Add the renderer process

The renderer becomes two programs: the adapter (t5deRenderEngine.dll, 32-bit, in IMVU's process) and a 64-bit renderer process (t5de-renderer.exe) drawing with Diligent Engine, fetched with FetchContent and pinned. For now a spike: the adapter starts the renderer process for each engine and signals each frame through a shared memory channel, and the renderer process draws a box into a child window in the client's 3D view.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

adapter/log.cpp

@@ -0,0 +1,39 @@
+#include "log.hpp"
+
+#include <share.h>
+#include <windows.h>
+
+#include <cstdio>
+#include <filesystem>
+#include <mutex>
+
+namespace t5de::log {
+
+namespace {
+
+std::FILE* open()
+{
+    wchar_t temp[MAX_PATH + 1];
+    const DWORD length = GetTempPathW(MAX_PATH + 1, temp);
+    if (length == 0 || length > MAX_PATH) {
+        return nullptr;
+    }
+    // Shared, so it can be read while the client runs.
+    return _wfsopen((std::filesystem::path(temp) / L"t5de-renderer.log").c_str(), L"w", _SH_DENYNO);
+}
+
+} // namespace
+
+void write(std::string_view line)
+{
+    static std::mutex mutex;
+    static std::FILE* file = open();
+    const std::scoped_lock lock(mutex);
+    if (file != nullptr) {
+        std::fwrite(line.data(), 1, line.size(), file);
+        std::fputc('\n', file);
+        std::fflush(file);
+    }
+}
+
+} // namespace t5de::log