Blender

blender

Blender runs here as a Python module (bpy, pinned): everything Blender does, no window. Scripts live in scenes/, run with $BLENDER_PYTHON, and harness_blender (on PYTHONPATH) gives you the scene, the camera, the export, the renders and the report in one import.

Build, export, render, verdict

"$BLENDER_PYTHON" scenes/hello.py                        # builds → out/model.glb, out/preview.png, out/turntable.mp4, out/report.json
"$BLENDER_PYTHON" "$BLENDER_TOOLCHAIN/verdict.py"        # judges out/ → the pane header, and which glTF the pane opens

import bpy
from harness_blender import fresh, frame_all, export_glb, render, turntable, export_stl, report
fresh()                                    # empty scene, millimetres, Workbench matcap
bpy.ops.mesh.primitive_cylinder_add(vertices=96, radius=45, depth=100, location=(0, 0, 50))
body = bpy.context.active_object
body.name = "Mug"                          # the name the pane's outliner shows
frame_all()                                # camera + key light framing everything
export_glb("out/model.glb")                # FIRST: the 3D pane reloads now, in place
render("out/preview.png")                  # a still, seconds (engine="CYCLES", samples=64 for a beauty shot)
turntable("out/turntable.mp4", seconds=4)  # the pane's Turntable tab; the scene is left as it was
report()                                   # what the verdict reads

What the pane shows, and how to feed it

The pane is a 3D viewport of the glTF, not a video player. export_glb carries everything it needs:

• Names and hierarchy: every renderable object under its Blender name, collections as the outliner's tree, parenting kept. Name objects, collections and materials for what they are.
• Facts per object (as glTF extras): dimensions and location in mm, rotation, scale, vertex / face / triangle counts, modifiers, materials, collections. Your own custom properties (obj["part_no"] = "A-12") appear in the properties panel too.
• Materials: Principled BSDF base colour, metallic, roughness, textures; diffuse_color is what Solid shading uses — set it to match.
• The scene camera and lights (KHR_lights_punctual): the user can look through the camera (numpad 0) and switch the lights on in Material / Rendered shading.
• Animation: keyframed objects play on the pane's timeline (obj.keyframe_insert(...), scene.frame_end, scene.render.fps).
• Units: the scene's unit scale travels with the export, so millimetres read as millimetres.

While a script runs, the helper writes .harness/build.json (step, turntable progress, failure) and the pane shows "Rebuilding · …" over the last good model. Exports are written to a hidden file and renamed into place, so the pane never reads half a file. Export after every meaningful change.

Modelling, the parts that matter

• Primitives: primitive_cube_add(size), primitive_cylinder_add(vertices, radius, depth), primitive_uv_sphere_add(radius), primitive_torus_add(major_radius, minor_radius), primitive_plane_add. Each becomes bpy.context.active_object; name it.
• Collections: c = bpy.data.collections.new("Lamp"); bpy.context.scene.collection.children.link(c), then move an object: for u in list(o.users_collection): u.objects.unlink(o) and c.objects.link(o).
• Modifiers (non-destructive, applied on export): o.modifiers.new("Bevel", "BEVEL") (width, segments, limit_method="ANGLE"), "SUBSURF" (levels), "BOOLEAN" (operation DIFFERENCE/UNION, object — hide the cutter with hide_render = True), "ARRAY", "MIRROR", "SOLIDIFY" (thickness — a clean way to give an open shape a wall), "SCREW", "DISPLACE".
• Smooth shading: bpy.ops.object.shade_smooth_by_angle(angle=math.radians(35)) on curved parts.
• Edit-mode ops when a modifier will not do: bmesh for exact geometry (bmesh.ops.extrude_face_region, inset, bevel, delete), then back to the mesh.
• Curves and text: bpy.data.curves.new(type="FONT") + body for lettering, extrude for depth.
• Materials: bpy.data.materials.new, use_nodes = True, Principled BSDF inputs Base Color, Roughness, Metallic; set diffuse_color too so Workbench and the pane's Solid mode show it.
• Units: fresh() puts the scene in millimetres. Model at real size; the report says the size.
• Cameras: frame_all(azimuth, elevation) for the shot; render(engine="CYCLES") for light, shadow and glass (CPU: 64 samples at 1280×720 is under a minute for a small scene).
• Animation: obj.keyframe_insert("location", frame=n); scene.frame_end; it exports and plays on the pane's timeline.
• Geometry Nodes exist (modifiers.new(type="NODES")) but hand-built node trees are long; prefer modifiers and bmesh unless the request is procedural by nature.

Rules

• Never write inside the package; out/ holds everything produced, scenes/ the scripts.
• First a blocky version (primitives, no bevels), export it, then render; then refine and export again. The live 3D scene is the proof; the turntable is the deliverable.
• Deliver out/model.glb (and .stl when it is for printing); say the size in mm.