add plugin camera desktop

plugins/camera_desktop/windows/logging.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <windows.h>
+
+#include <cstdio>
+#include <sstream>
+#include <string>
+
+// Diagnostic logging is opt-in and OFF by default, so the plugin stays quiet in
+// consumer apps and avoids the cost of OutputDebugString under a debugger. To
+// capture a trace for a bug report, set the environment variable
+// CAMERA_DESKTOP_LOG to any value other than "0" before launching, then
+// reproduce. Real errors still reach the app through the method channel
+// (result.Error / cameraError) regardless of this setting.
+inline bool DebugLogEnabled() {
+  static const bool enabled = [] {
+    char buf[16] = {};
+    DWORD n = GetEnvironmentVariableA("CAMERA_DESKTOP_LOG", buf, sizeof(buf));
+    if (n == 0) return false;             // not set
+    if (n >= sizeof(buf)) return true;    // set to some long value
+    return std::string(buf) != "0";
+  }();
+  return enabled;
+}
+
+inline void DebugLog(const std::string& msg) {
+  if (!DebugLogEnabled()) return;
+  std::string line = "[camera_desktop/windows] " + msg + "\n";
+  OutputDebugStringA(line.c_str());
+  std::fputs(line.c_str(), stderr);
+  std::fflush(stderr);
+}
+
+inline std::string WideToUtf8(const std::wstring& w) {
+  if (w.empty()) return {};
+  int size = WideCharToMultiByte(CP_UTF8, 0, w.data(), (int)w.size(),
+                                 nullptr, 0, nullptr, nullptr);
+  std::string s(size, '\0');
+  WideCharToMultiByte(CP_UTF8, 0, w.data(), (int)w.size(),
+                      s.data(), size, nullptr, nullptr);
+  return s;
+}
+
+inline std::string HrToString(HRESULT hr) {
+  std::ostringstream ss;
+  ss << "0x" << std::hex << static_cast<unsigned long>(hr);
+  return ss.str();
+}