From 36c9c1232ef8ad3906dee01a7c4e60bd90e64f4b Mon Sep 17 00:00:00 2001
From: Andrew Belt <andrewpbelt@gmail.com>
Date: Wed, 2 Nov 2022 04:13:02 -0400
Subject: [PATCH] Use sleep-based frame limiting instead of vsync since it's
 unreliable on buggy graphics drivers.

---
 src/window/Window.cpp | 41 ++++++++++++++++-------------------------
 1 file changed, 16 insertions(+), 25 deletions(-)

diff --git a/src/window/Window.cpp b/src/window/Window.cpp
index 986f5e7f..0065927c 100644
--- a/src/window/Window.cpp
+++ b/src/window/Window.cpp
@@ -91,8 +91,8 @@ struct Window::Internal {
 	bool ignoreNextMouseDelta = false;
 	double monitorRefreshRate = 0.0;
 	int frameSwapInterval = -1;
-	double frameTime = 0.0;
-	double lastFrameDuration = 0.0;
+	double frameTime = NAN;
+	double lastFrameDuration = NAN;
 
 	math::Vec lastMousePos;
 
@@ -298,6 +298,7 @@ Window::Window() {
 	glfwSetInputMode(win, GLFW_LOCK_KEY_MODS, 1);
 
 	glfwMakeContextCurrent(win);
+	glfwSwapInterval(0);
 	const GLFWvidmode* monitorMode = glfwGetVideoMode(glfwGetPrimaryMonitor());
 	if (monitorMode->refreshRate > 0) {
 		internal->monitorRefreshRate = monitorMode->refreshRate;
@@ -412,11 +413,11 @@ void Window::run() {
 
 void Window::step() {
 	double frameTime = system::getTime();
-	double lastFrameTime = internal->frameTime;
+	if (std::isfinite(internal->frameTime)) {
+		internal->lastFrameDuration = frameTime - internal->frameTime;
+	}
 	internal->frameTime = frameTime;
-	internal->lastFrameDuration = frameTime - lastFrameTime;
 	internal->fbCount = 0;
-	// DEBUG("%.2lf Hz", 1.0 / internal->lastFrameDuration);
 	// double t1 = 0.0, t2 = 0.0, t3 = 0.0, t4 = 0.0, t5 = 0.0;
 
 	// Make event handlers and step() have a clean NanoVG context
@@ -433,17 +434,6 @@ void Window::step() {
 	// In case glfwPollEvents() sets another OpenGL context
 	glfwMakeContextCurrent(win);
 
-	// Set swap interval
-	int frameSwapInterval = 0;
-	if (settings::frameRateLimit > 0.f) {
-		frameSwapInterval = std::ceil(internal->monitorRefreshRate / settings::frameRateLimit);
-	}
-
-	if (frameSwapInterval != internal->frameSwapInterval) {
-		glfwSwapInterval(frameSwapInterval);
-		internal->frameSwapInterval = frameSwapInterval;
-	}
-
 	// Call cursorPosCallback every frame, not just when the mouse moves
 	{
 		double xpos, ypos;
@@ -514,25 +504,26 @@ void Window::step() {
 			glClearColor(0.0, 0.0, 0.0, 1.0);
 			glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
 			nvgEndFrame(vg);
-			// t4 = system::getTime();
 		}
+		// t4 = system::getTime();
 	}
 
 	glfwSwapBuffers(win);
 
-	// On some platforms, glfwSwapBuffers() doesn't wait on monitor refresh, so we have to sleep as a fallback.
-	double frameDurationRemaining = getFrameDurationRemaining();
-	if (frameDurationRemaining > 0.0) {
-		std::this_thread::sleep_for(std::chrono::duration<double>(frameDurationRemaining));
+	// Limit frame rate
+	if (settings::frameRateLimit > 0) {
+		double remaining = getFrameDurationRemaining();
+		if (remaining > 0.0) {
+			system::sleep(remaining);
+		}
 	}
 
 	// t5 = system::getTime();
-
 	// DEBUG("pre-step %6.1f step %6.1f draw %6.1f nvgEndFrame %6.1f glfwSwapBuffers %6.1f total %6.1f",
 	// 	(t1 - frameTime) * 1e3f,
 	// 	(t2 - t1) * 1e3f,
 	// 	(t3 - t2) * 1e3f,
-	// 	(t4 - t2) * 1e3f,
+	// 	(t4 - t3) * 1e3f,
 	// 	(t5 - t4) * 1e3f,
 	// 	(t5 - frameTime) * 1e3f
 	// );
@@ -717,8 +708,8 @@ double Window::getLastFrameDuration() {
 
 
 double Window::getFrameDurationRemaining() {
-	double frameDurationDesired = 1.f / settings::frameRateLimit;
-	return frameDurationDesired - (system::getTime() - internal->frameTime);
+	double frameDuration = 1.f / settings::frameRateLimit;
+	return frameDuration - (system::getTime() - internal->frameTime);
 }