Add event for player changing game mode (#7355)

src/main/java/net/minecraftforge/client/ForgeHooksClient.java

@@ -32,6 +32,7 @@ import net.minecraft.client.gui.ClientBossInfo;
 import net.minecraft.client.gui.FontRenderer;
 import net.minecraft.client.gui.screen.MainMenuScreen;
 import net.minecraft.client.gui.screen.Screen;
+import net.minecraft.client.network.play.NetworkPlayerInfo;
 import net.minecraft.client.renderer.*;
 import net.minecraft.client.renderer.FogRenderer.FogType;
 import net.minecraft.client.renderer.color.BlockColors;
@@ -72,6 +73,7 @@ import net.minecraft.util.math.vector.Vector3f;
 import net.minecraft.util.text.ITextComponent;
 import net.minecraft.util.text.TextFormatting;
 import net.minecraft.util.text.TranslationTextComponent;
+import net.minecraft.world.GameType;
 import net.minecraft.world.IBlockDisplayReader;
 import net.minecraftforge.client.event.*;
 import net.minecraftforge.client.event.sound.PlaySoundEvent;
@@ -562,6 +564,15 @@ public class ForgeHooksClient
         return event;
     }
 
+    public static void onClientChangeGameMode(NetworkPlayerInfo info, GameType currentGameMode, GameType newGameMode)
+    {
+        if (currentGameMode != newGameMode)
+        {
+            ClientPlayerChangeGameModeEvent evt = new ClientPlayerChangeGameModeEvent(info, currentGameMode, newGameMode);
+            MinecraftForge.EVENT_BUS.post(evt);
+        }
+    }
+
     @SuppressWarnings("deprecation")
     public static IBakedModel handlePerspective(IBakedModel model, ItemCameraTransforms.TransformType type, MatrixStack stack)
     {

src/main/java/net/minecraftforge/client/event/ClientPlayerChangeGameModeEvent.java

@@ -0,0 +1,37 @@
+package net.minecraftforge.client.event;
+
+import net.minecraft.client.network.play.NetworkPlayerInfo;
+import net.minecraft.world.GameType;
+import net.minecraftforge.eventbus.api.Event;
+
+/**
+ * Fired before the client player is notified of a change in game mode from the server.
+ */
+public class ClientPlayerChangeGameModeEvent extends Event
+{
+    private final NetworkPlayerInfo info;
+    private final GameType currentGameMode;
+    private final GameType newGameMode;
+
+    public ClientPlayerChangeGameModeEvent(NetworkPlayerInfo info, GameType currentGameMode, GameType newGameMode)
+    {
+        this.info = info;
+        this.currentGameMode = currentGameMode;
+        this.newGameMode = newGameMode;
+    }
+
+    public NetworkPlayerInfo getInfo()
+    {
+        return info;
+    }
+
+    public GameType getCurrentGameMode()
+    {
+        return currentGameMode;
+    }
+
+    public GameType getNewGameMode()
+    {
+        return newGameMode;
+    }
+}

src/main/java/net/minecraftforge/common/ForgeHooks.java

@@ -789,6 +789,17 @@ public class ForgeHooks
         MinecraftForge.EVENT_BUS.post(new PlayerInteractEvent.LeftClickEmpty(player));
     }
 
+    public static boolean onChangeGameMode(PlayerEntity player, GameType currentGameMode, GameType newGameMode)
+    {
+        if (currentGameMode != newGameMode)
+        {
+            PlayerEvent.PlayerChangeGameModeEvent evt = new PlayerEvent.PlayerChangeGameModeEvent(player, currentGameMode, newGameMode);
+            MinecraftForge.EVENT_BUS.post(evt);
+            return !evt.isCanceled();
+        }
+        return true;
+    }
+
     private static ThreadLocal<Deque<LootTableContext>> lootContext = new ThreadLocal<Deque<LootTableContext>>();
     private static LootTableContext getLootTableContext()
     {

src/main/java/net/minecraftforge/event/entity/player/PlayerEvent.java

@@ -25,6 +25,7 @@ import net.minecraft.entity.item.ItemEntity;
 import net.minecraft.inventory.IInventory;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.RegistryKey;
+import net.minecraft.world.GameType;
 import net.minecraft.world.World;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.ForgeEventFactory;
@@ -510,4 +511,40 @@ public class PlayerEvent extends LivingEvent
             return this.toDim;
         }
     }
+
+    /**
+     * Fired when the game type of a server player is changed to a different value than what it was previously. Eg Creative to Survival, not Survival to Survival.
+     * If the event is cancelled the game mode of the player is not changed and the value of <code>newGameMode</code> is ignored.
+     */
+    @Cancelable
+    public static class PlayerChangeGameModeEvent extends PlayerEvent
+    {
+        private final GameType currentGameMode;
+        private GameType newGameMode;
+
+        public PlayerChangeGameModeEvent(PlayerEntity player, GameType currentGameMode, GameType newGameMode)
+        {
+            super(player);
+            this.currentGameMode = currentGameMode;
+            this.newGameMode = newGameMode;
+        }
+
+        public GameType getCurrentGameMode()
+        {
+            return currentGameMode;
+        }
+
+        public GameType getNewGameMode()
+        {
+            return newGameMode;
+        }
+
+        /**
+         * Sets the game mode the player will be changed to if this event is not cancelled.
+         */
+        public void setNewGameMode(GameType newGameMode)
+        {
+            this.newGameMode = newGameMode;
+        }
+    }
 }