Add F10 back-buffer screenshot (PNG, focus-independent)

Capture the rendered back buffer to a timestamped PNG next to the exe via
WIC, triggered by F10 (delivered even when unfocused). The capture runs in
render_frame just before Present so it includes the ImGui overlay, and reads
off the GPU so it works regardless of window focus, z-order, or occlusion. A
brief toast confirms the save (drawn the next frame, so it's never in the shot).
F10 chosen to avoid Steam's F12; its WM_SYSKEYDOWN is swallowed so Windows
doesn't enter menu mode. Documented in the Help menu + README.

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

README.md

@@ -81,7 +81,8 @@ and covers anything the hooked path doesn't (Vulkan, D3D9 — see Roadmap).
   assumption is visible. Streams created *after* injection are captured exactly.
 - **Debug-oriented UI:** the ImGui overlay is laid out for diagnosing the
   pipeline, not for end use. F1 hides it entirely so the window is a clean mirror
-  for RPT.
+  for RPT; F2 frees the operator cursor; **F10 saves a PNG screenshot** (back buffer,
+  written next to the exe) regardless of window focus or occlusion.
 
 ## Roadmap
 

host/src/d3d11_window.cpp

@@ -1,5 +1,7 @@
 #include "d3d11_window.hpp"
 
+#include <wincodec.h> // WIC PNG encoder for screenshots
+
 #include <imgui_impl_win32.h>
 
 // Forward declared in the ImGui Win32 backend; lets ImGui consume input first.
@@ -13,7 +15,56 @@ namespace coop
 namespace
 {
 constexpr wchar_t kWindowClass[] = L"CoopAllTheThingsWindow";
+
+// Encode a tightly-packed/row-pitched RGBA8 image to a PNG file via WIC. `src` is the
+// CPU-mapped staging copy of the back buffer (stride = row_pitch). Pure COM, so no
+// extra link dependency. Returns false on any failure (caller swallows it -- a missed
+// screenshot is never fatal).
+bool write_rgba8_png(const std::wstring& path, UINT width, UINT height, const BYTE* src, UINT row_pitch)
+{
+	ComPtr<IWICImagingFactory> factory;
+	if (FAILED(CoCreateInstance(CLSID_WICImagingFactory, nullptr, CLSCTX_INPROC_SERVER,
+	                            IID_PPV_ARGS(factory.GetAddressOf()))))
+	{
+		return false;
 	}
+	ComPtr<IWICBitmap> bitmap; // wrap the back-buffer bytes (RGBA, matches the swap chain)
+	if (FAILED(factory->CreateBitmapFromMemory(width, height, GUID_WICPixelFormat32bppRGBA, row_pitch,
+	                                           row_pitch * height, const_cast<BYTE*>(src),
+	                                           bitmap.GetAddressOf())))
+	{
+		return false;
+	}
+	ComPtr<IWICStream> stream;
+	if (FAILED(factory->CreateStream(stream.GetAddressOf())) ||
+	    FAILED(stream->InitializeFromFilename(path.c_str(), GENERIC_WRITE)))
+	{
+		return false;
+	}
+	ComPtr<IWICBitmapEncoder> encoder;
+	if (FAILED(factory->CreateEncoder(GUID_ContainerFormatPng, nullptr, encoder.GetAddressOf())) ||
+	    FAILED(encoder->Initialize(stream.Get(), WICBitmapEncoderNoCache)))
+	{
+		return false;
+	}
+	ComPtr<IWICBitmapFrameEncode> frame;
+	ComPtr<IPropertyBag2> props;
+	if (FAILED(encoder->CreateNewFrame(frame.GetAddressOf(), props.GetAddressOf())) ||
+	    FAILED(frame->Initialize(props.Get())) || FAILED(frame->SetSize(width, height)))
+	{
+		return false;
+	}
+	// Let the encoder pick its native pixel format; WriteSource converts our RGBA to it.
+	WICPixelFormatGUID fmt = GUID_WICPixelFormat32bppBGRA;
+	frame->SetPixelFormat(&fmt);
+	if (FAILED(frame->WriteSource(bitmap.Get(), nullptr)) || FAILED(frame->Commit()) ||
+	    FAILED(encoder->Commit()))
+	{
+		return false;
+	}
+	return true;
+}
+} // namespace
 
 D3D11Window::~D3D11Window()
 {
@@ -174,11 +225,69 @@ void D3D11Window::render_frame(const RenderCallback& render, UINT sync_interval)
 		render();
 	}
 
+	// Screenshot (F10): capture after the overlay is drawn but before Present -- the
+	// flip-model back buffer is undefined once presented.
+	if (!pending_screenshot_.empty())
+	{
+		if (save_backbuffer_png(pending_screenshot_))
+		{
+			saved_screenshot_ = pending_screenshot_;
+		}
+		pending_screenshot_.clear();
+	}
+
 	// sync_interval 1 (default) vsyncs to the monitor; 0 presents immediately so the
 	// caller can pace the flip itself (frame-sync to the game's published frames).
 	swap_chain_->Present(sync_interval, 0);
 }
 
