Use actual monitor refresh rate instead of 60 Hz as frame rate reference.

include/window.hpp

@@ -90,6 +90,7 @@ struct Window {
 	void setFullScreen(bool fullScreen);
 	bool isFullScreen();
 	bool isFrameOverdue();
+	double getMonitorRefreshRate();
 
 	std::shared_ptr<Font> loadFont(const std::string& filename);
 	std::shared_ptr<Image> loadImage(const std::string& filename);

src/app/MenuBar.cpp

@@ -339,11 +339,11 @@ struct FrameRateItem : ui::MenuItem {
 		ui::Menu* menu = new ui::Menu;
 
 		for (int i = 1; i <= 6; i++) {
-			float frameRate = 60.f / i;
+			double frameRate = APP->window->getMonitorRefreshRate() / i;
 
 			FrameRateValueItem* item = new FrameRateValueItem;
 			item->frameSwapInterval = i;
-			item->text = string::f("%.0f Hz", frameRate);
+			item->text = string::f("%.0lf Hz", frameRate);
 			item->rightText += CHECKMARK(settings::frameSwapInterval == i);
 			menu->addChild(item);
 		}

src/window.cpp

@@ -96,6 +96,7 @@ struct Window::Internal {
 
 	bool ignoreNextMouseDelta = false;
 	int frameSwapInterval = -1;
+	double monitorRefreshRate = -1;
 };
 
 
@@ -250,6 +251,8 @@ Window::Window() {
 
 	glfwMakeContextCurrent(win);
 	glfwSwapInterval(1);
+	const GLFWvidmode* monitorMode = glfwGetVideoMode(glfwGetPrimaryMonitor());
+	internal->monitorRefreshRate = monitorMode->refreshRate;
 
 	// Set window callbacks
 	glfwSetWindowSizeCallback(win, windowSizeCallback);
@@ -522,11 +525,14 @@ bool Window::isFrameOverdue() {
 	if (settings::frameSwapInterval == 0)
 		return false;
 	double frameDuration = glfwGetTime() - frameTimeStart;
-	// This is fudged a bit because it assumes the monitor refresh rate is 60 Hz.
-	double frameDeadline = settings::frameSwapInterval / 60.0;
+	double frameDeadline = settings::frameSwapInterval / internal->monitorRefreshRate;
 	return frameDuration > frameDeadline;
 }
 
+double Window::getMonitorRefreshRate() {
+	return internal->monitorRefreshRate;
+}
+
 std::shared_ptr<Font> Window::loadFont(const std::string& filename) {
 	auto sp = fontCache[filename].lock();
 	if (!sp) {