Creating Connected Textures

Connected textures are, as the name would imply, textures that connect with neighboring blocks.

The CTM renderer will draw the block faces by assembling 4 quadrants from the 5 available block textures. The normal texture.png is the block's "unconnected" texture, and is used when CTM is disabled or the block has nothing to connect to.
texture.png has the outside corner quadrants and texture_ctm.png contains the connections.

┌─────────────────┐ ┌────────────────────────────────┐
│ texture.png     │ │ texture_ctm.png                │
│ ╔══════╤══════╗ │ │  ──────┼────── ║ ─────┼───── ║ │
│ ║      │      ║ │ │ │      │      │║      │      ║ │
│ ║ 4/4  │ 4/5  ║ │ │ │ 0/0  │ 0/1  │║ 0/2  │ 0/3  ║ │
│ ╟──────┼──────╢ │ │ ┼──────┼──────┼╟──────┼──────╢ │
│ ║      │      ║ │ │ │      │      │║      │      ║ │
│ ║ 5/4  │ 5/5  ║ │ │ │ 1/0  │ 1/1  │║ 1/2  │ 1/3  ║ │
│ ╚══════╧══════╝ │ │  ──────┼────── ║ ─────┼───── ║ │
└─────────────────┘ │ ═══════╤═══════╝ ─────┼───── ╚ │
                    │ │      │      ││      │      │ │
                    │ │ 2/0  │ 2/1  ││ 2/2  │ 2/3  │ │
                    │ ┼──────┼──────┼┼──────┼──────┼ │
                    │ │      │      ││      │      │ │
                    │ │ 3/0  │ 3/1  ││ 3/2  │ 3/3  │ │
                    │ ═══════╧═══════╗ ─────┼───── ╔ │
                    └────────────────────────────────┘

For example, combining sections 4/4, 2/1, 5/4, and 3/1, we can generate a texture connected to the right!

╔══════╤═══════
║      │      │
║ 4/4  │ 2/1  │
╟──────┼──────┼
║      │      │
║ 5/4  │ 3/1  │
╚══════╧═══════

Combining sections 0/2, 2/3, 5/4, and 3/1, we can generate a texture in the shape of an L (connected to the right and up):

║ ─────┼───── ╚
║      │      │
║ 0/2  │ 2/3  │
╟──────┼──────┼
║      │      │
║ 5/4  │ 3/1  │
╚══════╧═══════

Example MCMeta file

(For a texture mypack/assets/textures/blocks/texture.png with a ctm texture mypack/assets/textures/blocks/texture_ctm.png)

mypack:blocks/texture.png.mcmeta

{
    "gtceu": {
        "connection_texture": "mypack:blocks/texture_ctm"
    }
}

The CTM texture layout is here for the unconnected texture and here for its connections. Its MCMeta metadata file is this one.