cleaner backend

Firmware/sdk/CMakeLists.txt

@@ -5,7 +5,25 @@ set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED YES)
 set(CMAKE_CXX_EXTENSIONS NO)
 
-add_library(cardboy_backend INTERFACE)
+add_subdirectory(backend_interface)
+
+set(CARDBOY_SDK_BACKEND_LIBRARY "" CACHE STRING "Backend implementation library for Cardboy SDK")
+set(_cardboy_backend_default "${CARDBOY_SDK_BACKEND_LIBRARY}")
+
+option(CARDBOY_BUILD_SFML "Build desktop SFML backend and launcher" ON)
+
+if (CARDBOY_BUILD_SFML)
+    add_subdirectory(backends/desktop)
+    if (DEFINED CARDBOY_DESKTOP_BACKEND_TARGET AND NOT CARDBOY_DESKTOP_BACKEND_TARGET STREQUAL "")
+        set(_cardboy_backend_default "${CARDBOY_DESKTOP_BACKEND_TARGET}")
+    endif ()
+endif ()
+
+if (_cardboy_backend_default STREQUAL "")
+    message(FATAL_ERROR "CARDBOY_SDK_BACKEND_LIBRARY is not set. Provide a backend implementation library or enable one of the available backends.")
+endif ()
+
+set(CARDBOY_SDK_BACKEND_LIBRARY "${_cardboy_backend_default}" CACHE STRING "Backend implementation library for Cardboy SDK" FORCE)
 
 add_library(cardboy_sdk STATIC
         src/app_system.cpp
@@ -17,67 +35,15 @@ target_include_directories(cardboy_sdk
 )
 
 target_compile_features(cardboy_sdk PUBLIC cxx_std_20)
-target_link_libraries(cardboy_sdk PUBLIC cardboy_backend)
 
-add_library(cardboy_apps STATIC
+target_link_libraries(cardboy_sdk
-        apps/menu_app.cpp
-        apps/clock_app.cpp
-        apps/tetris_app.cpp
-        apps/gameboy_app.cpp
-)
-
-target_include_directories(cardboy_apps
         PUBLIC
-        ${CMAKE_CURRENT_SOURCE_DIR}/include
+        cardboy_backend_interface
+        ${CARDBOY_SDK_BACKEND_LIBRARY}
 )
 
-target_link_libraries(cardboy_apps
+add_subdirectory(apps)
-        PUBLIC
-        cardboy_sdk
-        cardboy_backend
-)
-
-target_compile_features(cardboy_apps PUBLIC cxx_std_20)
-
-option(CARDBOY_BUILD_SFML "Build SFML harness" OFF)
 
 if (CARDBOY_BUILD_SFML)
-    include(FetchContent)
+    add_subdirectory(launchers/desktop)
-
-    set(SFML_BUILD_AUDIO OFF CACHE BOOL "Disable SFML audio module" FORCE)
-    set(SFML_BUILD_NETWORK OFF CACHE BOOL "Disable SFML network module" FORCE)
-    set(SFML_BUILD_EXAMPLES OFF CACHE BOOL "Disable SFML examples" FORCE)
-    set(SFML_BUILD_TESTS OFF CACHE BOOL "Disable SFML tests" FORCE)
-    set(SFML_USE_SYSTEM_DEPS OFF CACHE BOOL "Use bundled SFML dependencies" FORCE)
-
-    FetchContent_Declare(
-            SFML
-            GIT_REPOSITORY https://github.com/SFML/SFML.git
-            GIT_TAG        3.0.2
-            GIT_SHALLOW    ON
-    )
-    FetchContent_MakeAvailable(SFML)
-
-    target_include_directories(cardboy_backend
-            INTERFACE
-            ${CMAKE_CURRENT_SOURCE_DIR}/hosts/include
-    )
-
-    target_link_libraries(cardboy_backend
-            INTERFACE
-            SFML::Window
-            SFML::Graphics
-            SFML::System
-    )
-    add_executable(cardboy_desktop
-            hosts/sfml_main.cpp
-    )
-
-    target_link_libraries(cardboy_desktop
-            PRIVATE
-            cardboy_apps
-            cardboy_sdk
-    )
-
-    target_compile_features(cardboy_desktop PRIVATE cxx_std_20)
 endif ()

Firmware/sdk/apps/CMakeLists.txt

@@ -0,0 +1,18 @@
+add_library(cardboy_apps STATIC)
+
+set_target_properties(cardboy_apps PROPERTIES
+        EXPORT_NAME apps
+)
+
+target_link_libraries(cardboy_apps
+        PUBLIC
+        cardboy_sdk
+        ${CARDBOY_SDK_BACKEND_LIBRARY}
+)
+
+target_compile_features(cardboy_apps PUBLIC cxx_std_20)
+
+add_subdirectory(menu)
+add_subdirectory(clock)
+add_subdirectory(gameboy)
+add_subdirectory(tetris)

Firmware/sdk/apps/clock/CMakeLists.txt

@@ -0,0 +1,9 @@
+target_sources(cardboy_apps
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/clock_app.cpp
+)
+
+target_include_directories(cardboy_apps
+        PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+)

Firmware/sdk/apps/gameboy/CMakeLists.txt

@@ -0,0 +1,10 @@
+target_sources(cardboy_apps
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/gameboy_app.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/apps/peanut_gb.h
+)
+
+target_include_directories(cardboy_apps
+        PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+)

