Add UTF-8 filename support on Windows to ktxtools (KhronosGroup#788)

Fixes KhronosGroup#781.

utils/platform_utils.h

@@ -0,0 +1,63 @@
+// Copyright 2022-2023 The Khronos Group Inc.
+// Copyright 2022-2023 RasterGrid Kft.
+// SPDX-License-Identifier: Apache-2.0
+
+#pragma once
+
+#include "stdafx.h"
+#include <string>
+#include <iostream>
+#include <memory>
+#include <vector>
+#include <fmt/ostream.h>
+#include <fmt/printf.h>
+
+#if defined(_WIN32)
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN
+#endif
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+#include <shellapi.h>
+#endif
+
+#if defined(_WIN32) && !defined(_UNICODE)
+// For Windows, we convert the UTF-8 path to a UTF-16 path to force using the APIs
+// that correctly handle unicode characters
+inline std::wstring DecodeUTF8Path(std::string path) {
+    std::wstring result;
+    int len = MultiByteToWideChar(CP_UTF8, 0, path.c_str(), static_cast<int>(path.length()), NULL, 0);
+    if (len > 0)
+    {
+        result.resize(len);
+        MultiByteToWideChar(CP_UTF8, 0, path.c_str(), static_cast<int>(path.length()), &result[0], len);
+    }
+    return result;
+}
+#else
+// For other platforms there is no need for any conversion, they support UTF-8 natively
+inline std::string DecodeUTF8Path(std::string path) {
+    return path;
+}
+#endif
+
+inline void InitUTF8CLI(int& argc, _TCHAR* argv[]) {
+#if defined(_WIN32) && !defined(_UNICODE)
+    // Windows does not support UTF-8 argv so we have to manually acquire it
+    static std::vector<std::unique_ptr<_TCHAR[]>> utf8Argv(argc);
+    LPWSTR commandLine = GetCommandLineW();
+    LPWSTR* wideArgv = CommandLineToArgvW(commandLine, &argc);
+    for (int i = 0; i < argc; ++i) {
+        int byteSize = WideCharToMultiByte(CP_UTF8, 0, wideArgv[i], -1, nullptr, 0, nullptr, nullptr);
+        utf8Argv[i] = std::make_unique<_TCHAR[]>(byteSize);
+        WideCharToMultiByte(CP_UTF8, 0, wideArgv[i], -1, utf8Argv[i].get(), byteSize, nullptr, nullptr);
+        argv[i] = utf8Argv[i].get();
+    }
+#else
+    // Nothing to do for other platforms
+    (void)argc;
+    (void)argv;
+#endif
+}