Some native clipboard support for some platforms

I was hoping SDL2 would get this functionality eventually, but nope, proper clipboard support is staged for SDL3, which we're not going to see much of for at least a few more months. This will have to do for 98.0. The feature can be disabled at runtime from powder.pref.

Implementation status:

 - windows (via winapi): has the most friendly api so of course the implementation is flawless and uses every available optimization >_>
 - macos (via cocoa): I'm bad at cocoa so this is only as good as absolutely necessary; TODO: on-demand rendering
 - x11 (via xclip): I am NOT implementing icccm2; TODO: remove reliance on external tools
 - wayland (via wl-clipboard): oh god wayland oh why, you're almost as bad as x11; TODO: remove reliance on external tools
 - android: TODO; is there even a point?
 - emscripten: TODO; the tricky bit is that in a browser we can only get clipboard data when the user is giving it to us, so this will require some JS hackery that I'm not mentally prepared for right now; also I think the supported content types are very limited and you can't just define your own

x11 and wayland support are handled by a common backend which delegates clipboard management to xclip-like external programs, such as xclip itself or wl-clipboard, and can load custom command line templates from powder.pref for use with other such programs.

.github/macaa64-ghactions.ini

@@ -1,6 +1,7 @@
 [binaries]
 c = [ 'clang', '-arch', 'arm64' ]
 cpp = [ 'clang++', '-arch', 'arm64' ]
+objcpp = [ 'clang++', '-arch', 'arm64' ]
 strip = 'strip'
 
 [host_machine]

cross-examples/macaa64.ini

@@ -1,6 +1,7 @@
 [binaries]
 c = [ 'clang', '-arch', 'arm64' ]
 cpp = [ 'clang++', '-arch', 'arm64' ]
+objcpp = [ 'clang++', '-arch', 'arm64' ]
 strip = 'strip'
 
 [host_machine]

meson.build

@@ -362,6 +362,7 @@ else
 endif
 
 data_files = []
+powder_deps = []
 
 subdir('src')
 subdir('resources')
@@ -377,7 +378,7 @@ if host_platform == 'emscripten'
 endif
 
 if get_option('build_powder')
-	powder_deps = [
+	powder_deps += [
 		threads_dep,
 		zlib_dep,
 		png_dep,

meson_options.txt

@@ -280,3 +280,9 @@ option(
 	value: '',
 	description: 'Build date string, used by ghactions workflows, not useful otherwise'
 )
+option(
+	'platform_clipboard',
+	type: 'boolean',
+	value: true,
+	description: 'Enable platform clipboard, allows copying simulation data between different windows'
+)

src/PowderToySDL.cpp

@@ -5,6 +5,7 @@
 #include "gui/interface/Engine.h"
 #include "graphics/Graphics.h"
 #include "common/platform/Platform.h"
+#include "common/clipboard/Clipboard.h"
 #include <iostream>
 
 int desktopWidth = 1280;
@@ -113,6 +114,7 @@ void SDLOpen()
 		fprintf(stderr, "Initializing SDL (video subsystem): %s\n", SDL_GetError());
 		Platform::Exit(-1);
 	}
+	Clipboard::Init();
 
 	SDLSetScreen();
 
@@ -256,6 +258,7 @@ void SDLSetScreen()
 			Platform::Exit(-1);
 		}
 		SDL_RaiseWindow(sdl_window);
+		Clipboard::RecreateWindow();
 	}
 	SDL_RenderSetIntegerScale(sdl_renderer, newFrameOpsNorm.forceIntegerScaling ? SDL_TRUE : SDL_FALSE);
 	if (!(newFrameOpsNorm.resizable && SDL_GetWindowFlags(sdl_window) & SDL_WINDOW_MAXIMIZED))

src/common/clipboard/Clipboard.h

@@ -0,0 +1,14 @@
+#pragma once
+#include <memory>
+#include "common/String.h"
+
+class GameSave;
+
+namespace Clipboard
+{
+	const ByteString clipboardFormatName = "application/vnd.powdertoy.save";
+	void SetClipboardData(std::unique_ptr<GameSave> data);
+	const GameSave *GetClipboardData();
+	void Init();
+	void RecreateWindow();
+}

