M2(OpenGL): GL mock backend (no loader) + mock-backed capture coverage

Add render_gl.cpp (selectable as `gl`): renders the animated pattern with
scissored clears (glClear + glScissor -- GL 1.1, exported straight from
opengl32) and presents with SwapBuffers. No glad/submodule needed: a legacy
wglCreateContext + <GL/gl.h> suffices, so the planned loader dependency was
dropped. GL is bottom-left origin and the capture flips top-down, so the
frame-counter block is drawn at the GL top to land top-left in the captured
image. Window class gains CS_OWNDC for a stable GL DC; best-effort vsync via a
runtime wglSwapIntervalEXT lookup.

The GL SwapBuffers/wglSwapBuffers hook now bumps the shared present counter
(it's the GL present), so present_calls works for GL games too. mock_game_test
decodes GL frames through the existing glReadPixels capture path; 15/15 ctest.
Roadmap: OpenGL milestone done and removed (Vulkan renumbered to M2);
architecture/lessons/test docs updated.

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

README.md

@@ -137,21 +137,10 @@ Conventions for every milestone below:
   panel so it fits (content can be moved between columns / rows — the most detailed case
   should still fit). Land an automated harness check (drive-to-max → screenshot → assert no
   overflow) so later milestones that add UI keep it green. *Independent of the backend work;
-  every milestone below must preserve this test* (M3's red banner and Vulkan-layer checkbox
+  every milestone below must preserve this test* (M2's red banner and Vulkan-layer checkbox
   in particular).
 
-- **M2 — OpenGL (mock → capture coverage).**
+- **M2 — Vulkan (mock → capture).** The largest.
-  1. **Mock backend** (`render_gl.cpp`). Raw WGL context (`wglCreateContextAttribsARB`) with the
-     **glad** loader (new submodule, `Dav1dde/glad`). Background via `glClearColor`/`glClear`;
-     bar + block via `glScissor` + clear (shader-free GL 1.x). GL's framebuffer is
-     **bottom-left** origin, so the counter block is placed flipped so the captured (top-left)
-     pixel still decodes — matching the existing `glReadPixels` capture flip. Adds the
-     `.gitmodules` entry + the `coop_require_submodule()` check.
-  2. **Capture coverage.** The GL `SwapBuffers`/`wglSwapBuffers` + `glReadPixels` path already
-     ships; add a mock-backed regression that decodes the mock's frames through it (upgrading the
-     synthetic `opengl_hook_test` to a real animated game). Small.
-
-- **M3 — Vulkan (mock → capture).** The largest.
   1. **Mock backend** (`render_vk.cpp`). New submodules **Vulkan-Headers**
      (`KhronosGroup/Vulkan-Headers`, official) + **volk** (`zeux/volk`); raw
      `vkCreateWin32SurfaceKHR`, swap chain, per-frame acquire → clear → present. Background via
@@ -296,7 +285,7 @@ ctest --test-dir build -C Debug --output-on-failure
   endpoint format). Skips cleanly if the machine has no audio endpoint.
 - **`mock_game_test`** — comprehensive capture/audio/hook stress test against
   **`coop_mock_game`** (an animated, frame-numbered A/V test game under
-  [`tools/mock_game`](tools/mock_game) with selectable **DX9 / DX9Ex / DX10 / DX11 / DX12** backends and a
+  [`tools/mock_game`](tools/mock_game) with selectable **DX9 / DX9Ex / DX10 / DX11 / DX12 / OpenGL** backends and a
   configurable WASAPI tone). It launches the game, injects `coop_hook.dll`, opens the
   hook's shared video texture, and **decodes the frame number out of the captured pixels**
   to assert the mirror sees a *monotonic, advancing* sequence for each backend (the bar
@@ -457,6 +446,13 @@ Non-obvious things that cost time and constrain the design:
   so **one path serves both** — the GPU shared-surface fast path the plan sketched for D3D9Ex
   wasn't worth it (D3D9 games are light enough that the read-back cost is fine, and it dodges the
   cross-device keyed-mutex-less sync of a legacy shared surface).
+- **The OpenGL mock needs no GL loader.** Drawing the animated pattern with scissored clears
+  (`glClear` + `glScissor`) only touches **GL 1.1**, which `opengl32` exports directly — so the
+  planned **glad** submodule wasn't needed (a legacy `wglCreateContext` + `<GL/gl.h>` suffices).
+  GL's framebuffer is **bottom-left** origin and the capture flips it top-down, so the mock draws
+  the frame-counter block at the GL *top* (`y = h - block`) to land at the captured image's
+  top-left. The GL `SwapBuffers` hook now also bumps the shared present counter (it's the GL
+  present), so the Video panel's present rate works for GL games too.
 - **A render client that predates our injection has no knowable format — measure it.**
   We inject into already-running games, so we usually never see the game's
   `IAudioClient::Initialize`; the render-hook then assumes the device mix format for that

