+
+A beveled Bezier semicircle authored on bpy.types.Curve — splines.new('BEZIER'), bezier_points, bevel_depth — so the curve renders as a tube without a prior mesh conversion.
+Rendered headless by the example itself — click to zoom.
+blender --background --python examples/curve-bevel-arc/curve_bevel_arc.py --+ +
A runnable example that builds a beveled Bezier semicircle entirely through the curve data API — splines.new('BEZIER'), per-point bezier_points, and bevel_depth — so the curve renders as a tube without a prior mesh conversion.
What it witnesses: renderable curve tubes are curve datablocks, not meshes. The check asserts eight Bezier points, bevel_depth == 0.12, and that the depsgraph-evaluated mesh has the deterministic topology (850 verts, 840 faces for these resolution settings) with a Z span that rests on the floor ([≈0, 2 × bevel]).
# Cheap correctness check (no render) — the CI check:
+blender --background --python curve_bevel_arc.py --
+
+# Also render a still (EEVEE on a GPU host; use --engine cycles on GPU-less hosts):
+blender --background --python curve_bevel_arc.py -- --output arc.png
+blender --background --python curve_bevel_arc.py -- --output arc.png --engine cyclesIt exits non-zero on failure (wrong point count, bevel, topology, or Z span). The blender-smoke workflow runs the check on Blender 4.5 LTS and 5.1.
"""Beveled Bezier arc via the curve data API — a runnable example. + +Witnesses that renderable tubes are authored on `bpy.types.Curve` directly +(`splines.new('BEZIER')`, `bezier_points`, `bevel_depth`) — not by meshing +first or calling curve operators. The check asserts the closed-form point +count, bevel depth, and that the depsgraph-evaluated mesh has the +deterministic topology and Z span of a tube whose centerline sits at +`z = bevel_depth` (resting on the floor). + +By default it runs only the correctness check (no render) — the CI smoke +check. Pass --output to also render a still: + + blender --background --python curve_bevel_arc.py -- # check only + blender --background --python curve_bevel_arc.py -- --output c.png # + render +""" +import bpy, bmesh, sys, os, math, argparse + +N_POINTS = 8 +RADIUS = 1.5 +BEVEL = 0.12 +BEVEL_RES = 3 +RES_U = 12 +# measured for the parameters above — identical on 4.4 and 5.1 +EXPECT_VERTS = 850 +EXPECT_FACES = 840 + + +def build(): + bpy.ops.wm.read_factory_settings(use_empty=True) + curve = bpy.data.curves.new("Arc", 'CURVE') + curve.dimensions = '3D' + curve.bevel_depth = BEVEL + curve.bevel_resolution = BEVEL_RES + curve.resolution_u = RES_U + + spline = curve.splines.new('BEZIER') + spline.bezier_points.add(N_POINTS - 1) # one point exists already + for i, bp in enumerate(spline.bezier_points): + a = i / (N_POINTS - 1) * math.pi # semicircle in XY + # centerline at z=BEVEL so the tube rests on the floor + bp.co = (RADIUS * math.cos(a), RADIUS * math.sin(a), BEVEL) + bp.handle_left_type = 'AUTO' + bp.handle_right_type = 'AUTO' + + obj = bpy.data.objects.new("Arc", curve) + bpy.context.collection.objects.link(obj) + return obj + + +def check(obj): + curve = obj.data + if curve.splines[0].type != 'BEZIER': + print(f"ERROR: spline type {curve.splines[0].type} != BEZIER", file=sys.stderr) + return 3 + n = len(curve.splines[0].bezier_points) + if n != N_POINTS: + print(f"ERROR: bezier points {n} != {N_POINTS}", file=sys.stderr) + return 4 + if abs(curve.bevel_depth - BEVEL) > 1e-6: + print(f"ERROR: bevel_depth {curve.bevel_depth} != {BEVEL}", file=sys.stderr) + return 5 + + bpy.context.view_layer.update() + dg = bpy.context.evaluated_depsgraph_get() + ev = obj.evaluated_get(dg) + em = ev.to_mesh() + try: + got_v = len(em.vertices) + got_f = len(em.polygons) + zs = [v.co.z for v in em.vertices] + z_lo, z_hi = min(zs), max(zs) + finally: + ev.to_mesh_clear() + + if got_v != EXPECT_VERTS or got_f != EXPECT_FACES: + print(f"ERROR: evaluated topology verts={got_v} faces={got_f} != " + f"expected verts={EXPECT_VERTS} faces={EXPECT_FACES}", + file=sys.stderr) + return 6 + + # tube diameter ≈ 2 * bevel; centerline at z=BEVEL → span [0, 2*BEVEL] + if z_lo < -0.02 or z_lo > 0.03: + print(f"ERROR: tube does not rest on floor (z_lo={z_lo:.4f})", file=sys.stderr) + return 7 + if abs(z_hi - 2 * BEVEL) > 0.03: + print(f"ERROR: tube height {z_hi:.4f} != 2*bevel={2 * BEVEL:.4f}", + file=sys.stderr) + return 8 + + print(f"points={n} bevel={BEVEL} eval_verts={got_v} eval_faces={got_f} " + f"z={z_lo:.3f}..