hot corners: Pressure corner to trigger

In order to avoid accidental triggers, don't trigger the hot corner
until a given threshold is reached.

Fix #1100

Author: JoseExposito

src/HotCorners/HotCorner.vala

@@ -34,6 +34,12 @@ public class Gala.HotCorner : Object {
     public const string POSITION_BOTTOM_RIGHT = "hotcorner-bottomright";
     private const int BARRIER_SIZE = 30;
 
+    /**
+     * In order to avoid accidental triggers, don't trigger the hot corner until
+     * this threshold is reached.
+     */
+    private const int TRIGGER_PRESSURE_THRESHOLD = 50;
+
     /**
      * When the mouse pointer pressures the barrier without activating the hot corner,
      * release it when this threshold is reached.
@@ -135,14 +141,17 @@ public class Gala.HotCorner : Object {
         barrier.pressure_x += event.dx;
         barrier.pressure_y += event.dy;
 
-        if (!triggered && vertical_barrier.is_hit && horizontal_barrier.is_hit) {
-            trigger_hot_corner ();
-        }
-
         var pressure = (barrier == vertical_barrier) ?
             barrier.pressure_x.abs () :
             barrier.pressure_y.abs ();
 
+        if (!triggered && vertical_barrier.is_hit && horizontal_barrier.is_hit) {
+            if (pressure.abs () > TRIGGER_PRESSURE_THRESHOLD) {
+                trigger_hot_corner ();
+                pressure = 0;
+            }
+        }
+
         if (!triggered && pressure.abs () > RELEASE_PRESSURE_THRESHOLD) {
             barrier.release (event);
         }