diff --git a/CMakeLists.txt b/CMakeLists.txt
index b47dee3..69a3518 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -120,6 +120,7 @@ if(COOP_BUILD_HOOK)
 	add_subdirectory(hook)
 	enable_testing()
 	add_subdirectory(tools/audio_tone)  # coop_tone: audio source for the loopback test
+	add_subdirectory(tools/mock_game)   # coop_mock_game: A/V test game for the capture/hook tests
 	add_subdirectory(tools/audio_probe) # coop_audio_probe: inject + diagnose the render-hook
 	add_subdirectory(tools/input_probe) # coop_input_probe: inject + forward synthetic input
 	add_subdirectory(tests)
diff --git a/tools/mock_game/CMakeLists.txt b/tools/mock_game/CMakeLists.txt
new file mode 100644
index 0000000..8368f62
--- /dev/null
+++ b/tools/mock_game/CMakeLists.txt
@@ -0,0 +1,16 @@
+# CoopMockGame -- a tiny test "game" with an animated, frame-numbered render (DX11/DX12)
+# and a configurable WASAPI tone, used by the capture/audio/hook stress tests. Not shipped.
+add_executable(coop_mock_game
+	main.cpp
+	render_backend.cpp
+	render_dx11.cpp
+	render_dx12.cpp)
+
+# Reuses the shared ToneSource (also used by coop_tone + the audio hook self-test).
+target_include_directories(coop_mock_game PRIVATE ${CMAKE_SOURCE_DIR}/tools/audio_tone)
+
+target_link_libraries(coop_mock_game PRIVATE d3d11 d3d12 dxgi ole32)
+set_target_properties(coop_mock_game PROPERTIES OUTPUT_NAME "coop_mock_game")
+
+# Test fixture -> stage next to the tests (alongside coop_tone), not in the deployable root.
+coop_output_subdir(tests coop_mock_game)
diff --git a/tools/mock_game/main.cpp b/tools/mock_game/main.cpp
new file mode 100644
index 0000000..ed7c8f0
--- /dev/null
+++ b/tools/mock_game/main.cpp
@@ -0,0 +1,147 @@
+// CoopMockGame -- a tiny test "game" used to exercise the capture + audio + hook paths.
+//
+//   coop_mock_game.exe [dx11|dx12] [seconds] [rate] [channels] [bits] [pcm|float]
+//
+// It opens a normal visible window and renders an animated, frame-numbered pattern (see
+// render_backend.hpp): a moving bar + per-frame background colour make motion obvious, and
+// a top-left block encodes the exact frame number so a capture test can decode it and
+// detect dropped / duplicated / stale frames. With audio args it also plays a configurable
+// WASAPI tone (the same ToneSource coop_tone uses), so it doubles as an A/V source. seconds
+// = 0 runs until the window is closed. Console app so it can print its pid + status.
+#include <atomic>
+#include <cstdint>
+#include <cstdio>
+#include <string>
+#include <thread>
+
+#include <windows.h>
+
+#include "render_backend.hpp"
+#include "tone_source.hpp"
+
+namespace
+{
+std::atomic<bool> g_running{true};
+
+LRESULT CALLBACK wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
+{
+	if (msg == WM_DESTROY)
+	{
+		PostQuitMessage(0);
+		return 0;
+	}
+	return DefWindowProcW(hwnd, msg, wparam, lparam);
+}
+
+// Spawns the audio render loop on its own thread (WASAPI wants its own COM apartment).
