Phase 2: Present-hook video path (shared-texture mirror)

Add an injected IDXGISwapChain::Present / Present1 hook as a lower-latency,
border-free alternative to WGC. The hook copies the swapchain backbuffer into a
shared keyed-mutex texture (coop_video_<pid>); the host opens it by name and
samples it. New opt-in HookSubsys_Video (protocol v6 -> v7); the Video mirror
panel gains a WGC vs Hooked source toggle that installs/removes the subsystem.

Verified by present_hook_test (drives a real D3D11 swapchain end-to-end and reads
the rendered pixels back through the shared texture) and against Phantom Brave
(D3D9: hook installs cleanly and stays idle, WGC fallback). All 5 tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hook/CMakeLists.txt

@@ -3,6 +3,7 @@ add_library(coop_hook SHARED
 	src/xinput_hook.cpp
 	src/focus_spoof.cpp
 	src/audio_hook.cpp
+	src/present_hook.cpp
 	src/debug_log.cpp
 	src/hook_registry.cpp)
 
@@ -17,7 +18,9 @@ target_link_libraries(coop_hook PRIVATE
 	safetyhook::safetyhook
 	user32
 	ole32
-	mmdevapi)
+	mmdevapi
+	d3d11
+	dxgi)
 
 set_target_properties(coop_hook PROPERTIES OUTPUT_NAME "coop_hook")
 

hook/src/dllmain.cpp

@@ -20,6 +20,7 @@
 #include "focus_spoof.hpp"
 #include "hook_registry.hpp"
 #include "ipc_client.hpp"
+#include "present_hook.hpp"
 #include "xinput_hook.hpp"
 
 namespace
@@ -68,6 +69,7 @@ DWORD WINAPI worker_thread(LPVOID)
 	bool focus_installed = false;
 	bool audio_installed = false;
 	bool audio_ring_open = false;
+	bool video_installed = false;
 
 	// Each tick, reconcile each subsystem with the host's requested state: install
 	// what's wanted but missing (modules / the game window may appear lazily) and
@@ -120,6 +122,24 @@ DWORD WINAPI worker_thread(LPVOID)
 			coop::hook::logf("worker_thread: audio hooks removed (host request)");
 		}
 
+		// --- Video (Present-hook) ---
+		// Opt-in alternative to the host's WGC path; the host enables it on request.
+		const bool want_video = g_ipc.subsystem_install_requested(coop::HookSubsys_Video);
+		if (want_video && !video_installed)
+		{
+			video_installed = coop::hook::install_present_hooks(g_ipc);
+			if (video_installed)
+			{
+				coop::hook::logf("worker_thread: present hook installed");
+			}
+		}
+		else if (!want_video && video_installed)
+		{
+			coop::hook::remove_present_hooks();
+			video_installed = false;
+			coop::hook::logf("worker_thread: present hook removed (host request)");
+		}
+
 		if (audio_installed && !audio_ring_open)
 		{
 			const std::wstring name = coop::audio_ring_name(GetCurrentProcessId());
@@ -185,6 +205,7 @@ BOOL APIENTRY DllMain(HMODULE module, DWORD reason, LPVOID reserved)
 			coop::hook::remove_focus_spoof();
 			coop::hook::remove_xinput_hooks();
 			coop::hook::remove_audio_hooks();
+			coop::hook::remove_present_hooks();
 			coop::hook::hook_registry_reset();
 		}
 		break;

hook/src/ipc_client.hpp

@@ -169,6 +169,31 @@ public:
 		}
 	}
 
+	// --- Present-hook video channel ----------------------------------------
+
+	// Record that the game's Present() ran (diagnostic counter, hook is sole writer).
+	void note_present()
+	{
+		if (block_ != nullptr)
+		{
+			block_->video.present_calls += 1;
+		}
+	}
+
+	// Publish that a fresh backbuffer copy is in the shared texture (named
+	// coop_video_<pid>) with these dimensions/format; bumps the generation the host
+	// polls. The texture itself is shared out-of-band by name, not through here.
+	void publish_video_frame(std::uint32_t width, std::uint32_t height, std::uint32_t format)
+	{
+		if (block_ != nullptr)
+		{
+			block_->video.width = width;
+			block_->video.height = height;
+			block_->video.format = format;
+			block_->video.generation.fetch_add(1, std::memory_order_release);
+		}
+	}
+
 	// --- Hook registry -----------------------------------------------------
 
