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Optimizations

Untold Engine supports optional asset optimization workflows that reduce runtime memory, file size, and streaming cost. These steps are usually applied after exporting assets to .untold.

For exporter commands, flags, and expected output layout, see Using The Exporter.

ASTC Texture Compression

ASTC is a GPU-native block-compression format supported on all Apple Silicon and A-series devices. Converting textures to ASTC reduces texture memory by 4-8x compared to uncompressed RGBA8 and eliminates CPU-side decode. The GPU receives the compressed blocks directly.

ASTC compression is a post-export step run with texbake.py, separate from the exporters. This keeps the exporter's Blender Python environment free of extra dependencies.

Prerequisites

Install astcenc. The tool is resolved in this order:

  1. ASTCENC_BIN=/path/to/astcenc
  2. Tools/astcenc/astcenc beside the repo root
  3. astcenc on PATH

Single asset workflow

# 1. Export the asset
./scripts/export-untold \
  --input GameData/Models/robot/robot.usdz \
  --output GameData/Models/robot/robot.untold

# 2. Bake all textures in the Textures/ directory to .utex
python3 scripts/texbake.py --dir GameData/Models/robot/Textures/

# 3. Patch the .untold file to reference the .utex files
python3 scripts/texbake.py --patch-refs GameData/Models/robot/robot.untold

Tile export workflow

Tile exports produce many .untold files. Pass the tile output directory to --patch-refs and all .untold files inside are patched in one go:

# 1. Export tiles
./scripts/export-untold-tiles \
  --input GameData/Models/dungeon/dungeon.usdz \
  --output-dir GameData/Models/dungeon/tile_exports

# 2. Bake all textures
python3 scripts/texbake.py --dir GameData/Models/dungeon/tile_exports/Textures/

# 3. Patch all .untold files in the tile directory
python3 scripts/texbake.py --patch-refs GameData/Models/dungeon/tile_exports/

What the bake step does

  1. Converts every texture in the directory to .utex using astcenc:
  2. Base color and emissive: ASTC 4x4 sRGB
  3. Normal maps: ASTC 4x4 LDR
  4. Roughness, metallic, occlusion: ASTC 6x6 LDR
  5. Rewrites the .untold binary to point each texture reference at the new .utex file and sets the textureFormat field to the correct ASTC variant.
  6. The original PNG/JPEG files are left in place. The engine loads .utex when present and falls back to PNG/JPEG otherwise.

Single-file bake with slot override

For cases where filename-based slot detection is insufficient, pass --input and --slot directly:

python3 scripts/texbake.py \
  --input GameData/Models/robot/Textures/surface_data.png \
  --slot roughness

Available slots: base_color, normal, roughness, metallic, occlusion, orm, emissive, opacity, data.

LZ4 Geometry Compression

Pass --compress-geometry to export-untold or export-untold-tiles to compress the vertex and index chunks of the output .untold file with LZ4.

Prerequisites

Install the Python LZ4 package:

pip install lz4

Single asset

./scripts/export-untold \
  --input GameData/Models/robot/robot.usdz \
  --output GameData/Models/robot/robot.untold \
  --compress-geometry

Tile export

./scripts/export-untold-tiles \
  --input GameData/Models/dungeon/dungeon.usdz \
  --output-dir GameData/Models/dungeon/tile_exports \
  --tile-size-x 25 \
  --tile-size-y 10000 \
  --tile-size-z 25 \
  --compress-geometry

What compression does

  • Only the vertex_data and index_data chunks are compressed. Metadata chunks (string table, entity table, mesh table, material table, texture table) are always stored uncompressed.
  • The compressed format is LZ4 raw block (lz4.block, not lz4.frame), which matches Apple's COMPRESSION_LZ4_RAW algorithm used by the runtime decompressor.
  • Both the compressed size and the original uncompressed size are recorded in each chunk entry, so the runtime can allocate the exact decompression buffer without an extra read.
  • The content hash in the file header is computed over the compressed bytes, consistent with runtime validation.

Compression is compatible with all other flags including --validate, --generate-hlod, --generate-lod, and the ASTC texture bake workflow.