{z_hi:.3f}") + return 0 + + +def eevee_engine_id(): + return 'BLENDER_EEVEE' if bpy.app.version >= (5, 0, 0) else 'BLENDER_EEVEE_NEXT' + + +def render_still(obj, path, engine): + scene = bpy.context.scene + mat = bpy.data.materials.new("Rose") + mat.use_nodes = True + bsdf = mat.node_tree.nodes["Principled BSDF"] + bsdf.inputs["Base Color"].default_value = (0.92, 0.14, 0.42, 1.0) # rose + bsdf.inputs["Roughness"].default_value = 0.28 + obj.data.materials.append(mat) + obj.rotation_euler = (0.0, 0.0, math.radians(-20)) + + floor_me = bpy.data.meshes.new("Floor") + bm = bmesh.new() + try: + bmesh.ops.create_grid(bm, x_segments=1, y_segments=1, size=30.0) + bm.to_mesh(floor_me) + finally: + bm.free() + fmat = bpy.data.materials.new("Studio") + fmat.use_nodes = True + fb = fmat.node_tree.nodes["Principled BSDF"] + fb.inputs["Base Color"].default_value = (0.055, 0.06, 0.07, 1.0) + fb.inputs["Roughness"].default_value = 0.5 + floor_me.materials.append(fmat) + floor = bpy.data.objects.new("Floor", floor_me) + scene.collection.objects.link(floor) + wall = bpy.data.objects.new("Wall", floor_me.copy()) + wall.location = (0.0, 9.0, 0.0) + wall.rotation_euler = (math.radians(90), 0.0, 0.0) + scene.collection.objects.link(wall) + + world = bpy.data.worlds.new("World") + world.use_nodes = True + world.node_tree.nodes["Background"].inputs["Color"].default_value = (0.008, 0.009, 0.012, 1.0) + scene.world = world + + aim = bpy.data.objects.new("Aim", None) + aim.location = (0.0, 0.4, BEVEL) + scene.collection.objects.link(aim) + + def light(name, loc, energy, size, col): + ld = bpy.data.lights.new(name, 'AREA') + ld.energy = energy + ld.size = size + ld.color = col + ob = bpy.data.objects.new(name, ld) + ob.location = loc + scene.collection.objects.link(ob) + lc = ob.constraints.new('TRACK_TO') + lc.target = aim + lc.track_axis = 'TRACK_NEGATIVE_Z' + lc.up_axis = 'UP_Y' + + light("Key", (-3.5, -4.5, 5.5), 1400.0, 6.0, (1.0, 0.98, 0.94)) + light("Fill", (5.0, -3.5, 2.5), 320.0, 8.0, (0.8, 0.87, 1.0)) + light("Rim", (1.5, 4.5, 2.0), 420.0, 4.0, (1.0, 0.75, 0.45)) + + cam_data = bpy.data.cameras.new("Cam") + cam_data.lens = 50.0 + cam = bpy.data.objects.new("Cam", cam_data) + cam.location = (2.8, -4.0, 2.4) + scene.collection.objects.link(cam) + scene.camera = cam + track = cam.constraints.new('TRACK_TO') + track.target = aim + track.track_axis = 'TRACK_NEGATIVE_Z' + track.up_axis = 'UP_Y' + + scene.render.engine = 'CYCLES' if engine == 'cycles' else eevee_engine_id() + if engine == 'cycles': + scene.cycles.samples = 32 + else: + try: + scene.eevee.taa_render_samples = 64 + except AttributeError: + pass + scene.render.resolution_x = 1280 + scene.render.resolution_y = 720 + scene.render.image_settings.file_format = 'PNG' + scene.render.filepath = path + bpy.ops.render.render(write_still=True) + return os.path.exists(path) and os.path.getsize(path) > 0 + + +def main(): + argv = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else [] + p = argparse.ArgumentParser() + p.add_argument("--output", default=None, help="optional: render a still PNG here") + p.add_argument("--engine", default="eevee", choices=("eevee", "cycles"), + help="render engine for --output (cycles for GPU-less hosts)") + args = p.parse_args(argv) + + obj = build() + code = check(obj) + if code: + return code + + if args.output: + if not render_still(obj, os.path.abspath(args.output), args.engine): + print("ERROR: render produced no file", file=sys.stderr) + return 9 + print(f"rendered still {args.output}") + + print("curve-bevel-arc OK") + return 0 + + +if __name__ == "__main__": + try: + sys.exit(main()) + except Exception as e: + import traceback; traceback.print_exc(); print(f"FATAL: {e}", file=sys.stderr); sys.exit(1) ++
+ 
+
+ A relative shape key authored entirely through the data API — shape_key_add, per-vertex key_blocks data, and .value — read back from the depsgraph-evaluated mesh.
+witnesses Shape keys do not rewrite mesh.vertices: undeformed top z stays at Basis, and evaluated z matches basis + value × (key − basis).
+ View example +
+
+ A beveled Bezier semicircle authored on bpy.types.Curve — splines.new('BEZIER'), bezier_points, bevel_depth — so the curve renders as a tube without a prior mesh conversion.
+witnesses Curve tubes are curve datablocks: eight Bezier points, bevel_depth == 0.12, and the evaluated mesh has deterministic topology (850 verts, 840 faces) resting on the floor.
+ View example +