Firmware/sdk/apps/menu/CMakeLists.txt

@@ -0,0 +1,9 @@
+target_sources(cardboy_apps
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/menu_app.cpp
+)
+
+target_include_directories(cardboy_apps
+        PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+)

Firmware/sdk/apps/tetris/CMakeLists.txt

@@ -0,0 +1,9 @@
+target_sources(cardboy_apps
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/src/tetris_app.cpp
+)
+
+target_include_directories(cardboy_apps
+        PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+)

Firmware/sdk/backend_interface/CMakeLists.txt

@@ -0,0 +1,15 @@
+add_library(cardboy_backend_interface INTERFACE)
+
+set_target_properties(cardboy_backend_interface PROPERTIES
+        EXPORT_NAME backend_interface
+)
+
+target_include_directories(cardboy_backend_interface
+        INTERFACE
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+)
+
+target_sources(cardboy_backend_interface
+        INTERFACE
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/backend/backend_interface.hpp
+)

Firmware/sdk/backend_interface/include/cardboy/backend/backend_interface.hpp

@@ -0,0 +1,14 @@
+#pragma once
+
+#include <concepts>
+
+namespace cardboy::backend {
+
+template<typename Backend>
+concept BackendInterface = requires {
+    typename Backend::Framebuffer;
+    typename Backend::Input;
+    typename Backend::Clock;
+};
+
+} // namespace cardboy::backend

Firmware/sdk/backends/desktop/CMakeLists.txt

@@ -0,0 +1,40 @@
+include(FetchContent)
+
+set(SFML_BUILD_AUDIO OFF CACHE BOOL "Disable SFML audio module" FORCE)
+set(SFML_BUILD_NETWORK OFF CACHE BOOL "Disable SFML network module" FORCE)
+set(SFML_BUILD_EXAMPLES OFF CACHE BOOL "Disable SFML examples" FORCE)
+set(SFML_BUILD_TESTS OFF CACHE BOOL "Disable SFML tests" FORCE)
+set(SFML_USE_SYSTEM_DEPS OFF CACHE BOOL "Use bundled SFML dependencies" FORCE)
+
+FetchContent_Declare(
+        SFML
+        GIT_REPOSITORY https://github.com/SFML/SFML.git
+        GIT_TAG        3.0.2
+        GIT_SHALLOW    ON
+)
+FetchContent_MakeAvailable(SFML)
+
+add_library(cardboy_backend_desktop STATIC
+        src/desktop_backend.cpp
+)
+
+set_target_properties(cardboy_backend_desktop PROPERTIES
+        EXPORT_NAME backend_desktop
+)
+
+target_include_directories(cardboy_backend_desktop
+        PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/../../include
+)
+
+target_link_libraries(cardboy_backend_desktop
+        PUBLIC
+        cardboy_backend_interface
+        SFML::Window
+        SFML::Graphics
+        SFML::System
+)
+
+set(CARDBOY_DESKTOP_BACKEND_TARGET cardboy_backend_desktop PARENT_SCOPE)

Firmware/sdk/backends/desktop/include/cardboy/backend/backend_impl.hpp

@@ -5,4 +5,3 @@
 namespace cardboy::backend {
 using ActiveBackend = DesktopBackend;
 }
-

