From b3cbe36c08b830963e09752763df66dc3d281cd3 Mon Sep 17 00:00:00 2001
From: Philip Rebohle <philip.rebohle@tu-dortmund.de>
Date: Wed, 21 Jun 2023 16:33:06 +0200
Subject: [PATCH] [dxvk] Apply frame rate limit on presentation timeline

This may reduce latency as we no longer end up stalling subsequent
GPU submissions.
---
 src/dxvk/dxvk_presenter.cpp | 17 +++++++++++++----
 src/dxvk/dxvk_presenter.h   |  3 +++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/dxvk/dxvk_presenter.cpp b/src/dxvk/dxvk_presenter.cpp
index 857ecf57..10f13da2 100644
--- a/src/dxvk/dxvk_presenter.cpp
+++ b/src/dxvk/dxvk_presenter.cpp
@@ -108,10 +108,6 @@ namespace dxvk {
       m_swapchain, std::numeric_limits<uint64_t>::max(),
       sync.acquire, VK_NULL_HANDLE, &m_imageIndex);
 
-    bool vsync = mode == VK_PRESENT_MODE_FIFO_KHR
-              || mode == VK_PRESENT_MODE_FIFO_RELAXED_KHR;
-
-    m_fpsLimiter.delay(vsync);
     return status;
   }
 
@@ -134,6 +130,7 @@ namespace dxvk {
       m_frameQueue.push(frame);
       m_frameCond.notify_one();
     } else {
+      applyFrameRateLimit(mode);
       m_signal->signal(frameId);
     }
 
@@ -648,6 +645,14 @@ namespace dxvk {
   }
 
 
+  void Presenter::applyFrameRateLimit(VkPresentModeKHR mode) {
+    bool vsync = mode == VK_PRESENT_MODE_FIFO_KHR
+              || mode == VK_PRESENT_MODE_FIFO_RELAXED_KHR;
+
+    m_fpsLimiter.delay(vsync);
+  }
+
+
   void Presenter::runFrameThread() {
     env::setThreadName("dxvk-frame");
 
@@ -667,6 +672,10 @@ namespace dxvk {
       if (!frame.frameId)
         return;
 
+      // Apply the FPS limiter before signaling the frame event in
+      // order to reduce latency if the app uses it for frame pacing.
+      applyFrameRateLimit(frame.mode);
+
       // If the present operation has succeeded, actually wait for it to complete.
       // Don't bother with it on MAILBOX / IMMEDIATE modes since doing so would
       // restrict us to the display refresh rate on some platforms (XWayland).
diff --git a/src/dxvk/dxvk_presenter.h b/src/dxvk/dxvk_presenter.h
index 30247796..c5ba1273 100644
--- a/src/dxvk/dxvk_presenter.h
+++ b/src/dxvk/dxvk_presenter.h
@@ -294,6 +294,9 @@ namespace dxvk {
 
     void destroySurface();
 
+    void applyFrameRateLimit(
+            VkPresentModeKHR          mode);
+
     void runFrameThread();
 
   };