platform/windows: add optional DwmFlush() call to improve Windows capture

Invoke DwmFlush() before acquiring the next frame to alleviate visual stutter
during mouse movement at the cost of constraining the capture rate to the host's
monitor refresh.

Disabled by default; enable via "dwmflush" boolean configuration parameter.

CMakeLists.txt

@@ -122,6 +122,7 @@ if(WIN32)
 		ws2_32
 		d3d11 dxgi D3DCompiler
 		setupapi
+		dwmapi
 		)
 
 	set_source_files_properties(third-party/ViGEmClient/src/ViGEmClient.cpp PROPERTIES COMPILE_DEFINITIONS "UNICODE=1;ERROR_INVALID_DEVICE_OBJECT_PARAMETER=650")

docs/source/about/advanced_usage.rst

@@ -333,6 +333,25 @@ Example
         3840x1600,
       ]
 
+dwmflush
+^^^^^^^^
+
+Description
+   Invoke DwmFlush() to sync screen capture to the Windows presentation interval.
+
+   .. Caution:: Applies to Windows only. Alleviates visual stuttering during mouse movement, but causes the capture
+      rate to be limited to the host monitor's currently active refresh rate.
+
+Default
+   ``disabled``
+
+Examples
+
+   Windows
+      .. code-block:: text
+
+         dwmflush = enabled
+
 Audio
 -----
 

src_assets/common/assets/web/config.html

@@ -400,7 +400,18 @@
           You can select the video card you want to stream:<br />
           The appropriate values can be found using the following command:<br />
           tools\dxgi-info.exe<br />
-          <br />
+        </div>
+      </div>
+      <!--DwmFlush-->
+      <div class="mb-3" v-if="platform === 'windows'">
+        <label for="dwmflush" class="form-label">DwmFlush</label>
+        <select id="dwmflush" class="form-select" v-model="config.dwmflush">
+          <option value="disabled">Disabled</option>
+          <option value="enabled">Enabled</option>
+        </select>
+        <div class="form-text">
+          Improves capture latency during mouse movement.<br />
+          Enabling this may prevent the client's FPS from exceeding the host monitor's active refresh rate.
         </div>
       </div>
       <div class="mb-3" class="config-page" v-if="platform === 'linux'">
@@ -832,6 +843,7 @@
             this.config.key_rightalt_to_key_win || "disabled";
           this.config.gamepad = this.config.gamepad || "x360";
           this.config.upnp = this.config.upnp || "disabled";
+          this.config.dwmflush = this.config.dwmflush || "disabled";
           this.config.min_log_level = this.config.min_log_level || 2;
           this.config.origin_pin_allowed =
             this.config.origin_pin_allowed || "pc";

sunshine/config.cpp

@@ -226,9 +226,10 @@ video_t video {
     1,
     -1 }, // vt
 
-  {}, // encoder
-  {}, // adapter_name
-  {}, // output_name
+  {},   // encoder
+  {},   // adapter_name
+  {},   // output_name
+  false // dwmflush
 };
 
 audio_t audio {};
@@ -735,6 +736,7 @@ void apply_config(std::unordered_map<std::string, std::string> &&vars) {
   string_f(vars, "encoder", video.encoder);
   string_f(vars, "adapter_name", video.adapter_name);
   string_f(vars, "output_name", video.output_name);
+  bool_f(vars, "dwmflush", video.dwmflush);
 
   path_f(vars, "pkey", nvhttp.pkey);
   path_f(vars, "cert", nvhttp.cert);

sunshine/config.h

@@ -44,6 +44,7 @@ struct video_t {
   std::string encoder;
   std::string adapter_name;
   std::string output_name;
+  bool dwmflush;
 };
 
 struct audio_t {

sunshine/platform/windows/display.h

@@ -8,6 +8,7 @@
 #include <d3d11.h>
 #include <d3d11_4.h>
 #include <d3dcommon.h>
+#include <dwmapi.h>
 #include <dxgi.h>
 #include <dxgi1_2.h>
 
@@ -172,4 +173,4 @@ public:
 };
 } // namespace platf::dxgi
 
-#endif
+#endif

sunshine/platform/windows/display_base.cpp

@@ -20,6 +20,10 @@ capture_e duplication_t::next_frame(DXGI_OUTDUPL_FRAME_INFO &frame_info, std::ch
     return capture_status;
   }
 
+  if(config::video.dwmflush) {
+    DwmFlush();
+  }
+
   auto status = dup->AcquireNextFrame(timeout.count(), &frame_info, res_p);
 
   switch(status) {