 	// Publish the installed-hooks table (name / subsystem / installed / calls).

hook/src/present_hook.cpp

@@ -0,0 +1,384 @@
+#include "present_hook.hpp"
+
+#include <atomic>
+#include <mutex>
+
+#include <windows.h>
+
+#include <d3d11.h>
+#include <dxgi1_2.h>
+
+#include <safetyhook.hpp>
+
+#include "coop/shared_memory.hpp"
+#include "debug_log.hpp"
+#include "hook_registry.hpp"
+
+namespace coop::hook
+{
+
+namespace
+{
+
+// IDXGISwapChain vtable layout (frozen ABI). IUnknown 0..2, IDXGIObject 3..6,
+// IDXGIDeviceSubObject 7, then IDXGISwapChain: Present = 8, GetBuffer = 9.
+// IDXGISwapChain1 adds methods after IDXGISwapChain (18 methods, 0..17), so
+// Present1 sits at index 22. Flip-model D3D11/12 games present via Present1.
+constexpr unsigned kIdx_IDXGISwapChain_Present = 8;
+constexpr unsigned kIdx_IDXGISwapChain1_Present1 = 22;
+
+IpcClient* g_ipc = nullptr;
+unsigned long g_pid = 0;
+
+safetyhook::InlineHook g_hk_present;
+safetyhook::InlineHook g_hk_present1;
+int g_id_present = -1;
+int g_id_present1 = -1;
+
+std::atomic<std::uint64_t> g_present_calls{0};
+std::atomic<std::uint64_t> g_frames_shared{0};
+
+// The shared backbuffer copy and its keyed mutex, created lazily on the first
+// Present once we can see the game's device + backbuffer format. Guarded by
+// g_tex_mutex (touched only on the render thread, but install/remove may race).
+std::mutex g_tex_mutex;
+ID3D11Texture2D* g_shared_tex = nullptr;
+IDXGIKeyedMutex* g_shared_mutex = nullptr;
+HANDLE g_shared_handle = nullptr;
+UINT g_share_w = 0;
+UINT g_share_h = 0;
+DXGI_FORMAT g_share_fmt = DXGI_FORMAT_UNKNOWN;
+bool g_unsupported_logged = false;
+
+void* vtable_method(void* obj, unsigned index)
+{
+	return (*reinterpret_cast<void***>(obj))[index];
+}
+
+// Drop the shared texture/mutex/handle. Caller holds g_tex_mutex.
+void release_shared_locked()
+{
+	if (g_shared_mutex != nullptr)
+	{
+		g_shared_mutex->Release();
+		g_shared_mutex = nullptr;
+	}
+	if (g_shared_tex != nullptr)
+	{
+		g_shared_tex->Release();
+		g_shared_tex = nullptr;
+	}
+	if (g_shared_handle != nullptr)
+	{
+		CloseHandle(g_shared_handle);
+		g_shared_handle = nullptr;
+	}
+	g_share_w = g_share_h = 0;
+	g_share_fmt = DXGI_FORMAT_UNKNOWN;
+}
+
+// (Re)create the shared keyed-mutex texture for a w x h `fmt` backbuffer on the
+// game's `device`. Caller holds g_tex_mutex. Returns true if it's ready.
+bool ensure_shared_texture_locked(ID3D11Device* device, UINT w, UINT h, DXGI_FORMAT fmt)
+{
+	if (g_shared_tex != nullptr && g_share_w == w && g_share_h == h && g_share_fmt == fmt)
+	{
+		return true; // already matches the current backbuffer
+	}
+	release_shared_locked();
+
+	D3D11_TEXTURE2D_DESC desc{};
+	desc.Width = w;
+	desc.Height = h;
+	desc.MipLevels = 1;
+	desc.ArraySize = 1;
+	desc.Format = fmt;
+	desc.SampleDesc.Count = 1;
+	desc.Usage = D3D11_USAGE_DEFAULT;
+	desc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
+	desc.MiscFlags = D3D11_RESOURCE_MISC_SHARED_NTHANDLE | D3D11_RESOURCE_MISC_SHARED_KEYEDMUTEX;
+
+	ID3D11Texture2D* tex = nullptr;
+	HRESULT hr = device->CreateTexture2D(&desc, nullptr, &tex);
+	if (FAILED(hr) || tex == nullptr)
+	{
+		logf("present: CreateTexture2D(shared) failed hr=0x%08lX (%ux%u fmt=%d)",
+		     static_cast<unsigned long>(hr), w, h, static_cast<int>(fmt));
+		return false;
+	}
+
+	IDXGIResource1* res = nullptr;
+	hr = tex->QueryInterface(__uuidof(IDXGIResource1), reinterpret_cast<void**>(&res));
+	if (FAILED(hr) || res == nullptr)
+	{
+		logf("present: QI IDXGIResource1 failed hr=0x%08lX", static_cast<unsigned long>(hr));
+		tex->Release();
+		return false;
+	}
+	const std::wstring name = video_share_name(g_pid);
+	HANDLE handle = nullptr;
+	hr = res->CreateSharedHandle(nullptr, DXGI_SHARED_RESOURCE_READ | DXGI_SHARED_RESOURCE_WRITE,
+	                             name.c_str(), &handle);
+	res->Release();
