Implement SeString renderer

Dalamud/Interface/ImGuiSeStringRenderer/GfdFileView.cs

@@ -0,0 +1,134 @@
+using System.IO;
+using System.Runtime.InteropServices;
+
+namespace Dalamud.Interface.ImGuiSeStringRenderer;
+
+/// <summary>Reference member view of a .gfd file data.</summary>
+internal readonly unsafe ref struct GfdFileView
+{
+    private readonly ReadOnlySpan<byte> span;
+    private readonly bool directLookup;
+
+    /// <summary>Initializes a new instance of the <see cref="GfdFileView"/> struct.</summary>
+    /// <param name="span">The data.</param>
+    public GfdFileView(ReadOnlySpan<byte> span)
+    {
+        this.span = span;
+        if (span.Length < sizeof(GfdHeader))
+            throw new InvalidDataException($"Not enough space for a {nameof(GfdHeader)}");
+        if (span.Length < sizeof(GfdHeader) + (this.Header.Count * sizeof(GfdEntry)))
+            throw new InvalidDataException($"Not enough space for all the {nameof(GfdEntry)}");
+
+        var entries = this.Entries;
+        this.directLookup = true;
+        for (var i = 0; i < entries.Length && this.directLookup; i++)
+            this.directLookup &= i + 1 == entries[i].Id;
+    }
+
+    /// <summary>Gets the header.</summary>
+    public ref readonly GfdHeader Header => ref MemoryMarshal.AsRef<GfdHeader>(this.span);
+
+    /// <summary>Gets the entries.</summary>
+    public ReadOnlySpan<GfdEntry> Entries => MemoryMarshal.Cast<byte, GfdEntry>(this.span[sizeof(GfdHeader)..]);
+
+    /// <summary>Attempts to get an entry.</summary>
+    /// <param name="iconId">The icon ID.</param>
+    /// <param name="entry">The entry.</param>
+    /// <param name="followRedirect">Whether to follow redirects.</param>
+    /// <returns><c>true</c> if found.</returns>
+    public bool TryGetEntry(uint iconId, out GfdEntry entry, bool followRedirect = true)
+    {
+        if (iconId == 0)
+        {
+            entry = default;
+            return false;
+        }
+
+        var entries = this.Entries;
+        if (this.directLookup)
+        {
+            if (iconId <= entries.Length)
+            {
+                entry = entries[(int)(iconId - 1)];
+                return !entry.IsEmpty;
+            }
+
+            entry = default;
+            return false;
+        }
+
+        var lo = 0;
+        var hi = entries.Length;
+        while (lo <= hi)
+        {
+            var i = lo + ((hi - lo) >> 1);
+            if (entries[i].Id == iconId)
+            {
+                if (followRedirect && entries[i].Redirect != 0)
+                {
+                    iconId = entries[i].Redirect;
+                    lo = 0;
+                    hi = entries.Length;
+                    continue;
+                }
+
+                entry = entries[i];
+                return !entry.IsEmpty;
+            }
+
+            if (entries[i].Id < iconId)
+                lo = i + 1;
+            else
+                hi = i - 1;
+        }
+
+        entry = default;
+        return false;
+    }
+
+    /// <summary>Header of a .gfd file.</summary>
+    [StructLayout(LayoutKind.Sequential)]
+    public struct GfdHeader
+    {
+        /// <summary>Signature: "gftd0100".</summary>
+        public fixed byte Signature[8];
+
+        /// <summary>Number of entries.</summary>
+        public int Count;
+
+        /// <summary>Unused/unknown.</summary>
+        public fixed byte Padding[4];
+    }
+
+    /// <summary>An entry of a .gfd file.</summary>
+    [StructLayout(LayoutKind.Sequential, Size = 0x10)]
+    public struct GfdEntry
+    {
+        /// <summary>ID of the entry.</summary>
+        public ushort Id;
+
+        /// <summary>The left offset of the entry.</summary>
+        public ushort Left;
+
+        /// <summary>The top offset of the entry.</summary>
+        public ushort Top;
+
+        /// <summary>The width of the entry.</summary>
+        public ushort Width;
+
+        /// <summary>The height of the entry.</summary>
+        public ushort Height;
+
+        /// <summary>Unknown/unused.</summary>
+        public ushort Unk0A;
+
+        /// <summary>The redirected entry, maybe.</summary>
+        public ushort Redirect;
+
+        /// <summary>Unknown/unused.</summary>
+        public ushort Unk0E;
+
+        /// <summary>Gets a value indicating whether this entry is effectively empty.</summary>
+        public bool IsEmpty => this.Width == 0 || this.Height == 0;
+    }
+}