+void audio_thread(coop::tone::ToneFormat want)
+{
+	if (FAILED(CoInitializeEx(nullptr, COINIT_MULTITHREADED)))
+	{
+		return;
+	}
+	coop::tone::ToneSource tone;
+	if (tone.open(want, 440.0))
+	{
+		std::printf("MOCK_GAME audio: %u Hz %u ch %u-bit %s\n", tone.format().rate, tone.format().channels,
+		            tone.format().bits, tone.format().is_float ? "float" : "pcm");
+		std::fflush(stdout);
+		while (g_running.load(std::memory_order_relaxed))
+		{
+			tone.render_step(200);
+		}
+	}
+	else
+	{
+		std::printf("MOCK_GAME audio: failed to open requested format\n");
+	}
+	tone.close();
+	CoUninitialize();
+}
+} // namespace
+
+int main(int argc, char** argv)
+{
+	const std::string backend_name = argc > 1 ? argv[1] : "dx11";
+	const double seconds = argc > 2 ? std::strtod(argv[2], nullptr) : 0.0;
+	const bool want_audio = argc > 3;
+	coop::tone::ToneFormat audio_fmt;
+	if (want_audio)
+	{
+		audio_fmt.rate = static_cast<unsigned>(std::strtoul(argv[3], nullptr, 10));
+		audio_fmt.channels = argc > 4 ? static_cast<unsigned>(std::strtoul(argv[4], nullptr, 10)) : 2;
+		audio_fmt.bits = argc > 5 ? static_cast<unsigned>(std::strtoul(argv[5], nullptr, 10)) : 32;
+		audio_fmt.is_float = argc > 6 ? (std::string(argv[6]) == "float") : (audio_fmt.bits == 32);
+	}
+
+	constexpr std::uint32_t kW = 640, kH = 480;
+	const HINSTANCE inst = GetModuleHandleW(nullptr);
+	WNDCLASSEXW wc = {};
+	wc.cbSize = sizeof(wc);
+	wc.lpfnWndProc = wnd_proc;
+	wc.hInstance = inst;
+	wc.hCursor = LoadCursorW(nullptr, IDC_ARROW);
+	wc.lpszClassName = L"CoopMockGameWindow";
+	RegisterClassExW(&wc);
+
+	RECT r = {0, 0, static_cast<LONG>(kW), static_cast<LONG>(kH)};
+	AdjustWindowRect(&r, WS_OVERLAPPEDWINDOW, FALSE);
+	HWND hwnd = CreateWindowExW(0, wc.lpszClassName, L"CoopMockGame", WS_OVERLAPPEDWINDOW | WS_VISIBLE,
+	                            CW_USEDEFAULT, CW_USEDEFAULT, r.right - r.left, r.bottom - r.top, nullptr,
+	                            nullptr, inst, nullptr);
+	if (hwnd == nullptr)
+	{
+		std::printf("MOCK_GAME error: CreateWindow failed\n");
+		return 1;
+	}
+
+	auto backend = coop::mock::RenderBackend::create(backend_name);
+	if (!backend || !backend->init(hwnd, kW, kH))
+	{
+		std::printf("MOCK_GAME error: backend '%s' unavailable\n", backend_name.c_str());
+		return 2;
+	}
+
+	std::printf("MOCK_GAME pid=%lu backend=%s w=%u h=%u audio=%s\n", GetCurrentProcessId(), backend->name(),
+	            kW, kH, want_audio ? "yes" : "no");
+	std::fflush(stdout);
+
+	std::thread audio;
+	if (want_audio)
+	{
+		audio = std::thread(audio_thread, audio_fmt);
+	}
+
+	const ULONGLONG start = GetTickCount64();
+	std::uint32_t frame = 0;
+	for (;;)
+	{
+		MSG msg;
+		while (PeekMessageW(&msg, nullptr, 0, 0, PM_REMOVE))
+		{
+			if (msg.message == WM_QUIT)
+			{
+				g_running.store(false, std::memory_order_relaxed);
+			}
+			TranslateMessage(&msg);
+			DispatchMessageW(&msg);
+		}
+		if (!g_running.load(std::memory_order_relaxed))
+		{
+			break;
+		}
+		backend->render_and_present(frame++);
+		if (seconds > 0.0 && (GetTickCount64() - start) >= static_cast<ULONGLONG>(seconds * 1000.0))
+		{
+			break;
+		}
+	}
+
+	g_running.store(false, std::memory_order_relaxed);
+	if (audio.joinable())
+	{
+		audio.join();
+	}
+	std::printf("MOCK_GAME done: %u frames\n", frame);
+	return 0;
+}
diff --git a/tools/mock_game/render_backend.cpp b/tools/mock_game/render_backend.cpp
new file mode 100644
index 0000000..67f78c3
--- /dev/null
+++ b/tools/mock_game/render_backend.cpp
@@ -0,0 +1,19 @@
+#include "render_backend.hpp"
+
+namespace coop::mock
+{
+
+std::unique_ptr<RenderBackend> RenderBackend::create(const std::string& name)
+{
+	if (name == "dx11")
+	{
+		return create_dx11_backend();
+	}
+	if (name == "dx12")
+	{
+		return create_dx12_backend();
+	}
+	return nullptr;
+}
+
+} // namespace coop::mock
diff --git a/tools/mock_game/render_backend.hpp b/tools/mock_game/render_backend.hpp
new file mode 100644
index 0000000..821f5ab
--- /dev/null
+++ b/tools/mock_game/render_backend.hpp
@@ -0,0 +1,64 @@
+// Pluggable render backend for the mock game (a test fixture, not a shipped component).