+	if (FAILED(hr) || handle == nullptr)
+	{
+		logf("present: CreateSharedHandle failed hr=0x%08lX", static_cast<unsigned long>(hr));
+		tex->Release();
+		return false;
+	}
+
+	IDXGIKeyedMutex* mutex = nullptr;
+	hr = tex->QueryInterface(__uuidof(IDXGIKeyedMutex), reinterpret_cast<void**>(&mutex));
+	if (FAILED(hr) || mutex == nullptr)
+	{
+		logf("present: QI IDXGIKeyedMutex failed hr=0x%08lX", static_cast<unsigned long>(hr));
+		CloseHandle(handle);
+		tex->Release();
+		return false;
+	}
+
+	g_shared_tex = tex;
+	g_shared_mutex = mutex;
+	g_shared_handle = handle;
+	g_share_w = w;
+	g_share_h = h;
+	g_share_fmt = fmt;
+	logf("present: shared texture ready %ux%u fmt=%d name=%ls", w, h, static_cast<int>(fmt), name.c_str());
+	return true;
+}
+
+// Copy the swapchain's backbuffer into the shared texture and publish it.
+void capture_backbuffer(IDXGISwapChain* sc)
+{
+	ID3D11Texture2D* backbuf = nullptr;
+	if (FAILED(sc->GetBuffer(0, __uuidof(ID3D11Texture2D), reinterpret_cast<void**>(&backbuf))) ||
+	    backbuf == nullptr)
+	{
+		if (!g_unsupported_logged)
+		{
+			logf("present: backbuffer is not an ID3D11Texture2D (D3D12/D3D9?); video hook idle");
+			g_unsupported_logged = true;
+		}
+		return;
+	}
+
+	D3D11_TEXTURE2D_DESC bd{};
+	backbuf->GetDesc(&bd);
+
+	// Multisampled backbuffers would need ResolveSubresource; flip-model swapchains
+	// are single-sampled. Skip the rare MSAA case rather than mis-copy.
+	if (bd.SampleDesc.Count != 1)
+	{
+		backbuf->Release();
+		return;
+	}
+
+	ID3D11Device* device = nullptr;
+	backbuf->GetDevice(&device);
+	ID3D11DeviceContext* ctx = nullptr;
+	if (device != nullptr)
+	{
+		device->GetImmediateContext(&ctx);
+	}
+
+	bool shared = false;
+	if (device != nullptr && ctx != nullptr)
+	{
+		std::scoped_lock lock(g_tex_mutex);
+		if (ensure_shared_texture_locked(device, bd.Width, bd.Height, bd.Format) && g_shared_mutex != nullptr)
+		{
+			// Key 0 on both sides: a plain cross-process mutex on the texture (the
+			// keyed mutex is created released at key 0). Bounded wait so a stalled
+			// host consumer can never hang the game's render thread.
+			if (g_shared_mutex->AcquireSync(kVideoMutexKey, 8) == S_OK)
+			{
+				ctx->CopyResource(g_shared_tex, backbuf);
+				g_shared_mutex->ReleaseSync(kVideoMutexKey);
+				shared = true;
+			}
+		}
+	}
+
+	if (shared)
+	{
+		g_frames_shared.fetch_add(1, std::memory_order_relaxed);
+		if (g_ipc != nullptr)
+		{
+			g_ipc->publish_video_frame(bd.Width, bd.Height, static_cast<std::uint32_t>(bd.Format));
+		}
+	}
+
+	if (ctx != nullptr)
+	{
+		ctx->Release();
+	}
+	if (device != nullptr)
+	{
+		device->Release();
+	}
+	backbuf->Release();
+}
+
+HRESULT STDMETHODCALLTYPE hk_Present(IDXGISwapChain* sc, UINT sync_interval, UINT flags)
+{
+	hook_note_call(g_id_present);
+	g_present_calls.fetch_add(1, std::memory_order_relaxed);
+	if (g_ipc != nullptr)
+	{
+		g_ipc->note_present();
+	}
+	// DXGI_PRESENT_TEST presents nothing; don't bother copying for it.
+	if ((flags & DXGI_PRESENT_TEST) == 0)
+	{
+		capture_backbuffer(sc);
+	}
+	return g_hk_present.call<HRESULT>(sc, sync_interval, flags);
+}
+
+HRESULT STDMETHODCALLTYPE hk_Present1(IDXGISwapChain1* sc, UINT sync_interval, UINT flags,
+                                      const DXGI_PRESENT_PARAMETERS* params)
+{
+	hook_note_call(g_id_present1);
+	g_present_calls.fetch_add(1, std::memory_order_relaxed);
+	if (g_ipc != nullptr)
+	{
+		g_ipc->note_present();
+	}
+	if ((flags & DXGI_PRESENT_TEST) == 0)
+	{
+		capture_backbuffer(sc); // IDXGISwapChain1 derives from IDXGISwapChain
+	}
+	return g_hk_present1.call<HRESULT>(sc, sync_interval, flags, params);
+}
+
+// Create a throwaway device + swapchain purely to read IDXGISwapChain::Present
+// (and IDXGISwapChain1::Present1) addresses, so we can inline-hook them. The
+// inline hook patches the function itself, so it catches every swapchain in the
