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>

README.md

@@ -23,6 +23,7 @@ XInput game becomes Remote-Play-Together-able.
 | Forward input to game | DLL injection + XInput hook (SafetyHook) — game sees *only* our pad | `coop_hook.dll` | done |
 | Keep game running unfocused | Hook spoofs focus so the game polls while the host holds OS focus | `coop_hook.dll` | done |
 | Mirror video | Windows Graphics Capture of the game window, letterboxed into the host window | `coop_host.exe` | done |
+| Mirror video (alt) | Injected Present-hook copies the DXGI backbuffer into a shared keyed-mutex texture the host samples (lower latency, no capture border) | `coop_hook.dll` + `coop_host.exe` | done |
 | Mirror audio | Injected render-hook copies the game's WASAPI frames into a shared ring and silences the game locally (no echo); WASAPI process loopback is the automatic fallback | `coop_hook.dll` + `coop_host.exe` | done |
 | Host ↔ hook IPC | Named shared memory (seqlock for input, status back-channel) | `common/` | done |
 
@@ -131,11 +132,19 @@ Done:
   Replaces tailing `%TEMP%\coop_hook.log` (which stays as an opt-in file mirror).
   `coop_audio_probe` drains and prints the same stream headless.
 
+- **Present-hook video path. ✅** The injected DLL hooks `IDXGISwapChain::Present`
+  (and `Present1`) and copies the swapchain backbuffer into a shared keyed-mutex
+  texture (`coop_video_<pid>`); the host opens it by name and samples it — a
+  lower-latency, border-free alternative to WGC. It's an opt-in subsystem (the
+  **Video Present-hook** checkbox in the Injection panel, or just pick **Source:
+  Hooked (Present)** in the Video mirror panel, which installs it). Only DXGI
+  swapchains with an `ID3D11Texture2D` backbuffer are caught (the common D3D11
+  case); D3D9 / pure-D3D12 games keep WGC. Validated by `present_hook_test`
+  (drives a real D3D11 swapchain end-to-end and reads the pixels back through the
+  shared texture).
+
 Future work, roughly in priority order:
 
-- **Present-hook video path:** capture the game's frames by hooking
-  `IDXGISwapChain::Present` in the injected DLL and sharing the backbuffer via a
-  shared D3D11 texture, as a lower-latency / more stable alternative to WGC.
 - **Steam Input:** consume guest input through the Steam Input API directly
   rather than XInput.
 - **x86 support:** add an x86 build of `coop_hook.dll` plus an x86 injector
@@ -185,6 +194,12 @@ ctest --test-dir build -C Debug --output-on-failure
   COM vtables were discovered, the frames reached the ring (non-silent), the
   primary stream was silenced, and exactly one render stream was counted. Skips
   cleanly if the machine has no audio endpoint.
+- **`present_hook_test`** — in-process self-test of the Present-hook video path:
+  installs the hook, drives a real D3D11 swapchain in the same process (clears the
+  backbuffer to a known color and calls `Present`), and asserts the detour fired,
+  the backbuffer reached the shared keyed-mutex texture, and a second device can
+  open it by name and read the exact pixels back. Skips cleanly if the machine has
+  no D3D11 device.
 - **`audio_loopback_test`** — spawns `coop_tone.exe` (a standalone WASAPI
   sine-wave source under [`tools/audio_tone`](tools/audio_tone)) and verifies the
   shipping process-loopback capture (the fallback path) receives its audio by
@@ -223,7 +238,11 @@ person/account to receive the stream.
    **Attached**, a non-zero **XInput polled: N/s**, and **Focus spoof: active**.
 
 3. **Mirror video:** in the **Video mirror** panel, tick **Mirror game window** —
-   the host window now shows a live, letterboxed copy of the game.
+   the host window now shows a live, letterboxed copy of the game. **Source**
+   picks how the frames are grabbed: **WGC** (default, Windows Graphics Capture —
+   works for any window) or **Hooked (Present)** (the injected Present-hook's
+   shared texture — lower latency and no capture border, but only for DXGI /
+   D3D11 games; selecting it installs the video subsystem in the game).
 
 4. **Mirror audio:** in the **Audio mirror** panel, tick **Mirror game audio**.
    With the hook injected, **Source** shows **Hooked (no echo)** and the game's

common/include/coop/protocol.hpp

@@ -11,7 +11,7 @@ namespace coop
 
 // Bump whenever the layout of SharedBlock or CoopPadState changes. The hook
 // refuses to attach to a host with a mismatched version.
-inline constexpr std::uint32_t kProtocolVersion = 6;
+inline constexpr std::uint32_t kProtocolVersion = 7;
 
 // 'COOP' little-endian, used to sanity-check the mapping before trusting it.
 inline constexpr std::uint32_t kProtocolMagic = 0x504F4F43u;
@@ -66,7 +66,8 @@ enum HookSubsystem : std::uint32_t
 	HookSubsys_Input = 0, // XInput hooks (forward the guest pad)
 	HookSubsys_Focus = 1, // focus spoof (keep the game running unfocused)
 	HookSubsys_Audio = 2, // WASAPI render-hook (audio mirror without echo)
-	HookSubsys_Count = 3,
+	HookSubsys_Video = 3, // IDXGISwapChain::Present hook (shared-texture video mirror)
+	HookSubsys_Count = 4,
 };
 
