dwrite: Implement GetFontFamily() for system font collection.

dlls/dwrite/font.c

@@ -161,6 +161,8 @@ struct dwrite_fontface {
     LONG ref;
 };
 
+static HRESULT create_fontfamily(const WCHAR *familyname, IDWriteFontFamily **family);
+
 static inline struct dwrite_fontface *impl_from_IDWriteFontFace(IDWriteFontFace *iface)
 {
     return CONTAINING_RECORD(iface, struct dwrite_fontface, IDWriteFontFace_iface);
@@ -666,8 +668,16 @@ static UINT32 WINAPI dwritefontcollection_GetFontFamilyCount(IDWriteFontCollecti
 static HRESULT WINAPI dwritefontcollection_GetFontFamily(IDWriteFontCollection *iface, UINT32 index, IDWriteFontFamily **family)
 {
     struct dwrite_fontcollection *This = impl_from_IDWriteFontCollection(iface);
-    FIXME("(%p)->(%u %p): stub\n", This, index, family);
-    return E_NOTIMPL;
+
+    TRACE("(%p)->(%u %p)\n", This, index, family);
+
+    if (index >= This->count)
+    {
+        *family = NULL;
+        return E_FAIL;
+    }
+
+    return create_fontfamily(This->families[index], family);
 }
 
 static HRESULT WINAPI dwritefontcollection_FindFamilyName(IDWriteFontCollection *iface, const WCHAR *name, UINT32 *index, BOOL *exists)

dlls/dwrite/tests/font.c

@@ -526,6 +526,7 @@ todo_wine
 static void test_system_fontcollection(void)
 {
     IDWriteFontCollection *collection, *coll2;
+    IDWriteFontFamily *family;
     HRESULT hr;
     UINT32 i;
     BOOL ret;
@@ -546,6 +547,12 @@ static void test_system_fontcollection(void)
     i = IDWriteFontCollection_GetFontFamilyCount(collection);
     ok(i, "got %u\n", i);
 
+    /* invalid index */
+    family = (void*)0xdeadbeef;
+    hr = IDWriteFontCollection_GetFontFamily(collection, i, &family);
+    ok(hr == E_FAIL, "got 0x%08x\n", hr);
+    ok(family == NULL, "got %p\n", family);
+
     ret = FALSE;
     i = (UINT32)-1;
     hr = IDWriteFontCollection_FindFamilyName(collection, tahomaW, &i, &ret);