+//
+// The mock game renders an *animated* (never static) pattern so dropped / duplicated /
+// torn / stale frames are obvious both to the eye and to an automated capture test: a
+// moving bar + a per-frame background colour give visible motion, and a small top-left
+// "frame-counter" block encodes the exact frame number in its RGB so a test can decode it
+// from a captured pixel and assert the sequence advances (the DX12 rotating-backbuffer bug
+// showed up as a stuck/repeating counter). The backend is selectable (DX11 / DX12 today)
+// and structured so OpenGL / Vulkan can be added by implementing this interface.
+#pragma once
+
+#include <cstdint>
+#include <memory>
+#include <string>
+
+#include <windows.h>
+
+namespace coop::mock
+{
+
+// Encode a frame counter into an RGB triple (and back). R/G/B are the low 24 bits, so it
+// is unambiguous for ~16M frames. The swap chain is UNORM (not sRGB), so the bytes survive
+// a capture copy exactly. The capture test samples the frame-counter block and decodes it.
+inline void frame_to_rgb(std::uint32_t frame, std::uint8_t& r, std::uint8_t& g, std::uint8_t& b)
+{
+	r = static_cast<std::uint8_t>(frame & 0xFF);
+	g = static_cast<std::uint8_t>((frame >> 8) & 0xFF);
+	b = static_cast<std::uint8_t>((frame >> 16) & 0xFF);
+}
+
+inline std::uint32_t rgb_to_frame(std::uint8_t r, std::uint8_t g, std::uint8_t b)
+{
+	return static_cast<std::uint32_t>(r) | (static_cast<std::uint32_t>(g) << 8) |
+	       (static_cast<std::uint32_t>(b) << 16);
+}
+
+// Size (px) of the top-left frame-counter block the test samples.
+inline constexpr std::uint32_t kFrameBlock = 64;
+
+class RenderBackend
+{
+public:
+	virtual ~RenderBackend() = default;
+
+	// Bring up the device + swap chain on `hwnd` at the given client size. False on failure.
+	virtual bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) = 0;
+
+	// Draw frame `frame` (animated background + moving bar + the frame-counter block) and
+	// present it. One call per displayed frame.
+	virtual void render_and_present(std::uint32_t frame) = 0;
+
+	// Human-readable backend name (e.g. "dx11"), for logging.
+	[[nodiscard]] virtual const char* name() const = 0;
+
+	// Factory: returns a backend for `name` ("dx11" / "dx12"), or nullptr if unknown /
+	// unavailable on this machine.
+	static std::unique_ptr<RenderBackend> create(const std::string& name);
+};
+
+// Per-backend factories (defined in their own TUs; create() dispatches to them).
+std::unique_ptr<RenderBackend> create_dx11_backend();
+std::unique_ptr<RenderBackend> create_dx12_backend();
+
+} // namespace coop::mock
diff --git a/tools/mock_game/render_dx11.cpp b/tools/mock_game/render_dx11.cpp
new file mode 100644
index 0000000..1dd866f
--- /dev/null
+++ b/tools/mock_game/render_dx11.cpp
@@ -0,0 +1,116 @@
+// DX11 backend for the mock game. Renders the animated pattern entirely with region
+// clears (ID3D11DeviceContext1::ClearView) so it needs no shaders: an animated full-screen
+// background, a moving vertical bar, and the top-left frame-counter block.
