(ft_mutex);
+    init_font_families();
+#endif
+    return s_font_families;
+}
+
+
+const std::vector<std::string>
+pvt::font_style_list(string_view family)
+{
+#ifdef USE_FREETYPE
+    lock_guard ft_lock(ft_mutex);
+    init_font_families();
+#endif
+    auto it = s_font_styles.find(family);
+    if (it != s_font_styles.end())
+        return it->second;
+    else
+        return std::vector<std::string>();
+}
+
+
+const std::string
+pvt::font_filename(string_view family, string_view style)
+{
+    if (family.empty())
+        return std::string();
+
+#ifdef USE_FREETYPE
+    lock_guard ft_lock(ft_mutex);
+    init_font_families();
+#endif
+
+    std::string font = family;
+    if (!style.empty())
+        font = Strutil::fmt::format("{} {}", family, style);
+
+    auto it = s_font_filename_per_family.find(font);
+    if (it != s_font_filename_per_family.end())
+        return it->second;
+    else
+        return std::string();
+}
+
+
+
 OIIO_NAMESPACE_END

src/libOpenImageIO/imageio.cpp

@@ -505,6 +505,23 @@ getattribute(string_view name, TypeDesc type, void* val)
         *(ustring*)val = ustring(Strutil::join(font_list(), ";"));
         return true;
     }
+    if (name == "font_family_list" && type == TypeString) {
+        *(ustring*)val = ustring(Strutil::join(font_family_list(), ";"));
+        return true;
+    }
+    if (Strutil::starts_with(name, "font_style_list:") && type == TypeString) {
+        string_view family = name.substr(strlen("font_style_list:"));
+        *(ustring*)val = ustring(Strutil::join(font_style_list(family), ";"));
+        return true;
+    }
+    if (Strutil::starts_with(name, "font_filename:") && type == TypeString) {
+        std::vector<string_view> tokens;
+        Strutil::split(name, tokens, ":");
+        string_view family = tokens.size() >= 1 ? tokens[1] : string_view();
+        string_view style  = tokens.size() >= 2 ? tokens[2] : string_view();
+        *(ustring*)val     = ustring(font_filename(family, style));
+        return true;
+    }
     if (name == "filter_list" && type == TypeString) {
         std::vector<string_view> filternames;
         for (int i = 0, e = Filter2D::num_filters(); i < e; ++i)