More precise and faster spacebar slider (#593)

* Make slider speed independent from swipe distance

Swipe distances other than the default resulted in a slider that were
not easy to control.

* refactor: Add class Pointers.Sliding

It holds the states and the code needed to make the slider work.
'Pointer.sliding' is set to [null] when sliding is not in progress.

The implementation is changed not to depend on [downX] and [dx] but
instead use the pointer's [x] coordinate directly.

* Move the cursor further for faster slides

In sliding mode, compute the speed of the pointer and use it to increase
at which the cursor moves.

* refactor: Separate kind for cursor movement keys

This allows to define a key that moves the cursor more than one position
at a time.

This will be used to avoid lag during fast slider movements.

* Reduce lag when sliding quickly on the spacebar

Avoid sending key events in a loop while sliding quickly in a cursor
movement key. Key of kind Cursor_move are "multiplied", meaning a single
key event represents a movement of more than one position, reducing the
number of key events sent.
This is only for cursor move keys.

4 files changed, 119 insertions, 44 deletions

diff --git a/srcs/juloo.keyboard2/Config.java b/srcs/juloo.keyboard2/Config.java
index 70ccb94..9e9774b 100644
--- a/srcs/juloo.keyboard2/Config.java
+++ b/srcs/juloo.keyboard2/Config.java
@@ -132,7 +132,7 @@ public final class Config
     float swipe_scaling = Math.min(dm.widthPixels, dm.heightPixels) / 10.f * dpi_ratio;
     float swipe_dist_value = Float.valueOf(_prefs.getString("swipe_dist", "15"));
     swipe_dist_px = swipe_dist_value / 25.f * swipe_scaling;
-    slide_step_px = swipe_dist_px / 4.f;
+    slide_step_px = 0.2f * swipe_scaling;
     vibrate_custom = _prefs.getBoolean("vibrate_custom", false);
     vibrate_duration = _prefs.getInt("vibrate_duration", 20);
     longPressTimeout = _prefs.getInt("longpress_timeout", 600);
diff --git a/srcs/juloo.keyboard2/KeyEventHandler.java b/srcs/juloo.keyboard2/KeyEventHandler.java
index 01c4300..b6225f1 100644
--- a/srcs/juloo.keyboard2/KeyEventHandler.java
+++ b/srcs/juloo.keyboard2/KeyEventHandler.java
@@ -94,6 +94,7 @@ public final class KeyEventHandler implements Config.IKeyEventHandler
       case Compose_pending:
         _recv.set_compose_pending(true);
         break;
+      case Cursor_move: move_cursor(key.getCursorMove()); break;
     }
     update_meta_state(old_mods);
   }
@@ -222,8 +223,6 @@ public final class KeyEventHandler implements Config.IKeyEventHandler
       case REPLACE: send_context_menu_action(android.R.id.replaceText); break;
       case ASSIST: send_context_menu_action(android.R.id.textAssist); break;
       case AUTOFILL: send_context_menu_action(android.R.id.autofill); break;
-      case CURSOR_LEFT: move_cursor(-1); break;
-      case CURSOR_RIGHT: move_cursor(1); break;
     }
   }
 
diff --git a/srcs/juloo.keyboard2/KeyValue.java b/srcs/juloo.keyboard2/KeyValue.java
index 4462edf..da21d84 100644
--- a/srcs/juloo.keyboard2/KeyValue.java
+++ b/srcs/juloo.keyboard2/KeyValue.java
@@ -71,8 +71,6 @@ public final class KeyValue implements Comparable<KeyValue>
     SHARE,
     ASSIST,
     AUTOFILL,
-    CURSOR_LEFT,
-    CURSOR_RIGHT,
   }
 
   public static enum Placeholder
@@ -89,7 +87,8 @@ public final class KeyValue implements Comparable<KeyValue>
   public static enum Kind
   {
     Char, String, Keyevent, Event, Compose_pending, Modifier, Editing,
-    Placeholder
+    Placeholder,
+    Cursor_move // Value is encoded as a 16-bit integer
   }
 
   private static final int FLAGS_OFFSET = 19;
@@ -196,6 +195,12 @@ public final class KeyValue implements Comparable<KeyValue>
     return (_code & VALUE_BITS);
   }
 
+  /** Defined only when [getKind() == Kind.Cursor_move]. */
+  public short getCursorMove()
+  {
+    return (short)(_code & VALUE_BITS);
+  }
+
   /* Update the char and the symbol. */
   public KeyValue withChar(char c)
   {
@@ -325,6 +330,16 @@ public final class KeyValue implements Comparable<KeyValue>
     return editingKey(String.valueOf((char)symbol), action, FLAG_KEY_FONT);
   }
 