 // Maximum individual hooks reported in the registry (a few per subsystem).
@@ -134,6 +135,29 @@ struct HookControl
 	std::atomic<std::uint32_t> subsystem_disabled[HookSubsys_Count];
 };
 
+// Present-hook video channel. When the video subsystem is installed, the hook
+// copies the game's swapchain backbuffer into a shared keyed-mutex texture named
+// coop_video_<pid> and publishes its dimensions/format here; the host opens that
+// texture by name and samples it (a lower-latency alternative to WGC). The hook
+// is the sole writer. `generation` bumps on every published frame (0 = nothing
+// shared yet); width/height/format describe the currently shared texture, so the
+// host reopens it whenever they change. The keyed mutex uses key 0 on both sides.
+struct VideoShare
+{
+	std::atomic<std::uint32_t> generation; // bumps per published frame; 0 = none yet
+	std::uint32_t width;                   // shared texture dimensions / DXGI format
+	std::uint32_t height;
+	std::uint32_t format;                  // DXGI_FORMAT of the shared texture
+	std::uint64_t present_calls;           // cumulative Present() detours (diagnostic)
+};
+
+// The shared backbuffer texture is named per target pid, like the audio ring.
+inline constexpr wchar_t kVideoSharePrefix[] = L"Local\\coop_video_";
+
+// Keyed-mutex key both producer and consumer use (a plain cross-process mutex on
+// the texture; the keyed mutex is created released at key 0).
+inline constexpr std::uint64_t kVideoMutexKey = 0;
+
 // Top-level shared block. The host is the sole writer of pad state; the hook is
 // the sole reader. A seqlock (even = stable, odd = write in progress) lets the
 // reader grab a torn-free snapshot without a kernel lock on the hot path.
@@ -151,8 +175,8 @@ struct SharedBlock
 	// Host -> hook control (which subsystems to install).
 	HookControl control;
 
-	// Phase 2 appends the shared-texture handle/dimensions control fields here;
-	// keep new members at the end so existing offsets never shift.
+	// Hook -> host Present-hook video channel (shared-texture dimensions/format).
+	VideoShare video;
 };
 
 static_assert(std::atomic<std::uint32_t>::is_always_lock_free,

common/include/coop/shared_memory.hpp

@@ -128,4 +128,11 @@ inline std::wstring shared_memory_name(unsigned long target_pid)
 	return std::wstring(kSharedMemoryPrefix) + std::to_wstring(target_pid);
 }
 
+// Name of the Present-hook shared backbuffer texture (created by the hook with
+// CreateSharedHandle, opened by the host with OpenSharedResourceByName).
+inline std::wstring video_share_name(unsigned long target_pid)
+{
+	return std::wstring(kVideoSharePrefix) + std::to_wstring(target_pid);
+}
+
 } // namespace coop

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

host/CMakeLists.txt

@@ -14,6 +14,7 @@ add_executable(coop_host WIN32
 	src/ipc/ipc_server.cpp
 	src/capture/frame_renderer.cpp
 	src/capture/window_capture.cpp
+	src/capture/shared_texture.cpp
 	src/audio/audio_loopback.cpp
 	src/audio/process_loopback_capture.cpp)
 