src/common/clipboard/ClipboardImpls.template.h

@@ -0,0 +1,10 @@
+#ifdef CLIPBOARD_IMPLS_DECLARE
+# define IMPL_DEFINE(subsystem, factory) std::unique_ptr<ClipboardImpl> factory();
+#endif
+#ifdef CLIPBOARD_IMPLS_DEFINE
+# define IMPL_DEFINE(subsystem, factory) { subsystem, factory },
+#endif
+
+@impl_defs@
+
+#undef IMPL_DEFINE

src/common/clipboard/Cocoa.mm

@@ -0,0 +1,71 @@
+#include "Dynamic.h"
+#include "Clipboard.h"
+#include <Cocoa/Cocoa.h>
+#include <iostream>
+
+namespace Clipboard
+{
+	static int changeCount = -1;
+
+	class CocoaClipboardImpl : public ClipboardImpl
+	{
+	public:
+		void SetClipboardData() final override
+		{
+			@autoreleasepool
+			{
+				NSPasteboard *pasteboard = [NSPasteboard generalPasteboard];
+				NSString *format = [NSString stringWithUTF8String:clipboardFormatName.c_str()];
+				changeCount = [pasteboard declareTypes:[NSArray arrayWithObject:format] owner:nil];
+				std::vector<char> saveData;
+				SerializeClipboard(saveData);
+				const auto *base = &saveData[0];
+				auto size = saveData.size();
+				NSData *data = [NSData dataWithBytes:base length:size];
+				if (![pasteboard setData:data forType:format])
+				{
+					std::cerr << "cannot put save on clipboard: [pasteboard setData] failed" << std::endl;
+					return;
+				}
+			}
+			std::cerr << "put save on clipboard" << std::endl;
+		}
+
+		GetClipboardDataResult GetClipboardData() final override
+		{
+			GetClipboardDataChanged gdc;
+			@autoreleasepool
+			{
+				NSPasteboard *pasteboard = [NSPasteboard generalPasteboard];
+				int newChangeCount = [pasteboard changeCount];
+				if (changeCount == newChangeCount)
+				{
+					return GetClipboardDataUnchanged{};
+				}
+				changeCount = newChangeCount;
+				NSString *format = [NSString stringWithUTF8String:clipboardFormatName.c_str()];
+				NSString *available = [pasteboard availableTypeFromArray:[NSArray arrayWithObject:format]];
+				if (![available isEqualToString:format])
+				{
+					std::cerr << "not getting save from clipboard: no data" << std::endl;
+					return GetClipboardDataFailed{};
+				}
+				NSData *data = [pasteboard dataForType:format];
+				if (data == nil)
+				{
+					std::cerr << "not getting save from clipboard: [pasteboard dataForType] failed" << std::endl;
+					return GetClipboardDataFailed{};
+				}
+				auto *base = reinterpret_cast<const char *>([data bytes]);
+				auto size = [data length];
+				gdc.data = std::vector<char>(base, base + size);
+			}
+			return gdc;
+		}
+	};
+
+	std::unique_ptr<ClipboardImpl> CocoaClipboardFactory()
+	{
+		return std::make_unique<CocoaClipboardImpl>();
+	}
+}

