Add ability for custom detector rail output

patches/minecraft/net/minecraft/block/BlockRailDetector.java.patch

@@ -0,0 +1,11 @@
+--- ../src-base/minecraft/net/minecraft/block/BlockRailDetector.java
++++ ../src-work/minecraft/net/minecraft/block/BlockRailDetector.java
+@@ -156,6 +156,8 @@
+     {
+         if (((Boolean)p_180641_1_.func_177229_b(field_176574_M)).booleanValue())
+         {
++            int result = net.minecraftforge.event.ForgeEventFactory.onDetectorRailCompare(p_180641_3_, func_176572_a(p_180641_3_));
++            if (result > -1) return result;
+             List<EntityMinecartCommandBlock> list = this.<EntityMinecartCommandBlock>func_176571_a(p_180641_2_, p_180641_3_, EntityMinecartCommandBlock.class, new Predicate[0]);
+ 
+             if (!list.isEmpty())

src/main/java/net/minecraftforge/event/ForgeEventFactory.java

@@ -46,6 +46,7 @@ import net.minecraft.util.EnumHand;
 import net.minecraft.util.ResourceLocation;
 import net.minecraft.util.SoundCategory;
 import net.minecraft.util.SoundEvent;
+import net.minecraft.util.math.AxisAlignedBB;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.util.math.RayTraceResult;
 import net.minecraft.util.math.Vec3d;
@@ -101,6 +102,7 @@ import net.minecraftforge.event.world.BlockEvent;
 import net.minecraftforge.event.world.BlockEvent.MultiPlaceEvent;
 import net.minecraftforge.event.world.BlockEvent.NeighborNotifyEvent;
 import net.minecraftforge.event.world.BlockEvent.PlaceEvent;
+import net.minecraftforge.event.world.DetectorRailComparatorEvent;
 import net.minecraftforge.event.world.ExplosionEvent;
 import net.minecraftforge.event.world.WorldEvent;
 import net.minecraftforge.fml.common.ObfuscationReflectionHelper;
@@ -585,4 +587,11 @@ public class ForgeEventFactory
         return event.getTable();
     }
 
+    public static int onDetectorRailCompare(BlockPos pos, AxisAlignedBB box)
+    {
+        DetectorRailComparatorEvent evt = new DetectorRailComparatorEvent(pos, box);
+        MinecraftForge.EVENT_BUS.post(evt);
+        return evt.getRedstonePower();
+    }
+
 }

src/main/java/net/minecraftforge/event/world/DetectorRailComparatorEvent.java

@@ -0,0 +1,59 @@
+package net.minecraftforge.event.world;
+
+import net.minecraft.util.math.AxisAlignedBB;
+import net.minecraft.util.math.BlockPos;
+import net.minecraftforge.fml.common.eventhandler.Event;
+
+/**
+ * This event is fired serverside whenever a Detector Rail looks for a minecart to get a comparator value from
+ * in {@link net.minecraft.block.BlockRailDetector#getComparatorInputOverride}.
+ * This event is not cancelable.
+ * This event is fired on the {@link net.minecraftforge.common.MinecraftForge#EVENT_BUS}.
+ */
+public class DetectorRailComparatorEvent extends Event
+{
+
+    private final BlockPos pos;
+    private final AxisAlignedBB searchBox;
+    private int redstonePower;
+
+    public DetectorRailComparatorEvent(BlockPos pos, AxisAlignedBB searchBox)
+    {
+        this.pos = pos;
+        this.searchBox = searchBox;
+        this.redstonePower = -1;
+    }
+
+    /**
+     * @return The position of the Detector Rail
+     */
+    public BlockPos getPos()
+    {
+        return pos;
+    }
+
+    /**
+     * @return The bounding box that is to be searched for minecarts
+     */
+    public AxisAlignedBB getSearchBox()
+    {
+        return searchBox;
+    }
+
+    /**
+     * @return The redstone signal strength to give the comparator. Values below 0 mean vanilla logic will run.
+     */
+    public int getRedstonePower()
+    {
+        return redstonePower;
+    }
+
+    /**
+     * Set the redstone power to give the comparator. Values below 0 mean vanilla logic will run.
+     */
+    public void setRedstonePower(int redstonePower)
+    {
+        this.redstonePower = redstonePower;
+    }
+
+}