+  /** A key that moves the cursor [d] times to the right. If [d] is negative,
+      it moves the cursor [abs(d)] times to the left. */
+  public static KeyValue cursorMoveKey(int d)
+  {
+    int symbol = (d < 0) ? 0xE008 : 0xE006;
+    return new KeyValue(String.valueOf((char)symbol), Kind.Cursor_move,
+        ((short)d) & 0xFFFF,
+        FLAG_SPECIAL | FLAG_SECONDARY | FLAG_KEY_FONT);
+  }
+
   /** A key that do nothing but has a unique ID. */
   private static KeyValue placeholderKey(Placeholder id)
   {
@@ -507,8 +522,8 @@ public final class KeyValue implements Comparable<KeyValue>
       case "pasteAsPlainText": return editingKey(0xE035, Editing.PASTE_PLAIN);
       case "undo": return editingKey(0xE036, Editing.UNDO);
       case "redo": return editingKey(0xE037, Editing.REDO);
-      case "cursor_left": return editingKey(0xE008, Editing.CURSOR_LEFT);
-      case "cursor_right": return editingKey(0xE006, Editing.CURSOR_RIGHT);
+      case "cursor_left": return cursorMoveKey(-1);
+      case "cursor_right": return cursorMoveKey(1);
       // These keys are not used
       case "replaceText": return editingKey("repl", Editing.REPLACE);
       case "textAssist": return editingKey(0xE038, Editing.ASSIST);
diff --git a/srcs/juloo.keyboard2/Pointers.java b/srcs/juloo.keyboard2/Pointers.java
index 4a1c2d0..4d6ff9a 100644
--- a/srcs/juloo.keyboard2/Pointers.java
+++ b/srcs/juloo.keyboard2/Pointers.java
@@ -139,7 +139,7 @@ public final class Pointers implements Handler.Callback
     if (ptr.hasFlagsAny(FLAG_P_SLIDING))
     {
       clearLatched();
-      onTouchUp_sliding(ptr);
+      ptr.sliding.onTouchUp(ptr);
       return;
     }
     stopKeyRepeat(ptr);
@@ -248,6 +248,11 @@ public final class Pointers implements Handler.Callback
     Pointer ptr = getPtr(pointerId);
     if (ptr == null)
       return;
+    if (ptr.hasFlagsAny(FLAG_P_SLIDING))
+    {
+      ptr.sliding.onTouchMove(ptr, x);
+      return;
+    }
 
     // The position in a IME windows is clampled to view.
     // For a better up swipe behaviour, set the y position to a negative value when clamped.
@@ -255,12 +260,6 @@ public final class Pointers implements Handler.Callback
     float dx = x - ptr.downX;
     float dy = y - ptr.downY;
 
-    if (ptr.hasFlagsAny(FLAG_P_SLIDING))
-    {
-      onTouchMove_sliding(ptr, dx);
-      return;
-    }
-
     float dist = Math.abs(dx) + Math.abs(dy);
     Integer direction;
     if (dist < _config.swipe_dist_px)
@@ -290,7 +289,7 @@ public final class Pointers implements Handler.Callback
             (newValue.equals(ptr.key.getKeyValue(5))
              || newValue.equals(ptr.key.getKeyValue(6))))
         {
-          startSliding(ptr, dy);
+          startSliding(ptr, x);
         }
         _handler.onPointerDown(newValue, true);
       }
@@ -425,34 +424,11 @@ public final class Pointers implements Handler.Callback
 
   // Sliding
 
-  void startSliding(Pointer ptr, float initial_dy)
+  void startSliding(Pointer ptr, float x)
   {
     stopKeyRepeat(ptr);
     ptr.flags |= FLAG_P_SLIDING;
-    ptr.sliding_count = (int)(initial_dy / _config.slide_step_px);
-  }
-
-  /** Handle a sliding pointer going up. Latched modifiers are not cleared to
-      allow easy adjustments to the cursors. The pointer is cancelled. */
-  void onTouchUp_sliding(Pointer ptr)
-  {
-    removePtr(ptr);
-    _handler.onPointerFlagsChanged(false);
-  }
-
-  /** Handle move events for sliding pointers. [dx] is distance travelled from
-      [downX]. */
-  void onTouchMove_sliding(Pointer ptr, float dx)
-  {
-    int count = (int)(dx / _config.slide_step_px);
-    if (count == ptr.sliding_count)
-      return;
-    int key_index = (count < ptr.sliding_count) ? 5 : 6;
-    KeyValue newValue = _handler.modifyKey(ptr.key.keys[key_index], ptr.modifiers);
-    ptr.sliding_count = count;
-    ptr.value = newValue;
-    if (newValue != null)
-      _handler.onPointerHold(newValue, ptr.modifiers);
+    ptr.sliding = new Sliding(x);
   }
 
