HostDisplay: Add GetHostRefreshRate() function

Only implemented in Windows for now.

src/core/host_display.cpp

@@ -15,6 +15,11 @@
 #include <vector>
 Log_SetChannel(HostDisplay);
 
+#ifdef _WIN32
+#include "common/windows_headers.h"
+#include <dwmapi.h>
+#endif
+
 HostDisplayTexture::~HostDisplayTexture() = default;
 
 HostDisplay::~HostDisplay() = default;
@@ -85,6 +90,43 @@ bool HostDisplay::SetDisplayPixels(HostDisplayPixelFormat format, u32 width, u32
   return true;
 }
 
+bool HostDisplay::GetHostRefreshRate(float* refresh_rate)
+{
+#ifdef _WIN32
+  static HMODULE dwm_module = nullptr;
+  static HRESULT(STDAPICALLTYPE * get_timing_info)(HWND hwnd, DWM_TIMING_INFO * pTimingInfo) = nullptr;
+  static bool load_tried = false;
+  if (!load_tried)
+  {
+    load_tried = true;
+    dwm_module = LoadLibrary("dwmapi.dll");
+    if (dwm_module)
+    {
+      std::atexit([]() {
+        FreeLibrary(dwm_module);
+        dwm_module = nullptr;
+      });
+      get_timing_info =
+        reinterpret_cast<decltype(get_timing_info)>(GetProcAddress(dwm_module, "DwmGetCompositionTimingInfo"));
+    }
+  }
+
+  DWM_TIMING_INFO ti = {};
+  ti.cbSize = sizeof(ti);
+  HRESULT hr = get_timing_info(nullptr, &ti);
+  if (SUCCEEDED(hr))
+  {
+    if (ti.rateRefresh.uiNumerator == 0 || ti.rateRefresh.uiDenominator == 0)
+      return false;
+
+    *refresh_rate = static_cast<float>(ti.rateRefresh.uiNumerator) / static_cast<float>(ti.rateRefresh.uiDenominator);
+    return true;
+  }
+#endif
+
+  return false;
+}
+
 void HostDisplay::SetSoftwareCursor(std::unique_ptr<HostDisplayTexture> texture, float scale /*= 1.0f*/)
 {
   m_cursor_texture = std::move(texture);