Underlay in FTB StoneBlock 4

Underlay lets you place a second block in the same space as another block. Carpets are the classic example: you can put one under a chest, a bed, a sign, a torch or any other block that has open space beneath it.^[1]

It works in Survival, so you can use it in a normal playthrough.^[1]

How you use it

1. Right click a block face with the block you want to place, for example under an upside-down stair.^[1]
2. Right click it again with another item to swap it quickly.^[1]
3. Left click it to remove it.^[1]

These placed blocks are called overlays. They aren't block entities. They're fake versions of the item you place, and that's what lets two things share one block space.^[1]

What you can place

By default, the overlay blocks are carpets, trapdoors, buttons, rails, slabs and pressure plates.^[1]

The mod's config file is config/Underlay/underlay.json. Use overlay_blocks to add blocks you can place as overlays, exclude_blocks to remove blocks from the allowed set, and target_exclude_blocks to stop overlays from being placed on certain blocks.^[1]

In this pack

The pack ships the NeoForge build of Underlay, a hotfix release of the mod.^[2]

Good news: there's nothing to craft to get started with Underlay. In this pack, no recipes produce items from the mod, and no quests involve it. You use blocks you already have, so you can start decorating right away.^[1]

What it does

Underlay lets you place a second block, such as a carpet, in the same space as another block that leaves room beneath it. Chests, beds, signs, torches and upside-down stairs are all examples. It works in Survival too.^[1]

Your first steps

1. Grab a carpet. Carpets are one of the blocks the mod allows as overlays by default.^[1]
2. Right click a block face with the carpet in your hand, for example under an upside-down stair, and it is placed.^[1]
3. Right click again with a different item to swap it quickly.^[1]
4. Left click the overlay to remove it.^[1]

What you can place

By default the mod allows carpets, trapdoors, buttons, rails, slabs and pressure plates as overlays. The mod's project page says other blocks, such as grass, can be added through its config. I can't confirm whether this pack changed that list, so check in-game if a block doesn't place.^[1]

Tweaking it

The mod reads its settings from a file called underlay.json in the Underlay config folder. Use overlay_blocks to add blocks, exclude_blocks to remove them, and target_exclude_blocks to stop overlays from being placed on certain blocks.^[1]

Unverified Whether this pack ships a customized underlay.json (extra or excluded blocks) could not be confirmed from the available sources.

Jade tooltips

This version includes a Jade option called "Show Underlay overlay tooltips". If you use Jade, it can show tooltips for overlays you look at.^[3]

Underlay has no machines, multiblocks, power, fluids or item automation. It is a placement mod, and everything it does comes down to one trick: putting a second block into a space that already holds a block.^[1]

How overlays work

Underlay lets you place carpets, and other blocks, under any block that has space beneath it. Chests, beds, signs and torches are all fair game. The things you place are called overlays.^[1]

Overlays are not block entities. They are fake versions of the item you place, and that is how two things can share one block space.^[1]

Placing, replacing and removing

1. Right click a block face while holding a block to place it as an overlay. For example, you can put a carpet under an upside-down stair.^[1]
2. Right click again with a different item to swap the overlay quickly.^[1]
3. Left click the overlay to remove it.^[1]

All of this works in Survival, so you don't need Creative mode.^[1]

What can be an overlay

By default, the blocks you can place as overlays are carpets, trapdoors, buttons, rails, slabs and pressure plates.^[1]

The pack leaves both overlay_blocks and exclude_blocks as empty lists. So the pack adds no extra overlay blocks and excludes none. You get the default set above.^[1][4]

Jade

The mod's language file includes a Jade option called "Show Underlay overlay tooltips". If you use Jade, you can toggle whether overlays get their own tooltip.^[3]

Unverified The project page says some versions of Underlay integrate with Create and Flashback. The sources don't confirm what that integration does, or whether it is active in this pack.

Underlay keeps its settings in a single file, config/Underlay/underlay.json. In this pack, the two options you'll care about are overlay_blocks and exclude_blocks.^[1][4]

How the pack sets them

• overlay_blocks is an empty list in this pack. The pack doesn't add any extra blocks to the overlay list. In the mod, this option is where you'd add blocks such as grass.^[1][4]
• exclude_blocks is also an empty list in this pack. The pack doesn't remove any blocks from the overlay list. In the mod, this option is used to exclude blocks.^[1][4]

Because both lists are empty, you get the mod's built-in behavior. By default, you can place carpets, trapdoors, buttons, rails, slabs and pressure plates as overlays. To place one, right click a block face with the block. Right click again with another item to replace it, or left click to remove it.^[1][4]

Unverified The mod also has a target_exclude_blocks option, which stops overlays from being placed on certain blocks. The pack file we have doesn't show a value for it, so how this pack sets it is unverified.

FTB StoneBlock 4 1.21.0 ships Underlay in its 1.0.4 hotfix build, the NeoForge jar for Minecraft 1.21.1. The notes below come from the mod's own changelogs, newest first. I left out changes that only apply to Fabric. The sources here include no pack changelog entries for this mod.^[2]

Changes up to the version in the pack

• 1.0.4 hotfix: overlay changes are now broadcast to everyone correctly (Forge and NeoForge), and a WorldEdit mixin failure was fixed.^[5]
• 1.0.4: added WorldEdit support. There is also a new option called place_on_replaceable_blocks, which is false by default. If you enable it, you can place blocks inside things like grass without breaking them. You can also set the OP level needed for the /underlay command in Underlay's config, and that command lets you edit config entries.^[6]
• 1.0.3: performance improvements. Overlays are now rendered differently, baked into chunks.^[7]
• 1.0.2: fixed a wrong Jade mixin on Neo 1.21.1 and fixed the Jade plugin loading on dedicated servers. You can no longer place a block where an overlay of the same block already exists. A new config option called target_exclude_blocks was added, a list of blocks you cannot place overlays on.^[8]
• 1.0.1: placement now works like vanilla, so you can click any face to place an overlay and can have an upper and a bottom slab, for example. It also brought various performance improvements and some rendering fixes for 1.21.11.^[9]
• 1.0.0 hotfix: reverted the raycast fix.^[10]
• 0.9.9: fixed Z-fighting in all versions and added Jade integration to Neo and Forge on 1.20.1, 1.21 and 1.21.1. It was the last release before 1.0.0.^[11]
• 0.9.8: fixed overlays rendering with the wrong lighting when certain shaders are in use, fixed broken rendering in 1.21.9 and later, and fixed shading issues on Neo and Forge.^[12]
• 0.9.7: fixed a crash with Create Nuclear, a placement bug where clicking the bottom face counted as a valid overlay placement, and an overlay sync bug.^[13]