Firmware/sdk/backends/desktop/include/cardboy/backend/desktop_backend.hpp

@@ -0,0 +1,186 @@
+#pragma once
+
+#include "cardboy/sdk/platform.hpp"
+#include "cardboy/sdk/services.hpp"
+
+#include <SFML/Graphics.hpp>
+#include <SFML/Window/Keyboard.hpp>
+#include <chrono>
+#include <cstdint>
+#include <filesystem>
+#include <limits>
+#include <random>
+#include <string>
+#include <string_view>
+#include <thread>
+#include <unordered_map>
+#include <vector>
+
+namespace cardboy::backend::desktop {
+
+constexpr int kPixelScale = 2;
+
+class DesktopRuntime;
+
+class DesktopBuzzer final : public cardboy::sdk::IBuzzer {
+public:
+    void tone(std::uint32_t, std::uint32_t, std::uint32_t) override {}
+    void beepRotate() override {}
+    void beepMove() override {}
+    void beepLock() override {}
+    void beepLines(int) override {}
+    void beepLevelUp(int) override {}
+    void beepGameOver() override {}
+};
+
+class DesktopBattery final : public cardboy::sdk::IBatteryMonitor {
+public:
+    [[nodiscard]] bool hasData() const override { return false; }
+};
+
+class DesktopStorage final : public cardboy::sdk::IStorage {
+public:
+    [[nodiscard]] bool readUint32(std::string_view ns, std::string_view key, std::uint32_t& out) override;
+    void               writeUint32(std::string_view ns, std::string_view key, std::uint32_t value) override;
+
+private:
+    std::unordered_map<std::string, std::uint32_t> data;
+
+    static std::string composeKey(std::string_view ns, std::string_view key);
+};
+
+class DesktopRandom final : public cardboy::sdk::IRandom {
+public:
+    DesktopRandom();
+
+    [[nodiscard]] std::uint32_t nextUint32() override;
+
+private:
+    std::mt19937                                 rng;
+    std::uniform_int_distribution<std::uint32_t> dist;
+};
+
+class DesktopHighResClock final : public cardboy::sdk::IHighResClock {
+public:
+    DesktopHighResClock();
+
+    [[nodiscard]] std::uint64_t micros() override;
+
+private:
+    const std::chrono::steady_clock::time_point start;
+};
+
+class DesktopPowerManager final : public cardboy::sdk::IPowerManager {
+public:
+    void               setSlowMode(bool enable) override { slowMode = enable; }
+    [[nodiscard]] bool isSlowMode() const override { return slowMode; }
+
+private:
+    bool slowMode = false;
+};
+
+class DesktopFilesystem final : public cardboy::sdk::IFilesystem {
+public:
+    DesktopFilesystem();
+
+    bool                      mount() override;
+    [[nodiscard]] bool        isMounted() const override { return mounted; }
+    [[nodiscard]] std::string basePath() const override { return basePathPath.string(); }
+
+private:
+    std::filesystem::path basePathPath;
+    bool                  mounted = false;
+};
+
+class DesktopFramebuffer final : public cardboy::sdk::FramebufferFacade<DesktopFramebuffer> {
+public:
+    explicit DesktopFramebuffer(DesktopRuntime& runtime);
+
+    [[nodiscard]] int  width_impl() const;
+    [[nodiscard]] int  height_impl() const;
+    void               drawPixel_impl(int x, int y, bool on);
+    void               clear_impl(bool on);
+    void               frameReady_impl();
+    void               sendFrame_impl(bool clearAfterSend);
+    [[nodiscard]] bool frameInFlight_impl() const { return false; }
+
+private:
+    DesktopRuntime& runtime;
+};
+
+class DesktopInput final : public cardboy::sdk::InputFacade<DesktopInput> {
+public:
+    explicit DesktopInput(DesktopRuntime& runtime);
+
+    cardboy::sdk::InputState readState_impl();
+    void                     handleKey(sf::Keyboard::Key key, bool pressed);
+
+private:
+    DesktopRuntime&          runtime;
+    cardboy::sdk::InputState state{};
+};
+
+class DesktopClock final : public cardboy::sdk::ClockFacade<DesktopClock> {
+public:
+    explicit DesktopClock(DesktopRuntime& runtime);
+
+    std::uint32_t millis_impl();
+    void          sleep_ms_impl(std::uint32_t ms);
+
+private:
+    DesktopRuntime&                             runtime;
+    const std::chrono::steady_clock::time_point start;
+};
+
+class DesktopRuntime {
+public:
+    DesktopRuntime();
+
+    cardboy::sdk::Services& serviceRegistry();
+    void                    processEvents();
+    void                    presentIfNeeded();
+    void                    sleepFor(std::uint32_t ms);
+
+    [[nodiscard]] bool isRunning() const { return running; }
+
+    DesktopFramebuffer framebuffer;
+    DesktopInput       input;
+    DesktopClock       clock;
+
+private:
+    friend class DesktopFramebuffer;
+    friend class DesktopInput;
+    friend class DesktopClock;
+
+    void setPixel(int x, int y, bool on);
+    void clearPixels(bool on);
+
+    sf::RenderWindow          window;
+    sf::Texture               texture;
+    sf::Sprite                sprite;
+    std::vector<std::uint8_t> pixels;
+    bool                      dirty          = true;
+    bool                      running        = true;
+    bool                      clearNextFrame = true;
+
+    DesktopBuzzer          buzzerService;
+    DesktopBattery         batteryService;
+    DesktopStorage         storageService;
+    DesktopRandom          randomService;
+    DesktopHighResClock    highResService;
+    DesktopPowerManager    powerService;
+    DesktopFilesystem      filesystemService;
+    cardboy::sdk::Services services{};
+};
+
+struct Backend {
+    using Framebuffer = DesktopFramebuffer;
+    using Input       = DesktopInput;
+    using Clock       = DesktopClock;
+};
+
+} // namespace cardboy::backend::desktop
+
+namespace cardboy::backend {
+using DesktopBackend = desktop::Backend;
+} // namespace cardboy::backend