host/src/capture/shared_texture.cpp

@@ -0,0 +1,128 @@
+#include "capture/shared_texture.hpp"
+
+#include "coop/protocol.hpp"
+#include "coop/shared_memory.hpp"
+
+namespace coop
+{
+
+bool SharedTextureSource::init(ID3D11Device* device)
+{
+	if (device == nullptr || FAILED(device->QueryInterface(IID_PPV_ARGS(&device_))))
+	{
+		return false;
+	}
+	device_->GetImmediateContext(&ctx_);
+	return ctx_ != nullptr;
+}
+
+void SharedTextureSource::reset()
+{
+	srv_.Reset();
+	private_.Reset();
+	mutex_.Reset();
+	shared_.Reset();
+	pid_ = 0;
+	width_ = height_ = format_ = 0;
+	last_generation_ = 0;
+	frames_copied_ = 0;
+}
+
+bool SharedTextureSource::reopen(unsigned long pid, const VideoShareView& share)
+{
+	srv_.Reset();
+	private_.Reset();
+	mutex_.Reset();
+	shared_.Reset();
+	width_ = height_ = format_ = 0;
+	pid_ = pid;
+
+	if (pid == 0 || share.width == 0 || share.height == 0)
+	{
+		return false; // the hook hasn't shared a backbuffer yet
+	}
+
+	const std::wstring name = video_share_name(pid);
+	if (FAILED(device_->OpenSharedResourceByName(name.c_str(),
+	                                             DXGI_SHARED_RESOURCE_READ | DXGI_SHARED_RESOURCE_WRITE,
+	                                             IID_PPV_ARGS(&shared_))) ||
+	    shared_ == nullptr)
+	{
+		return false;
+	}
+	if (FAILED(shared_.As(&mutex_)) || mutex_ == nullptr)
+	{
+		shared_.Reset();
+		return false;
+	}
+
+	// Private copy we sample from, so we only hold the keyed mutex during the copy.
+	D3D11_TEXTURE2D_DESC desc{};
+	desc.Width = share.width;
+	desc.Height = share.height;
+	desc.MipLevels = 1;
+	desc.ArraySize = 1;
+	desc.Format = static_cast<DXGI_FORMAT>(share.format);
+	desc.SampleDesc.Count = 1;
+	desc.Usage = D3D11_USAGE_DEFAULT;
+	desc.BindFlags = D3D11_BIND_SHADER_RESOURCE;
+	if (FAILED(device_->CreateTexture2D(&desc, nullptr, &private_)) || private_ == nullptr)
+	{
+		mutex_.Reset();
+		shared_.Reset();
+		return false;
+	}
+	if (FAILED(device_->CreateShaderResourceView(private_.Get(), nullptr, &srv_)))
+	{
+		srv_.Reset();
+		private_.Reset();
+		mutex_.Reset();
+		shared_.Reset();
+		return false;
+	}
+
+	width_ = share.width;
+	height_ = share.height;
+	format_ = share.format;
+	return true;
+}
+
+bool SharedTextureSource::update(const VideoShareView& share, unsigned long pid)
+{
+	if (device_ == nullptr || pid == 0)
+	{
+		reset();
+		return false;
+	}
+
+	// (Re)open whenever the target or the published backbuffer geometry changes.
+	if (pid != pid_ || share.width != width_ || share.height != height_ || share.format != format_)
+	{
+		if (!reopen(pid, share))
+		{
+			return srv_ != nullptr; // couldn't open yet; keep any prior frame
+		}
+		last_generation_ = 0; // force a copy of the current frame
+	}
+
+	if (shared_ == nullptr || mutex_ == nullptr)
+	{
+		return srv_ != nullptr;
+	}
+	if (share.generation == last_generation_)
+	{
+		return srv_ != nullptr; // no new frame; keep showing the last copy
+	}
+
+	// Bounded wait so a stalled producer can't hang the host's render thread.
+	if (mutex_->AcquireSync(kVideoMutexKey, 8) == S_OK)
+	{
+		ctx_->CopyResource(private_.Get(), shared_.Get());
+		mutex_->ReleaseSync(kVideoMutexKey);
+		last_generation_ = share.generation;
+		++frames_copied_;
+	}
+	return srv_ != nullptr;
+}
+
+} // namespace coop

host/src/capture/shared_texture.hpp

@@ -0,0 +1,69 @@
+// Host-side consumer of the injected Present-hook's shared backbuffer texture.
+// Opens the keyed-mutex texture the hook publishes (coop_video_<pid>) by name,
+// copies the latest frame into a private texture under the keyed mutex, and
+// exposes an SRV the FrameRenderer can draw -- the lower-latency alternative to
+// Windows Graphics Capture. See hook/src/present_hook.cpp and coop/protocol.hpp.
+#pragma once
+
+#include <cstdint>
+#include <string>
+
+#include <d3d11_1.h>
+#include <wrl/client.h>
+
+#include "ipc/ipc_server.hpp"
+
+namespace coop
+{
+
+class SharedTextureSource
+{
+public:
+	// Binds to the host's device (must support ID3D11Device1). Returns false if not.
+	bool init(ID3D11Device* device);
+
+	// Polls the hook's video channel for `pid`. (Re)opens the shared texture when
+	// the pid/dimensions/format change, and copies the newest frame into the
+	// private texture under the keyed mutex. Returns true if a frame is available
+	// to draw (sticky: keeps the last copy until a new one or a reset).
+	bool update(const VideoShareView& share, unsigned long pid);
+
+	// Drop the opened resources (target changed / mirror turned off).
+	void reset();
+
+	[[nodiscard]] ID3D11ShaderResourceView* srv() const
+	{
+		return srv_.Get();
+	}
+	[[nodiscard]] std::uint32_t width() const
+	{
+		return width_;
+	}
+	[[nodiscard]] std::uint32_t height() const
+	{
+		return height_;
+	}
+	[[nodiscard]] std::uint64_t frames_copied() const
+	{
+		return frames_copied_;
+	}
+
+private:
+	bool reopen(unsigned long pid, const VideoShareView& share);
+
+	Microsoft::WRL::ComPtr<ID3D11Device1> device_;
+	Microsoft::WRL::ComPtr<ID3D11DeviceContext> ctx_;
+	Microsoft::WRL::ComPtr<ID3D11Texture2D> shared_; // opened from the hook, by name
+	Microsoft::WRL::ComPtr<IDXGIKeyedMutex> mutex_;
+	Microsoft::WRL::ComPtr<ID3D11Texture2D> private_; // our sampled copy
+	Microsoft::WRL::ComPtr<ID3D11ShaderResourceView> srv_;
+
+	unsigned long pid_ = 0;
+	std::uint32_t width_ = 0;
+	std::uint32_t height_ = 0;
+	std::uint32_t format_ = 0;
+	std::uint32_t last_generation_ = 0;
+	std::uint64_t frames_copied_ = 0;
+};
+
+} // namespace coop

host/src/capture_panel.cpp

@@ -3,13 +3,21 @@
 #include <cstdio>
 
 #include "imgui.h"
+#include "injection_panel.hpp"
 
 namespace coop
 {
 
+namespace
+{
+const ImVec4 kGreen(0.4f, 1.0f, 0.4f, 1.0f);
+const ImVec4 kRed(1.0f, 0.45f, 0.4f, 1.0f);
+} // namespace
+
 bool CapturePanel::init(ID3D11Device* device)
 {
 	device_ = device;
+	shared_.init(device); // best effort; the Hooked source is unavailable if it fails
 	return renderer_.init(device);
 }
 
