nost: touch piano mode (#830)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Touch piano mode. Allows piano keys to be played with the touch screen.
Since the touch screen is still needed for menu navigation (including
during songs) a toggle switch is added so that the user can flip between
navigation mode and piano mode.

The touch targets are pixel-perfect. Don't let the game's piano
animations fool you.

## Testing

src/spice2x/games/nost/nost.cpp

@@ -1,5 +1,6 @@
 #include "nost.h"
 #include "poke.h"
+#include "touch_mode.h"
 #include "hooks/setupapihook.h"
 #include "touch/native/nativetouchhook.h"
 #include "avs/game.h"
@@ -7,6 +8,7 @@
 namespace games::nost {
 
     bool ENABLE_POKE = false;
+    bool ENABLE_TOUCH_MODE = false;
 
     NostGame::NostGame() : Game("Nostalgia") {
     }
@@ -40,6 +42,9 @@ namespace games::nost {
         setupapihook_add(touch_settings);
 
         nativetouch::hook(avs::game::DLL_INSTANCE);
+        if (ENABLE_TOUCH_MODE) {
+            touch_mode::enable();
+        }
     }
 
     void NostGame::post_attach() {
@@ -49,6 +54,9 @@ namespace games::nost {
     }
 
     void NostGame::detach() {
+        if (ENABLE_TOUCH_MODE) {
+            touch_mode::disable();
+        }
         if (ENABLE_POKE) {
             poke::disable();
         }

src/spice2x/games/nost/nost.h

@@ -5,6 +5,7 @@
 namespace games::nost {
 
     extern bool ENABLE_POKE;
+    extern bool ENABLE_TOUCH_MODE;
 
     class NostGame : public games::Game {
     public:

src/spice2x/games/nost/touch_mode.cpp

@@ -0,0 +1,233 @@
+#include "touch_mode.h"
+
+#include <atomic>
+#include <mutex>
+#include <unordered_map>
+
+#include "touch/native/nativetouchhook.h"
+#include "util/logging.h"
+
+namespace games::nost::touch_mode {
+
+    // native contact positions feed piano input directly. native events reach the game
+    // in nav mode and are suppressed in piano mode. mode-button contacts are always
+    // suppressed and change that routing after release.
+    static constexpr LONG PIANO_LEFT_GAP = 11;
+    static constexpr LONG PIANO_RIGHT_GAP = 10;
+    static constexpr uint32_t PIANO_KEY_COUNT = 28;
+
+    struct TouchGeometry {
+        HWND window = nullptr;
+        RECT mode_button {};
+        LONG client_width = 0;
+        LONG client_height = 0;
+
+        bool valid() const {
+            return window != nullptr && client_width > 0 && client_height > 0;
+        }
+    };
+
+    struct NativeContact {
+        POINT position {};
+
+        // position contains game-client coordinates
+        bool client_position_valid = false;
+
+        // down began on the mode switch button; remains true through up
+        bool mode_button = false;
+    };
+
+    static std::atomic_bool accept_events { false };
+    static std::atomic<Mode> current_mode_state { Mode::Nav };
+    static std::mutex state_mutex;
+    static TouchGeometry touch_geometry;
+
+    // native contacts are kept by ID so each contact contributes exactly one position
+    static std::unordered_map<DWORD, NativeContact> active_contacts;
+
+    // a hardware button release requests one change after all contacts are released
+    static bool mode_change_pending = false;
+
+    static void reset_state_locked() {
+        current_mode_state.store(Mode::Nav, std::memory_order_release);
+        touch_geometry = {};
+        active_contacts.clear();
+        mode_change_pending = false;
+    }
+
+    // hardware contacts arrive in screen coordinates
+    static bool native_touch_in_button(const nativetouch::NativeTouchEvent &event) {
+        if (!touch_geometry.valid()) {
+            return false;
+        }
+
+        POINT position { event.x, event.y };
+        if (!ScreenToClient(touch_geometry.window, &position)) {
+            return false;
+        }
+        return PtInRect(&touch_geometry.mode_button, position) != FALSE;
+    }
+
+    static bool update_touch_state(const nativetouch::NativeTouchEvent &event) {
+        std::lock_guard<std::mutex> lock(state_mutex);
+
+        // first, process down / move events
+        if (event.down || event.move) {
+            auto contact = active_contacts.try_emplace(event.id).first;
+
+            // keep track of IDs that began as a down on the mode switch button
+            if (event.down) {
+                contact->second.mode_button = native_touch_in_button(event);
+            }
+
+            // check for valid position
+            POINT position { event.x, event.y };
+            if (touch_geometry.window != nullptr &&
+                ScreenToClient(touch_geometry.window, &position)) {
+                contact->second.position = position;
+                contact->second.client_position_valid = true;
+            }
+        }
+
+        const auto contact = active_contacts.find(event.id);
+        const bool mode_button_contact = contact != active_contacts.end() &&
+            contact->second.mode_button;
+
+        // process up events
+        if (event.up) {
+            active_contacts.erase(event.id);
+
+            // if a contact that began down event on the mode switch button has
+            // been released, a mode switch is now pending
+            if (mode_button_contact) {
+                mode_change_pending = true;
+            }
+
+            // apply the change on the final hardware up. switching earlier would
+            // split another contact's down and up events across different modes
+            if (mode_change_pending && active_contacts.empty()) {
+                mode_change_pending = false;
+                const auto next_mode = current_mode() == Mode::Nav ? Mode::Piano : Mode::Nav;
+                current_mode_state.store(next_mode, std::memory_order_release);
+            }
+        }
+        return mode_button_contact;
+    }
+
+    // install the Nostalgia-specific native touch interception
+    void enable() {
+        if (accept_events.exchange(true, std::memory_order_acq_rel)) {
+            return;
+        }
+
+        {
+            std::lock_guard<std::mutex> lock(state_mutex);
+            reset_state_locked();
+        }
+
+        nativetouch::set_input_filter(filter_native_touch);
+        log_info("nost::touch", "enabled");
+    }
+
+    void disable() {
+        if (!accept_events.exchange(false, std::memory_order_acq_rel)) {
+            return;
+        }
+
+        nativetouch::set_input_filter(nullptr);
+
+        std::lock_guard<std::mutex> lock(state_mutex);
+        reset_state_locked();
+    }
+
+    bool enabled() {
+        return accept_events.load(std::memory_order_acquire);
+    }
+
+    Mode current_mode() {
+        return current_mode_state.load(std::memory_order_acquire);
+    }
+
+    // publish the rendered overlay button rectangle in game-client pixels
+    void publish_button_bounds(HWND window, const RECT &client_bounds) {
+        TouchGeometry next {};
+        RECT client_rect {};
+        if (window != nullptr && GetClientRect(window, &client_rect) &&
+            client_rect.right > 0 && client_rect.bottom > 0) {
+            next.window = window;
+            next.mode_button = client_bounds;
+            next.client_width = client_rect.right;
+            next.client_height = client_rect.bottom;
+        }
+
+        std::lock_guard<std::mutex> lock(state_mutex);
+        touch_geometry = next;
+    }
+
+    // return the active 28-key piano bitfield for the PANB input update
+    uint32_t piano_key_state() {
+        if (!enabled() || current_mode() != Mode::Piano) {
+            return 0;
+        }
+
+        std::lock_guard<std::mutex> lock(state_mutex);
+        if (current_mode() != Mode::Piano || !touch_geometry.valid()) {
+            return 0;
+        }
+
+        uint32_t state = 0;
+        for (const auto &contact : active_contacts) {
+            // invalid position or mode-button contact; ignore these contacts
+            if (!contact.second.client_position_valid || contact.second.mode_button) {
+                continue;
+            }
+
+            const auto &position = contact.second.position;
+
+            // outside the client area or on the mode button; ignore these contacts
+            if (position.x < 0 || position.x >= touch_geometry.client_width ||
+                position.y < 0 || position.y >= touch_geometry.client_height ||
+                PtInRect(&touch_geometry.mode_button, position)) {
+                continue;
+            }
+
+            // divide the inset width evenly; touches in either side gap clamp to
+            // the nearest outer key so the physical screen edges remain playable
+            const auto piano_width =
+                touch_geometry.client_width - PIANO_LEFT_GAP - PIANO_RIGHT_GAP;
+            uint32_t key = 0;
+            if (position.x >= touch_geometry.client_width - PIANO_RIGHT_GAP) {
+                key = PIANO_KEY_COUNT - 1;
+            } else if (position.x >= PIANO_LEFT_GAP && piano_width > 0) {
+                key = static_cast<uint32_t>(
+                    (position.x - PIANO_LEFT_GAP) * PIANO_KEY_COUNT / piano_width);
+            }
+            state |= UINT32_C(1) << key;
+        }
+
+        return state;
+    }
+
+    // update native contacts and report whether this event should be hidden from the game
+    bool filter_native_touch(const nativetouch::NativeTouchEvent &event) {
+        // synthetic events are outside this hardware-only feature
+        if (!enabled() || event.synthetic) {
+            // false leaves the event visible to the game
+            return false;
+        }
+
+        // snapshot routing before an up event can commit a pending mode switch
+        const bool piano_mode_before_update = current_mode() == Mode::Piano;
+
+        // update the contact lifetime and commit any pending switch when safe
+        const bool mode_button_contact = update_touch_state(event);
+
+        // hide every event in a contact that began on the mode switch button
+        if (mode_button_contact) {
+            return true;
+        }
+
+        // piano mode consumes hardware events; nav mode forwards them to the game
+        return piano_mode_before_update;
+    }
+}

src/spice2x/games/nost/touch_mode.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <cstdint>
+#include <windows.h>
+
+#include "touch/native/nativetouchhook.h"
+
+namespace games::nost::touch_mode {
+
+    // nav mode forwards contacts to the game; piano mode converts them into piano keys
+    enum class Mode {
+        Nav,
+        Piano,
+    };
+
+    void enable();
+    void disable();
+    bool enabled();
+
+    Mode current_mode();
+
+    void publish_button_bounds(HWND window, const RECT &client_bounds);
+
+    uint32_t piano_key_state();
+
+    bool filter_native_touch(const nativetouch::NativeTouchEvent &event);
+}