From 057961a1aec9d82b24337c96c2ed902d4b3bc4c8 Mon Sep 17 00:00:00 2001
From: Robin Kertels <robin.kertels@gmail.com>
Date: Wed, 7 Feb 2024 00:12:01 +0100
Subject: [PATCH] [d3d9] Use most recently used swapchain for
 GetFrontBufferData

---
 src/d3d9/d3d9_device.cpp    |  6 +++++-
 src/d3d9/d3d9_device.h      | 14 ++++++++++++++
 src/d3d9/d3d9_swapchain.cpp | 10 ++++++++++
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/d3d9/d3d9_device.cpp b/src/d3d9/d3d9_device.cpp
index a5fc7f5da32..ce3cd9c6108 100644
--- a/src/d3d9/d3d9_device.cpp
+++ b/src/d3d9/d3d9_device.cpp
@@ -1083,7 +1083,10 @@ namespace dxvk {
     if (unlikely(iSwapChain != 0))
       return D3DERR_INVALIDCALL;
 
-    return m_implicitSwapchain->GetFrontBufferData(pDestSurface);
+    // In windowed mode, GetFrontBufferData takes a screenshot of the entire screen.
+    // We use the last used swapchain as a workaround.
+    // Total War: Medieval 2 relies on this.
+    return m_mostRecentlyUsedSwapchain->GetFrontBufferData(pDestSurface);
   }
 
 
@@ -7813,6 +7816,7 @@ namespace dxvk {
     }
     else
       m_implicitSwapchain = new D3D9SwapChainEx(this, pPresentationParameters, pFullscreenDisplayMode);
+      m_mostRecentlyUsedSwapchain = m_implicitSwapchain.ptr();
 
     if (pPresentationParameters->EnableAutoDepthStencil) {
       D3D9_COMMON_TEXTURE_DESC desc;
diff --git a/src/d3d9/d3d9_device.h b/src/d3d9/d3d9_device.h
index 2fc74c83656..e72ac514c50 100644
--- a/src/d3d9/d3d9_device.h
+++ b/src/d3d9/d3d9_device.h
@@ -1241,6 +1241,18 @@ namespace dxvk {
 
     uint64_t GetCurrentSequenceNumber();
 
+    D3D9SwapChainEx* GetLastUsedSwapchain() {
+      return m_mostRecentlyUsedSwapchain;
+    }
+
+    void SetLastUsedSwapchain(D3D9SwapChainEx* swapchain) {
+      m_mostRecentlyUsedSwapchain = swapchain;
+    }
+
+    void ResetLastUsedSwapchain() {
+      m_mostRecentlyUsedSwapchain = m_implicitSwapchain.ptr();
+    }
+
     Com<D3D9InterfaceEx>            m_parent;
     D3DDEVTYPE                      m_deviceType;
     HWND                            m_window;
@@ -1403,6 +1415,8 @@ namespace dxvk {
     HWND                            m_fullscreenWindow         = NULL;
     std::atomic<uint32_t>           m_losableResourceCounter   = { 0 };
 
+    D3D9SwapChainEx*                m_mostRecentlyUsedSwapchain = nullptr;
+
 #ifdef D3D9_ALLOW_UNMAPPING
     lru_list<D3D9CommonTexture*>    m_mappedTextures;
 #endif
diff --git a/src/d3d9/d3d9_swapchain.cpp b/src/d3d9/d3d9_swapchain.cpp
index a19ca55aafa..6dddb6929b2 100644
--- a/src/d3d9/d3d9_swapchain.cpp
+++ b/src/d3d9/d3d9_swapchain.cpp
@@ -65,6 +65,14 @@ namespace dxvk {
     if (this_thread::isInModuleDetachment())
       return;
 
+    {      
+      D3D9DeviceLock lock = m_parent->LockDevice();
+
+      if (m_parent->GetLastUsedSwapchain() == this) {
+        m_parent->ResetLastUsedSwapchain();
+      }
+    }
+
     DestroyBackBuffers();
 
     ResetWindowProc(m_window);
@@ -112,6 +120,8 @@ namespace dxvk {
           DWORD    dwFlags) {
     D3D9DeviceLock lock = m_parent->LockDevice();
 
+    m_parent->SetLastUsedSwapchain(this);
+
     if (unlikely(m_parent->IsDeviceLost()))
       return D3DERR_DEVICELOST;