DiscIO/DirectoryBlob: Add ability to have a start-of-file offset for a file ContentSource.

Source/Core/DiscIO/DirectoryBlob.cpp

@@ -97,11 +97,15 @@ bool DiscContent::Read(u64* offset, u64* length, u8** buffer) const
   {
     const u64 bytes_to_read = std::min(m_size - offset_in_content, *length);
 
-    if (std::holds_alternative<std::string>(m_content_source))
+    if (std::holds_alternative<ContentFile>(m_content_source))
     {
-      File::IOFile file(std::get<std::string>(m_content_source), "rb");
-      if (!file.Seek(offset_in_content, SEEK_SET) || !file.ReadBytes(*buffer, bytes_to_read))
+      const auto& content = std::get<ContentFile>(m_content_source);
+      File::IOFile file(content.m_filename, "rb");
+      if (!file.Seek(content.m_offset + offset_in_content, SEEK_SET) ||
+          !file.ReadBytes(*buffer, bytes_to_read))
+      {
         return false;
+      }
     }
     else if (std::holds_alternative<const u8*>(m_content_source))
     {
@@ -136,14 +140,14 @@ void DiscContentContainer::Add(u64 offset, u64 size, ContentSource source)
 u64 DiscContentContainer::CheckSizeAndAdd(u64 offset, const std::string& path)
 {
   const u64 size = File::GetSize(path);
-  Add(offset, size, path);
+  Add(offset, size, ContentFile{path, 0});
   return size;
 }
 
 u64 DiscContentContainer::CheckSizeAndAdd(u64 offset, u64 max_size, const std::string& path)
 {
   const u64 size = std::min(File::GetSize(path), max_size);
-  Add(offset, size, path);
+  Add(offset, size, ContentFile{path, 0});
   return size;
 }
 
@@ -791,7 +795,7 @@ void DirectoryBlobPartition::WriteDirectory(const File::FSTEntry& parent_entry,
       WriteEntryName(name_offset, entry.virtualName, name_table_offset);
 
       // write entry to virtual disc
-      m_contents.Add(*data_offset, entry.size, entry.physicalName);
+      m_contents.Add(*data_offset, entry.size, ContentFile{entry.physicalName, 0});
 
       // 32 KiB aligned - many games are fine with less alignment, but not all
       *data_offset = Common::AlignUp(*data_offset + entry.size, 0x8000ull);

Source/Core/DiscIO/DirectoryBlob.h

@@ -33,8 +33,18 @@ class DirectoryBlobReader;
 // Returns true if the path is inside a DirectoryBlob and doesn't represent the DirectoryBlob itself
 bool ShouldHideFromGameList(const std::string& volume_path);
 
+// Content chunk that is loaded from a file in the host file system.
+struct ContentFile
+{
+  // Path where the file can be found.
+  std::string m_filename;
+
+  // Offset from the start of the file where the first byte of this content chunk is.
+  u64 m_offset;
+};
+
 using ContentSource =
-    std::variant<std::string,          // File
+    std::variant<ContentFile,          // File
                  const u8*,            // Memory
                  DirectoryBlobReader*  // Partition (which one it is is determined by m_offset)
                  >;