+#include "render_backend.hpp"
+
+#include <d3d11_1.h>
+#include <dxgi1_2.h>
+#include <wrl/client.h>
+
+using Microsoft::WRL::ComPtr;
+
+namespace coop::mock
+{
+namespace
+{
+class Dx11Backend : public RenderBackend
+{
+public:
+	bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) override
+	{
+		width_ = width;
+		height_ = height;
+
+		const D3D_FEATURE_LEVEL levels[] = {D3D_FEATURE_LEVEL_11_1, D3D_FEATURE_LEVEL_11_0};
+		ComPtr<ID3D11DeviceContext> ctx0;
+		if (FAILED(D3D11CreateDevice(nullptr, D3D_DRIVER_TYPE_HARDWARE, nullptr, 0, levels,
+		                             static_cast<UINT>(std::size(levels)), D3D11_SDK_VERSION,
+		                             device_.GetAddressOf(), nullptr, ctx0.GetAddressOf())))
+		{
+			return false;
+		}
+		if (FAILED(ctx0.As(&ctx_))) // ClearView needs ID3D11DeviceContext1
+		{
+			return false;
+		}
+
+		ComPtr<IDXGIDevice> dxgi_device;
+		ComPtr<IDXGIAdapter> adapter;
+		ComPtr<IDXGIFactory2> factory;
+		if (FAILED(device_.As(&dxgi_device)) || FAILED(dxgi_device->GetAdapter(adapter.GetAddressOf())) ||
+		    FAILED(adapter->GetParent(IID_PPV_ARGS(factory.GetAddressOf()))))
+		{
+			return false;
+		}
+
+		DXGI_SWAP_CHAIN_DESC1 desc = {};
+		desc.Width = width;
+		desc.Height = height;
+		desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM; // UNORM (not sRGB) so the frame code is exact
+		desc.SampleDesc.Count = 1;
+		desc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
+		desc.BufferCount = 2;
+		desc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
+		if (FAILED(factory->CreateSwapChainForHwnd(device_.Get(), hwnd, &desc, nullptr, nullptr,
+		                                           swap_.GetAddressOf())))
+		{
+			return false;
+		}
+		factory->MakeWindowAssociation(hwnd, DXGI_MWA_NO_ALT_ENTER);
+
+		// D3D11 flip-model: GetBuffer(0) stays the live back buffer, so one RTV is reused.
+		ComPtr<ID3D11Texture2D> back;
+		if (FAILED(swap_->GetBuffer(0, IID_PPV_ARGS(back.GetAddressOf()))) ||
+		    FAILED(device_->CreateRenderTargetView(back.Get(), nullptr, rtv_.GetAddressOf())))
+		{
+			return false;
+		}
+		return true;
+	}
+
+	void render_and_present(std::uint32_t frame) override
+	{
+		// Animated background: each channel sweeps at a different rate -> constant motion.
+		const float bg[4] = {static_cast<float>((frame * 2) % 256) / 255.0f,
+		                     static_cast<float>((frame * 3) % 256) / 255.0f,
+		                     static_cast<float>((frame * 5) % 256) / 255.0f, 1.0f};
+		ctx_->ClearRenderTargetView(rtv_.Get(), bg);
+
+		// Moving vertical bar (obvious motion; a dropped frame makes it jump).
+		const float white[4] = {1.0f, 1.0f, 1.0f, 1.0f};
+		const LONG span = width_ > 24 ? static_cast<LONG>(width_ - 24) : 1;
+		const LONG bx = static_cast<LONG>((frame * 4) % static_cast<std::uint32_t>(span));
+		const D3D11_RECT bar = {bx, 0, bx + 24, static_cast<LONG>(height_)};
+		ctx_->ClearView(rtv_.Get(), white, &bar, 1);
+
+		// Frame-counter block (top-left): RGB encodes the exact frame number for the test.
+		std::uint8_t r = 0, g = 0, b = 0;
+		frame_to_rgb(frame, r, g, b);
+		const float code[4] = {r / 255.0f, g / 255.0f, b / 255.0f, 1.0f};
+		const D3D11_RECT block = {0, 0, static_cast<LONG>(kFrameBlock), static_cast<LONG>(kFrameBlock)};
+		ctx_->ClearView(rtv_.Get(), code, &block, 1);
+
+		swap_->Present(1, 0); // vsync -> a game-like cadence
+	}
+
+	[[nodiscard]] const char* name() const override
+	{
+		return "dx11";
+	}
+
+private:
+	std::uint32_t width_ = 0;
+	std::uint32_t height_ = 0;
+	ComPtr<ID3D11Device> device_;
+	ComPtr<ID3D11DeviceContext1> ctx_;
+	ComPtr<IDXGISwapChain1> swap_;
+	ComPtr<ID3D11RenderTargetView> rtv_;
+};
+} // namespace
+
+std::unique_ptr<RenderBackend> create_dx11_backend()
+{
+	return std::make_unique<Dx11Backend>();
+}
+
+} // namespace coop::mock
diff --git a/tools/mock_game/render_dx12.cpp b/tools/mock_game/render_dx12.cpp
new file mode 100644
index 0000000..73589f0
--- /dev/null
+++ b/tools/mock_game/render_dx12.cpp
@@ -0,0 +1,198 @@
+// DX12 backend for the mock game. Renders the same animated pattern as the DX11 backend
+// (animated background + moving bar + top-left frame-counter block) so the capture tests
+// can verify the DX12 capture path against an identical, frame-numbered source.