src/common/clipboard/Dynamic.cpp

@@ -0,0 +1,120 @@
+#include "Dynamic.h"
+#include "client/GameSave.h"
+#include "prefs/GlobalPrefs.h"
+#include "PowderToySDL.h"
+#include <SDL_syswm.h>
+#include <iostream>
+
+namespace Clipboard
+{
+#define CLIPBOARD_IMPLS_DECLARE
+#include "ClipboardImpls.h"
+#undef CLIPBOARD_IMPLS_DECLARE
+
+	struct ClipboardImplEntry
+	{
+		SDL_SYSWM_TYPE subsystem;
+		std::unique_ptr<ClipboardImpl> (*factory)();
+	} clipboardImpls[] = {
+#define CLIPBOARD_IMPLS_DEFINE
+#include "ClipboardImpls.h"
+#undef CLIPBOARD_IMPLS_DEFINE
+		{ SDL_SYSWM_UNKNOWN, nullptr },
+	};
+
+	std::unique_ptr<GameSave> clipboardData;
+	std::unique_ptr<ClipboardImpl> clipboard;
+
+	void InvokeClipboardSetClipboardData()
+	{
+		if (clipboard)
+		{
+			if (clipboardData)
+			{
+				clipboard->SetClipboardData(); // this either works or it doesn't, we don't care
+			}
+			else
+			{
+				std::cerr << "cannot put save on clipboard: no data to transfer" << std::endl;
+			}
+		}
+	}
+
+	void SerializeClipboard(std::vector<char> &saveData)
+	{
+		std::tie(std::ignore, saveData) = clipboardData->Serialise();
+	}
+
+	void SetClipboardData(std::unique_ptr<GameSave> data)
+	{
+		clipboardData = std::move(data);
+		InvokeClipboardSetClipboardData();
+	}
+
+	void InvokeClipboardGetClipboardData()
+	{
+		if (clipboard)
+		{
+			auto result = clipboard->GetClipboardData();
+			if (std::holds_alternative<ClipboardImpl::GetClipboardDataUnchanged>(result))
+			{
+				std::cerr << "not getting save from clipboard, data unchanged" << std::endl;
+				return;
+			}
+			if (std::holds_alternative<ClipboardImpl::GetClipboardDataUnknown>(result))
+			{
+				return;
+			}
+			clipboardData.reset();
+			auto *data = std::get_if<ClipboardImpl::GetClipboardDataChanged>(&result);
+			if (!data)
+			{
+				return;
+			}
+			try
+			{
+				clipboardData = std::make_unique<GameSave>(data->data);
+			}
+			catch (const ParseException &e)
+			{
+				std::cerr << "got bad save from clipboard: " << e.what() << std::endl;
+				return;
+			}
+			std::cerr << "got save from clipboard" << std::endl;
+		}
+	}
+
+	const GameSave *GetClipboardData()
+	{
+		InvokeClipboardGetClipboardData();
+		return clipboardData.get();
+	}
+
+	void Init()
+	{
+	}
+
+	int currentSubsystem;
+
+	void RecreateWindow()
+	{
+		// old window is gone (or doesn't exist), associate clipboard data with the new one
+		SDL_SysWMinfo info;
+		SDL_VERSION(&info.version);
+		SDL_GetWindowWMInfo(sdl_window, &info);
+		clipboard.reset();
+		currentSubsystem = info.subsystem;
+		if (GlobalPrefs::Ref().Get<bool>("NativeClipboard.Enabled", true))
+		{
+			for (auto *impl = clipboardImpls; impl->factory; ++impl)
+			{
+				if (impl->subsystem == currentSubsystem)
+				{
+					clipboard = impl->factory();
+					break;
+				}
+			}
+		}
+		InvokeClipboardSetClipboardData();
+	}
+}

src/common/clipboard/Dynamic.h

@@ -0,0 +1,45 @@
+#pragma once
+#include "common/String.h"
+#include <vector>
+#include <variant>
+#include <memory>
+
+class GameSave;
+
+namespace Clipboard
+{
+	class ClipboardImpl
+	{
+	public:
+		virtual ~ClipboardImpl() = default;
+
+		virtual void SetClipboardData() = 0;
+
+		struct GetClipboardDataUnchanged
+		{
+		};
+		struct GetClipboardDataChanged
+		{
+			std::vector<char> data;
+		};
+		struct GetClipboardDataFailed
+		{
+		};
+		struct GetClipboardDataUnknown
+		{
+		};
+		using GetClipboardDataResult = std::variant<
+			GetClipboardDataUnchanged,
+			GetClipboardDataChanged,
+			GetClipboardDataFailed,
+			GetClipboardDataUnknown
+		>;
+		virtual GetClipboardDataResult GetClipboardData() = 0;
+	};
+
+	extern std::unique_ptr<GameSave> clipboardData;
+
+	void SerializeClipboard(std::vector<char> &saveData);
+
+	extern int currentSubsystem;
+}

