From d64fec9cfb53f70ba0afff26fde9ef353f21e283 Mon Sep 17 00:00:00 2001
From: MkfsSion <mkfssion@mkfssion.com>
Date: Sun, 9 Aug 2026 14:29:54 +0800
Subject: [PATCH] ArcFormats: Support Silky's MMO image format

* Tested game: https://vndb.org/v449

Signed-off-by: MkfsSion <mkfssion@mkfssion.com>
---
 ArcFormats/ArcFormats.csproj |  1 +
 ArcFormats/Silky/ImageAKB.cs | 26 ++++++++++++++++++--
 ArcFormats/Silky/ImageMMO.cs | 46 ++++++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 2 deletions(-)
 create mode 100644 ArcFormats/Silky/ImageMMO.cs

diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index c5a51c084..e154c3596 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -281,6 +281,7 @@
     <Compile Include="Psp\ArcQPK.cs" />
     <Compile Include="QoiCodec.cs" />
     <Compile Include="ScrPlayer\ImageIMG.cs" />
+    <Compile Include="Silky\ImageMMO.cs" />
     <Compile Include="SingleFileArchive.cs" />
     <Compile Include="Software House Parsley\ArcCG3.cs" />
     <Compile Include="Software House Parsley\ArcScn.cs" />
diff --git a/ArcFormats/Silky/ImageAKB.cs b/ArcFormats/Silky/ImageAKB.cs
index a6f28da15..b1186ff3f 100644
--- a/ArcFormats/Silky/ImageAKB.cs
+++ b/ArcFormats/Silky/ImageAKB.cs
@@ -40,6 +40,7 @@ internal class AkbMetaData : ImageMetaData
         public uint     Flags;
         public string   BaseFileName;
         public uint     DataOffset;
+        public bool     TopDownOrder;
     }
 
     [Export(typeof(ImageFormat))]
@@ -150,13 +151,34 @@ public byte[] Unpack (byte[] background = null)
             var pixels = new byte[m_info.InnerHeight * inner_stride];
             using (var lz = new LzssStream (m_input, LzssMode.Decompress, true))
             {
-                for (int pos = pixels.Length - inner_stride; pos >= 0; pos -= inner_stride)
+                if (m_info.TopDownOrder)
                 {
-                    if (inner_stride != lz.Read (pixels, pos, inner_stride))
+                    if (lz.Read(pixels, 0, pixels.Length) != pixels.Length)
+                    {
                         throw new InvalidFormatException();
+                    }
+                }
+                else
+                {
+                    for (int pos = pixels.Length - inner_stride; pos >= 0; pos -= inner_stride)
+                    {
+                        if (inner_stride != lz.Read (pixels, pos, inner_stride))
+                            throw new InvalidFormatException();
+                    }
                 }
+
             }
             RestoreDelta (pixels, inner_stride);
+            if (m_info.TopDownOrder)
+            {
+                var tmp_stride = new byte[inner_stride];
+                for (int i = 0, j = m_info.InnerHeight - 1; i < j; ++i, --j)
+                {
+                    Buffer.BlockCopy(pixels, j * inner_stride, tmp_stride, 0, inner_stride);
+                    Buffer.BlockCopy(pixels, i * inner_stride, pixels, j * inner_stride, inner_stride);
+                    Buffer.BlockCopy(tmp_stride, 0, pixels, i * inner_stride, inner_stride);
+                }
+            }
             if (null == background && m_info.InnerWidth == m_info.Width && m_info.InnerHeight == m_info.Height)
                 return pixels;
 
diff --git a/ArcFormats/Silky/ImageMMO.cs b/ArcFormats/Silky/ImageMMO.cs
new file mode 100644
index 000000000..0846f0687
--- /dev/null
+++ b/ArcFormats/Silky/ImageMMO.cs
@@ -0,0 +1,46 @@
+using System.ComponentModel.Composition;
+
+// [070223][Silky's] Himekishi Angelica ~Anata tte, Hontou ni Saitei no Kuzu Da wa!~
+
+namespace GameRes.Formats.Silky
+{
+    [Export(typeof(ImageFormat))]
+    public class MmoFormat : AkbFormat
+    {
+        public override string Tag => "MMO";
+        public override string Description => "Silky's MMO image format";
+        public override uint Signature => 0x204F4D4D; // 'MMO '
+
+        public MmoFormat()
+        {
+            Signatures = new[] { Signature };
+        }
+
+        public override ImageMetaData ReadMetaData(IBinaryStream file)
+        {
+            file.Position += 4;
+            var metaData = new AkbMetaData();
+            metaData.TopDownOrder = true;
+            metaData.Flags = 0;
+            metaData.OffsetX = file.ReadInt32();
+            metaData.OffsetY = file.ReadInt32();
+            metaData.InnerWidth = file.ReadInt32() - metaData.OffsetX;
+            metaData.InnerHeight = file.ReadInt32() - metaData.OffsetY;
+            // Not sure if there are any other pixel encoding
+            metaData.BPP = 24;
+            // Skip 8 byte unknown field
+            file.Position += 8;
+            metaData.Width = file.ReadUInt32();
+            metaData.Height = file.ReadUInt32();
+            // Skip another 4 byte unknown field
+            file.Position += 4;
+            metaData.DataOffset = (uint)file.Position;
+            // FIXME: Implement reliable way to detect difference image and find the corresponding base image name Find base image
+            // Unlike AKB format, MMO format has neither mark for difference image nor the name of its base image file embedded.
+            // Also, there doesn't seem to have a constant naming pattern even in the same game.
+            metaData.BaseFileName = null;
+            metaData.Background = new byte[4];
+            return metaData;
+        }
+    }
+}
\ No newline at end of file