Firmware/sdk/backends/desktop/src/desktop_backend.cpp

@@ -0,0 +1,235 @@
+#include "cardboy/backend/desktop_backend.hpp"
+
+#include "cardboy/sdk/display_spec.hpp"
+
+#include <SFML/Graphics.hpp>
+#include <SFML/Window.hpp>
+
+#include <algorithm>
+#include <chrono>
+#include <cstdlib>
+#include <stdexcept>
+#include <system_error>
+
+namespace cardboy::backend::desktop {
+
+bool DesktopStorage::readUint32(std::string_view ns, std::string_view key, std::uint32_t& out) {
+    auto it = data.find(composeKey(ns, key));
+    if (it == data.end())
+        return false;
+    out = it->second;
+    return true;
+}
+
+void DesktopStorage::writeUint32(std::string_view ns, std::string_view key, std::uint32_t value) {
+    data[composeKey(ns, key)] = value;
+}
+
+std::string DesktopStorage::composeKey(std::string_view ns, std::string_view key) {
+    std::string result;
+    result.reserve(ns.size() + key.size() + 1);
+    result.append(ns.begin(), ns.end());
+    result.push_back(':');
+    result.append(key.begin(), key.end());
+    return result;
+}
+
+DesktopRandom::DesktopRandom() : rng(std::random_device{}()), dist(0u, std::numeric_limits<std::uint32_t>::max()) {}
+
+std::uint32_t DesktopRandom::nextUint32() { return dist(rng); }
+
+DesktopHighResClock::DesktopHighResClock() : start(std::chrono::steady_clock::now()) {}
+
+std::uint64_t DesktopHighResClock::micros() {
+    const auto now = std::chrono::steady_clock::now();
+    return static_cast<std::uint64_t>(std::chrono::duration_cast<std::chrono::microseconds>(now - start).count());
+}
+
+DesktopFilesystem::DesktopFilesystem() {
+    if (const char* env = std::getenv("CARDBOY_ROM_DIR"); env && *env) {
+        basePathPath = std::filesystem::path(env);
+    } else {
+        basePathPath = std::filesystem::current_path() / "roms";
+    }
+}
+
+bool DesktopFilesystem::mount() {
+    std::error_code ec;
+    if (std::filesystem::exists(basePathPath, ec)) {
+        mounted = std::filesystem::is_directory(basePathPath, ec);
+    } else {
+        mounted = std::filesystem::create_directories(basePathPath, ec);
+    }
+    return mounted;
+}
+
+DesktopFramebuffer::DesktopFramebuffer(DesktopRuntime& runtime) : runtime(runtime) {}
+
+int DesktopFramebuffer::width_impl() const { return cardboy::sdk::kDisplayWidth; }
+
+int DesktopFramebuffer::height_impl() const { return cardboy::sdk::kDisplayHeight; }
+
+void DesktopFramebuffer::drawPixel_impl(int x, int y, bool on) { runtime.setPixel(x, y, on); }
+
+void DesktopFramebuffer::clear_impl(bool on) { runtime.clearPixels(on); }
+
+void DesktopFramebuffer::frameReady_impl() {
+    if (runtime.clearNextFrame) {
+        runtime.clearPixels(false);
+        runtime.clearNextFrame = false;
+    }
+}
+
+void DesktopFramebuffer::sendFrame_impl(bool clearAfterSend) {
+    runtime.clearNextFrame = clearAfterSend;
+    runtime.dirty          = true;
+}
+
+DesktopInput::DesktopInput(DesktopRuntime& runtime) : runtime(runtime) {}
+
+cardboy::sdk::InputState DesktopInput::readState_impl() { return state; }
+
+void DesktopInput::handleKey(sf::Keyboard::Key key, bool pressed) {
+    switch (key) {
+        case sf::Keyboard::Key::Up:
+            state.up = pressed;
+            break;
+        case sf::Keyboard::Key::Down:
+            state.down = pressed;
+            break;
+        case sf::Keyboard::Key::Left:
+            state.left = pressed;
+            break;
+        case sf::Keyboard::Key::Right:
+            state.right = pressed;
+            break;
+        case sf::Keyboard::Key::Z:
+        case sf::Keyboard::Key::A:
+            state.a = pressed;
+            break;
+        case sf::Keyboard::Key::X:
+        case sf::Keyboard::Key::S:
+            state.b = pressed;
+            break;
+        case sf::Keyboard::Key::Space:
+            state.select = pressed;
+            break;
+        case sf::Keyboard::Key::Enter:
+            state.start = pressed;
+            break;
+        default:
+            break;
+    }
+}
+
+DesktopClock::DesktopClock(DesktopRuntime& runtime) : runtime(runtime), start(std::chrono::steady_clock::now()) {}
+
+std::uint32_t DesktopClock::millis_impl() {
+    const auto now = std::chrono::steady_clock::now();
+    return static_cast<std::uint32_t>(std::chrono::duration_cast<std::chrono::milliseconds>(now - start).count());
+}
+
+void DesktopClock::sleep_ms_impl(std::uint32_t ms) { runtime.sleepFor(ms); }
+
+DesktopRuntime::DesktopRuntime() :
+    window(sf::VideoMode(
+                   sf::Vector2u{cardboy::sdk::kDisplayWidth * kPixelScale, cardboy::sdk::kDisplayHeight * kPixelScale}),
+           "Cardboy Desktop"),
+    texture(), sprite(texture),
+    pixels(static_cast<std::size_t>(cardboy::sdk::kDisplayWidth * cardboy::sdk::kDisplayHeight) * 4, 0),
+    framebuffer(*this), input(*this), clock(*this) {
+    window.setFramerateLimit(60);
+    if (!texture.resize(sf::Vector2u{cardboy::sdk::kDisplayWidth, cardboy::sdk::kDisplayHeight}))
+        throw std::runtime_error("Failed to allocate texture for desktop framebuffer");
+    sprite.setTexture(texture, true);
+    sprite.setScale(sf::Vector2f{static_cast<float>(kPixelScale), static_cast<float>(kPixelScale)});
+    clearPixels(false);
+    presentIfNeeded();
+
+    services.buzzer       = &buzzerService;
+    services.battery      = &batteryService;
+    services.storage      = &storageService;
+    services.random       = &randomService;
+    services.highResClock = &highResService;
+    services.powerManager = &powerService;
+    services.filesystem   = &filesystemService;
+}
+
+cardboy::sdk::Services& DesktopRuntime::serviceRegistry() { return services; }
+
+void DesktopRuntime::setPixel(int x, int y, bool on) {
+    if (x < 0 || y < 0 || x >= cardboy::sdk::kDisplayWidth || y >= cardboy::sdk::kDisplayHeight)
+        return;
+    const std::size_t  idx   = static_cast<std::size_t>(y * cardboy::sdk::kDisplayWidth + x) * 4;
+    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
+    pixels[idx + 0]          = value;
+    pixels[idx + 1]          = value;
+    pixels[idx + 2]          = value;
+    pixels[idx + 3]          = 255;
+    dirty                    = true;
+}
+
+void DesktopRuntime::clearPixels(bool on) {
+    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
+    for (std::size_t i = 0; i < pixels.size(); i += 4) {
+        pixels[i + 0] = value;
+        pixels[i + 1] = value;
+        pixels[i + 2] = value;
+        pixels[i + 3] = 255;
+    }
+    dirty = true;
+}
+
+void DesktopRuntime::processEvents() {
+    while (auto eventOpt = window.pollEvent()) {
+        const sf::Event& event = *eventOpt;
+
+        if (event.is<sf::Event::Closed>()) {
+            running = false;
+            window.close();
+            continue;
+        }
+
+        if (const auto* keyPressed = event.getIf<sf::Event::KeyPressed>()) {
+            input.handleKey(keyPressed->code, true);
+            continue;
+        }
+
+        if (const auto* keyReleased = event.getIf<sf::Event::KeyReleased>()) {
+            input.handleKey(keyReleased->code, false);
+            continue;
+        }
+    }
+}
+
+void DesktopRuntime::presentIfNeeded() {
+    if (!dirty)
+        return;
+    texture.update(pixels.data());
+    window.clear(sf::Color::Black);
+    window.draw(sprite);
+    window.display();
+    dirty = false;
+}
+
+void DesktopRuntime::sleepFor(std::uint32_t ms) {
+    const auto target = std::chrono::steady_clock::now() + std::chrono::milliseconds(ms);
+    do {
+        processEvents();
+        presentIfNeeded();
+        if (!running)
+            std::exit(0);
+        if (ms == 0)
+            return;
+        const auto now = std::chrono::steady_clock::now();
+        if (now >= target)
+            return;
+        const auto remaining = std::chrono::duration_cast<std::chrono::milliseconds>(target - now);
+        if (remaining.count() > 2)
+            std::this_thread::sleep_for(std::min<std::chrono::milliseconds>(remaining, std::chrono::milliseconds(8)));
+        else
+            std::this_thread::yield();
+    } while (true);
+}
+
+} // namespace cardboy::backend::desktop