src/common/clipboard/External.cpp

@@ -0,0 +1,232 @@
+#include "Dynamic.h"
+#include "Clipboard.h"
+#include "client/GameSave.h"
+#include "prefs/GlobalPrefs.h"
+#include "PowderToySDL.h"
+#include <iostream>
+#include <stdio.h>
+#include <optional>
+#include <algorithm>
+#include <signal.h>
+#include <map>
+#include <SDL_syswm.h>
+
+namespace Clipboard
+{
+	struct Preset
+	{
+		ByteString inCommand;
+		ByteString formatsCommand;
+		ByteString outCommand;
+		std::optional<int> defaultForSubsystem;
+	};
+	std::map<ByteString, Preset> builtInPresets = {
+		{ "xclip", {
+			"xclip -selection clipboard -target %s",
+			"xclip -out -selection clipboard -target TARGETS",
+			"xclip -out -selection clipboard -target %s",
+			SDL_SYSWM_X11,
+		} },
+		{ "wl-clipboard", {
+			"wl-copy --type %s",
+			"wl-paste --list-types",
+			"wl-paste --type %s",
+			SDL_SYSWM_WAYLAND,
+		} },
+	};
+
+	static ByteString SubstFormat(ByteString str)
+	{
+		if (auto split = str.SplitBy("%s"))
+		{
+			str = split.Before() + clipboardFormatName + split.After();
+		}
+		return str;
+	}
+
+	static std::optional<Preset> GetPreset()
+	{
+		std::optional<ByteString> name = GlobalPrefs::Ref().Get("NativeClipboard.External.Type", ByteString("auto"));
+		if (name == "custom")
+		{
+			auto getCommand = [](ByteString key) -> std::optional<ByteString> {
+				auto fullKey = "NativeClipboard.External." + key;
+				auto value = GlobalPrefs::Ref().Get<ByteString>(fullKey);
+				if (!value)
+				{
+					std::cerr << "custom external clipboard command preset: missing " << fullKey << std::endl;
+					return std::nullopt;
+				}
+				return *value;
+			};
+			auto inCommand      = getCommand("In");
+			auto formatsCommand = getCommand("Formats");
+			auto outCommand     = getCommand("Out");
+			if (!inCommand || !formatsCommand || !outCommand)
+			{
+				return std::nullopt;
+			}
+			return Preset{
+				SubstFormat(*inCommand),
+				SubstFormat(*formatsCommand),
+				SubstFormat(*outCommand),
+			};
+		}
+		if (name == "auto")
+		{
+			name.reset();
+			for (auto &[ presetName, preset ] : builtInPresets)
+			{
+				if (preset.defaultForSubsystem && *preset.defaultForSubsystem == currentSubsystem)
+				{
+					name = presetName;
+				}
+			}
+			if (!name)
+			{
+				std::cerr << "no built-in external clipboard command preset for SDL window subsystem " << currentSubsystem << std::endl;
+				return std::nullopt;
+			}
+		}
+		auto it = builtInPresets.find(*name);
+		if (it == builtInPresets.end())
+		{
+			std::cerr << "no built-in external clipboard command preset with name " << *name << std::endl;
+			return std::nullopt;
+		}
+		return Preset{
+			SubstFormat(it->second.inCommand),
+			SubstFormat(it->second.formatsCommand),
+			SubstFormat(it->second.outCommand),
+		};
+	}
+
+	class ExternalClipboardImpl : public ClipboardImpl
+	{
+	public:
+		ExternalClipboardImpl()
+		{
+			signal(SIGPIPE, SIG_IGN); // avoids problems with popen
+		}
+
+		void SetClipboardData() final override
+		{
+			auto preset = GetPreset();
+			if (!preset)
+			{
+				return;
+			}
+			auto handle = popen(preset->inCommand.c_str(), "we");
+			if (!handle)
+			{
+				std::cerr << "failed to set clipboard data: popen: " << strerror(errno) << std::endl;
+				return;
+			}
+			auto bail = false;
+			std::vector<char> saveData;
+			SerializeClipboard(saveData);
+			if (fwrite(&saveData[0], 1, saveData.size(), handle) != saveData.size())
+			{
+				std::cerr << "failed to set clipboard data: fwrite: " << strerror(errno) << std::endl;
+				bail = true;
+			}
+			auto status = pclose(handle);
+			if (bail)
+			{
+				return;
+			}
+			if (status == -1)
+			{
+				std::cerr << "failed to set clipboard data: pclose: " << strerror(errno) << std::endl;
+				return;
+			}
+			if (status)
+			{
+				std::cerr << "failed to set clipboard data: " << preset->inCommand << ": wait4 status code " << status << std::endl;
+				return;
+			}
+		}
+
+		GetClipboardDataResult GetClipboardData() final override
+		{
+			auto getTarget = [](ByteString command) -> std::optional<std::vector<char>> {
+				if (!command.size())
+				{
+					return std::nullopt;
+				}
+				auto handle = popen(command.c_str(), "re");
+				if (!handle)
+				{
+					std::cerr << "cannot get save from clipboard: popen: " << strerror(errno) << std::endl;
+					return std::nullopt;
+				}
+				constexpr auto blockSize = 0x10000;
+				std::vector<char> data;
+				auto bail = false;
+				while (true)
+				{
+					auto pos = data.size();
+					data.resize(pos + blockSize);
+					auto got = fread(&data[pos], 1, blockSize, handle);
+					if (got != blockSize)
+					{
+						if (ferror(handle))
+						{
+							std::cerr << "cannot get save from clipboard: fread: " << strerror(errno) << std::endl;
+							bail = true;
+							break;
+						}
+						if (feof(handle))
+						{
+							data.resize(data.size() - blockSize + got);
+							break;
+						}
+					}
+				}
+				auto status = pclose(handle);
+				if (bail)
+				{
+					return std::nullopt;
+				}
+				if (status == -1)
+				{
+					std::cerr << "cannot get save from clipboard: pclose: " << strerror(errno) << std::endl;
+					return std::nullopt;
+				}
+				if (status)
+				{
+					std::cerr << "cannot get save from clipboard: " << command << ": wait4 status code " << status << std::endl;
+					return std::nullopt;
+				}
+				return data;
+			};
+			auto preset = GetPreset();
+			if (!preset)
+			{
+				return GetClipboardDataUnknown{};
+			}
+			auto formatsOpt = getTarget(preset->formatsCommand);
+			if (!formatsOpt)
+			{
+				return GetClipboardDataUnknown{};
+			}
+			auto formats = ByteString(formatsOpt->begin(), formatsOpt->end()).PartitionBy('\n');
+			if (std::find(formats.begin(), formats.end(), clipboardFormatName) == formats.end())
+			{
+				std::cerr << "not getting save from clipboard: no data" << std::endl;
+				return GetClipboardDataFailed{};
+			}
+			auto saveDataOpt = getTarget(preset->outCommand);
+			if (!saveDataOpt)
+			{
+				return GetClipboardDataFailed{};
+			}
+			return GetClipboardDataChanged{ std::move(*saveDataOpt) };
+		}
+	};
+
+	std::unique_ptr<ClipboardImpl> ExternalClipboardFactory()
+	{
+		return std::make_unique<ExternalClipboardImpl>();
+	}
+}

