This is a Blender (4.0 or higher) plugin for partitioning a collection of objects into a grid of tiles, and exporting each tile as a glTF.

It was written for use with the Infinity Engine in Decentraland - see the Decentrally repository for more information.

• It slices, it dices, and it exports to glTF!
• Supports Draco compression
• Exports tileset data to JSON
• Configurable tile size and origin

• Download the latest version from the Releases page
• In Blender, go to Edit > Preferences > Addons > Install
• Select the .zip file
• Once installed ensure the plugin is activated (ticked) in the list of Addons

The plugin panel can be found in 3D Viewport -> Sidebar -> DCL Toolkit -> Scene Slicer

• Place your scene in a collection
• In the "DCL Toolkit" sidebar panel, under "Scene Slicer: Export":
  • Choose your collection in the dropdown
  • Configure output path (see below)
  • Configure grid size (see below)
  • Click the "Preview" button and check the grid layout
  • Click the "Slice and Export" button
  • The glTF and tileset.json files will be exported
  • You can cancel the Slice by pressing escape
  • You can delete the _sliced collection that is created after verifying the scene was properly sliced

• You can press Esc to cancel the Slice
• Ensure objects are in positive positions on all axis, eg above the ground (Z+), as well as X+ and Y+, relative to the world origin
• Avoid excessively high poly-counts - tile creation can take several seconds per-tile in excessively complicated scenes, resulting in extended slicing times.
• Avoid having vertexs at the intersections of tiles as this can cause problems with the booleans.
  Eg, don't have the floor at 0 as this will intersect/align with the bottom of the grid. Raise it slightly to avoid problems. If you're getting weird artefacts and janky meshes when slicing, it's most likely due to a bad mesh or vertexs aligning perfectly with the edge of a tile.

The following options are available in the Scene Slicer panel:

• Export collection

  • Choose the collection of objects you wish to export
  • Click the refresh symbol if your collection is not in the dropdown
  • All objects within the collection will be exported - visbility is ignored

• Output folder

  • Blender uses // for relative paths
  • Use //tiles to output to a folder named tiles in current file location
  • The glTF files and the tileset.json file describing the tileset will be exported here

• Grid size

  • Suggest using 1/4 parcel size or smaller for good results
  • Grid size must be less than 1/2 your total parcel size
  • Smaller grid sizes will take longer to process as they contain more tiles
  • Larger grid sizes will result in the tiles being unloaded closer to the player
  • Consider having a larger vertical axis
  • Click the "Preview" button to visualise the slicing grid

Some additonal options are available in the "Advanced Settings" panel.

• Bool solver method:
  Choose between Exact or Fast - Exact has better results but slower performance.

• Ignore '_collider' meshes:
  If enabled, ignore any meshes with _collider in the name.

• JSON minify:
  Significantly reduces JSON export file size - disable for dev; enable for production.

• glTF:

  • Draco compression:
    Toggle the use of Draco compression on glTF exports. Note that most 3D viewers do not support Draco. Disable for dev; enable for production.

  • Export format:
    Choose between GLB or GLTF Separate. Recommend GLTF as it supports externalised textures.

  • Filename prefix:
    Specify naming convention for output files.

  • Swizzle XY:
    Export to Y+ up - this applies to both the glTF files and the tileset.json. Recommend enabled at all times, unless you know what you're doing.

  • Tile origin:
    Set the origin position for exported tiles, can be min, center, or max. Recommend using "Center".

The addon peforms roughly the following process when the "Export" button is clicked:

• Work out bounding boxes for all objects in collection
• Work out grid size and origin based on overall collection bounding box
• Loop through each grid tile and check for objects with intersecting bounding boxes (see caveat #1)
• Duplicate all objects in the tile, which:
  • Adds an intersection boolean to limit the geometry to the tile bounds
  • Adds a triangulate modifier
  • Applies all modifiers (mirrors, bevels, etc)
  • Updates the objects origin (see Advanced settings - Tile origin)
• Double check we have some mesh data in the tile after applying all the bools
• Export the duplicated objects and remove them

• Problem: After slicing I see strange new cubes taking up whole tiles
  Solution: This is usually a problem with mesh geometry aligning with tile boundaries. Check the meshes in the area of the cube, and avoid having verts/edges exactly level with the tile boundary. You can also set the Bool solver method to "Exact" in the Advanced Settings.

• Problem: Some objects dissapear/don't get sliced
  Solution: Can be caused by an object containting multiple, separate meshes. Split the object mesh by selecting all faces in edit mode and using P -> Loose Parts.
  You may also need to apply rotation and scale for the object.
  Avoid ngons.

• Problem: The Slicer bounds extend past/below the bounds of my scene
  Solution: The bounds are based on the bounding boxes of all objects in the collection. Check your object bounding boxes. You can enable them in the Object Panel -> Viewport Display -> Bounds

• Problem: foo
  Solution: solution

NOTE: Positions and indexes are in XYZ order, with Z representing the vertical (up) axis unless Swizzle YZ is enabled, to enable Y+ up

The addon exports a JSON structure describing the tileset to tileset.json. It contains the following information:

{
    "version"        : "0.2.0",           // Version of plugin used to export tileset
    "name"           : "park",            // Name of the tileset (the collection name)
    "tileset_size"   : [ 7,   6,   2   ], // The total size (in tiles) of the tileset
    "tileset_origin" : [ 0.0, 0.0, 0.0 ], // The origin position of the tileset
    "tile_dimensions": [ 8.0, 8.0, 4.0 ], // The size (in Blender units) of each tile
    "tile_format"    : "GLTF_SEPARATE",   // glTF format, possible values are GLB, GLTF_SEPARATE
    "tile_origin"    : "CENTER",          // Possible values are CENTER, TILE_MIN, TILE_MAX
    "tiles"          : [                  // A nested array of tiles 
        [
            [
                { 
                    "index"     : [ 0, 0, 0 ],       // The index of this tile in the tiles array
                    "src"       : "tile_0_0_0",      // glTF filename, extension set by tile_format 
                    "pos_center": [ 4.0, 4.0, 2.0 ], // The tile center 
                    "pos_min"   : [ 0.0, 0.0, 0.0 ], // The minimum bounds of this tile
                    "pos_max"   : [ 8.0, 8.0, 4.0 ]  // The maximum bounds of the tile
                }, // ... etc, for each tile
            ],
        ],
    ]
}

1. Tile occupancy is determined by rectangular bounding boxes, this can result in tiles being incorrectly considered to be "occupied" and processed when they do not contain any mesh data.
   A basic tri-count is done after applying all modifiers and tiles with 0 tris are skipped. This mostly works, but sometimes can result in blank tiles.
2. Does not support Curves
3. Object visibility is ignored - if it's in the collection, it gets exported

[x] Add option to flip tileset.json YZ on export
[x] Add version number to panel/JSON [x] Add a way for user to interrupt process
[x] Stop UI from locking up
[x] Remove rigidbodies from sliced objects [ ] Bug: parented objects end up in wrong place after slicing [ ] Make all collections objects visible to avoid error with exporter
[ ] Allow user to export individual tiles
[ ] Add batch-exporter
[ ] Move tiles to own groups
[ ] Parent tile objects to an empty for easier management?