Firmware/sdk/hosts/include/cardboy/backend/desktop_backend.hpp

@@ -1,15 +1,97 @@
 #pragma once
 
 #include "cardboy/sdk/platform.hpp"
+#include "cardboy/sdk/services.hpp"
 
+#include <SFML/Graphics.hpp>
 #include <SFML/Window/Keyboard.hpp>
 #include <chrono>
 #include <cstdint>
+#include <filesystem>
+#include <limits>
+#include <random>
+#include <string>
+#include <string_view>
+#include <thread>
+#include <unordered_map>
+#include <vector>
 
 namespace cardboy::backend::desktop {
 
+constexpr int kPixelScale = 2;
+
 class DesktopRuntime;
 
+class DesktopBuzzer final : public cardboy::sdk::IBuzzer {
+public:
+    void tone(std::uint32_t, std::uint32_t, std::uint32_t) override {}
+    void beepRotate() override {}
+    void beepMove() override {}
+    void beepLock() override {}
+    void beepLines(int) override {}
+    void beepLevelUp(int) override {}
+    void beepGameOver() override {}
+};
+
+class DesktopBattery final : public cardboy::sdk::IBatteryMonitor {
+public:
+    [[nodiscard]] bool hasData() const override { return false; }
+};
+
+class DesktopStorage final : public cardboy::sdk::IStorage {
+public:
+    [[nodiscard]] bool readUint32(std::string_view ns, std::string_view key, std::uint32_t& out) override;
+    void               writeUint32(std::string_view ns, std::string_view key, std::uint32_t value) override;
+
+private:
+    std::unordered_map<std::string, std::uint32_t> data;
+
+    static std::string composeKey(std::string_view ns, std::string_view key);
+};
+
+class DesktopRandom final : public cardboy::sdk::IRandom {
+public:
+    DesktopRandom();
+
+    [[nodiscard]] std::uint32_t nextUint32() override;
+
+private:
+    std::mt19937                                 rng;
+    std::uniform_int_distribution<std::uint32_t> dist;
+};
+
+class DesktopHighResClock final : public cardboy::sdk::IHighResClock {
+public:
+    DesktopHighResClock();
+
+    [[nodiscard]] std::uint64_t micros() override;
+
+private:
+    const std::chrono::steady_clock::time_point start;
+};
+
+class DesktopPowerManager final : public cardboy::sdk::IPowerManager {
+public:
+    void               setSlowMode(bool enable) override { slowMode = enable; }
+    [[nodiscard]] bool isSlowMode() const override { return slowMode; }
+
+private:
+    bool slowMode = false;
+};
+
+class DesktopFilesystem final : public cardboy::sdk::IFilesystem {
+public:
+    DesktopFilesystem();
+
+    bool                      mount() override;
+    [[nodiscard]] bool        isMounted() const override { return mounted; }
+    [[nodiscard]] std::string basePath() const override { return basePathPath.string(); }
+
+private:
+    std::filesystem::path basePathPath;
+    bool                  mounted = false;
+};
+
 class DesktopFramebuffer final : public cardboy::sdk::FramebufferFacade<DesktopFramebuffer> {
 public:
     explicit DesktopFramebuffer(DesktopRuntime& runtime);
@@ -50,6 +132,47 @@ private:
     const std::chrono::steady_clock::time_point start;
 };
 
