From d4e1305413bb12b95a7de93b58231153955da6f3 Mon Sep 17 00:00:00 2001
From: Sam Atkins <atkinssj@serenityos.org>
Date: Thu, 26 Oct 2023 16:48:52 +0100
Subject: [PATCH] LibGfx: Make OpenType versioned tables more consistent

Maxp had the shared fields duplicated, and OS2 embedded each version's
struct in the next. Instead, let's use inheritance to avoid duplicating
shared fields while still allowing them to be directly accessed.

While I'm at it, rename the Maxp and GPOS table structs to just be
VersionX_Y, because they're not ambiguous with anything else.

LibGfx: Rename GPOSHeader to HeaderVersion1_0

Because there's a version 1.1 as well, which we'll eventually want to
support.
---
 .../Libraries/LibGfx/Font/OpenType/Tables.cpp |  8 +++---
 .../Libraries/LibGfx/Font/OpenType/Tables.h   | 26 ++++++++-----------
 2 files changed, 15 insertions(+), 19 deletions(-)

diff --git a/Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp b/Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp
index 706d8dc08f..2b2b4c471c 100644
--- a/Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp
+++ b/Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp
@@ -124,15 +124,15 @@ ErrorOr<Maxp> Maxp::from_slice(ReadonlyBytes slice)
     Version16Dot16 const& version = *bit_cast<Version16Dot16 const*>(slice.data());
 
     if (version.major == 0 && version.minor == 5) {
-        if (slice.size() < sizeof(MaximumProfileVersion0_5))
+        if (slice.size() < sizeof(Version0_5))
             return Error::from_string_literal("Could not load Maxp: Not enough data");
-        return Maxp(bit_cast<MaximumProfileVersion0_5 const*>(slice.data()));
+        return Maxp(bit_cast<Version0_5 const*>(slice.data()));
     }
 
     if (version.major == 1 && version.minor == 0) {
-        if (slice.size() < sizeof(MaximumProfileVersion1_0))
+        if (slice.size() < sizeof(Version1_0))
             return Error::from_string_literal("Could not load Maxp: Not enough data");
-        return Maxp(bit_cast<MaximumProfileVersion1_0 const*>(slice.data()));
+        return Maxp(bit_cast<Version1_0 const*>(slice.data()));
     }
 
     return Error::from_string_literal("Could not load Maxp: Unrecognized version");
diff --git a/Userland/Libraries/LibGfx/Font/OpenType/Tables.h b/Userland/Libraries/LibGfx/Font/OpenType/Tables.h
index 57d3696e90..535f6047c1 100644
--- a/Userland/Libraries/LibGfx/Font/OpenType/Tables.h
+++ b/Userland/Libraries/LibGfx/Font/OpenType/Tables.h
@@ -176,15 +176,13 @@ public:
     u16 num_glyphs() const;
 
 private:
-    struct [[gnu::packed]] MaximumProfileVersion0_5 {
+    struct [[gnu::packed]] Version0_5 {
         Version16Dot16 version;
         BigEndian<u16> num_glyphs;
     };
-    static_assert(AssertSize<MaximumProfileVersion0_5, 6>());
+    static_assert(AssertSize<Version0_5, 6>());
 
-    struct [[gnu::packed]] MaximumProfileVersion1_0 {
-        Version16Dot16 version;
-        BigEndian<u16> num_glyphs;
+    struct [[gnu::packed]] Version1_0 : Version0_5 {
         BigEndian<u16> max_points;
         BigEndian<u16> max_contours;
         BigEndian<u16> max_composite_points;
@@ -199,16 +197,16 @@ private:
         BigEndian<u16> max_component_elements;
         BigEndian<u16> max_component_depths;
     };
-    static_assert(AssertSize<MaximumProfileVersion1_0, 32>());
+    static_assert(AssertSize<Version1_0, 32>());
 
-    Maxp(Variant<MaximumProfileVersion0_5 const*, MaximumProfileVersion1_0 const*> data)
+    Maxp(Variant<Version0_5 const*, Version1_0 const*> data)
         : m_data(move(data))
     {
         VERIFY(m_data.visit([](auto const* any) { return any != nullptr; }));
     }
 
     // NOTE: Whichever pointer is present is non-null, but Variant can't contain references.
-    Variant<MaximumProfileVersion0_5 const*, MaximumProfileVersion1_0 const*> m_data;
+    Variant<Version0_5 const*, Version1_0 const*> m_data;
 };
 
 struct GlyphHorizontalMetrics {
@@ -325,15 +323,13 @@ private:
     };
     static_assert(AssertSize<Version0, 78>());
 
-    struct [[gnu::packed]] Version1 {
-        Version0 version0;
+    struct [[gnu::packed]] Version1 : Version0 {
         BigEndian<u32> ul_code_page_range1;
         BigEndian<u32> ul_code_page_range2;
     };
     static_assert(AssertSize<Version1, 86>());
 
-    struct [[gnu::packed]] Version2 {
-        Version1 version1;
+    struct [[gnu::packed]] Version2 : Version1 {
         BigEndian<i16> sx_height;
         BigEndian<i16> s_cap_height;
         BigEndian<u16> us_default_char;
@@ -698,14 +694,14 @@ static_assert(AssertSize<ClassDefFormat2, 4>());
 class GPOS {
 public:
     // https://learn.microsoft.com/en-us/typography/opentype/spec/gpos#gpos-header
-    struct [[gnu::packed]] GPOSHeader {
+    struct [[gnu::packed]] Version1_0 {
         BigEndian<u16> major_version;
         BigEndian<u16> minor_version;
         Offset16 script_list_offset;
         Offset16 feature_list_offset;
         Offset16 lookup_list_offset;
     };
-    static_assert(AssertSize<GPOSHeader, 10>());
+    static_assert(AssertSize<Version1_0, 10>());
 
     // https://learn.microsoft.com/en-us/typography/opentype/spec/gpos#pair-adjustment-positioning-format-1-adjustments-for-glyph-pairs
     struct [[gnu::packed]] PairPosFormat1 {
@@ -755,7 +751,7 @@ public:
         Y_ADVANCE_DEVICE = 0x0080,
     };
 
-    GPOSHeader const& header() const { return *bit_cast<GPOSHeader const*>(m_slice.data()); }
+    Version1_0 const& header() const { return *bit_cast<Version1_0 const*>(m_slice.data()); }
 
     Optional<i16> glyph_kerning(u16 left_glyph_id, u16 right_glyph_id) const;