@@ -19,35 +27,89 @@ void CapturePanel::draw_ui(const FrameStats& stats)
 	ImGui::SetNextWindowSize(ImVec2(360, 0), ImGuiCond_FirstUseEver);
 	ImGui::Begin("Video mirror");
 
-	const bool have_target = target_ != nullptr && IsWindow(target_);
-	ImGui::BeginDisabled(!have_target);
-	if (ImGui::Checkbox("Mirror game window", &enabled_))
+	const unsigned long hook_pid = injection_ != nullptr ? injection_->target_pid() : 0;
+	const bool have_wgc_target = target_ != nullptr && IsWindow(target_);
+	const bool have_hook = hook_pid != 0;
+	const bool have_source = source_ == Source_Hooked ? have_hook : have_wgc_target;
+
+	ImGui::BeginDisabled(!have_source);
+	if (ImGui::Checkbox("Mirror game window", &enabled_) && !enabled_)
 	{
-		if (!enabled_)
+		capture_.stop();
+		shared_.reset();
+		if (injection_ != nullptr)
 		{
-			capture_.stop();
+			injection_->request_video(false); // stop the in-game Present hook
 		}
 	}
 	ImGui::EndDisabled();
-	if (!have_target)
-	{
-		ImGui::TextDisabled("Inject into a game first (its window is the source).");
-	}
 
-	// Start/restart capture when enabled and the target window changes.
-	if (enabled_ && have_target && capture_.target() != target_)
+	// Source selector. Switching tears down the other source and (un)installs the
+	// Present hook so the game only pays for the path actually in use.
+	ImGui::TextUnformatted("Source:");
+	ImGui::SameLine();
+	int prev_source = source_;
+	ImGui::RadioButton("WGC", &source_, Source_Wgc);
+	ImGui::SameLine();
+	ImGui::RadioButton("Hooked (Present)", &source_, Source_Hooked);
+	if (source_ != prev_source)
 	{
-		if (!capture_.start(target_, device_))
+		capture_.stop();
+		shared_.reset();
+		if (injection_ != nullptr)
 		{
-			enabled_ = false;
-			ImGui::TextColored(ImVec4(1.0f, 0.45f, 0.4f, 1.0f), "Failed to start capture.");
+			injection_->request_video(enabled_ && source_ == Source_Hooked);
 		}
 	}
 
-	if (capture_.running())
+	if (!have_source)
 	{
-		ImGui::TextColored(ImVec4(0.4f, 1.0f, 0.4f, 1.0f), "Capturing %ux%u", capture_.frame_width(),
-		                   capture_.frame_height());
+		ImGui::TextDisabled(source_ == Source_Hooked
+		                        ? "Inject into a game first (the Present hook is the source)."
+		                        : "Inject into a game first (its window is the source).");
+	}
+
+	if (source_ == Source_Wgc)
+	{
+		// Start/restart WGC capture when enabled and the target window changes.
+		if (enabled_ && have_wgc_target && capture_.target() != target_)
+		{
+			if (!capture_.start(target_, device_))
+			{
+				enabled_ = false;
+				ImGui::TextColored(kRed, "Failed to start capture.");
+			}
+		}
+		if (capture_.running())
+		{
+			ImGui::TextColored(kGreen, "Capturing %ux%u (WGC)", capture_.frame_width(), capture_.frame_height());
+		}
+	}
+	else // Source_Hooked
+	{
+		if (enabled_ && injection_ != nullptr)
+		{
+			// Keep the subsystem requested (a fresh inject may have reset control).
+			if (!injection_->video_requested())
+			{
+				injection_->request_video(true);
+			}
+			const VideoShareView share = injection_->video_share();
+			if (shared_.frames_copied() > 0 && shared_.width() > 0)
+			{
+				ImGui::TextColored(kGreen, "Mirroring %ux%u (hooked, %llu frames)", shared_.width(),
+				                   shared_.height(), static_cast<unsigned long long>(shared_.frames_copied()));
+			}
+			else if (share.present_calls > 0)
+			{
+				ImGui::TextColored(kGreen, "Present hooked (%llu calls); opening shared texture...",
+				                   static_cast<unsigned long long>(share.present_calls));
+			}
+			else
+			{
+				ImGui::TextDisabled("Waiting for hooked frames (the game may not render via DXGI).");
+			}
+		}
 	}
 
 	draw_perf_graphs(stats);
@@ -95,7 +157,22 @@ void CapturePanel::draw_perf_graphs(const FrameStats& stats)
 
 void CapturePanel::render(ID3D11DeviceContext* ctx, std::uint32_t dst_w, std::uint32_t dst_h)
 {
-	if (capture_.running())
+	if (!enabled_)
+	{
+		return;
+	}
+	if (source_ == Source_Hooked)
+	{
+		if (injection_ == nullptr)
+		{
+			return;
+		}
+		if (shared_.update(injection_->video_share(), injection_->target_pid()) && shared_.srv() != nullptr)
+		{
+			renderer_.draw(ctx, shared_.srv(), shared_.width(), shared_.height(), dst_w, dst_h);
+		}
+	}
+	else if (capture_.running())
 	{
 		capture_.draw_latest(renderer_, ctx, dst_w, dst_h);
 	}

host/src/capture_panel.hpp

@@ -1,5 +1,7 @@
-// Owns the video-mirror pipeline (WGC capture + frame renderer) and its UI.
-// The target window comes from the injected hook's reported game HWND.
+// Owns the video-mirror pipeline and its UI. Two interchangeable sources feed the
+// same letterboxed renderer: Windows Graphics Capture (no injection, the default)
+// and the injected Present-hook's shared backbuffer texture (lower latency, needs
+// the video subsystem hooked). The target window/pid come from the injected hook.
 #pragma once
 