+class DesktopRuntime {
+public:
+    DesktopRuntime();
+
+    cardboy::sdk::Services& serviceRegistry();
+    void                    processEvents();
+    void                    presentIfNeeded();
+    void                    sleepFor(std::uint32_t ms);
+
+    [[nodiscard]] bool isRunning() const { return running; }
+
+    DesktopFramebuffer framebuffer;
+    DesktopInput       input;
+    DesktopClock       clock;
+
+private:
+    friend class DesktopFramebuffer;
+    friend class DesktopInput;
+    friend class DesktopClock;
+
+    void setPixel(int x, int y, bool on);
+    void clearPixels(bool on);
+
+    sf::RenderWindow          window;
+    sf::Texture               texture;
+    sf::Sprite                sprite;
+    std::vector<std::uint8_t> pixels;
+    bool                      dirty          = true;
+    bool                      running        = true;
+    bool                      clearNextFrame = true;
+
+    DesktopBuzzer          buzzerService;
+    DesktopBattery         batteryService;
+    DesktopStorage         storageService;
+    DesktopRandom          randomService;
+    DesktopHighResClock    highResService;
+    DesktopPowerManager    powerService;
+    DesktopFilesystem      filesystemService;
+    cardboy::sdk::Services services{};
+};
+
 struct Backend {
     using Framebuffer = DesktopFramebuffer;
     using Input       = DesktopInput;

Firmware/sdk/hosts/sfml_main.cpp

@@ -4,354 +4,9 @@
 #include "cardboy/apps/tetris_app.hpp"
 #include "cardboy/backend/desktop_backend.hpp"
 #include "cardboy/sdk/app_system.hpp"
-#include "cardboy/sdk/display_spec.hpp"
-#include "cardboy/sdk/services.hpp"
 
