Comparators don't detect flowing items

Mark as ''Intended''
This is intended: comparators cannot detect items flowing away from it. The hopper must be pointing at the comparator.

The hopper must be pointing at the comparator.

no it doesn't

place a hopper facing away from the comperator and place a item in, the comperator will turn on

Confirmed for 16w05b

Confirmed for

• 16w06a

Please link to this comment in the description

The following is based on decompiled version of Minecraft 1.8 using MCP. All method and class names are the names used in the decompiled version.

When a hopper receives an item its cooldown is set to 8 ticks. So it has to wait 8 ticks until it can pass an item. The problem is that hoppers can collect the item of containers above them as well. This means even though the hopper which just received an item is on cooldown, the hopper below it can collect the item. This causes hoppers to transfer item downwards much faster than horizontally. Another problem that acts here is that (if I understand it correctly) redstone updates are not applied immediately. So when a horizontal hopper chain transports an item, the comparator is able to detect the item due to the cooldown of 8 ticks. However when the item is transported downwards, when the comparator is updated the item is no longer in the hopper.

This could be fixed by having hoppers collect items from hoppers above them only, when they are disabled by a redstone signal. The fix would be needed for the public static boolean func_145891_a(IHopper p_145891_0_) method of the net.minecraft.tileentity.TileEntityHopper class.

public static boolean func_145891_a(IHopper p_145891_0_)
{
    IInventory var1 = func_145884_b(p_145891_0_);

    if (var1 != null)
    {
        EnumFacing var2 = EnumFacing.DOWN;

        if (func_174917_b(var1, var2))
        {
            return false;
        }

        if (var1 instanceof ISidedInventory)
        {
            //...
        }
        else
        {
            // Added the following lines
            // Imported net.minecraft.entity.item.EntityMinecartHopper
            if (var1 instanceof TileEntityHopper) {
                if (BlockHopper.getActiveStateFromMetadata(((TileEntityHopper) var1).getBlockMetadata())) {
                    return false;
                }
            }
            else if (var1 instanceof EntityMinecartHopper) {
                if (!((EntityMinecartHopper) var1).getBlocked()) {
                    return false;
                }
            }
            
            int var7 = var1.getSizeInventory();

            for (int var8 = 0; var8 < var7; ++var8)
            {
                if (func_174915_a(p_145891_0_, var1, var8, var2))
                {
                    return true;
                }
            }
        }
    }
    else
    {
        //...
    }

    return false;
}

Idk why it's closed because it is still happening on 19w08b for me..