 #include <cstdint>
@@ -8,23 +10,33 @@
 #include <windows.h>
 
 #include "capture/frame_renderer.hpp"
+#include "capture/shared_texture.hpp"
 #include "capture/window_capture.hpp"
 #include "ui/app_chrome.hpp"
 
 namespace coop
 {
 
+class InjectionPanel;
+
 class CapturePanel
 {
 public:
 	bool init(ID3D11Device* device);
 
-	// The window to mirror (0 if none yet); typically the injected game's HWND.
+	// The window to mirror via WGC (0 if none yet); typically the injected game's HWND.
 	void set_target(HWND target)
 	{
 		target_ = target;
 	}
 
+	// The injection panel supplies the target pid + Present-hook video channel and
+	// lets this panel install/remove the video subsystem when the source is Hooked.
+	void set_injection(InjectionPanel* injection)
+	{
+		injection_ = injection;
+	}
+
 	// `stats` are the host's render frame-timing, drawn as the mirror's
 	// frametime / FPS graphs (this window is what the mirror renders into).
 	void draw_ui(const FrameStats& stats);
@@ -33,13 +45,22 @@ public:
 	void render(ID3D11DeviceContext* ctx, std::uint32_t dst_w, std::uint32_t dst_h);
 
 private:
+	enum Source : int
+	{
+		Source_Wgc = 0,    // Windows Graphics Capture
+		Source_Hooked = 1, // injected Present-hook shared texture
+	};
+
 	void draw_perf_graphs(const FrameStats& stats);
 
 	ID3D11Device* device_ = nullptr;
 	FrameRenderer renderer_;
 	WindowCapture capture_;
+	SharedTextureSource shared_;
+	InjectionPanel* injection_ = nullptr;
 	HWND target_ = nullptr;
 	bool enabled_ = false;
+	int source_ = Source_Wgc;
 };
 
 } // namespace coop

host/src/injection_panel.cpp

@@ -96,6 +96,7 @@ void InjectionPanel::inject_selected()
 	server_.set_subsystem_enabled(HookSubsys_Input, want_input_);
 	server_.set_subsystem_enabled(HookSubsys_Focus, want_focus_);
 	server_.set_subsystem_enabled(HookSubsys_Audio, want_audio_);
+	server_.set_subsystem_enabled(HookSubsys_Video, want_video_);
 
 	const InjectResult result = inject_dll(selected_pid_, hook_dll_path());
 	if (result.status == InjectStatus::Ok)
@@ -147,7 +148,7 @@ void InjectionPanel::publish(const std::array<PadInfo, kMaxPads>& pads)
 
 void InjectionPanel::draw_hook_list(const HookStatusView& status)
 {
-	static const char* kSubsysName[] = {"Input", "Focus", "Audio"};
+	static const char* kSubsysName[] = {"Input", "Focus", "Audio", "Video"};
 
 	const std::uint32_t n = status.hook_entry_count < kMaxHookEntries ? status.hook_entry_count : kMaxHookEntries;
 	if (n == 0)
@@ -181,7 +182,7 @@ void InjectionPanel::draw_hook_list(const HookStatusView& status)
 				{
 					ImGui::TableNextRow();
 					ImGui::TableNextColumn();
-					ImGui::TextDisabled("%s", kSubsysName[sub < 3 ? sub : 0]);
+					ImGui::TextDisabled("%s", kSubsysName[sub < HookSubsys_Count ? sub : 0]);
 					ImGui::TableNextColumn();
 					ImGui::TableNextColumn();
 					header_done = true;
@@ -235,6 +236,7 @@ void InjectionPanel::draw_subsystem_controls(const HookStatusView& status)
 	    {"Input forwarding (XInput)", HookSubsys_Input, &want_input_, "controller input reaches the game"},
 	    {"Focus spoof", HookSubsys_Focus, &want_focus_, "the game keeps running unfocused"},
 	    {"Audio render-hook", HookSubsys_Audio, &want_audio_, "audio mirror without echo"},
+	    {"Video Present-hook", HookSubsys_Video, &want_video_, "Video mirror can use the hooked source"},
 	};
 
 	for (const Row& r : rows)

