feat(nui-libgdx): replace touch pointer removal logic with configurable stickiness

Author: BenjaminAmos

nui-libgdx/src/main/java/org/terasology/nui/backends/libgdx/LibGDXMouseDevice.java

@@ -31,6 +31,13 @@ public class LibGDXMouseDevice implements MouseDevice {
     // The maximum number of touches that LibGDX supports on Android is 20.
     // See https://github.com/libgdx/libgdx/blob/5eac848925d6e1f24070f887cbfaf99bb8bc4a63/backends/gdx-backend-android/src/com/badlogic/gdx/backends/android/AndroidInput.java#L99
     private static final int MAX_POINTERS = 20;
+    // The default value has been calibrated by trial and error, mostly. You can set your own stickiness in the constructor.
+    private static final int DEFAULT_POINTER_STICKINESS = 4;
+    /**
+     * Defines how "sticky" a pointer is, meaning how many updates it should be retained for after the touch is released.
+     * This value can be fine-tuned based on the desired general responsiveness of the UI.
+     */
+    private final int pointerStickiness;
     /**
      * Flags a pointer for "removal" when it is no longer present on the screen.
      *
@@ -43,11 +50,20 @@ public class LibGDXMouseDevice implements MouseDevice {
      * The removePointer variable is used to delay this removal by a single update, so that UI widgets have time
      * to register the removal first (e.g. for button de-presses).
      */
-    private boolean[] removePointer;
+    private final int[] pointerCooldowns;
 
     public LibGDXMouseDevice() {
+        this(DEFAULT_POINTER_STICKINESS);
+    }
+
+    /**
+     * @param pointerStickiness Defines how "sticky" a pointer is,
+     *                          meaning how many updates it should be retained for after the touch is released.
+     */
+    public LibGDXMouseDevice(int pointerStickiness) {
         NUIInputProcessor.init();
-        removePointer = new boolean[MAX_POINTERS];
+        this.pointerStickiness = pointerStickiness;
+        pointerCooldowns = new int[MAX_POINTERS];
     }
 
     @Override
@@ -72,15 +88,12 @@ public Vector2i getPosition(int pointer) {
 
         if (Gdx.app.getType() == Application.ApplicationType.Android) {
             if (Gdx.input.isTouched(pointer)) {
-                removePointer[pointer] = false;
-            } else {
-                if (removePointer[pointer]) {
-                    // Since touches are mapped to pointers on Android, reset the pointer when not currently touching.
-                    // Set the pointer to an off-screen location, so it acts as if it were not present.
-                    return new Vector2i(Integer.MAX_VALUE, Integer.MAX_VALUE);
-                } else {
-                    removePointer[pointer] = true;
-                }
+                pointerCooldowns[pointer] = pointerStickiness;
+            } else if (pointerCooldowns[pointer] <= 0) {
+                pointerCooldowns[pointer] = 0;
+                // Since touches are mapped to pointers on Android, reset the pointer when not currently touching.
+                // Set the pointer to an off-screen location, so it acts as if it were not present.
+                return new Vector2i(Integer.MAX_VALUE, Integer.MAX_VALUE);
             }
         }
 
@@ -106,6 +119,11 @@ public boolean isButtonDown(int button) {
 
     @Override
     public void update() {
+        for (int pointer = 0; pointer < MAX_POINTERS; pointer++) {
+            if (pointerCooldowns[pointer] > 0) {
+                pointerCooldowns[pointer]--;
+            }
+        }
     }
 
     /**