SPIGOT-1571: Add Entity Glide Events.

By: 0x277F <0x277F@gmail.com>

paper-api/src/main/java/org/bukkit/entity/LivingEntity.java

@@ -366,4 +366,19 @@ public interface LivingEntity extends Attributable, Entity, Damageable, Projecti
      * @return whether the operation was successful
      */
     public boolean setLeashHolder(Entity holder);
+
+    /**
+     * Checks to see if an entity is gliding, such as using an Elytra.
+     * @return True if this entity is gliding.
+     */
+    public boolean isGliding();
+
+    /**
+     * Makes entity start or stop gliding. This will work even if an Elytra
+     * is not equipped, but will be reverted by the server immediately after
+     * unless an event-cancelling mechanism is put in place.
+     * @param gliding True if the entity is gliding.
+     */
+    public void setGliding(boolean gliding);
+
 }

paper-api/src/main/java/org/bukkit/event/entity/EntityToggleGlideEvent.java

@@ -0,0 +1,50 @@
+package org.bukkit.event.entity;
+
+import org.bukkit.entity.LivingEntity;
+import org.bukkit.event.Cancellable;
+import org.bukkit.event.HandlerList;
+
+/**
+ * Sent when an entity's gliding status is toggled with an Elytra.
+ * Examples of when this event would be called:
+ * <ul>
+ *     <li>Player presses the jump key while in midair and using an Elytra</li>
+ *     <li>Player lands on ground while they are gliding (with an Elytra)</li>
+ * </ul>
+ * This can be visually estimated by the animation in which a player turns horizontal.
+ */
+public class EntityToggleGlideEvent extends EntityEvent implements Cancellable {
+    private static final HandlerList handlers = new HandlerList();
+
+    private boolean cancel = false;
+    private final boolean isGliding;
+
+    public EntityToggleGlideEvent(LivingEntity who, final boolean isGliding) {
+        super(who);
+        this.isGliding = isGliding;
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return cancel;
+    }
+
+    @Override
+    public void setCancelled(boolean cancel) {
+        this.cancel = cancel;
+    }
+
+    public boolean isGliding() {
+        return isGliding;
+    }
+
+    @Override
+    public HandlerList getHandlers() {
+        return handlers;
+    }
+
+    public static HandlerList getHandlerList() {
+        return handlers;
+    }
+
+}