+void D3D11Window::request_screenshot(std::wstring path)
+{
+	pending_screenshot_ = std::move(path);
+}
+
+std::wstring D3D11Window::take_screenshot_result()
+{
+	std::wstring result;
+	result.swap(saved_screenshot_);
+	return result;
+}
+
+bool D3D11Window::save_backbuffer_png(const std::wstring& path)
+{
+	ComPtr<ID3D11Texture2D> back;
+	if (FAILED(swap_chain_->GetBuffer(0, IID_PPV_ARGS(back.GetAddressOf()))))
+	{
+		return false;
+	}
+	D3D11_TEXTURE2D_DESC desc{};
+	back->GetDesc(&desc);
+
+	// A CPU-readable staging copy we can Map (the back buffer itself isn't readable).
+	D3D11_TEXTURE2D_DESC staging = desc;
+	staging.Usage = D3D11_USAGE_STAGING;
+	staging.BindFlags = 0;
+	staging.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
+	staging.MiscFlags = 0;
+	ComPtr<ID3D11Texture2D> cpu;
+	if (FAILED(device_->CreateTexture2D(&staging, nullptr, cpu.GetAddressOf())))
+	{
+		return false;
+	}
+	context_->CopyResource(cpu.Get(), back.Get());
+
+	D3D11_MAPPED_SUBRESOURCE map{};
+	if (FAILED(context_->Map(cpu.Get(), 0, D3D11_MAP_READ, 0, &map)))
+	{
+		return false;
+	}
+	// The swap chain is DXGI_FORMAT_R8G8B8A8_UNORM (see create_device), i.e. RGBA bytes.
+	const bool ok =
+	    write_rgba8_png(path, desc.Width, desc.Height, static_cast<const BYTE*>(map.pData), map.RowPitch);
+	context_->Unmap(cpu.Get(), 0);
+	return ok;
+}
+
 LRESULT CALLBACK D3D11Window::wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
 {
 	if (msg == WM_NCCREATE)
@@ -204,6 +313,15 @@ LRESULT CALLBACK D3D11Window::wnd_proc(HWND hwnd, UINT msg, WPARAM wparam, LPARA
 			self->resize_height_ = HIWORD(lparam);
 		}
 		return 0;
+	case WM_SYSKEYDOWN:
+		// F10 is our screenshot key; ImGui already saw this message (handler runs above),
+		// so swallow it here to stop DefWindowProc from flicking into Win32 menu mode.
+		// Alt+F4 (VK_F4) falls through to DefWindowProc so it still closes the window.
+		if (wparam == VK_F10)
+		{
+			return 0;
+		}
+		break;
 	case WM_DESTROY:
 		// Reached by the close button, Alt+F4 (DefWindowProc turns it into WM_CLOSE ->
 		// DestroyWindow), and our own teardown. Esc deliberately does NOT quit -- it's a

host/src/d3d11_window.hpp

@@ -8,6 +8,7 @@
 #include <wrl/client.h>
 
 #include <functional>
+#include <string>
 
 namespace coop
 {
@@ -36,6 +37,16 @@ public:
 	// flip to the game's published frames instead of the monitor).
 	void render_frame(const RenderCallback& render, UINT sync_interval = 1);
 
+	// Request a PNG screenshot of the next rendered frame, saved to `path`. The capture
+	// happens inside render_frame just before Present, so it includes the ImGui overlay,
+	// and reads the back buffer off the GPU -- independent of window focus, z-order, or
+	// occlusion (works even when the window is fully covered). One-shot.
+	void request_screenshot(std::wstring path);
+
+	// If render_frame saved a screenshot since the last call, returns its path and clears
+	// the result (so a confirmation shows once); otherwise returns an empty string.
+	[[nodiscard]] std::wstring take_screenshot_result();
+
 	[[nodiscard]] HWND hwnd() const
 	{
 		return hwnd_;
@@ -56,8 +67,11 @@ private:
 	void create_render_target();
 	void release_render_target();
 	void handle_resize(UINT width, UINT height);
+	bool save_backbuffer_png(const std::wstring& path);
 
 	HWND hwnd_ = nullptr;
+	std::wstring pending_screenshot_; // set by request_screenshot, consumed in render_frame
+	std::wstring saved_screenshot_;   // last successfully written shot, for a UI confirmation
 	bool resize_pending_ = false;
 	UINT resize_width_ = 0;
 	UINT resize_height_ = 0;

host/src/main.cpp

@@ -6,6 +6,8 @@
 // this window via Windows Graphics Capture (Video mirror panel).
 
