directwrite, coretext: implement substitutions

This adds simple and sensible substitutions for generic font family
names. A helper function is introduced to reduce code duplication.

3 files changed, 59 insertions, 0 deletions

diff --git a/libass/ass_coretext.c b/libass/ass_coretext.c
index 3553324..877018d 100644
--- a/libass/ass_coretext.c
+++ b/libass/ass_coretext.c
@@ -25,6 +25,12 @@
 
 #define SAFE_CFRelease(x) do { if (x) CFRelease(x); } while(0)
 
+static const ASS_FontMapping font_substitutions[] = {
+    {"sans-serif", "Helvetica"},
+    {"serif", "Times"},
+    {"monospace", "Courier"}
+};
+
 static char *cfstr2buf(CFStringRef string)
 {
     const int encoding = kCFStringEncodingUTF8;
@@ -266,10 +272,18 @@ static char *get_fallback(void *priv, const char *family, uint32_t codepoint)
     return res_family;
 }
 
+static void get_substitutions(void *priv, const char *name,
+                              ASS_FontProviderMetaData *meta)
+{
+    const int n = sizeof(font_substitutions) / sizeof(font_substitutions[0]);
+    ass_map_font(font_substitutions, n, name, meta);
+}
+
 static ASS_FontProviderFuncs coretext_callbacks = {
     .check_glyph        = check_glyph,
     .destroy_font       = destroy_font,
     .match_fonts        = match_fonts,
+    .get_substitutions  = get_substitutions,
     .get_fallback       = get_fallback,
 };
 
diff --git a/libass/ass_directwrite.c b/libass/ass_directwrite.c
index 86b0b4b..f11deb6 100644
--- a/libass/ass_directwrite.c
+++ b/libass/ass_directwrite.c
@@ -31,6 +31,12 @@
 #define NAME_MAX_LENGTH 256
 #define FALLBACK_DEFAULT_FONT L"Arial"
 
+static const ASS_FontMapping font_substitutions[] = {
+    {"sans-serif", "Arial"},
+    {"serif", "Times New Roman"},
+    {"monospace", "Courier New"}
+};
+
 /*
  * The private data stored for every font, detected by this backend.
  */
@@ -624,6 +630,13 @@ static void scan_fonts(IDWriteFactory *factory,
     }
 }
 
+static void get_substitutions(void *priv, const char *name,
+                              ASS_FontProviderMetaData *meta)
+{
+    const int n = sizeof(font_substitutions) / sizeof(font_substitutions[0]);
+    ass_map_font(font_substitutions, n, name, meta);
+}
+
 /*
  * Called by libass when the provider should perform the
  * specified task
@@ -633,6 +646,7 @@ static ASS_FontProviderFuncs directwrite_callbacks = {
     .check_glyph        = check_glyph,
     .destroy_font       = destroy_font,
     .destroy_provider   = destroy_provider,
+    .get_substitutions  = get_substitutions,
     .get_fallback       = get_fallback,
 };
 
diff --git a/libass/ass_fontselect.h b/libass/ass_fontselect.h
index c989e1a..1e0959e 100644
--- a/libass/ass_fontselect.h
+++ b/libass/ass_fontselect.h
@@ -177,6 +177,37 @@ struct ass_font_stream {
     void *priv;
 };
 
+
+typedef struct ass_font_mapping ASS_FontMapping;
+
+struct ass_font_mapping {
+    const char *from;
+    const char *to;
+};
+
+/**
+ * Simple font substitution helper. This can be used to implement basic
+ * mappings from one name to another. This is useful for supporting
+ * generic font families in font providers.
+ *
+ * \param map list of mappings
+ * \param len length of list of mappings
+ * \param name font name to map from
+ * \param meta metadata struct, mapped fonts will be stored into this
+ */
+inline void ass_map_font(const ASS_FontMapping *map, int len, const char *name,
+                         ASS_FontProviderMetaData *meta)
+{
+    for (int i = 0; i < len; i++) {
+        if (strcasecmp(map[i].from, name) == 0) {
+            meta->n_fullname = 1;
+            meta->fullnames = calloc(1, sizeof(char *));
+            meta->fullnames[0] = strdup(map[i].to);
+            return;
+        }
+    }
+}
+
 ASS_FontSelector *
 ass_fontselect_init(ASS_Library *library,
                     FT_Library ftlibrary, const char *family,