From 9f758b0032a94182eecbef24c4ed53c65590830b Mon Sep 17 00:00:00 2001
From: Magnus Norddahl <dpjudas@users.noreply.github.com>
Date: Tue, 26 Mar 2019 10:40:43 +0100
Subject: [PATCH] - implement vid_maxfps

---
 .../vulkan/system/vk_framebuffer.cpp          | 40 +++++++++++++++++++
 src/rendering/vulkan/system/vk_framebuffer.h  |  3 ++
 2 files changed, 43 insertions(+)

diff --git a/src/rendering/vulkan/system/vk_framebuffer.cpp b/src/rendering/vulkan/system/vk_framebuffer.cpp
index ca667e5d34..3ab6b51e8c 100644
--- a/src/rendering/vulkan/system/vk_framebuffer.cpp
+++ b/src/rendering/vulkan/system/vk_framebuffer.cpp
@@ -59,10 +59,14 @@
 #include "vulkan/system/vk_swapchain.h"
 #include "doomerrors.h"
 
+#include <chrono>
+#include <thread>
+
 void Draw2D(F2DDrawer *drawer, FRenderState &state);
 void DoWriteSavePic(FileWriter *file, ESSType ssformat, uint8_t *scr, int width, int height, sector_t *viewsector, bool upsidedown);
 
 EXTERN_CVAR(Bool, vid_vsync)
+EXTERN_CVAR(Int, vid_maxfps)
 EXTERN_CVAR(Bool, r_drawvoxels)
 EXTERN_CVAR(Int, gl_tonemap)
 EXTERN_CVAR(Int, screenblocks)
@@ -189,6 +193,8 @@ void VulkanFrameBuffer::Update()
 
 	Flush3D.Unclock();
 
+	FPSLimit();
+	
 	Finish.Reset();
 	Finish.Clock();
 
@@ -217,6 +223,40 @@ void VulkanFrameBuffer::Update()
 	Super::Update();
 }
 
+void VulkanFrameBuffer::FPSLimit()
+{
+	using namespace std::chrono;
+	using namespace std::this_thread;
+
+	if (vid_maxfps <= 0 || vid_vsync)
+		return;
+
+	uint64_t targetWakeTime = fpsLimitTime + 1'000'000 / vid_maxfps;
+
+	while (true)
+	{
+		fpsLimitTime = duration_cast<microseconds>(steady_clock::now().time_since_epoch()).count();
+		int64_t timeToWait = targetWakeTime - fpsLimitTime;
+
+		if (timeToWait > 1'000'000 || timeToWait <= 0)
+		{
+			break;
+		}
+
+		if (timeToWait <= 2'000'000)
+		{
+			// We are too close to the deadline. OS sleep is not precise enough to wake us before it elapses.
+			// Yield execution and check time again.
+			sleep_for(nanoseconds(0));
+		}
+		else
+		{
+			// Sleep, but try to wake before deadline.
+			sleep_for(milliseconds(timeToWait - 1'000'000));
+		}
+	}
+}
+
 void VulkanFrameBuffer::DeleteFrameObjects()
 {
 	FrameDeleteList.Images.clear();
diff --git a/src/rendering/vulkan/system/vk_framebuffer.h b/src/rendering/vulkan/system/vk_framebuffer.h
index 6926063052..0e0d26fcf8 100644
--- a/src/rendering/vulkan/system/vk_framebuffer.h
+++ b/src/rendering/vulkan/system/vk_framebuffer.h
@@ -107,6 +107,7 @@ private:
 	void CopyScreenToBuffer(int w, int h, void *data);
 	void UpdateShadowMap();
 	void DeleteFrameObjects();
+	void FPSLimit();
 
 	std::unique_ptr<VkShaderManager> mShaderManager;
 	std::unique_ptr<VkSamplerManager> mSamplerManager;
@@ -131,6 +132,8 @@ private:
 
 	int lastSwapWidth = 0;
 	int lastSwapHeight = 0;
+
+	uint64_t fpsLimitTime = 0;
 };
 
 inline VulkanFrameBuffer *GetVulkanFrameBuffer() { return static_cast<VulkanFrameBuffer*>(screen); }