-#include <SFML/Graphics.hpp>
-#include <SFML/Window.hpp>
-
-#include <algorithm>
-#include <chrono>
 #include <cstdio>
-#include <cstdint>
-#include <cstdlib>
 #include <exception>
-#include <filesystem>
-#include <limits>
-#include <optional>
-#include <random>
-#include <stdexcept>
-#include <string>
-#include <string_view>
-#include <thread>
-#include <unordered_map>
-#include <vector>
-
-namespace cardboy::backend::desktop {
-
-constexpr int kPixelScale = 2;
-
-class DesktopBuzzer final : public cardboy::sdk::IBuzzer {
-public:
-    void tone(std::uint32_t, std::uint32_t, std::uint32_t) override {}
-    void beepRotate() override {}
-    void beepMove() override {}
-    void beepLock() override {}
-    void beepLines(int) override {}
-    void beepLevelUp(int) override {}
-    void beepGameOver() override {}
-};
-
-class DesktopBattery final : public cardboy::sdk::IBatteryMonitor {
-public:
-    [[nodiscard]] bool hasData() const override { return false; }
-};
-
-class DesktopStorage final : public cardboy::sdk::IStorage {
-public:
-    [[nodiscard]] bool readUint32(std::string_view ns, std::string_view key, std::uint32_t& out) override {
-        auto it = data.find(composeKey(ns, key));
-        if (it == data.end())
-            return false;
-        out = it->second;
-        return true;
-    }
-
-    void writeUint32(std::string_view ns, std::string_view key, std::uint32_t value) override {
-        data[composeKey(ns, key)] = value;
-    }
-
-private:
-    std::unordered_map<std::string, std::uint32_t> data;
-
-    static std::string composeKey(std::string_view ns, std::string_view key) {
-        std::string result;
-        result.reserve(ns.size() + key.size() + 1);
-        result.append(ns.begin(), ns.end());
-        result.push_back(':');
-        result.append(key.begin(), key.end());
-        return result;
-    }
-};
-
-class DesktopRandom final : public cardboy::sdk::IRandom {
-public:
-    DesktopRandom() : rng(std::random_device{}()), dist(0u, std::numeric_limits<std::uint32_t>::max()) {}
-
-    [[nodiscard]] std::uint32_t nextUint32() override { return dist(rng); }
-
-private:
-    std::mt19937                               rng;
-    std::uniform_int_distribution<std::uint32_t> dist;
-};
-
-class DesktopHighResClock final : public cardboy::sdk::IHighResClock {
-public:
-    DesktopHighResClock() : start(std::chrono::steady_clock::now()) {}
-
-    [[nodiscard]] std::uint64_t micros() override {
-        const auto now = std::chrono::steady_clock::now();
-        return static_cast<std::uint64_t>(
-                std::chrono::duration_cast<std::chrono::microseconds>(now - start).count());
-    }
-
-private:
-    const std::chrono::steady_clock::time_point start;
-};
-
-class DesktopPowerManager final : public cardboy::sdk::IPowerManager {
-public:
-    void setSlowMode(bool enable) override { slowMode = enable; }
-    [[nodiscard]] bool isSlowMode() const override { return slowMode; }
-
-private:
-    bool slowMode = false;
-};
-
-class DesktopFilesystem final : public cardboy::sdk::IFilesystem {
-public:
-    DesktopFilesystem() {
-        if (const char* env = std::getenv("CARDBOY_ROM_DIR"); env && *env) {
-            basePathPath = std::filesystem::path(env);
-        } else {
-            basePathPath = std::filesystem::current_path() / "roms";
-        }
-    }
-
-    bool mount() override {
-        std::error_code ec;
-        if (std::filesystem::exists(basePathPath, ec)) {
-            mounted = std::filesystem::is_directory(basePathPath, ec);
-        } else {
-            mounted = std::filesystem::create_directories(basePathPath, ec);
-        }
-        return mounted;
-    }
-
-    [[nodiscard]] bool isMounted() const override { return mounted; }
-    [[nodiscard]] std::string basePath() const override { return basePathPath.string(); }
-
-private:
-    std::filesystem::path basePathPath;
-    bool                  mounted = false;
-};
-
-class DesktopRuntime {
-private:
-    friend class DesktopFramebuffer;
-    friend class DesktopInput;
-    friend class DesktopClock;
-
-    sf::RenderWindow            window;
-    sf::Texture                 texture;
-    sf::Sprite                  sprite;
-    std::vector<std::uint8_t>   pixels; // RGBA buffer
-    bool                        dirty         = true;
-    bool                        running       = true;
-    bool                        clearNextFrame = true;
-
-    DesktopBuzzer        buzzerService;
-    DesktopBattery       batteryService;
-    DesktopStorage       storageService;
-    DesktopRandom        randomService;
-    DesktopHighResClock  highResService;
-    DesktopPowerManager  powerService;
-    DesktopFilesystem    filesystemService;
-    cardboy::sdk::Services services{};
-
-public:
-    DesktopRuntime();
-
-    DesktopFramebuffer framebuffer;
-    DesktopInput       input;
-    DesktopClock       clock;
-
-    cardboy::sdk::Services& serviceRegistry() { return services; }
-
-    void processEvents();
-    void presentIfNeeded();
-    void sleepFor(std::uint32_t ms);
-
-    [[nodiscard]] bool isRunning() const { return running; }
-
-private:
-    void setPixel(int x, int y, bool on);
-    void clearPixels(bool on);
-};
-
-DesktopRuntime::DesktopRuntime()
-    : window(sf::VideoMode(sf::Vector2u{cardboy::sdk::kDisplayWidth * kPixelScale,
-                                        cardboy::sdk::kDisplayHeight * kPixelScale}),
-             "Cardboy Desktop"),
-      texture(),
-      sprite(texture),
-      pixels(static_cast<std::size_t>(cardboy::sdk::kDisplayWidth * cardboy::sdk::kDisplayHeight) * 4, 0),
-      framebuffer(*this),
-      input(*this),
-      clock(*this) {
-    window.setFramerateLimit(60);
-    if (!texture.resize(sf::Vector2u{cardboy::sdk::kDisplayWidth, cardboy::sdk::kDisplayHeight}))
-        throw std::runtime_error("Failed to allocate texture for desktop framebuffer");
-    sprite.setTexture(texture, true);
-    sprite.setScale(sf::Vector2f{static_cast<float>(kPixelScale), static_cast<float>(kPixelScale)});
-    clearPixels(false);
-    presentIfNeeded();
-
-    services.buzzer       = &buzzerService;
-    services.battery      = &batteryService;
-    services.storage      = &storageService;
-    services.random       = &randomService;
-    services.highResClock = &highResService;
-    services.powerManager = &powerService;
-    services.filesystem   = &filesystemService;
-}
-
-void DesktopRuntime::setPixel(int x, int y, bool on) {
-    if (x < 0 || y < 0 || x >= cardboy::sdk::kDisplayWidth || y >= cardboy::sdk::kDisplayHeight)
-        return;
-    const std::size_t idx = static_cast<std::size_t>(y * cardboy::sdk::kDisplayWidth + x) * 4;
-    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
-    pixels[idx + 0]         = value;
-    pixels[idx + 1]         = value;
-    pixels[idx + 2]         = value;
-    pixels[idx + 3]         = 255;
-    dirty                   = true;
-}
-
-void DesktopRuntime::clearPixels(bool on) {
-    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
-    for (std::size_t i = 0; i < pixels.size(); i += 4) {
-        pixels[i + 0] = value;
-        pixels[i + 1] = value;
-        pixels[i + 2] = value;
-        pixels[i + 3] = 255;
-    }
-    dirty = true;
-}
-
-void DesktopRuntime::processEvents() {
-    while (auto eventOpt = window.pollEvent()) {
-        const sf::Event& event = *eventOpt;
-
-        if (event.is<sf::Event::Closed>()) {
-            running = false;
-            window.close();
-            continue;
-        }
-
-        if (const auto* keyPressed = event.getIf<sf::Event::KeyPressed>()) {
-            input.handleKey(keyPressed->code, true);
-            continue;
-        }
-
-        if (const auto* keyReleased = event.getIf<sf::Event::KeyReleased>()) {
-            input.handleKey(keyReleased->code, false);
-            continue;
-        }
-    }
-}
-
-void DesktopRuntime::presentIfNeeded() {
-    if (!dirty)
-        return;
-    texture.update(pixels.data());
-    window.clear(sf::Color::Black);
-    window.draw(sprite);
-    window.display();
-    dirty = false;
-}
-
-void DesktopRuntime::sleepFor(std::uint32_t ms) {
-    const auto target = std::chrono::steady_clock::now() + std::chrono::milliseconds(ms);
-    do {
-        processEvents();
-        presentIfNeeded();
-        if (!running)
-            std::exit(0);
-        if (ms == 0)
-            return;
-        const auto now = std::chrono::steady_clock::now();
-        if (now >= target)
-            return;
-        const auto remaining = std::chrono::duration_cast<std::chrono::milliseconds>(target - now);
-        if (remaining.count() > 2)
-            std::this_thread::sleep_for(std::min<std::chrono::milliseconds>(remaining, std::chrono::milliseconds(8)));
-        else
-            std::this_thread::yield();
-    } while (true);
-}
- 
-DesktopFramebuffer::DesktopFramebuffer(DesktopRuntime& runtime) : runtime(runtime) {}
-
-int DesktopFramebuffer::width_impl() const { return cardboy::sdk::kDisplayWidth; }
-
-int DesktopFramebuffer::height_impl() const { return cardboy::sdk::kDisplayHeight; }
-
-void DesktopFramebuffer::drawPixel_impl(int x, int y, bool on) { runtime.setPixel(x, y, on); }
-
-void DesktopFramebuffer::clear_impl(bool on) { runtime.clearPixels(on); }
-
-void DesktopFramebuffer::frameReady_impl() {
-    if (runtime.clearNextFrame) {
-        runtime.clearPixels(false);
-        runtime.clearNextFrame = false;
-    }
-}
-
-void DesktopFramebuffer::sendFrame_impl(bool clearAfterSend) {
-    runtime.clearNextFrame = clearAfterSend;
-    runtime.dirty          = true;
-}
-
-DesktopInput::DesktopInput(DesktopRuntime& runtime) : runtime(runtime) {}
-
-cardboy::sdk::InputState DesktopInput::readState_impl() { return state; }
-
-void DesktopInput::handleKey(sf::Keyboard::Key key, bool pressed) {
-    switch (key) {
-        case sf::Keyboard::Key::Up:
-            state.up = pressed;
-            break;
-        case sf::Keyboard::Key::Down:
-            state.down = pressed;
-            break;
-        case sf::Keyboard::Key::Left:
-            state.left = pressed;
-            break;
-        case sf::Keyboard::Key::Right:
-            state.right = pressed;
-            break;
-        case sf::Keyboard::Key::Z:
-        case sf::Keyboard::Key::A:
-            state.a = pressed;
-            break;
-        case sf::Keyboard::Key::X:
-        case sf::Keyboard::Key::S:
-            state.b = pressed;
-            break;
-        case sf::Keyboard::Key::Space:
-            state.select = pressed;
-            break;
-        case sf::Keyboard::Key::Enter:
-            state.start = pressed;
-            break;
-        default:
-            break;
-    }
-}
-
-DesktopClock::DesktopClock(DesktopRuntime& runtime)
-    : runtime(runtime), start(std::chrono::steady_clock::now()) {}
-
-std::uint32_t DesktopClock::millis_impl() {
-    const auto now = std::chrono::steady_clock::now();
-    return static_cast<std::uint32_t>(
-            std::chrono::duration_cast<std::chrono::milliseconds>(now - start).count());
-}
-
-void DesktopClock::sleep_ms_impl(std::uint32_t ms) { runtime.sleepFor(ms); }
-
-} // namespace cardboy::backend::desktop
 