src/common/clipboard/Null.cpp

@@ -0,0 +1,22 @@
+#include "Clipboard.h"
+#include "client/GameSave.h"
+
+namespace Clipboard
+{
+	void SetClipboardData(std::unique_ptr<GameSave> data)
+	{
+	}
+
+	const GameSave *GetClipboardData()
+	{
+		return nullptr;
+	}
+
+	void Init()
+	{
+	}
+
+	void RecreateWindow()
+	{
+	}
+}

src/common/clipboard/Windows.cpp

@@ -0,0 +1,226 @@
+#include "Dynamic.h"
+#include "Clipboard.h"
+#include "client/GameSave.h"
+#include "common/platform/Platform.h"
+#include "PowderToySDL.h"
+#include <SDL.h>
+#include <SDL_syswm.h>
+#include <iostream>
+#include <windows.h>
+
+namespace Clipboard
+{
+	class WindowsClipboardImpl : public ClipboardImpl
+	{
+		UINT saveClipboardFormat = 0;
+		HWND ourHwnd = NULL;
+		DWORD seqNumber = 0; // 0 is invalid
+
+		class ClipboardSession
+		{
+			bool open = false;
+
+		public:
+			ClipboardSession(HWND ourHwnd)
+			{
+				if (ourHwnd)
+				{
+					open = ::OpenClipboard(ourHwnd);
+				}
+			}
+
+			~ClipboardSession()
+			{
+				if (open)
+				{
+					::CloseClipboard();
+				}
+			}
+
+			explicit operator bool() const
+			{
+				return open;
+			}
+		};
+
+		void Transfer()
+		{
+			if (!saveClipboardFormat)
+			{
+				std::cerr << "cannot transfer save data: save clipboard format not registered" << std::endl;
+				return;
+			}
+			if (!clipboardData)
+			{
+				std::cerr << "cannot transfer save data: no data to transfer" << std::endl;
+				return;
+			}
+			std::vector<char> saveData;
+			SerializeClipboard(saveData);
+			auto handle = std::unique_ptr<void, decltype(&::GlobalFree)>(::GlobalAlloc(GMEM_MOVEABLE, saveData.size()), GlobalFree);
+			if (!handle)
+			{
+				std::cerr << "cannot transfer save data: GlobalAlloc failed: " << ::GetLastError() << std::endl;
+				return;
+			}
+			{
+				auto data = std::unique_ptr<void, decltype(&::GlobalUnlock)>(::GlobalLock(handle.get()), ::GlobalUnlock);
+				auto base = reinterpret_cast<char *>(data.get());
+				std::copy(saveData.begin(), saveData.end(), base);
+			}
+			if (!::SetClipboardData(saveClipboardFormat, handle.get()))
+			{
+				std::cerr << "cannot transfer save data: SetClipboardData failed: " << ::GetLastError() << std::endl;
+				return;
+			}
+			handle.release(); // windows owns it now
+			auto newSeqNumber = ::GetClipboardSequenceNumber();
+			if (newSeqNumber)
+			{
+				seqNumber = newSeqNumber;
+			}
+			std::cerr << "transferred save data" << std::endl;
+		}
+
+		static int TransferWatchWrapper(void *userdata, SDL_Event *event)
+		{
+			return reinterpret_cast<WindowsClipboardImpl *>(userdata)->TransferWatch(event);
+		}
+
+		int TransferWatch(SDL_Event *event)
+		{
+			// SDL documentation says we have to be very careful with what we do here because
+			// the callback can come from any random thread, and we indeed are: WM_RENDERFORMAT
+			// and WM_RENDERALLFORMATS are only posted to windows that have announced data on
+			// the clipboard, and only our main thread ever owns a window, so we don't touch
+			// the WindowsClipboardImpl outside of these events.
+			switch (event->type)
+			{
+			case SDL_SYSWMEVENT:
+				switch (event->syswm.msg->msg.win.msg)
+				{
+				case WM_RENDERFORMAT:
+					if (event->syswm.msg->msg.win.wParam == saveClipboardFormat)
+					{
+						Transfer(); 
+					}
+					break; 
+
+				case WM_RENDERALLFORMATS:
+					{
+						ClipboardSession cs(ourHwnd);
+						if (cs)
+						{
+							if (ourHwnd && ::GetClipboardOwner() == ourHwnd)
+							{
+								Transfer();
+							}
+						}
+						else
+						{