host/src/injection_panel.hpp

@@ -49,6 +49,32 @@ public:
 		server_.drain_logs(std::forward<F>(emit));
 	}
 
+	// --- Present-hook video path (consumed by the Video mirror panel) ----------
+
+	[[nodiscard]] unsigned long target_pid() const
+	{
+		return server_.target_pid();
+	}
+
+	// The hook's Present-hook video channel snapshot (shared-texture descriptor).
+	[[nodiscard]] VideoShareView video_share() const
+	{
+		return server_.video_share();
+	}
+
+	// Request the Present-hook video subsystem be installed/removed. Keeps the
+	// Injection panel's own checkbox in sync, so the Video panel can drive it.
+	void request_video(bool on)
+	{
+		want_video_ = on;
+		server_.set_subsystem_enabled(HookSubsys_Video, on);
+	}
+
+	[[nodiscard]] bool video_requested() const
+	{
+		return want_video_;
+	}
+
 private:
 	void refresh_processes();
 	void inject_selected();
@@ -72,7 +98,8 @@ private:
 	bool want_input_ = true;
 	bool want_focus_ = true;
 	bool want_audio_ = true;
-	bool injected_ = false; // a hook DLL is loaded in the target
+	bool want_video_ = false; // Present-hook video path: opt-in (WGC is the default)
+	bool injected_ = false;   // a hook DLL is loaded in the target
 
 	// Heartbeat liveness tracking (is the injected DLL responding?).
 	std::uint32_t last_heartbeat_ = 0;

host/src/ipc/ipc_server.cpp

@@ -88,6 +88,22 @@ HookStatusView IpcServer::hook_status() const
 	return view;
 }
 
+VideoShareView IpcServer::video_share() const
+{
+	VideoShareView v;
+	if (block_ == nullptr)
+	{
+		return v;
+	}
+	const VideoShare& s = block_->video;
+	v.generation = s.generation.load(std::memory_order_acquire);
+	v.width = s.width;
+	v.height = s.height;
+	v.format = s.format;
+	v.present_calls = s.present_calls;
+	return v;
+}
+
 void IpcServer::set_subsystem_enabled(std::uint32_t subsystem, bool enabled)
 {
 	if (block_ != nullptr && subsystem < HookSubsys_Count)

host/src/ipc/ipc_server.hpp

@@ -38,6 +38,16 @@ struct HookStatusView
 	HookEntry hook_entries[kMaxHookEntries] = {};
 };
 
+// Plain snapshot of the Present-hook video channel for the Video mirror panel.
+struct VideoShareView
+{
+	std::uint32_t generation = 0;   // bumps per shared frame; 0 = nothing shared yet
+	std::uint32_t width = 0;        // shared texture dimensions / DXGI format
+	std::uint32_t height = 0;
+	std::uint32_t format = 0;
+	std::uint64_t present_calls = 0; // cumulative Present() detours (diagnostic)
+};
+
 class IpcServer
 {
 public:
@@ -53,6 +63,9 @@ public:
 	// Reads the hook's diagnostics back-channel (zeroed if not started).
 	[[nodiscard]] HookStatusView hook_status() const;
 
+	// Reads the Present-hook video channel (zeroed if not started).
+	[[nodiscard]] VideoShareView video_share() const;
+
 	// Request a hook subsystem be installed (true) or removed (false). The hook
 	// reconciles on its next tick. No-op if not started.
 	void set_subsystem_enabled(std::uint32_t subsystem, bool enabled);

host/src/main.cpp

@@ -75,6 +75,7 @@ int run()
 		MessageBoxW(nullptr, L"Failed to initialize the video mirror.", L"CoopAllTheThings", MB_ICONERROR);
 		return 1;
 	}
+	capture.set_injection(&injection); // for the Present-hook (Hooked) video source
 
 	// The overlay can be hidden (F1) so the window is a clean mirror for Remote
 	// Play Together; the pipelines keep running underneath either way.

tests/CMakeLists.txt

@@ -58,3 +58,24 @@ target_link_libraries(audio_hook_test PRIVATE
 	mmdevapi)
 
 add_test(NAME audio_hook_test COMMAND audio_hook_test)
+
+# In-process self-test for the Present-hook video path. Reuses the shipping
+# present_hook.cpp and drives a real D3D11 swapchain in the same process, so it
+# exercises the IDXGISwapChain::Present inline hook, the shared keyed-mutex
+# texture, and the open-by-name / readback contract (the video analogue of
+# audio_hook_test). Skips on a machine without a D3D11 device.
+add_executable(present_hook_test
+	present_hook_test.cpp
+	${CMAKE_SOURCE_DIR}/hook/src/present_hook.cpp
+	${CMAKE_SOURCE_DIR}/hook/src/debug_log.cpp
+	${CMAKE_SOURCE_DIR}/hook/src/hook_registry.cpp)
+
+target_include_directories(present_hook_test PRIVATE ${CMAKE_SOURCE_DIR}/hook/src)
+
+target_link_libraries(present_hook_test PRIVATE
+	coop_common
+	safetyhook::safetyhook
+	d3d11
+	dxgi)
+
+add_test(NAME present_hook_test COMMAND present_hook_test)