   /** Return the [FLAG_P_*] flags that correspond to pressing [kv]. */
@@ -489,8 +465,8 @@ public final class Pointers implements Handler.Callback
     public int flags;
     /** Identify timeout messages. */
     public int timeoutWhat;
-    /** Number of event already caused by sliding. */
-    public int sliding_count;
+    /** [null] when not in sliding mode. */
+    public Sliding sliding;
 
     public Pointer(int p, KeyboardData.Key k, KeyValue v, float x, float y, Modifiers m)
     {
@@ -503,7 +479,7 @@ public final class Pointers implements Handler.Callback
       modifiers = m;
       flags = (v == null) ? 0 : pointer_flags_of_kv(v);
       timeoutWhat = -1;
-      sliding_count = 0;
+      sliding = null;
     }
 
     public boolean hasFlagsAny(int has)
@@ -512,6 +488,91 @@ public final class Pointers implements Handler.Callback
     }
   }
 
+  public final class Sliding
+  {
+    /** Accumulated distance since last event. */
+    float d = 0.f;
+    /** The slider speed changes depending on the pointer speed. */
+    float speed = 1.f;
+    /** Coordinate of the last move. */
+    float last_x;
+    /** [System.currentTimeMillis()] at the time of the last move. */
+    long last_move_ms;
+
+    public Sliding(float x)
+    {
+      last_x = x;
+      last_move_ms = System.currentTimeMillis();
+    }
+
+    static final float SPEED_SMOOTHING = 0.7f;
+    /** Avoid absurdly large values. */
+    static final float SPEED_MAX = 4.f;
+
+    public void onTouchMove(Pointer ptr, float x)
+    {
+      d += (x - last_x) * speed / _config.slide_step_px;
+      update_speed(x);
+      // Send an event when [abs(d)] exceeds [1].
+      int d_ = (int)d;
+      if (d_ != 0)
+      {
+        d -= d_;
+        int key_index = (d_ < 0) ? 5 : 6;
+        ptr.value = _handler.modifyKey(ptr.key.keys[key_index], ptr.modifiers);
+        send_key(ptr, Math.abs(d_));
+      }
+    }
+
+    /** Handle a sliding pointer going up. Latched modifiers are not
+        cleared to allow easy adjustments to the cursors. The pointer is
+        cancelled. */
+    public void onTouchUp(Pointer ptr)
+    {
+      removePtr(ptr);
+      _handler.onPointerFlagsChanged(false);
+    }
+
+    /** Send the pressed key [n] times. */
+    void send_key(Pointer ptr, int n)
+    {
+      if (ptr.value == null)
+        return;
+      // Avoid looping if possible to avoid lag while sliding fast
+      KeyValue multiplied = multiply_key(ptr.value, n);
+      if (multiplied != null)
+        _handler.onPointerHold(multiplied, ptr.modifiers);
+      else
+        for (int i = 0; i < n; i++)
+          _handler.onPointerHold(ptr.value, ptr.modifiers);
+    }
+
+    /** Return a key performing the same action as [kv] but [n] times. Returns
+        [null] if [kv] cannot be multiplied. */
+    KeyValue multiply_key(KeyValue kv, int n)
+    {
+      switch (kv.getKind())
+      {
+        case Cursor_move:
+          return KeyValue.cursorMoveKey(kv.getCursorMove() * n);
+      }
+      return null;
+    }
+
+    /** [speed] is computed from the elapsed time and distance traveled
+        between two move events. Exponential smoothing is used to smooth out
+        the noise. Sets [last_move_ms] and [last_x]. */
+    void update_speed(float x)
+    {
+      long now = System.currentTimeMillis();
+      float instant_speed = Math.min(SPEED_MAX,
+          Math.abs(x - last_x) / (float)(now - last_move_ms) + 1.f);
+      speed = speed + (instant_speed - speed) * SPEED_SMOOTHING;
+      last_move_ms = now;
+      last_x = x;
+    }
+  }
+
   /** Represent modifiers currently activated.
       Sorted in the order they should be evaluated. */
   public static final class Modifiers