+							std::cerr << "cannot place save on clipboard: OpenClipboard failed: " << ::GetLastError() << std::endl;
+						}
+					}
+					break;
+				}
+				break;
+			}
+			return 0;
+		}
+
+	public:
+		WindowsClipboardImpl()
+		{
+			SDL_SysWMinfo info;
+			SDL_VERSION(&info.version);
+			SDL_GetWindowWMInfo(sdl_window, &info);
+			ourHwnd = info.info.win.window;
+			saveClipboardFormat = ::RegisterClipboardFormatW(Platform::WinWiden(clipboardFormatName).c_str());
+			if (!saveClipboardFormat)
+			{
+				std::cerr << "cannot register save clipboard format: RegisterClipboardFormatW failed: " << ::GetLastError() << std::endl;
+				return;
+			}
+			std::cerr << "save clipboard format registered" << std::endl;
+			SDL_EventState(SDL_SYSWMEVENT, SDL_ENABLE);
+			SDL_AddEventWatch(&WindowsClipboardImpl::TransferWatchWrapper, this);
+		}
+
+		~WindowsClipboardImpl()
+		{
+			SDL_DelEventWatch(&WindowsClipboardImpl::TransferWatchWrapper, this);
+			SDL_EventState(SDL_SYSWMEVENT, SDL_DISABLE);
+		}
+
+		void SetClipboardData() final override
+		{
+			if (!saveClipboardFormat)
+			{
+				std::cerr << "cannot announce save on clipboard: save clipboard format not registered" << std::endl;
+				return;
+			}
+			ClipboardSession cs(ourHwnd);
+			if (!cs)
+			{
+				std::cerr << "cannot announce save on clipboard: OpenClipboard failed: " << ::GetLastError() << std::endl;
+				return;
+			}
+			if (!::EmptyClipboard())
+			{
+				std::cerr << "cannot announce save on clipboard: EmptyClipboard failed: " << ::GetLastError() << std::endl;
+				return;
+			}
+			::SetClipboardData(saveClipboardFormat, NULL);
+			std::cerr << "announced save on clipboard" << std::endl;
+		}
+
+		GetClipboardDataResult GetClipboardData() final override
+		{
+			// Note that the data from the local clipboard is left alone if any error occurs so
+			// the local clipboard keeps working even in the worst case.
+			if (!saveClipboardFormat)
+			{
+				std::cerr << "cannot get save from clipboard: save clipboard format not registered" << std::endl;
+				return GetClipboardDataUnknown{};
+			}
+			ClipboardSession cs(ourHwnd);
+			if (!cs)
+			{
+				std::cerr << "cannot get save from clipboard: OpenClipboard failed: " << ::GetLastError() << std::endl;
+				return GetClipboardDataUnknown{};
+			}
+			auto newSeqNumber = ::GetClipboardSequenceNumber();
+			if (seqNumber && newSeqNumber && seqNumber == newSeqNumber)
+			{
+				std::cerr << "not getting save from clipboard, data unchanged" << std::endl;
+				return GetClipboardDataUnchanged{};
+			}
+			seqNumber = newSeqNumber;
+			if (!::IsClipboardFormatAvailable(saveClipboardFormat))
+			{
+				std::cerr << "not getting save from clipboard: no data" << std::endl;
+				return GetClipboardDataFailed{};
+			}
+			auto handle = ::GetClipboardData(saveClipboardFormat);
+			if (!handle)
+			{
+				std::cerr << "cannot get save from clipboard: GetClipboardData failed: " << ::GetLastError() << std::endl;
+				return GetClipboardDataFailed{};
+			}
+			auto size = ::GlobalSize(handle);
+			auto data = std::unique_ptr<void, decltype(&::GlobalUnlock)>(::GlobalLock(handle), ::GlobalUnlock);
+			if (!data)
+			{
+				std::cerr << "cannot get save from clipboard: GlobalLock failed: " << ::GetLastError() << std::endl;
+				return GetClipboardDataFailed{};
+			}
+			auto base = reinterpret_cast<const char *>(data.get());
+			return GetClipboardDataChanged{ std::vector<char>(base, base + size) };
+		}
+	};
+
+	std::unique_ptr<ClipboardImpl> WindowsClipboardFactory()
+	{
+		return std::make_unique<WindowsClipboardImpl>();
+	}
+}

