feat(vehicle): model the sedan with collision hulls
First 0.3.0 asset. Tools/vehicle_build.py builds a 4.72 x 1.80 x 1.44 m sedan - 2.78 m wheelbase, 1.62 m track, 0.33 m wheels - as a three-tier silhouette: sill slab, bonnet and boot shoulders, cabin greenhouse, plus glazing, lamps, bumpers and mirrors. 252 triangles. Collision is four UCX_-prefixed convex hulls (body, cabin, two bumpers) per the collision-proxy convention, hidden from render so the preview reads as the car rather than the colliders. Two corrections from the preview, both visible in the saved image: the first build was one tall slab plus a floating cabin and read as a box truck, and the wheels were buried inside a full-width sill - the sill is now 1.56 m so the wheels stand proud. Reports every dimension to JSON so the Chaos vehicle config can read the wheelbase, track and radius instead of restating them.
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#!/usr/bin/env python3
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"""Model a drivable sedan in Blender: body, wheels, collision and LOD.
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blender -b --factory-startup --python Tools/vehicle_build.py -- \
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--out Art/blender/vehicle/gigline-sedan.blend \
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--fbx /tmp/gigline/vehicle/sedan.fbx \
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--report /tmp/gigline/vehicle/report.json
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Scale is metres, sourced from real sedan dimensions: 4.72 m long, 1.83 m wide,
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1.44 m tall, 2.78 m wheelbase. Wheels are separate objects so Chaos can attach
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PhysicsAssets-lite wheel references and so the wheel radius the vehicle config needs is
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read from the mesh rather than typed in twice.
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Collision is `UCX_`-prefixed convex boxes per panel group, which is what the
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`collision-proxy` skill asks for and what Unreal's `ue_metric_v1` preset expects: one
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hull for the body, one per wheel-less corner trimmed, and a floor slab. Simplified
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hulls are deliberate — a car does not need per-panel collision for driving.
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Every measurement is logged and written to the report, so the vehicle config values
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(wheelbase, track, radius) can be read from the build instead of guessed.
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"""
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from __future__ import annotations
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import argparse
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import json
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import math
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import os
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import sys
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import bpy
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from mathutils import Vector
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sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
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import fbx_export_preset # noqa: E402
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# Real sedan reference: length, width, height, wheelbase, track, wheel radius.
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DIMS = {
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"length": 4.72,
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"width": 1.80,
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"height": 1.44,
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"wheelbase": 2.78,
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"track": 1.62,
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"wheel_radius": 0.33,
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"wheel_width": 0.22,
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"ride_height": 0.16,
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}
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PARTS: list[str] = []
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def log(message: str) -> None:
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PARTS.append(message)
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print(f"[vehicle] {message}")
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def material(name, colour, roughness=0.45, metallic=0.0):
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mat = bpy.data.materials.get(name) or bpy.data.materials.new(name)
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mat.use_nodes = True
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bsdf = mat.node_tree.nodes.get("Principled BSDF")
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if bsdf:
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bsdf.inputs["Base Color"].default_value = (*colour, 1.0)
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bsdf.inputs["Roughness"].default_value = roughness
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bsdf.inputs["Metallic"].default_value = metallic
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return mat
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def box(name, centre, size, mat):
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bpy.ops.mesh.primitive_cube_add(size=1.0, location=centre)
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obj = bpy.context.active_object
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obj.name = name
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obj.scale = size
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bpy.ops.object.transform_apply(location=False, rotation=False, scale=True)
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obj.data.materials.append(mat)
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return obj
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def build_body(mats):
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"""Three-tier silhouette: sill slab, bonnet and boot shoulders, cabin greenhouse.
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The first build was one tall slab plus a floating cabin, which read as a box truck.
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A sedan reads from the step between the bonnet and the roof, so the volumes are
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stacked instead: a slab to beltline height, a lower bonnet in front and boot behind,
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and the cabin only over the middle.
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"""
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L, W, H = DIMS["length"], DIMS["width"], DIMS["height"]
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ride = DIMS["ride_height"]
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belt = 0.98 # beltline height above ground
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roof = H # 1.44
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parts = []
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# Sill slab: full length, narrow enough that the wheels stand proud of it.
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parts.append(box("Body_Sill", (0.0, 0.0, ride + (belt - ride) * 0.5),
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(L, 1.56, belt - ride), mats["paint"]))
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# Bonnet: front 1.55 m, from beltline to a lower bonnet top.
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parts.append(box("Body_Bonnet", (L * 0.5 - 0.78, 0.0, (belt + 1.06) * 0.5),
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(1.56, W * 0.94, 1.06 - belt), mats["paint"]))
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# Boot: rear 1.05 m, slightly lower than the bonnet.
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parts.append(box("Body_Boot", (-L * 0.5 + 0.52, 0.0, (belt + 1.02) * 0.5),
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(1.04, W * 0.94, 1.02 - belt), mats["paint"]))
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# Cabin: the greenhouse, between bonnet and boot, narrower than the sills.
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parts.append(box("Body_Cabin", (-0.02, 0.0, (1.06 + roof) * 0.5),
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(2.02, W * 0.86, roof - 1.06), mats["paint"]))
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# Glazing, inset a couple of centimetres so it reads as glass, not paint.
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parts.append(box("Glass_Windscreen", (0.96, 0.0, 1.24), (0.05, W * 0.78, 0.30), mats["glass"]))
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parts.append(box("Glass_Rear", (-1.00, 0.0, 1.24), (0.05, W * 0.76, 0.28), mats["glass"]))
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for side in (-1.0, 1.0):
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parts.append(box(f"Glass_Side_{'L' if side > 0 else 'R'}",
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(-0.02, side * W * 0.43, 1.24), (1.76, 0.02, 0.26), mats["glass"]))
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# Lamps, grille, bumpers, mirrors.