+// process -- we can release the dummy after. `present1_out` may stay null on
+// platforms without DXGI 1.2.
+void* grab_present_address(void** present1_out)
+{
+	*present1_out = nullptr;
+	WNDCLASSEXW wc{};
+	wc.cbSize = sizeof(wc);
+	wc.lpfnWndProc = DefWindowProcW;
+	wc.hInstance = GetModuleHandleW(nullptr);
+	wc.lpszClassName = L"coop_present_probe";
+	RegisterClassExW(&wc);
+	HWND hwnd = CreateWindowExW(0, wc.lpszClassName, L"", WS_OVERLAPPEDWINDOW, 0, 0, 8, 8, nullptr, nullptr,
+	                            wc.hInstance, nullptr);
+	if (hwnd == nullptr)
+	{
+		return nullptr;
+	}
+
+	DXGI_SWAP_CHAIN_DESC scd{};
+	scd.BufferCount = 1;
+	scd.BufferDesc.Width = 8;
+	scd.BufferDesc.Height = 8;
+	scd.BufferDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
+	scd.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
+	scd.OutputWindow = hwnd;
+	scd.SampleDesc.Count = 1;
+	scd.Windowed = TRUE;
+	scd.SwapEffect = DXGI_SWAP_EFFECT_DISCARD;
+
+	IDXGISwapChain* swapchain = nullptr;
+	ID3D11Device* device = nullptr;
+	ID3D11DeviceContext* ctx = nullptr;
+	const HRESULT hr = D3D11CreateDeviceAndSwapChain(nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, nullptr, 0,
+	                                                 D3D11_SDK_VERSION, &scd, &swapchain, &device, nullptr, &ctx);
+	void* present = nullptr;
+	if (SUCCEEDED(hr) && swapchain != nullptr)
+	{
+		present = vtable_method(swapchain, kIdx_IDXGISwapChain_Present);
+		IDXGISwapChain1* sc1 = nullptr;
+		if (SUCCEEDED(swapchain->QueryInterface(__uuidof(IDXGISwapChain1), reinterpret_cast<void**>(&sc1))) &&
+		    sc1 != nullptr)
+		{
+			*present1_out = vtable_method(sc1, kIdx_IDXGISwapChain1_Present1);
+			sc1->Release();
+		}
+	}
+	else
+	{
+		logf("present: D3D11CreateDeviceAndSwapChain(probe) failed hr=0x%08lX", static_cast<unsigned long>(hr));
+	}
+	if (ctx != nullptr)
+	{
+		ctx->Release();
+	}
+	if (device != nullptr)
+	{
+		device->Release();
+	}
+	if (swapchain != nullptr)
+	{
+		swapchain->Release();
+	}
+	DestroyWindow(hwnd);
+	UnregisterClassW(wc.lpszClassName, wc.hInstance);
+	return present;
+}
+
+} // namespace
+
+bool install_present_hooks(IpcClient& ipc)
+{
+	g_ipc = &ipc;
+	g_pid = GetCurrentProcessId();
+	if (g_hk_present)
+	{
+		return true; // already installed
+	}
+
+	g_id_present = hook_register("IDXGISwapChain::Present", HookSubsys_Video);
+	g_id_present1 = hook_register("IDXGISwapChain1::Present1", HookSubsys_Video);
+
+	void* present1 = nullptr;
+	void* present = grab_present_address(&present1);
+	if (present == nullptr)
+	{
+		hook_set_installed(g_id_present, false);
+		hook_set_installed(g_id_present1, false);
+		return false;
+	}
+	g_hk_present = safetyhook::create_inline(present, reinterpret_cast<void*>(&hk_Present));
+	if (present1 != nullptr)
+	{
+		g_hk_present1 = safetyhook::create_inline(present1, reinterpret_cast<void*>(&hk_Present1));
+	}
+	g_unsupported_logged = false;
+	hook_set_installed(g_id_present, static_cast<bool>(g_hk_present));
+	hook_set_installed(g_id_present1, static_cast<bool>(g_hk_present1));
+	logf("install_present_hooks: present=%p hooked=%d present1=%p hooked=%d", present,
+	     static_cast<bool>(g_hk_present) ? 1 : 0, present1, static_cast<bool>(g_hk_present1) ? 1 : 0);
+	return static_cast<bool>(g_hk_present);
+}
+
+void remove_present_hooks()
+{
+	g_hk_present = {};
+	g_hk_present1 = {};
+	hook_set_installed(g_id_present, false);
+	hook_set_installed(g_id_present1, false);
+	{
+		std::scoped_lock lock(g_tex_mutex);
+		release_shared_locked();
+	}
+	g_present_calls.store(0, std::memory_order_relaxed);
+	g_frames_shared.store(0, std::memory_order_relaxed);
+	g_ipc = nullptr;
+}
+
+std::uint64_t present_calls()
+{
+	return g_present_calls.load(std::memory_order_relaxed);
+}
+
+std::uint64_t present_frames_shared()
+{
+	return g_frames_shared.load(std::memory_order_relaxed);
+}
+
+} // namespace coop::hook