src/common/clipboard/meson.build

@@ -0,0 +1,39 @@
+if get_option('platform_clipboard')
+	clipboard_impl_factories = []
+	if host_platform == 'windows'
+		powder_files += files('Windows.cpp')
+		clipboard_impl_factories += [
+			[ 'SDL_SYSWM_WINDOWS', 'WindowsClipboardFactory' ],
+		]
+	elif host_platform == 'darwin'
+		if get_option('build_powder')
+			add_languages('objcpp', native: false)
+			powder_deps += [
+				dependency('Cocoa'),
+			]
+		endif
+		powder_files += files([
+			'Cocoa.mm',
+		])
+		clipboard_impl_factories += [
+			[ 'SDL_SYSWM_COCOA', 'CocoaClipboardFactory' ],
+		]
+	elif host_platform == 'android'
+		# TODO
+	elif host_platform == 'emscripten'
+		# TODO
+	else
+		powder_files += files([
+			'External.cpp',
+		])
+		clipboard_impl_factories += [
+			[ 'SDL_SYSWM_X11', 'ExternalClipboardFactory' ],
+			[ 'SDL_SYSWM_WAYLAND', 'ExternalClipboardFactory' ],
+		]
+	endif
+	powder_files += files('Dynamic.cpp')
+else
+	powder_files += files('Null.cpp')
+endif
+render_files += files('Null.cpp')
+font_files += files('Null.cpp')

src/common/meson.build

@@ -4,4 +4,5 @@ common_files += files(
 	'tpt-thread-local.cpp',
 )
 