tests/present_hook_test.cpp

@@ -0,0 +1,227 @@
+// In-process self-test for the Present-hook video path (hook/src/present_hook.cpp).
+// This process plays both "game" and "host": it installs the Present hook, then
+// creates its own D3D11 swapchain, clears the backbuffer to a known color, and
+// calls Present -- exactly as a game would. With the hook live, that Present must
+// (1) fire the detour, (2) copy the backbuffer into the shared keyed-mutex
+// texture, and (3) publish the descriptor to the IPC video channel. A second
+// device then opens the shared texture by name and reads it back, proving the
+// CreateSharedHandle / OpenSharedResourceByName / keyed-mutex / CopyResource
+// contract both the hook and the host rely on -- with no game and no Steam.
+//
+// Requires a D3D11 device; on a headless / no-GPU machine it reports SKIP and
+// exits 0 (mirrors audio_hook_test).
+
+#include <cstdint>
+#include <cstdio>
+#include <vector>
+
+#include <windows.h>
+
+#include <d3d11_1.h>
+#include <dxgi1_2.h>
+
+#include "coop/protocol.hpp"
+#include "coop/shared_memory.hpp"
+#include "ipc_client.hpp"
+#include "present_hook.hpp"
+
+using namespace coop;
+
+namespace
+{
+
+int g_failures = 0;
+
+void check(bool ok, const char* what)
+{
+	if (!ok)
+	{
+		std::printf("  FAIL: %s\n", what);
+		++g_failures;
+	}
+}
+
+template <typename T>
+void release(T*& p)
+{
+	if (p)
+	{
+		p->Release();
+		p = nullptr;
+	}
+}
+
+constexpr UINT kW = 256;
+constexpr UINT kH = 256;
+// Distinctive clear color; UNORM bytes are ~ {51, 102, 153, 255}.
+constexpr float kClear[4] = {0.20f, 0.40f, 0.60f, 1.0f};
+
+bool near_byte(std::uint8_t got, int expected)
+{
+	return std::abs(static_cast<int>(got) - expected) <= 2;
+}
+
+} // namespace
+
+int main()
+{
+	// --- Host side: SharedBlock (named by our pid) so the hook's IpcClient connects.
+	SharedMemory shm;
+	if (!shm.create(shared_memory_name(GetCurrentProcessId()), sizeof(SharedBlock)))
+	{
+		std::printf("FAIL: create shared memory\n");
+		return 1;
+	}
+	auto* block = shm.as<SharedBlock>(); // OS zero-fills the mapping
+	block->version = kProtocolVersion;
+	block->sequence.store(0, std::memory_order_relaxed);
+	block->magic = kProtocolMagic;
+
+	hook::IpcClient ipc;
+	check(ipc.connect(10, 5), "IPC client connect");
+
+	// --- Install the Present hook (inline-hooks IDXGISwapChain::Present). ---
+	if (!hook::install_present_hooks(ipc))
+	{
+		std::printf("SKIP: could not install the Present hook (no D3D11 device?)\n");
+		return 0;
+	}
+
+	// --- Game side: our own swapchain on a hidden window; render + Present. ---
+	WNDCLASSEXW wc{};
+	wc.cbSize = sizeof(wc);
+	wc.lpfnWndProc = DefWindowProcW;
+	wc.hInstance = GetModuleHandleW(nullptr);
+	wc.lpszClassName = L"coop_present_test";
+	RegisterClassExW(&wc);
+	HWND hwnd = CreateWindowExW(0, wc.lpszClassName, L"", WS_OVERLAPPEDWINDOW, 0, 0, kW, kH, nullptr, nullptr,
+	                            wc.hInstance, nullptr);
+
+	DXGI_SWAP_CHAIN_DESC scd{};
+	scd.BufferCount = 2;
+	scd.BufferDesc.Width = kW;
+	scd.BufferDesc.Height = kH;
+	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;
+	HRESULT hr = D3D11CreateDeviceAndSwapChain(nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, nullptr, 0,
+	                                           D3D11_SDK_VERSION, &scd, &swapchain, &device, nullptr, &ctx);
+	if (FAILED(hr) || swapchain == nullptr)
+	{
+		std::printf("SKIP: could not create a D3D11 swapchain (hr=0x%08lX)\n", static_cast<unsigned long>(hr));
+		hook::remove_present_hooks();
+		return 0;
+	}
+
+	// Clear the backbuffer to the known color, then Present (fires the detour).
+	for (int frame = 0; frame < 3; ++frame)
+	{
+		ID3D11Texture2D* back = nullptr;
+		if (SUCCEEDED(swapchain->GetBuffer(0, __uuidof(ID3D11Texture2D), reinterpret_cast<void**>(&back))))
+		{
+			ID3D11RenderTargetView* rtv = nullptr;
+			if (SUCCEEDED(device->CreateRenderTargetView(back, nullptr, &rtv)))
+			{
+				ctx->ClearRenderTargetView(rtv, kClear);
+				ctx->Flush();
+				rtv->Release();
+			}
+			back->Release();
+		}
+		swapchain->Present(0, 0);
+	}
+
+	std::printf("present_calls=%llu frames_shared=%llu video{gen=%u %ux%u fmt=%u}\n",
+	            static_cast<unsigned long long>(hook::present_calls()),
+	            static_cast<unsigned long long>(hook::present_frames_shared()),
+	            block->video.generation.load(), block->video.width, block->video.height, block->video.format);
+
+	check(hook::present_calls() >= 3, "Present detour fired");
+	check(hook::present_frames_shared() > 0, "backbuffer copied into the shared texture");
+	check(block->video.generation.load() > 0, "video generation published to IPC");
+	check(block->video.width == kW && block->video.height == kH, "shared dimensions published");
+	check(block->video.format == DXGI_FORMAT_R8G8B8A8_UNORM, "shared format published");
+
+	// --- Consumer side: open the shared texture by name (second device), copy it
+	//     into a staging texture, map it, and verify the clear color survived. ---
+	{
+		ID3D11Device* devB = nullptr;
+		ID3D11DeviceContext* ctxB = nullptr;
+		if (SUCCEEDED(D3D11CreateDevice(nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, nullptr, 0,
+		                                D3D11_SDK_VERSION, &devB, nullptr, &ctxB)))
+		{
+			ID3D11Device1* dev1 = nullptr;
+			devB->QueryInterface(IID_PPV_ARGS(&dev1));
+			const std::wstring name = video_share_name(GetCurrentProcessId());
+			ID3D11Texture2D* sharedB = nullptr;
+			IDXGIKeyedMutex* km = nullptr;
+			if (dev1 != nullptr &&
+			    SUCCEEDED(dev1->OpenSharedResourceByName(name.c_str(),
+			                                             DXGI_SHARED_RESOURCE_READ | DXGI_SHARED_RESOURCE_WRITE,
+			                                             IID_PPV_ARGS(&sharedB))))
+			{
+				sharedB->QueryInterface(IID_PPV_ARGS(&km));
+
+				D3D11_TEXTURE2D_DESC sd{};
+				sharedB->GetDesc(&sd);
+				sd.Usage = D3D11_USAGE_STAGING;
+				sd.BindFlags = 0;
+				sd.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
+				sd.MiscFlags = 0;
+				ID3D11Texture2D* staging = nullptr;
+				check(SUCCEEDED(devB->CreateTexture2D(&sd, nullptr, &staging)), "create staging texture");
+
+				if (km != nullptr && staging != nullptr && km->AcquireSync(kVideoMutexKey, 1000) == S_OK)
+				{
+					ctxB->CopyResource(staging, sharedB);
+					km->ReleaseSync(kVideoMutexKey);
+
+					D3D11_MAPPED_SUBRESOURCE mapped{};
+					if (SUCCEEDED(ctxB->Map(staging, 0, D3D11_MAP_READ, 0, &mapped)))
+					{
+						const auto* px = static_cast<const std::uint8_t*>(mapped.pData);
+						std::printf("readback pixel0 = {%u,%u,%u,%u}\n", px[0], px[1], px[2], px[3]);
+						check(near_byte(px[0], 51) && near_byte(px[1], 102) && near_byte(px[2], 153),
+						      "shared texture carries the rendered color");
+						ctxB->Unmap(staging, 0);
+					}
+					else
+					{
+						check(false, "map staging texture");
+					}
+				}
+				else
+				{
+					check(false, "acquire keyed mutex + copy shared texture");
+				}
+				release(staging);
+			}
+			else
+			{
+				check(false, "open shared texture by name");
+			}
+			release(km);
+			release(sharedB);
+			release(dev1);
+		}
+		release(ctxB);
+		release(devB);
+	}
+
+	release(swapchain);
+	release(ctx);
+	release(device);
+	DestroyWindow(hwnd);
+	UnregisterClassW(wc.lpszClassName, wc.hInstance);
+	hook::remove_present_hooks();
+
+	std::printf(g_failures == 0 ? "PRESENT HOOK TEST PASS\n" : "PRESENT HOOK TEST FAILED (%d)\n", g_failures);
+	return g_failures == 0 ? 0 : 1;
+}

