optional preview frame

src/app/RenderCadenceApp.h

@@ -5,6 +5,7 @@
 #include "RuntimeLayerController.h"
 #include "../logging/Logger.h"
 #include "../control/RuntimeStateJson.h"
+#include "../preview/PreviewWindowThread.h"
 #include "../telemetry/TelemetryHealthMonitor.h"
 #include "../video/DeckLinkInput.h"
 #include "../video/DeckLinkOutput.h"
@@ -94,6 +95,7 @@ public:
 			return false;
 		}
 
+		StartPreviewWindow();
 		StartOptionalVideoOutput();
 		mTelemetryHealth.Start(mFrameExchange, mOutput, mOutputThread, mRenderThread);
 		StartHttpServer();
@@ -106,6 +108,7 @@ public:
 	{
 		mHttpServer.Stop();
 		mTelemetryHealth.Stop();
+		mPreviewWindow.Stop();
 		mOutputThread.Stop();
 		mOutput.Stop();
 		mRuntimeLayers.Stop();
@@ -228,6 +231,24 @@ private:
 		}
 	}
 
+	void StartPreviewWindow()
+	{
+		if (!mConfig.previewEnabled)
+			return;
+
+		PreviewWindowConfig previewConfig;
+		previewConfig.enabled = true;
+		previewConfig.fps = mConfig.previewFps;
+		std::string error;
+		if (mPreviewWindow.Start(mFrameExchange, previewConfig, error))
+		{
+			Log("preview", "Preview window thread started.");
+			return;
+		}
+
+		LogWarning("preview", "Preview window did not start: " + error);
+	}
+
 	std::string BuildStateJson()
 	{
 		CadenceTelemetrySnapshot telemetry = mHttpTelemetry.Sample(mFrameExchange, mOutput, mOutputThread, mRenderThread);
@@ -281,6 +302,7 @@ private:
 	TelemetryHealthMonitor mTelemetryHealth;
 	CadenceTelemetry mHttpTelemetry;
 	HttpControlServer mHttpServer;
+	PreviewWindowThread mPreviewWindow;
 	RuntimeLayerController mRuntimeLayers;
 	std::function<DeckLinkInputMetrics()> mDeckLinkInputMetricsProvider;
 	uint64_t mLastInputCapturedFrames = 0;