hook/src/opengl_hook.cpp

@@ -240,6 +240,10 @@ BOOL WINAPI hk_SwapBuffers(HDC hdc)
 	if (outer)
 	{
 		t_in_swap = true;
+		if (g_ipc != nullptr)
+		{
+			g_ipc->note_present(); // SwapBuffers is the GL present (counts toward video.present_calls)
+		}
 		capture_gl(hdc);
 	}
 	const BOOL r = g_hk_swapbuffers.stdcall<BOOL>(hdc); // __stdcall: call() is __cdecl on x86 -> crash
@@ -258,6 +262,10 @@ BOOL WINAPI hk_wglSwapBuffers(HDC hdc)
 	if (outer)
 	{
 		t_in_swap = true;
+		if (g_ipc != nullptr)
+		{
+			g_ipc->note_present(); // wglSwapBuffers is the GL present
+		}
 		capture_gl(hdc);
 	}
 	const BOOL r = g_hk_wglswap.stdcall<BOOL>(hdc); // __stdcall: call() is __cdecl on x86 -> crash

tests/mock_game_test.cpp

@@ -522,6 +522,7 @@ int main()
 		return 0;
 	}
 
+	test_video_capture("gl", device);
 	test_video_capture("dx9ex", device);
 	test_video_capture("dx9", device);
 	test_video_capture("dx10", device);

tools/mock_game/CMakeLists.txt

@@ -6,12 +6,13 @@ add_executable(coop_mock_game
 	render_dx11.cpp
 	render_dx12.cpp
 	render_dx10.cpp
-	render_dx09.cpp)
+	render_dx09.cpp
+	render_gl.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 d3d10 d3d9 dxgi ole32)
+target_link_libraries(coop_mock_game PRIVATE d3d11 d3d12 d3d10 d3d9 dxgi ole32 opengl32 gdi32)
 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.

tools/mock_game/main.cpp

@@ -1,6 +1,6 @@
 // CoopMockGame -- a tiny test "game" used to exercise the capture + audio + hook paths.
 //
-//   coop_mock_game.exe [dx9|dx9ex|dx10|dx11|dx12] [seconds] [rate] [channels] [bits] [pcm|float]
+//   coop_mock_game.exe [dx9|dx9ex|dx10|dx11|dx12|gl] [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
@@ -78,6 +78,7 @@ int main(int argc, char** argv)
 	const HINSTANCE inst = GetModuleHandleW(nullptr);
 	WNDCLASSEXW wc = {};
 	wc.cbSize = sizeof(wc);
+	wc.style = CS_OWNDC; // a stable private DC, so the OpenGL backend can keep one GL context
 	wc.lpfnWndProc = wnd_proc;
 	wc.hInstance = inst;
 	wc.hCursor = LoadCursorW(nullptr, IDC_ARROW);

tools/mock_game/render_backend.cpp

@@ -25,6 +25,10 @@ std::unique_ptr<RenderBackend> RenderBackend::create(const std::string& name)
 	{
 		return create_dx9_backend(/*ex=*/false);
 	}
+	if (name == "gl" || name == "opengl")
+	{
+		return create_gl_backend();
+	}
 	return nullptr;
 }
 

tools/mock_game/render_backend.hpp

@@ -62,5 +62,6 @@ std::unique_ptr<RenderBackend> create_dx11_backend();
 std::unique_ptr<RenderBackend> create_dx12_backend();
 std::unique_ptr<RenderBackend> create_dx10_backend();
 std::unique_ptr<RenderBackend> create_dx9_backend(bool ex); // ex: D3D9Ex vs plain D3D9
+std::unique_ptr<RenderBackend> create_gl_backend();
 
