By name: gltf-asset-optimization description: Reduce the size of glTF/GLB 3D assets to cut Git LFS bandwidth/storage while keeping them loadable by the editor's Bevy 0.18 glTF loader. Use when shrinking .glb/.gltf files in assets/, addressing LFS quota/bandwidth, or when a model is too large. Produces plain glTF 2.0 (no Draco/meshopt/quantization, which Bevy cannot read).
glTF/GLB Asset Optimization
Large .glb/.ktx2 assets in assets/ are tracked by Git LFS. Every clone pulls
the LFS objects at HEAD, and GitHub bills that bandwidth to the repo owner
(including forks and anonymous clones). Shrinking the assets that ship at HEAD
is the most direct way to lower the recurring bill.
Hard constraint: stay Bevy-0.18-safe
The editor loads models through Bevy 0.18's glTF loader, which does not support these extensions (see https://docs.rs/bevy_gltf/0.18.0/bevy_gltf/):
KHR_draco_mesh_compression,EXT_meshopt_compression,KHR_mesh_quantizationKHR_texture_basisu,EXT_texture_webp,EXT_mesh_gpu_instancing
So the usual 5–10× geometry-compression tools (gltfpack, gltf-transform optimize
defaults, Draco) produce files that fail to render in the editor. Output must be
plain glTF 2.0 core. Always verify extensionsRequired is empty before committing.
Step 1: Diagnose where the bytes are
npx @gltf-transform/cli inspect path/to/model.glb
- Geometry-dominated (many meshes, large vertex/index counts, few/no textures):
the only Bevy-safe lever is reducing triangle count + dropping unused attributes.
Common in CAD exports (over-tessellated,
f32positions, unusedTEXCOORD_0). - Texture-dominated (large embedded PNG/JPEG): resize/re-encode textures, but keep them as PNG/JPEG (Bevy can't read basisu/webp here).
Step 2: Optimize (use the bundled script)
# keep-ratio = fraction of triangles to KEEP (default 0.25)
scripts/optimize-glb.sh assets/<model>.glb 0.25
The script runs a lossless cleanup (drop unused UVs, weld, join, prune; no
compression/instancing) then decimates triangles, and verifies the result needs no
extensions. By default it overwrites the input; the original is recoverable with
git checkout -- assets/<model>.glb (LFS-tracked).
Equivalent manual pipeline:
npx @gltf-transform/cli optimize in.glb tmp.glb \
--compress false --texture-compress false --instance false --palette false --simplify false
npx @gltf-transform/cli simplify tmp.glb out.glb --ratio 0.25 --error 0.01
Choosing a ratio
Size scales ~linearly with triangle ratio for uncompressed geometry. Reference
numbers from a 119 MB CAD drone (edu-450-v2-drone.glb, geometry-only):
| keep-ratio | result | reduction | use when |
|---|---|---|---|
| lossless only | 105 MB | 12% | never decimate (hero asset, close-ups) |
| 0.5 | 57 MB | 52% | curved surfaces, mid-distance |
| 0.25 | 32 MB | 73% | good default for viewport props |
| 0.1 | 15 MB | 87% | small-in-viewport, aggressive |
Tune with: lower --ratio for more reduction; if curved surfaces look faceted, raise
it. If gaps open between separate parts, add --lock-border true to the simplify step
(reduces achievable savings on multi-shell models). GLB_SIMPLIFY_ERROR env var caps
the simplification error (default 0.01).
Step 3: Verify before committing
- Confirm Bevy-safe: the script aborts unless
extensionsRequiredis empty. - Visual check: open the output in the editor (drag into a schematic) or https://gltf.report. Watch for faceting on curved surfaces and gaps between parts.
- Do not commit (the developer commits). Note the asset is LFS-tracked.
Prefer not to ship it at all
If an asset is optional or only used by one example, consider removing it from LFS and
loading it on demand (the editor supports remote glb path="https://…" via the
web_asset plugin). Eliminating a HEAD asset saves its full size on every clone.
Note: a dead/remote URL must point at a reachable host — otherwise use a local path.