 using cardboy::backend::desktop::DesktopRuntime;
 
@@ -361,7 +16,7 @@ int main() {
 
         cardboy::sdk::AppContext context(runtime.framebuffer, runtime.input, runtime.clock);
         context.services = &runtime.serviceRegistry();
-        cardboy::sdk::AppSystem  system(context);
+        cardboy::sdk::AppSystem system(context);
 
         system.registerApp(apps::createMenuAppFactory());
         system.registerApp(apps::createClockAppFactory());

Firmware/sdk/include/cardboy/sdk/backend.hpp

@@ -3,3 +3,8 @@
 #include "platform.hpp"
 
 #include "cardboy/backend/backend_impl.hpp"
+#include "cardboy/backend/backend_interface.hpp"
+
+namespace cardboy::backend {
+static_assert(BackendInterface<ActiveBackend>, "ActiveBackend must provide Framebuffer, Input, Clock types");
+} // namespace cardboy::backend

Firmware/sdk/launchers/desktop/CMakeLists.txt

@@ -0,0 +1,16 @@
+add_executable(cardboy_desktop
+        src/main.cpp
+)
+
+set_target_properties(cardboy_desktop PROPERTIES
+        EXPORT_NAME desktop_launcher
+)
+
+target_link_libraries(cardboy_desktop
+        PRIVATE
+        cardboy_apps
+        cardboy_sdk
+        ${CARDBOY_SDK_BACKEND_LIBRARY}
+)
+
+target_compile_features(cardboy_desktop PRIVATE cxx_std_20)

Firmware/sdk/launchers/desktop/src/main.cpp

@@ -0,0 +1,33 @@
+#include "cardboy/apps/clock_app.hpp"
+#include "cardboy/apps/gameboy_app.hpp"
+#include "cardboy/apps/menu_app.hpp"
+#include "cardboy/apps/tetris_app.hpp"
+#include "cardboy/backend/desktop_backend.hpp"
+#include "cardboy/sdk/app_system.hpp"
+
+#include <cstdio>
+#include <exception>
+
+using cardboy::backend::desktop::DesktopRuntime;
+
+int main() {
+    try {
+        DesktopRuntime runtime;
+
+        cardboy::sdk::AppContext context(runtime.framebuffer, runtime.input, runtime.clock);
+        context.services = &runtime.serviceRegistry();
+        cardboy::sdk::AppSystem system(context);
+
+        system.registerApp(apps::createMenuAppFactory());
+        system.registerApp(apps::createClockAppFactory());
+        system.registerApp(apps::createGameboyAppFactory());
+        system.registerApp(apps::createTetrisAppFactory());
+
+        system.run();
+    } catch (const std::exception& ex) {
+        std::fprintf(stderr, "Cardboy desktop runtime failed: %s\n", ex.what());
+        return 1;
+    }
+
+    return 0;
+}