 } // namespace coop::mock

tools/mock_game/render_gl.cpp

@@ -0,0 +1,125 @@
+// OpenGL backend for the mock game. Renders the animated pattern with scissored clears
+// (glClear + glScissor -- all GL 1.1, exported straight from opengl32, so **no loader /
+// submodule** is needed) and presents with SwapBuffers, so the OpenGL capture hook
+// (SwapBuffers / wglSwapBuffers + glReadPixels) sees a genuine GL present.
+//
+// GL's framebuffer is bottom-left origin and the capture flips it vertically to top-down, so
+// the frame-counter block is drawn at the GL *top* (y = h-block) to land at the captured
+// image's top-left where the test samples it.
+#include "render_backend.hpp"
+
+#include <windows.h>
+
+#include <GL/gl.h>
+
+namespace coop::mock
+{
+namespace
+{
+class GlBackend : public RenderBackend
+{
+public:
+	bool init(HWND hwnd, std::uint32_t width, std::uint32_t height) override
+	{
+		width_ = width;
+		height_ = height;
+		hwnd_ = hwnd;
+		hdc_ = GetDC(hwnd);
+		if (hdc_ == nullptr)
+		{
+			return false;
+		}
+		PIXELFORMATDESCRIPTOR pfd = {};
+		pfd.nSize = sizeof(pfd);
+		pfd.nVersion = 1;
+		pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
+		pfd.iPixelType = PFD_TYPE_RGBA;
+		pfd.cColorBits = 32;
+		pfd.cAlphaBits = 8;
+		pfd.iLayerType = PFD_MAIN_PLANE;
+		const int pf = ChoosePixelFormat(hdc_, &pfd);
+		if (pf == 0 || !SetPixelFormat(hdc_, pf, &pfd))
+		{
+			return false;
+		}
+		hglrc_ = wglCreateContext(hdc_); // legacy context is enough for GL 1.1 clears
+		if (hglrc_ == nullptr || !wglMakeCurrent(hdc_, hglrc_))
+		{
+			return false;
+		}
+		// vsync if available (a game-like cadence; avoids spinning uncapped). Runtime extension
+		// lookup -- no loader/submodule needed.
+		using PFN_wglSwapIntervalEXT = BOOL(WINAPI*)(int);
+		if (auto swap_interval = reinterpret_cast<PFN_wglSwapIntervalEXT>(wglGetProcAddress("wglSwapIntervalEXT")))
+		{
+			swap_interval(1);
+		}
+		return true;
+	}
+
+	void render_and_present(std::uint32_t frame) override
+	{
+		const GLsizei w = static_cast<GLsizei>(width_);
+		const GLsizei h = static_cast<GLsizei>(height_);
+		glViewport(0, 0, w, h);
+
+		// Animated background (whole framebuffer).
+		glDisable(GL_SCISSOR_TEST);
+		glClearColor(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);
+		glClear(GL_COLOR_BUFFER_BIT);
+
+		glEnable(GL_SCISSOR_TEST);
+		// Moving vertical bar (full height).
+		const std::uint32_t span = width_ > 24 ? width_ - 24 : 1;
+		const GLint bx = static_cast<GLint>((frame * 4) % span);
+		glScissor(bx, 0, 24, h);
+		glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
+		glClear(GL_COLOR_BUFFER_BIT);
+
+		// Frame-counter block at the GL top-left (y = h - block) so it lands top-left after the
+		// capture's vertical flip.
+		std::uint8_t r = 0, g = 0, b = 0;
+		frame_to_rgb(frame, r, g, b);
+		glScissor(0, h - static_cast<GLint>(kFrameBlock), static_cast<GLsizei>(kFrameBlock),
+		          static_cast<GLsizei>(kFrameBlock));
+		glClearColor(r / 255.0f, g / 255.0f, b / 255.0f, 1.0f);
+		glClear(GL_COLOR_BUFFER_BIT);
+		glDisable(GL_SCISSOR_TEST);
+
+		SwapBuffers(hdc_); // the capture hook intercepts this
+	}
+
+	[[nodiscard]] const char* name() const override
+	{
+		return "gl";
+	}
+
+	~GlBackend() override
+	{
+		wglMakeCurrent(nullptr, nullptr);
+		if (hglrc_ != nullptr)
+		{
+			wglDeleteContext(hglrc_);
+		}
+		if (hdc_ != nullptr && hwnd_ != nullptr)
+		{
+			ReleaseDC(hwnd_, hdc_);
+		}
+	}
+
+private:
+	std::uint32_t width_ = 0;
+	std::uint32_t height_ = 0;
+	HWND hwnd_ = nullptr;
+	HDC hdc_ = nullptr;
+	HGLRC hglrc_ = nullptr;
+};
+} // namespace
+
+std::unique_ptr<RenderBackend> create_gl_backend()
+{
+	return std::make_unique<GlBackend>();
+}
+
+} // namespace coop::mock