tools/audio_probe/main.cpp

@@ -242,12 +242,15 @@ int wmain(int argc, wchar_t** argv)
 		const std::uint64_t produced = ring->frames_produced.load(std::memory_order_relaxed);
 		const std::uint64_t overruns = ring->overruns.load(std::memory_order_relaxed);
 		const bool fmt_ready = coop::audio_ring_format_ready(*ring);
+		const std::uint32_t vgen = block->video.generation.load(std::memory_order_acquire);
+		const std::uint64_t vpresent = block->video.present_calls;
 
 		std::printf("[%4.1fs] hb=%u streams=%u peak=%.4f ring{fmt=%d %uHz/%uch/%ubit produced=%llu "
-		            "overruns=%llu}\n",
+		            "overruns=%llu} video{present=%llu gen=%u %ux%u}\n",
 		            (t + 1) * 0.5, heartbeat, streams, peak, fmt_ready ? 1 : 0, ring->sample_rate,
 		            ring->channels, ring->bits, static_cast<unsigned long long>(produced),
-		            static_cast<unsigned long long>(overruns));
+		            static_cast<unsigned long long>(overruns), static_cast<unsigned long long>(vpresent),
+		            vgen, block->video.width, block->video.height);
 		for (std::uint32_t i = 0; i < coop::kMaxAudioStreams && i < streams; ++i)
 		{
 			const coop::AudioStreamInfo& s = status.audio_streams[i];
@@ -261,7 +264,7 @@ int wmain(int argc, wchar_t** argv)
 	}
 
 	// Dump the hook registry so the installed-hooks list can be verified headless.
-	static const char* kSubsys[] = {"Input", "Focus", "Audio"};
+	static const char* kSubsys[] = {"Input", "Focus", "Audio", "Video"};
 	std::printf("\nInstalled hooks (%u):\n", status.hook_entry_count);
 	for (std::uint32_t i = 0; i < status.hook_entry_count && i < coop::kMaxHookEntries; ++i)
 	{