Texture Baking (Cycles)

The execution model is in blender-core. UVs come from blender-retopology-uv and materials from blender-pbr-materials.

One call

scripts/bake_maps.py -- --low SM_Crate --high Crate_high Crate_bolts --maps normal ao curvature id \
   --res 2048 --samples 64 --margin-px 16 --pack-orm --out //textures

Self-bake (procedural → textures, no --high): --low SM_Crate --maps basecolor roughness metallic normal --pack-orm. The script picks the GPU (OptiX/CUDA/HIP/Metal/oneAPI) and falls back to CPU, creates the target images with correct color spaces, cleans up its temporary nodes, and saves T_<name>_<N|AO|CURV|BC|R|M|ORM...>.png.

Preparation checklist (most bake bugs come from this list)

1. Low poly: UVs unwrapped, no overlaps (stacked/mirrored islands moved +1 U), padding ≥ 8 px at the bake resolution, scale applied.
2. Hard edges = UV seams on the low poly. Use either smooth shading with the bake handling gradients, or hard edges split at seams. Never put a hard edge inside a UV island.
3. Triangulate the low poly the same way the engine will, or export the triangulated mesh. Mismatched triangulation shows as shading seams.
4. High poly covers the low completely and pokes out of it only a little. Floaters (bolts, panel details) can hover just above the surface, but must stay within the extrusion distance.
5. Names: X_low / X_high pairs. Bake per part, or explode the parts apart (move each pair along an axis) so neighbouring parts don't project onto each other, then put them back.
6. Apply modifiers on the high poly as needed (multires and subd are evaluated automatically).

Rays: extrusion vs cage

• --extrusion (meters) pushes the ray origin outward from the low surface. It must be greater than the farthest distance the high poly sticks out of the low. The default is 2% of the low's diagonal; max_ray_distance is 2 × extrusion.
• Cage (--cage Crate_cage): a copy of the low with the same topology, inflated (Displace/"Push"). Use it when uniform extrusion fails (sharp concave corners, thin parts). Edit the cage locally where rays miss.
• Too small: holes or missing details. Too large: other parts of the mesh project in (intersections, "ghosting").

Map guide

Map	Space	Notes
normal	Non-Color, tangent, OpenGL (--directx for Unreal)	16-sample AA is plenty; 8-bit PNG is fine for games
ao	Non-Color	64–256 samples; bake with the high only (no ground) unless contact AO is wanted
curvature	Non-Color, 0.5 = flat	derived from the baked normal (convex white / concave dark); drives edge wear
id	sRGB	one flat color per high-poly material; use materials as masks
thickness	Non-Color	AO with inside rays; dark = thin; for SSS/translucency masks
basecolor/metallic/opacity	via emission override	reads the Principled inputs of the source materials (also procedural chains)
roughness, emit, combined	native Cycles passes	combined = lit result (lightmaps, stylized)
position	float	gradient masks
ORM = R:AO G:Roughness B:Metallic, the glTF/Unreal standard. Unity uses a different packing (blender-pbr-materials).

Fixing common artifacts

Symptom	Cause	Fix
Wavy lines on cylinders	low poly too low, smoothing gradients	add segments, use a cage, or more support on the low
Skewed details (bolts lean)	ray direction follows the averaged low normals	hard edges + seams, a cage, or bake the floater separately
Black/garbage areas	rays miss or hit the back faces	raise extrusion, fix flipped normals (blender-asset-qa), check high coverage
Seams visible in engine	margin too small, hard edge without a seam, different tangents	margin ≥ 16 px @2k, seams at hard edges, export tangents (MikkTSpace)
Details from a neighbouring part	parts too close	explode the bake, or bake per object pair
Inverted green look in engine	OpenGL/DirectX mismatch	--directx for Unreal, or flip G in the texture importer
Stepping/banding	8-bit with large flat gradients	bake to 16-bit (float_buffer) and dither on export

Baking non-PBR data

• Vertex colors: bake.target = "VERTEX_COLORS" with an active color attribute (useful for mobile and Roblox-free shading).
• Lightmaps: bake combined onto UV2 (--uv-layer UVMap_Lightmap) with the scene lights.
• Multires (no separate high object): bake.use_multires=True, bake.type="NORMALS"|"DISPLACEMENT"|"VECTOR_DISPLACEMENT", bake.use_lores_mesh=True, then bpy.ops.object.bake_image(). The viewport level is the low, the sculpt level is the high.

Gotchas

• The target image must be the active Image Texture node in every material of the low object (the script handles this).
• Baking in Cycles uses the active UV map (--uv-layer to pick).
• Images aren't saved automatically: img.save() or save_render. Packed or internal images disappear on reload.
• 5.2: the Cycles texture cache (.tx) is for render memory and doesn't affect bake results.
• Run blender-asset-qa on low + high first, because flipped normals and floating chunks produce most bake garbage.