Added a configurable release delay on qukey release

When releasing a qukey, allow a short timeout in case a subsequent key was released
effectively simultaneously, treating that near-simultaneous release as intended to use the
alternate (i.e. modifier) keycode.

src/Kaleidoscope/Qukeys.cpp

@@ -85,11 +85,14 @@ uint8_t Qukeys::qukeys_count = 0;
 
 bool Qukeys::active_ = true;
 uint16_t Qukeys::time_limit_ = 250;
+uint8_t Qukeys::release_delay_ = 0;
 QueueItem Qukeys::key_queue_[] = {};
 uint8_t Qukeys::key_queue_length_ = 0;
 byte Qukeys::qukey_state_[] = {};
 bool Qukeys::flushing_queue_ = false;
 
+constexpr uint16_t QUKEYS_RELEASE_DELAY_OFFSET = 4096;
+
 // Empty constructor; nothing is stored at the instance level
 Qukeys::Qukeys(void) {}
 
@@ -116,7 +119,7 @@ void Qukeys::enqueue(uint8_t key_addr) {
     flushQueue();
   }
   key_queue_[key_queue_length_].addr = key_addr;
-  key_queue_[key_queue_length_].start_time = (uint16_t)millis();
+  key_queue_[key_queue_length_].start_time = millis();
   key_queue_length_++;
   addr::mask(key_addr);
 }
@@ -175,7 +178,7 @@ void Qukeys::flushKey(bool qukey_state, uint8_t keyswitch_state) {
   memcpy(Keyboard.keyReport.allkeys, hid_report.allkeys, sizeof(hid_report));
 
   // Last, if the key is still down, add its code back in
-  if (keyswitch_state | IS_PRESSED)
+  if (keyswitch_state & IS_PRESSED)
     handleKeyswitchEvent(keycode, row, col, IS_PRESSED | WAS_PRESSED);
 
   // Now that we're done sending the report(s), Qukeys can process events again:
@@ -197,22 +200,29 @@ void Qukeys::flushQueue(int8_t index) {
     return;
   for (int8_t i = 0; i < index; i++) {
     if (key_queue_length_ == 0)
-      break;
+      return;
     flushKey(QUKEY_STATE_ALTERNATE, IS_PRESSED | WAS_PRESSED);
   }
+  if (isQukey(key_queue_[0].addr)) {
+    flushKey(QUKEY_STATE_PRIMARY, IS_PRESSED | WAS_PRESSED);
+  } else {
     flushKey(QUKEY_STATE_PRIMARY, WAS_PRESSED);
+  }
 }
 
 // Flush all the non-qukey keys from the front of the queue
 void Qukeys::flushQueue() {
   // flush keys until we find a qukey:
-  while (key_queue_length_ > 0 &&
+  while (key_queue_length_ > 0 && !isQukey(key_queue_[0].addr)) {
-         ! isDualUse(key_queue_[0].addr) &&
-         lookupQukey(key_queue_[0].addr) == QUKEY_NOT_FOUND) {
     flushKey(QUKEY_STATE_PRIMARY, IS_PRESSED | WAS_PRESSED);
   }
 }
 
+inline
+bool Qukeys::isQukey(uint8_t addr) {
+  return (isDualUse(addr) || lookupQukey(addr) != QUKEY_NOT_FOUND);
+}
+
 Key Qukeys::keyScanHook(Key mapped_key, byte row, byte col, uint8_t key_state) {
 
   // If key_addr is not a physical key, ignore it; some other plugin injected it
@@ -279,6 +289,14 @@ Key Qukeys::keyScanHook(Key mapped_key, byte row, byte col, uint8_t key_state) {
       }
       return mapped_key;
     }
+    // If there's a release delay in effect, the released key is a qukey, and there's at
+    // least one key after it in the queue, delay this key's release event:
+    if (release_delay_ > 0 &&
+        isQukey(key_addr) &&
+        queue_index < (key_queue_length_ - 1)) {
+      key_queue_[queue_index].start_time = millis() + QUKEYS_RELEASE_DELAY_OFFSET;
+      return Key_NoKey;
+    }
     flushQueue(queue_index);
     flushQueue();
     return Key_NoKey;
@@ -314,10 +332,23 @@ Key Qukeys::keyScanHook(Key mapped_key, byte row, byte col, uint8_t key_state) {
 }
 
 void Qukeys::preReportHook(void) {
+
+  uint16_t current_time = millis();
+
+  if (release_delay_ > 0) {
+    int16_t diff_time = key_queue_[0].start_time - current_time;
+    if (diff_time > 0) {
+      int16_t delay_window = QUKEYS_RELEASE_DELAY_OFFSET - release_delay_;
+      if (diff_time < delay_window) {
+        flushKey(QUKEY_STATE_ALTERNATE, WAS_PRESSED);
+        flushQueue();
+      }
+    }
+  }
+
   // If the qukey has been held longer than the time limit, set its
   // state to the alternate keycode and add it to the report
   while (key_queue_length_ > 0) {
-    uint16_t current_time = millis();
     if ((current_time - key_queue_[0].start_time) > time_limit_) {
       flushKey(QUKEY_STATE_ALTERNATE, IS_PRESSED | WAS_PRESSED);
       flushQueue();

src/Kaleidoscope/Qukeys.h

@@ -94,6 +94,9 @@ class Qukeys : public KaleidoscopePlugin {
   static void setTimeout(uint16_t time_limit) {
     time_limit_ = time_limit;
   }
+  static void setReleaseDelay(uint8_t release_delay) {
+    release_delay_ = release_delay;
+  }
 
   static Qukey * qukeys;
   static uint8_t qukeys_count;
@@ -101,6 +104,7 @@ class Qukeys : public KaleidoscopePlugin {
  private:
   static bool active_;
   static uint16_t time_limit_;
+  static uint8_t release_delay_;
   static QueueItem key_queue_[QUKEYS_QUEUE_MAX];
   static uint8_t key_queue_length_;
   static bool flushing_queue_;
@@ -120,6 +124,7 @@ class Qukeys : public KaleidoscopePlugin {
   static void flushKey(bool qukey_state, uint8_t keyswitch_state);
   static void flushQueue(int8_t index);
   static void flushQueue(void);
+  static bool isQukey(uint8_t addr);
 
   static Key keyScanHook(Key mapped_key, byte row, byte col, uint8_t key_state);
   static void preReportHook(void);