Synchronize HID keyboard state on first event

When an AOA HID keyboard is registered, CAPSLOCK and NUMLOCK are both
disabled, regardless of the state of the computer keyboard.

To synchronize the state, on first key event, inject CAPSLOCK and/or
NUMLOCK if necessary.

app/src/hid_keyboard.c

@@ -237,6 +237,45 @@ end:
     return true;
 }
 
+
+static bool
+push_mod_lock_state(struct sc_hid_keyboard *kb, uint16_t sdl_mod) {
+    bool capslock = sdl_mod & KMOD_CAPS;
+    bool numlock = sdl_mod & KMOD_NUM;
+    if (!capslock && !numlock) {
+        // Nothing to do
+        return true;
+    }
+
+    struct sc_hid_event hid_event;
+    if (!sc_hid_keyboard_event_init(&hid_event)) {
+        LOGW("Could not initialize HID keyboard event");
+        return false;
+    }
+
+#define SC_SCANCODE_CAPSLOCK SDL_SCANCODE_CAPSLOCK
+#define SC_SCANCODE_NUMLOCK SDL_SCANCODE_NUMLOCKCLEAR
+    unsigned i = 0;
+    if (capslock) {
+        hid_event.buffer[HID_KEYBOARD_INDEX_KEYS + i] = SC_SCANCODE_CAPSLOCK;
+        ++i;
+    }
+    if (numlock) {
+        hid_event.buffer[HID_KEYBOARD_INDEX_KEYS + i] = SC_SCANCODE_NUMLOCK;
+        ++i;
+    }
+
+    if (!sc_aoa_push_hid_event(kb->aoa, &hid_event)) {
+        sc_hid_event_destroy(&hid_event);
+        LOGW("Could request HID event");
+        return false;
+    }
+
+    LOGD("HID keyboard state synchronized");
+
+    return true;
+}
+
 static void
 sc_key_processor_process_key(struct sc_key_processor *kp,
                              const SDL_KeyboardEvent *event) {
@@ -251,6 +290,13 @@ sc_key_processor_process_key(struct sc_key_processor *kp,
     struct sc_hid_event hid_event;
     // Not all keys are supported, just ignore unsupported keys
     if (convert_hid_keyboard_event(kb, &hid_event, event)) {
+        if (!kb->mod_lock_synchronized) {
+            // Inject CAPSLOCK and/or NUMLOCK if necessary to synchronize
+            // keyboard state
+            if (push_mod_lock_state(kb, event->keysym.mod)) {
+                kb->mod_lock_synchronized = true;
+            }
+        }
         if (!sc_aoa_push_hid_event(kb->aoa, &hid_event)) {
             sc_hid_event_destroy(&hid_event);
             LOGW("Could request HID event");
@@ -282,6 +328,8 @@ sc_hid_keyboard_init(struct sc_hid_keyboard *kb, struct sc_aoa *aoa) {
     // Reset all states
     memset(kb->keys, false, SC_HID_KEYBOARD_KEYS);
 
+    kb->mod_lock_synchronized = false;
+
     static const struct sc_key_processor_ops ops = {
         .process_key = sc_key_processor_process_key,
         .process_text = sc_key_processor_process_text,

app/src/hid_keyboard.h

@@ -31,6 +31,8 @@ struct sc_hid_keyboard {
 
     struct sc_aoa *aoa;
     bool keys[SC_HID_KEYBOARD_KEYS];
+
+    bool mod_lock_synchronized;
 };
 
 bool