 #include <cstdint>
+#include <cstdio>
+#include <string>
 
 #include <windows.h>
 
@@ -18,6 +20,7 @@
 #include "audio_panel.hpp"
 #include "capture_panel.hpp"
 #include "controllers_panel.hpp"
+#include "coop/tool_paths.hpp"
 #include "d3d11_window.hpp"
 #include "imgui_layer.hpp"
 #include "inject/mkb_forward.hpp"
@@ -26,13 +29,59 @@
 #include "log_panel.hpp"
 #include "ui/app_chrome.hpp"
 
-#ifdef COOP_WITH_STEAM
-#include <string>
-#endif
-
 namespace
 {
 
+// Timestamped screenshot path next to the exe (e.g. coop_shot_20260622_143501.png).
+std::wstring screenshot_path()
+{
+	SYSTEMTIME st{};
+	GetLocalTime(&st);
+	wchar_t name[64];
+	swprintf(name, static_cast<int>(std::size(name)), L"coop_shot_%04u%02u%02u_%02u%02u%02u.png", st.wYear,
+	         st.wMonth, st.wDay, st.wHour, st.wMinute, st.wSecond);
+	return coop::exe_directory() + name;
+}
+
+// Just the filename of a path, narrowed to UTF-8 for an ImGui confirmation toast.
+std::string screenshot_basename(const std::wstring& path)
+{
+	const std::size_t slash = path.find_last_of(L"\\/");
+	const std::wstring file = slash == std::wstring::npos ? path : path.substr(slash + 1);
+	if (file.empty())
+	{
+		return {};
+	}
+	const int n = WideCharToMultiByte(CP_UTF8, 0, file.c_str(), static_cast<int>(file.size()), nullptr, 0,
+	                                  nullptr, nullptr);
+	std::string out(static_cast<std::size_t>(n), '\0');
+	WideCharToMultiByte(CP_UTF8, 0, file.c_str(), static_cast<int>(file.size()), out.data(), n, nullptr, nullptr);
+	return out;
+}
+
+// Brief fading "saved" confirmation after an F10 screenshot (bottom-left, non-interactive
+// so it never steals a click). It's drawn the frame *after* the capture, so it never lands
+// in the shot itself.
+void draw_screenshot_toast(double seconds_since, const std::string& name)
+{
+	const float fade = 1.0f - static_cast<float>(seconds_since) / 2.5f;
+	if (fade <= 0.0f || name.empty())
+	{
+		return;
+	}
+	const ImGuiViewport* vp = ImGui::GetMainViewport();
+	ImGui::SetNextWindowPos(ImVec2(vp->WorkPos.x + 12.0f, vp->WorkPos.y + vp->WorkSize.y - 44.0f));
+	ImGui::SetNextWindowBgAlpha(0.45f * fade);
+	const ImGuiWindowFlags flags = ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoInputs |
+	                               ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoSavedSettings |
+	                               ImGuiWindowFlags_NoFocusOnAppearing | ImGuiWindowFlags_NoNav;
+	ImGui::Begin("##shot_toast", nullptr, flags);
+	ImGui::PushStyleColor(ImGuiCol_Text, ImVec4(0.6f, 1.0f, 0.6f, fade));
+	ImGui::Text("Saved screenshot: %s", name.c_str());
+	ImGui::PopStyleColor();
+	ImGui::End();
+}
+
 #ifdef COOP_WITH_STEAM
 // Absolute path to the bundled Steam Input action manifest (next to the exe).
 std::string steam_manifest_path()
@@ -151,6 +200,8 @@ int run()
 	// Play Together; the pipelines keep running underneath either way.
 	bool show_overlay = true;
 	double overlay_hidden_at = 0.0;
+	double last_shot_at = -10.0; // when the last F10 screenshot was saved (for the toast)
+	std::string last_shot_name;
 	coop::UiState ui;
 	// Persist the "Debug details" verbosity in the .ini. Register before the first
 	// begin_frame() below, which is when ImGui loads the .ini and replays our handler.
@@ -210,6 +261,10 @@ int run()
 		{
 			injection.toggle_cursor_release(); // free/clip the operator's mouse for clipping games
 		}
+		if (ImGui::IsKeyPressed(ImGuiKey_F10, false))
+		{
+			window.request_screenshot(screenshot_path()); // captured at Present, overlay included
+		}
 
 		if (show_overlay)
 		{
@@ -234,6 +289,7 @@ int run()
 			{
 				log.draw();
 			}
+			draw_screenshot_toast(ImGui::GetTime() - last_shot_at, last_shot_name);
 		}
 		else
 		{
@@ -265,6 +321,14 @@ int run()
 			    imgui.end_frame();
 		    },
 		    sync_interval);
+
+		// render_frame saves a pending F10 screenshot just before Present; pick up the
+		// result here so next frame shows the confirmation toast (kept out of the shot).
+		if (std::wstring shot = window.take_screenshot_result(); !shot.empty())
+		{
+			last_shot_at = ImGui::GetTime();
+			last_shot_name = screenshot_basename(shot);
+		}
 	}
 
 	return 0;

host/src/ui/app_chrome.cpp

@@ -201,6 +201,7 @@ float draw_main_menu_bar(UiState& ui, const FrameStats& stats)
 	{
 		ImGui::TextDisabled("F1      hide/show this overlay");
 		ImGui::TextDisabled("F2      release/clip the operator cursor");
+		ImGui::TextDisabled("F10     save a screenshot (PNG, next to the exe)");
 		ImGui::TextDisabled("Alt+F4  quit (or File -> Exit)");
 		ImGui::Separator();
 		ImGui::TextDisabled("This window is what Remote Play");