+subdir('clipboard')
 subdir('platform')

src/gui/game/GameModel.cpp

@@ -19,6 +19,7 @@
 #include "client/SaveInfo.h"
 #include "client/http/ExecVoteRequest.h"
 #include "common/platform/Platform.h"
+#include "common/clipboard/Clipboard.h"
 #include "graphics/Renderer.h"
 #include "simulation/Air.h"
 #include "simulation/GOLString.h"
@@ -1371,12 +1372,12 @@ void GameModel::TransformPlaceSave(Mat2<int> transform, Vec2<int> nudge)
 
 void GameModel::SetClipboard(std::unique_ptr<GameSave> save)
 {
-	clipboard = std::move(save);
+	Clipboard::SetClipboardData(std::move(save));
 }
 
 const GameSave *GameModel::GetClipboard() const
 {
-	return clipboard.get();
+	return Clipboard::GetClipboardData();
 }
 
 const GameSave *GameModel::GetTransformedPlaceSave() const

src/gui/game/GameModel.h

@@ -50,9 +50,6 @@ class GameModel
 
 private:
 	std::vector<Notification*> notifications;
-	//int clipboardSize;
-	//unsigned char * clipboardData;
-	std::unique_ptr<GameSave> clipboard;
 	std::unique_ptr<GameSave> placeSave;
 	std::unique_ptr<GameSave> transformedPlaceSave;
 	std::deque<String> consoleLog;

src/gui/game/GameView.cpp

@@ -1656,20 +1656,27 @@ void GameView::OnFileDrop(ByteString filename)
 		return;
 	}
 
-	auto saveFile = Client::Ref().LoadSaveFile(filename);
-	if (!saveFile)
-		return;
-	if (saveFile->GetError().length())
-	{
-		new ErrorMessage("Error loading save", "Dropped save file could not be loaded: " + saveFile->GetError());
-		return;
-	}
+
 	if (filename.EndsWith(".stm"))
 	{
+		auto saveFile = Client::Ref().GetStamp(filename);
+		if (!saveFile || !saveFile->GetGameSave())
+		{
+			new ErrorMessage("Error loading stamp", "Dropped stamp could not be loaded: " + saveFile->GetError());
+			return;
+		}
 		c->LoadStamp(saveFile->TakeGameSave());
 	}
 	else
 	{
+		auto saveFile = Client::Ref().LoadSaveFile(filename);
+		if (!saveFile)
+			return;
+		if (saveFile->GetError().length())
+		{
+			new ErrorMessage("Error loading save", "Dropped save file could not be loaded: " + saveFile->GetError());
+			return;
+		}
 		c->LoadSaveFile(std::move(saveFile));
 	}
 

src/meson.build

@@ -176,6 +176,18 @@ configure_file(
 	configuration: elements_conf_data
 )
 
+clipboard_impl_defs = []
+foreach impl_subsys_factory : clipboard_impl_factories
+	clipboard_impl_defs += 'IMPL_DEFINE(' + impl_subsys_factory[0] + ', ' + impl_subsys_factory[1] + ')'
+endforeach
+clipboard_impls_data = configuration_data()
+clipboard_impls_data.set('impl_defs', '\n'.join(clipboard_impl_defs))
+configure_file(
+	input: 'common/clipboard/ClipboardImpls.template.h',
+	output: 'ClipboardImpls.h',
+	configuration: clipboard_impls_data
+)
+
 simulation_tool_defs = []
 foreach tool_name_id : simulation_tool_ids
 	simulation_tool_defs += 'TOOL_DEFINE(' + tool_name_id[0] + ', ' + tool_name_id[1].to_string() + ');'

src/prefs/Prefs.h

@@ -1,6 +1,7 @@
 #pragma once
 #include "common/String.h"
 #include <json/json.h>
+#include <optional>
 
 class Prefs
 {
@@ -35,7 +36,7 @@ public:
 	Prefs(ByteString path);
 
 	template<class Type>
-	Type Get(ByteString path, Type defaultValue) const
+	std::optional<Type> Get(ByteString path) const
 	{
 		auto value = GetJson(root, path);
 		if (value != Json::nullValue)
@@ -48,6 +49,17 @@ public:
 			{
 			}
 		}
+		return std::nullopt;
+	}
+
+	template<class Type>
+	Type Get(ByteString path, Type defaultValue) const
+	{
+		auto value = Get<Type>(path);
+		if (value)
+		{
+			return *value;
+		}
 		return defaultValue;
 	}