Blender Game Optimization skill

Game Optimization

The execution model is in blender-core. Always re-run blender-asset-qa after optimizing.

Procedure

1. Measure: scripts/mesh_stats.py -- --objects ... --budget mobile|roblox|web|vr|console|pc. It returns tris, estimated draw calls, materials, texture VRAM, bones, and the over-budget items.
2. Clean: make_lods.py --cleanup (merge by distance 0.1 mm, dissolve degenerate, delete loose). Remove hidden faces: back-to-back faces and faces under other parts (qa_check → back_to_back, plus manual xray).
3. Reduce in this order (cheapest visual loss first): hidden/interior geometry → unnecessary edge loops on flat areas (Limited Dissolve 1–5°) → over-segmented cylinders → Decimate → bake detail to normals (blender-texture-baking).
4. Materials: merge to 1–2 per asset (atlas / trim sheet / shared tiling material). Each material slot per mesh is roughly one draw call.
5. LODs: scripts/make_lods.py -- --objects SM_X --rename creates _LOD1.._LOD3 at 50/25/12.5%. Check every LOD silhouette with look/review_shots.
6. Re-measure, then QA, then export (blender-export-pipelines).

Budgets (guidance per asset, 2026)

Platform	Hero char tris	Prop tris	Mats/asset	Max texture	Bones
Mobile	5–15k	0.3–3k	1–2	1024	≤75
Roblox	body ≤10,742 (head 4k, torso 1.75k, limb 1,248); accessory/clothing 4k	≤20k per MeshPart	1 (SurfaceAppearance)	1024 (PBR), 4k max	R15 + optional
Web (three.js/Babylon)	10–30k	1–10k	1–2	2048	≤100
Standalone VR (Quest)	10–40k	1–10k	1–3	2048	≤100
Console / PC	50–150k	5–50k	2–6	4096	150–300
UE5 Nanite (static)	—	millions OK	few	4096+	n/a
Whole-scene limits matter more than single assets: mobile ≈ 100–300k tris visible and < 100–200 draw calls; PC ≈ millions of tris and < 2–5k draw calls.

Decimate modes

Mode	Use	Notes
COLLAPSE (ratio)	organic, scans, LODs	use_symmetry, vertex group factor to protect faces/hands; triangulates
UNSUBDIV (iterations)	meshes made by subdividing quads	restores the quad grid cleanly
DISSOLVE (planar, angle)	hard-surface / CAD	delimit {"SEAM","SHARP","MATERIAL","UV"}; keeps the silhouette, makes n-gons → triangulate on export
Protect UV seams and silhouette: decimate a copy, then compare. If UVs tear at LOD1, the ratio is too aggressive for that topology, so re-unwrap or use a manual LOD.

The hidden cost: vertex splits

GPU vertex count = unique (position, normal, UV, color) combinations. Every UV seam and hard edge duplicates vertices, so engine vertex counts are often 1.5–3× Blender's. Minimize seams where they aren't needed, keep hard edges = seams (so the split happens once), and don't add vertex colors or extra UV sets you don't use.

LOD rules

• Halve the tris per level. Switch at screen size ~0.5 / 0.25 / 0.125 (UE "Screen Size", Unity LOD Group %, Godot lod_bias auto).
• LODs keep the same materials (or fewer: merge them at LOD2+), same pivot, same bounds.
• Skeletal LODs: remove finger/face bones at LOD2+ (the engine bone-reduction tools handle this). Keep the skinning on the same skeleton.
• Far LOD / foliage: impostor/billboard. Unreal Nanite (static, opaque/masked) and Godot's auto mesh LOD can replace a hand-made chain.
• Roblox: no manual LODs. RenderFidelity=Automatic does it. Keep each MeshPart ≤ 20k tris and use a simple CollisionFidelity (Box/Hull) for non-walkable parts.

Draw calls and batching

• Merge static meshes that share a material and are always seen together (join objects). Don't merge across large areas, because that defeats frustum/occlusion culling.
• Instancing: repeated objects as linked duplicates (Alt+D, shared mesh) or collection instances. They export as instances (glTF EXT_mesh_gpu_instancing with export_gpu_instances) or as one mesh + transforms in the engine.
• Atlases/trim sheets: put many props on one texture set. Trim sheets let walls, panels and pipes share one 2k material.
• Texture memory (upper bound, uncompressed RGBA8 + mips): 1k = 5.3 MB, 2k = 21 MB, 4k = 85 MB. Engines compress (BC7/ASTC ≈ 4–8×). Pack grayscale maps into ORM channels to cut it 3×.

Collision

Keep collision separate and simple: boxes/convex hulls of ≤ 32–255 verts. UE UCX_<Mesh>_##, Godot -colonly/-convcolonly suffix, Unity MeshCollider on a simplified mesh, Roblox CollisionFidelity. Never use the render mesh as a physics mesh for anything that moves.

Rig and animation cost

Limit to 4 influences per vertex (vertex_group_limit_total(limit=4) + normalize). Remove non-deforming bones from the export (use_armature_deform_only). Bake constraints and drivers to keys. Shape keys cost memory per vertex, so drop unused ones and keep only deltas (glTF sparse accessors handle this).

Gotchas

• Decimate on meshes with unapplied modifiers: make_lods.py evaluates them first. Other paths need you to apply them.
• Join (Ctrl+J) merges materials and UV maps by name. Rename the UV maps identically first, or the UVs get lost.
• The Weld modifier is the non-destructive merge by distance. Use mode="CONNECTED" to avoid welding separate parts.
• Triangulate before measuring if the engine will. Quads already count as 2 tris in the stats.