From adfe8a9dcbb638f883863180a6d8dff20a331826 Mon Sep 17 00:00:00 2001
From: Sam Atkins <sam@ladybird.org>
Date: Fri, 14 Mar 2025 11:32:05 +0000
Subject: [PATCH] LibWeb/CSS: Add functions that report font format/technology
 support

Both `@supports` and `@font-face` need this. There may be some automatic
way of querying whether our renderer supports these, but I couldn't
figure it out, so here's a basic hard-coded list. I think the font-tech
list has false negatives, as I don't know enough about fonts to
determine what we support accurately.
---
 Libraries/LibWeb/CSS/FontFace.cpp | 53 +++++++++++++++++++++++++++++++
 Libraries/LibWeb/CSS/FontFace.h   |  3 ++
 2 files changed, 56 insertions(+)

diff --git a/Libraries/LibWeb/CSS/FontFace.cpp b/Libraries/LibWeb/CSS/FontFace.cpp
index a4f1836ce32..bc3bcf74a15 100644
--- a/Libraries/LibWeb/CSS/FontFace.cpp
+++ b/Libraries/LibWeb/CSS/FontFace.cpp
@@ -398,4 +398,57 @@ GC::Ref<WebIDL::Promise> FontFace::load()
     return font_face.loaded();
 }
 
+bool font_format_is_supported(FlyString const& name)
+{
+    // https://drafts.csswg.org/css-fonts-4/#font-format-definitions
+    // FIXME: Determine this automatically somehow?
+    if (name.equals_ignoring_ascii_case("collection"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("embedded-opentype"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("opentype"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("svg"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("truetype"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("woff"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("woff2"sv))
+        return true;
+    return false;
+}
+
+bool font_tech_is_supported(FlyString const& name)
+{
+    // https://drafts.csswg.org/css-fonts-4/#font-tech-definitions
+    // FIXME: Determine this automatically somehow?
+    if (name.equals_ignoring_ascii_case("features-opentype"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("features-aat"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("features-graphite"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("variations"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("color-colrv0"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("color-colrv1"sv))
+        return true;
+    if (name.equals_ignoring_ascii_case("color-svg"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("color-sbix"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("color-cbdt"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("palettes"sv))
+        return false;
+    if (name.equals_ignoring_ascii_case("incremental"sv))
+        return false;
+    // https://drafts.csswg.org/css-fonts-5/#font-tech-definitions
+    if (name.equals_ignoring_ascii_case("avar2"sv))
+        return false;
+    return false;
+}
+
 }
diff --git a/Libraries/LibWeb/CSS/FontFace.h b/Libraries/LibWeb/CSS/FontFace.h
index c54a0a986c9..3f8da2edf9d 100644
--- a/Libraries/LibWeb/CSS/FontFace.h
+++ b/Libraries/LibWeb/CSS/FontFace.h
@@ -113,4 +113,7 @@ private:
     bool m_is_css_connected { false };
 };
 
+bool font_format_is_supported(FlyString const& name);
+bool font_tech_is_supported(FlyString const& name);
+
 }