Add: concept of a RandomAccessFile to replace the FIO slot functions

1 files changed, 58 insertions, 0 deletions

diff --git a/src/random_access_file_type.h b/src/random_access_file_type.h
new file mode 100644
index 000000000..ce0e9e358
--- /dev/null
+++ b/src/random_access_file_type.h
@@ -0,0 +1,58 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+ /** @file random_access_file_type.h Class related to random access to files. */
+
+#ifndef RANDOM_ACCESS_FILE_TYPE_H
+#define RANDOM_ACCESS_FILE_TYPE_H
+
+#include "fileio_type.h"
+#include <string>
+
+/**
+ * A file from which bytes, words and double words are read in (potentially) a random order.
+ *
+ * This is mostly intended to be used for things that can be read from GRFs when needed, so
+ * the graphics but also the sounds. This also ties into the spritecache as it uses these
+ * files to load the sprites from when needed.
+ */
+class RandomAccessFile {
+	/** The number of bytes to allocate for the buffer. */
+	static constexpr int BUFFER_SIZE = 512;
+
+	std::string filename;            ///< Full name of the file; relative path to subdir plus the extension of the file.
+	std::string simplified_filename; ///< Simplified lowecase name of the file; only the name, no path or extension.
+
+	FILE *file_handle;               ///< File handle of the open file.
+	size_t pos;                      ///< Position in the file of the end of the read buffer.
+
+	byte *buffer;                    ///< Current position within the local buffer.
+	byte *buffer_end;                ///< Last valid byte of buffer.
+	byte buffer_start[BUFFER_SIZE];  ///< Local buffer when read from file.
+
+public:
+	RandomAccessFile(const std::string &filename, Subdirectory subdir);
+	RandomAccessFile(const RandomAccessFile&) = delete;
+	void operator=(const RandomAccessFile&) = delete;
+
+	virtual ~RandomAccessFile();
+
+	const std::string &GetFilename() const;
+	const std::string &GetSimplifiedFilename() const;
+
+	size_t GetPos() const;
+	void SeekTo(size_t pos, int mode);
+
+	byte ReadByte();
+	uint16 ReadWord();
+	uint32 ReadDword();
+
+	void ReadBlock(void *ptr, size_t size);
+	void SkipBytes(int n);
+};
+
+#endif /* RANDOM_ACCESS_FILE_TYPE_H */