hook/src/present_hook.hpp

@@ -0,0 +1,35 @@
+// Injected Present-hook video path: hooks IDXGISwapChain::Present in the target
+// game, copies the swapchain backbuffer into a shared keyed-mutex texture
+// (coop_video_<pid>), and publishes its dimensions/format to the host over IPC.
+// The host opens that texture by name and samples it -- a lower-latency, more
+// stable alternative to Windows Graphics Capture (which composites off the
+// desktop and can stutter / show a capture border).
+//
+// Only DXGI swapchains (D3D10/11/12-backed games) are caught; the backbuffer
+// must be an ID3D11Texture2D (the common D3D11 case). Games on D3D9 or a pure
+// D3D12 resource path won't engage this hook -- WGC stays as the fallback.
+#pragma once
+
+#include "ipc_client.hpp"
+
+namespace coop::hook
+{
+
+// Installs the Present hook. Grabs IDXGISwapChain::Present from a throwaway
+// swapchain and inline-hooks it, so every swapchain in the process is caught.
+// `ipc` must outlive the hook (used to publish the shared-texture descriptor).
+// Returns true once the hook is in place; safe to call repeatedly.
+bool install_present_hooks(IpcClient& ipc);
+
+// Removes the Present hook and releases the shared texture (best effort).
+void remove_present_hooks();
+
+// --- Diagnostics (used by the self-test) -----------------------------------
+
+// Cumulative Present() detours observed.
+std::uint64_t present_calls();
+
+// Frames actually copied into the shared texture (a backbuffer we could share).
+std::uint64_t present_frames_shared();
+
+} // namespace coop::hook