Cherry pick several improvements from 1.13

- Move container opening (and gui handling) into a separate class
 - Move turtle/computer placement code onto the block
 - GUIs now use gui{Left,Top} instead of calculating it manually.
 - IPeripheralTile is now exposed in the API.

src/main/java/dan200/computercraft/api/media/IMedia.java

@@ -7,6 +7,7 @@
 package dan200.computercraft.api.media;
 
 import dan200.computercraft.api.filesystem.IMount;
+import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.util.SoundEvent;
 import net.minecraft.world.World;
@@ -16,7 +17,9 @@ import javax.annotation.Nullable;
 
 /**
  * Represents an item that can be placed in a disk drive and used by a Computer.
- * Implement this interface on your Item class to allow it to be used in the drive.
+ *
+ * Implement this interface on your {@link Item} class to allow it to be used in the drive. Alternatively, register
+ * a {@link IMediaProvider}.
  */
 public interface IMedia
 {

src/main/java/dan200/computercraft/api/media/IMediaProvider.java

@@ -23,7 +23,7 @@ public interface IMediaProvider
      * Produce an IMedia implementation from an ItemStack.
      *
      * @param stack The stack from which to extract the media information.
-     * @return An IMedia implementation, or null if the item is not something you wish to handle
+     * @return An {@link IMedia} implementation, or {@code null} if the item is not something you wish to handle
      * @see dan200.computercraft.api.ComputerCraftAPI#registerMediaProvider(IMediaProvider)
      */
     @Nullable

src/main/java/dan200/computercraft/api/peripheral/IPeripheralProvider.java

@@ -6,6 +6,7 @@
 
 package dan200.computercraft.api.peripheral;
 
+import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.EnumFacing;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
@@ -16,6 +17,8 @@ import javax.annotation.Nullable;
 /**
  * This interface is used to create peripheral implementations for blocks.
  *
+ * If you have a {@link TileEntity} which acts as a peripheral, you may alternatively implement {@link IPeripheralTile}.
+ *
  * @see dan200.computercraft.api.ComputerCraftAPI#registerPeripheralProvider(IPeripheralProvider)
  */
 @FunctionalInterface

src/main/java/dan200/computercraft/api/peripheral/IPeripheralTile.java

@@ -0,0 +1,32 @@
+/*
+ * This file is part of the public ComputerCraft API - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. This API may be redistributed unmodified and in full only.
+ * For help using the API, and posting your mods, visit the forums at computercraft.info.
+ */
+package dan200.computercraft.api.peripheral;
+
+import net.minecraft.util.EnumFacing;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.World;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+/**
+ * A {@link net.minecraft.tileentity.TileEntity} which may act as a peripheral.
+ *
+ * If you need more complex capabilities (such as handling TEs not belonging to your mod), you should use
+ * {@link IPeripheralProvider}.
+ */
+public interface IPeripheralTile
+{
+    /**
+     * Get the peripheral on the given {@code side}.
+     *
+     * @param side The side to get the peripheral from.
+     * @return A peripheral, or {@code null} if there is not a peripheral here.
+     * @see IPeripheralProvider#getPeripheral(World, BlockPos, EnumFacing)
+     */
+    @Nullable
+    IPeripheral getPeripheral( @Nonnull EnumFacing side );
+}

src/main/java/dan200/computercraft/api/turtle/event/TurtleBlockEvent.java

@@ -19,7 +19,6 @@ import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.World;
 import net.minecraftforge.common.util.FakePlayer;
 import net.minecraftforge.event.world.BlockEvent;
-import net.minecraftforge.fml.common.eventhandler.Cancelable;
 
 import javax.annotation.Nonnull;
 import java.util.Map;
@@ -37,7 +36,6 @@ import java.util.Objects;
  * Be aware that some events (such as {@link TurtleInventoryEvent}) do not necessarily interact
  * with a block, simply objects within that block space.
  */
-@Cancelable
 public abstract class TurtleBlockEvent extends TurtlePlayerEvent
 {
     private final World world;
@@ -84,7 +82,6 @@ public abstract class TurtleBlockEvent extends TurtlePlayerEvent
      *
      * @see TurtleAction#DIG
      */
-    @Cancelable
     public static class Dig extends TurtleBlockEvent
     {
         private final IBlockState block;
@@ -142,7 +139,6 @@ public abstract class TurtleBlockEvent extends TurtlePlayerEvent
      *
      * @see TurtleAction#MOVE
      */
-    @Cancelable
     public static class Move extends TurtleBlockEvent
     {
         public Move( @Nonnull ITurtleAccess turtle, @Nonnull FakePlayer player, @Nonnull World world, @Nonnull BlockPos pos )
@@ -156,7 +152,6 @@ public abstract class TurtleBlockEvent extends TurtlePlayerEvent
      *
      * @see TurtleAction#PLACE
      */
-    @Cancelable
     public static class Place extends TurtleBlockEvent
     {
         private final ItemStack stack;
@@ -188,7 +183,6 @@ public abstract class TurtleBlockEvent extends TurtlePlayerEvent
      *
      * @see TurtleAction#INSPECT
      */
-    @Cancelable
     public static class Inspect extends TurtleBlockEvent
     {
         private final IBlockState state;
@@ -229,7 +223,7 @@ public abstract class TurtleBlockEvent extends TurtlePlayerEvent
         /**
          * Add new information to the inspection result. Note this will override fields with the same name.
          *
-         * @param newData The data to add. Note all values should be convertable to Lua (see
+         * @param newData The data to add. Note all values should be convertible to Lua (see
          *                {@link dan200.computercraft.api.peripheral.IPeripheral#callMethod(IComputerAccess, ILuaContext, int, Object[])}).
          */
         public void addData( @Nonnull Map<String, ?> newData )

src/main/java/dan200/computercraft/api/turtle/event/TurtleInventoryEvent.java

@@ -48,7 +48,6 @@ public abstract class TurtleInventoryEvent extends TurtleBlockEvent
      *
      * @see TurtleAction#SUCK
      */
-    @Cancelable
     public static class Suck extends TurtleInventoryEvent
     {
         public Suck( @Nonnull ITurtleAccess turtle, @Nonnull FakePlayer player, @Nonnull World world, @Nonnull BlockPos pos, @Nullable IItemHandler handler )
@@ -62,7 +61,6 @@ public abstract class TurtleInventoryEvent extends TurtleBlockEvent
      *
      * @see TurtleAction#DROP
      */
-    @Cancelable
     public static class Drop extends TurtleInventoryEvent
     {
         private final ItemStack stack;