From 56395c9bc86557720074073427d0ceaee44559cc Mon Sep 17 00:00:00 2001
From: Philip Rebohle <philip.rebohle@tu-dortmund.de>
Date: Mon, 2 Aug 2021 19:11:35 +0200
Subject: [PATCH] [d3d11] Re-implement frame latency events using Win32
 semaphore

Matches native DXGI behaviour more accurately, and fixes a hang in
Shin Megami Tensei 3.
---
 src/d3d11/d3d11_swapchain.cpp | 20 ++++++++++++++------
 src/d3d11/d3d11_swapchain.h   |  4 ++--
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/d3d11/d3d11_swapchain.cpp b/src/d3d11/d3d11_swapchain.cpp
index c250bf77e..b803d37c0 100644
--- a/src/d3d11/d3d11_swapchain.cpp
+++ b/src/d3d11/d3d11_swapchain.cpp
@@ -177,9 +177,16 @@ namespace dxvk {
     if (MaxLatency == 0 || MaxLatency > DXGI_MAX_SWAP_CHAIN_BUFFERS)
       return DXGI_ERROR_INVALID_CALL;
 
-    m_frameLatency = MaxLatency;
+    if (m_frameLatencyEvent) {
+      // Windows DXGI does not seem to handle the case where the new maximum
+      // latency is less than the current value, and some games relying on
+      // this behaviour will hang if we attempt to decrement the semaphore.
+      // Thus, only increment the semaphore as necessary.
+      if (MaxLatency > m_frameLatency)
+        ReleaseSemaphore(m_frameLatencyEvent, MaxLatency - m_frameLatency, nullptr);
+    }
 
-    SyncFrameLatency();
+    m_frameLatency = MaxLatency;
     return S_OK;
   }
 
@@ -367,10 +374,10 @@ namespace dxvk {
 
 
   void D3D11SwapChain::CreateFrameLatencyEvent() {
-    m_frameLatencySignal = new sync::Win32Fence(m_frameId);
+    m_frameLatencySignal = new sync::CallbackFence(m_frameId);
 
     if (m_desc.Flags & DXGI_SWAP_CHAIN_FLAG_FRAME_LATENCY_WAITABLE_OBJECT)
-      m_frameLatencyEvent = CreateEvent(nullptr, false, true, nullptr);
+      m_frameLatencyEvent = CreateSemaphore(nullptr, m_frameLatency, DXGI_MAX_SWAP_CHAIN_BUFFERS, nullptr);
   }
 
 
@@ -558,8 +565,9 @@ namespace dxvk {
     m_frameLatencySignal->wait(m_frameId - GetActualFrameLatency());
 
     if (m_frameLatencyEvent) {
-      // Signal event with the same value that we'd wait for during the next present.
-      m_frameLatencySignal->setEvent(m_frameLatencyEvent, m_frameId - GetActualFrameLatency() + 1);
+      m_frameLatencySignal->setCallback(m_frameId, [cFrameLatencyEvent = m_frameLatencyEvent] () {
+        ReleaseSemaphore(cFrameLatencyEvent, 1, nullptr);
+      });
     }
   }
 
diff --git a/src/d3d11/d3d11_swapchain.h b/src/d3d11/d3d11_swapchain.h
index 530fdca3e..8fc9fe10c 100644
--- a/src/d3d11/d3d11_swapchain.h
+++ b/src/d3d11/d3d11_swapchain.h
@@ -6,7 +6,7 @@
 
 #include "../dxvk/dxvk_swapchain_blitter.h"
 
-#include "../util/sync/sync_signal_win32.h"
+#include "../util/sync/sync_signal.h"
 
 namespace dxvk {
   
@@ -107,7 +107,7 @@ namespace dxvk {
     uint32_t                m_frameLatency = DefaultFrameLatency;
     uint32_t                m_frameLatencyCap = 0;
     HANDLE                  m_frameLatencyEvent = nullptr;
-    Rc<sync::Win32Fence>    m_frameLatencySignal;
+    Rc<sync::CallbackFence> m_frameLatencySignal;
 
     bool                    m_dirty = true;
     bool                    m_vsync = true;