+#include "render_backend.hpp"
+
+#include <d3d12.h>
+#include <dxgi1_4.h>
+#include <wrl/client.h>
+
+using Microsoft::WRL::ComPtr;
+
+namespace coop::mock
+{
+namespace
+{
+constexpr UINT kBackBuffers = 3; // DX12 rotates these explicitly -- the case the capture must get right
+
+class Dx12Backend : public RenderBackend
+{
+public:
+	bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) override
+	{
+		width_ = width;
+		height_ = height;
+
+		if (FAILED(D3D12CreateDevice(nullptr, D3D_FEATURE_LEVEL_11_0, IID_PPV_ARGS(device_.GetAddressOf()))))
+		{
+			return false;
+		}
+
+		D3D12_COMMAND_QUEUE_DESC qd = {};
+		qd.Type = D3D12_COMMAND_LIST_TYPE_DIRECT;
+		if (FAILED(device_->CreateCommandQueue(&qd, IID_PPV_ARGS(queue_.GetAddressOf()))))
+		{
+			return false;
+		}
+
+		ComPtr<IDXGIFactory4> factory;
+		if (FAILED(CreateDXGIFactory1(IID_PPV_ARGS(factory.GetAddressOf()))))
+		{
+			return false;
+		}
+		DXGI_SWAP_CHAIN_DESC1 desc = {};
+		desc.Width = width;
+		desc.Height = height;
+		desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
+		desc.SampleDesc.Count = 1;
+		desc.BufferUsage = DXGI_USAGE_RENDER_TARGET_OUTPUT;
+		desc.BufferCount = kBackBuffers;
+		desc.SwapEffect = DXGI_SWAP_EFFECT_FLIP_DISCARD;
+		ComPtr<IDXGISwapChain1> sc1;
+		if (FAILED(factory->CreateSwapChainForHwnd(queue_.Get(), hwnd, &desc, nullptr, nullptr,
+		                                           sc1.GetAddressOf())) ||
+		    FAILED(sc1.As(&swap_)))
+		{
+			return false;
+		}
+		factory->MakeWindowAssociation(hwnd, DXGI_MWA_NO_ALT_ENTER);
+
+		D3D12_DESCRIPTOR_HEAP_DESC hd = {};
+		hd.Type = D3D12_DESCRIPTOR_HEAP_TYPE_RTV;
+		hd.NumDescriptors = kBackBuffers;
+		if (FAILED(device_->CreateDescriptorHeap(&hd, IID_PPV_ARGS(rtv_heap_.GetAddressOf()))))
+		{
+			return false;
+		}
+		rtv_stride_ = device_->GetDescriptorHandleIncrementSize(D3D12_DESCRIPTOR_HEAP_TYPE_RTV);
+		D3D12_CPU_DESCRIPTOR_HANDLE h = rtv_heap_->GetCPUDescriptorHandleForHeapStart();
+		for (UINT i = 0; i < kBackBuffers; ++i)
+		{
+			if (FAILED(swap_->GetBuffer(i, IID_PPV_ARGS(targets_[i].GetAddressOf()))))
+			{
+				return false;
+			}
+			device_->CreateRenderTargetView(targets_[i].Get(), nullptr, h);
+			rtv_handles_[i] = h;
+			h.ptr += rtv_stride_;
+			if (FAILED(device_->CreateCommandAllocator(D3D12_COMMAND_LIST_TYPE_DIRECT,
+			                                           IID_PPV_ARGS(allocs_[i].GetAddressOf()))))
+			{
+				return false;
+			}
+		}
+		if (FAILED(device_->CreateCommandList(0, D3D12_COMMAND_LIST_TYPE_DIRECT, allocs_[0].Get(), nullptr,
+		                                      IID_PPV_ARGS(list_.GetAddressOf()))))
+		{
+			return false;
+		}
+		list_->Close();
+
+		if (FAILED(device_->CreateFence(0, D3D12_FENCE_FLAG_NONE, IID_PPV_ARGS(fence_.GetAddressOf()))))
+		{
+			return false;
+		}
+		fence_event_ = CreateEventW(nullptr, FALSE, FALSE, nullptr);
+		return fence_event_ != nullptr;
+	}
+
+	void render_and_present(std::uint32_t frame) override
+	{
+		const UINT idx = swap_->GetCurrentBackBufferIndex();
+		allocs_[idx]->Reset();
+		list_->Reset(allocs_[idx].Get(), nullptr);
+
+		transition(targets_[idx].Get(), D3D12_RESOURCE_STATE_PRESENT, D3D12_RESOURCE_STATE_RENDER_TARGET);
+
+		// Animated background (full RT clear).
