optional preview frame

src/preview/PreviewConfig.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <string>
+
+namespace RenderCadenceCompositor
+{
+constexpr double kDefaultPreviewFps = 30.0;
+constexpr double kMinimumPreviewFps = 1.0;
+
+struct PreviewWindowConfig
+{
+	bool enabled = false;
+	double fps = kDefaultPreviewFps;
+	std::string title = "Render Cadence Preview";
+};
+
+inline double NormalizePreviewFps(double fps)
+{
+	return fps >= kMinimumPreviewFps ? fps : kDefaultPreviewFps;
+}
+
+inline unsigned PreviewTimerIntervalMilliseconds(double fps)
+{
+	const double normalizedFps = NormalizePreviewFps(fps);
+	const int intervalMilliseconds = static_cast<int>(1000.0 / normalizedFps);
+	return static_cast<unsigned>(intervalMilliseconds > 0 ? intervalMilliseconds : 1);
+}
+}