+		const float bg[4] = {static_cast<float>((frame * 2) % 256) / 255.0f,
+		                     static_cast<float>((frame * 3) % 256) / 255.0f,
+		                     static_cast<float>((frame * 5) % 256) / 255.0f, 1.0f};
+		list_->ClearRenderTargetView(rtv_handles_[idx], bg, 0, nullptr);
+
+		// Moving vertical bar.
+		const float white[4] = {1.0f, 1.0f, 1.0f, 1.0f};
+		const LONG span = width_ > 24 ? static_cast<LONG>(width_ - 24) : 1;
+		const LONG bx = static_cast<LONG>((frame * 4) % static_cast<std::uint32_t>(span));
+		const D3D12_RECT bar = {bx, 0, bx + 24, static_cast<LONG>(height_)};
+		list_->ClearRenderTargetView(rtv_handles_[idx], white, 1, &bar);
+
+		// Frame-counter block (top-left).
+		std::uint8_t r = 0, g = 0, b = 0;
+		frame_to_rgb(frame, r, g, b);
+		const float code[4] = {r / 255.0f, g / 255.0f, b / 255.0f, 1.0f};
+		const D3D12_RECT block = {0, 0, static_cast<LONG>(kFrameBlock), static_cast<LONG>(kFrameBlock)};
+		list_->ClearRenderTargetView(rtv_handles_[idx], code, 1, &block);
+
+		transition(targets_[idx].Get(), D3D12_RESOURCE_STATE_RENDER_TARGET, D3D12_RESOURCE_STATE_PRESENT);
+		list_->Close();
+		ID3D12CommandList* lists[] = {list_.Get()};
+		queue_->ExecuteCommandLists(1, lists);
+
+		swap_->Present(1, 0);
+		wait_for_gpu(); // simple per-frame sync (mock game: correctness over throughput)
+	}
+
+	[[nodiscard]] const char* name() const override
+	{
+		return "dx12";
+	}
+
+	~Dx12Backend() override
+	{
+		if (fence_ != nullptr)
+		{
+			wait_for_gpu();
+		}
+		if (fence_event_ != nullptr)
+		{
+			CloseHandle(fence_event_);
+		}
+	}
+
+private:
+	void transition(ID3D12Resource* res, D3D12_RESOURCE_STATES from, D3D12_RESOURCE_STATES to)
+	{
+		D3D12_RESOURCE_BARRIER b = {};
+		b.Type = D3D12_RESOURCE_BARRIER_TYPE_TRANSITION;
+		b.Transition.pResource = res;
+		b.Transition.StateBefore = from;
+		b.Transition.StateAfter = to;
+		b.Transition.Subresource = D3D12_RESOURCE_BARRIER_ALL_SUBRESOURCES;
+		list_->ResourceBarrier(1, &b);
+	}
+
+	void wait_for_gpu()
+	{
+		const UINT64 v = ++fence_value_;
+		queue_->Signal(fence_.Get(), v);
+		if (fence_->GetCompletedValue() < v)
+		{
+			fence_->SetEventOnCompletion(v, fence_event_);
+			WaitForSingleObject(fence_event_, INFINITE);
+		}
+	}
+
+	std::uint32_t width_ = 0;
+	std::uint32_t height_ = 0;
+	ComPtr<ID3D12Device> device_;
+	ComPtr<ID3D12CommandQueue> queue_;
+	ComPtr<IDXGISwapChain3> swap_;
+	ComPtr<ID3D12DescriptorHeap> rtv_heap_;
+	UINT rtv_stride_ = 0;
+	ComPtr<ID3D12Resource> targets_[kBackBuffers];
+	D3D12_CPU_DESCRIPTOR_HANDLE rtv_handles_[kBackBuffers] = {};
+	ComPtr<ID3D12CommandAllocator> allocs_[kBackBuffers];
+	ComPtr<ID3D12GraphicsCommandList> list_;
+	ComPtr<ID3D12Fence> fence_;
+	UINT64 fence_value_ = 0;
+	HANDLE fence_event_ = nullptr;
+};
+} // namespace
+
+std::unique_ptr<RenderBackend> create_dx12_backend()
+{
+	return std::make_unique<Dx12Backend>();
+}
+
+} // namespace coop::mock