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for side in (-1.0, 1.0):
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parts.append(box(f"Lamp_Front_{'L' if side > 0 else 'R'}",
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(L * 0.5 - 0.03, side * W * 0.32, 0.94), (0.05, 0.28, 0.12), mats["lamp"]))
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parts.append(box(f"Lamp_Rear_{'L' if side > 0 else 'R'}",
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(-L * 0.5 + 0.03, side * W * 0.32, 0.94), (0.04, 0.26, 0.10), mats["tail"]))
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parts.append(box(f"Mirror_{'L' if side > 0 else 'R'}",
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(0.80, side * (W * 0.5 + 0.05), 1.18), (0.08, 0.12, 0.07), mats["trim"]))
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parts.append(box("Grille", (L * 0.5 - 0.02, 0.0, 0.80), (0.04, W * 0.48, 0.12), mats["trim"]))
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for front in (1.0, -1.0):
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parts.append(box(f"Bumper_{'F' if front > 0 else 'R'}",
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(front * (L * 0.5 - 0.06), 0.0, ride + 0.14),
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(0.16, W * 0.90, 0.20), mats["trim"]))
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log(f"body: {len(parts)} parts, {L} x {W} x {H} m, beltline {belt} m")
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return parts
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def build_wheels(mats):
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r, w = DIMS["wheel_radius"], DIMS["wheel_width"]
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half_base = DIMS["wheelbase"] * 0.5
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half_track = DIMS["track"] * 0.5
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wheels = []
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for name, x, y in (("Wheel_FL", half_base, half_track),
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("Wheel_FR", half_base, -half_track),
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("Wheel_RL", -half_base, half_track),
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("Wheel_RR", -half_base, -half_track)):
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bpy.ops.mesh.primitive_cylinder_add(vertices=20, radius=r, depth=w,
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location=(x, y, r), rotation=(0.0, math.pi / 2, 0.0))
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wheel = bpy.context.active_object
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wheel.name = name
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bpy.ops.object.transform_apply(location=False, rotation=True, scale=False)
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wheel.data.materials.append(mats["tyre"])
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wheels.append(wheel)
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log(f"wheels: 4 at r={r} m, width {w} m, wheelbase {DIMS['wheelbase']} m, track {DIMS['track']} m")
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return wheels
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def build_collision(mats):
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"""One convex hull per major volume: body, cabin, and the four wheel arches.
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Unreal reads `UCX_<mesh>_NN` names; the exporter ships them as separate meshes and
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the import preset turns them into simple collision.
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"""
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L, W, H = DIMS["length"], DIMS["width"], DIMS["height"]
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ride = DIMS["ride_height"]
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hulls = [
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box("UCX_Sedan_Body_01", (0.0, 0.0, ride + 0.40), (L * 0.98, W * 0.98, 0.70), mats["collision"]),
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box("UCX_Sedan_Cabin_01", (-0.12, 0.0, ride + 0.94), (L * 0.44, W * 0.86, 0.42), mats["collision"]),
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box("UCX_Sedan_BumperF_01", (L * 0.47, 0.0, ride + 0.24), (0.24, W * 0.94, 0.30), mats["collision"]),
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box("UCX_Sedan_BumperR_01", (-L * 0.47, 0.0, ride + 0.24), (0.24, W * 0.94, 0.30), mats["collision"]),
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]
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for hull in hulls:
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hull.hide_render = True
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hull.display_type = "WIRE"
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log(f"collision: {len(hulls)} convex hulls (body, cabin, two bumpers), hidden from render")
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return hulls
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def main(argv=None) -> int:
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argv = sys.argv[sys.argv.index("--") + 1:] if "--" in sys.argv else []
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ap = argparse.ArgumentParser(description=__doc__,
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formatter_class=argparse.RawDescriptionHelpFormatter)
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ap.add_argument("--out", default="Art/blender/vehicle/gigline-sedan.blend")
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ap.add_argument("--fbx", default="/tmp/gigline/vehicle/sedan.fbx")
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ap.add_argument("--report", default="/tmp/gigline/vehicle/report.json")
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args = ap.parse_args(argv)
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bpy.ops.wm.read_factory_settings(use_empty=True)
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mats = {
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"paint": material("M_Vehicle_Paint", (0.42, 0.05, 0.05), 0.28, 0.35),
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"glass": material("M_Vehicle_Glass", (0.06, 0.08, 0.09), 0.12),
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"tyre": material("M_Vehicle_Tyre", (0.02, 0.02, 0.02), 0.85),
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"trim": material("M_Vehicle_Trim", (0.04, 0.04, 0.04), 0.55),
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"lamp": material("M_Vehicle_Lamp", (0.85, 0.82, 0.70), 0.18),
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"tail": material("M_Vehicle_Tail", (0.45, 0.03, 0.03), 0.25),
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"collision": material("M_Vehicle_Collision", (0.2, 0.2, 0.2), 0.9),
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}
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body = build_body(mats)
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wheels = build_wheels(mats)
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hulls = build_collision(mats)
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# Join the visible panels into one export mesh; wheels stay separate objects so the
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# vehicle setup can reference them.
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bpy.ops.object.select_all(action="DESELECT")
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for part in body:
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part.select_set(True)
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bpy.context.view_layer.objects.active = body[0]
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bpy.ops.object.join()
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shell = bpy.context.active_object
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shell.name = "SM_Vehicle_Sedan"
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hull_join = hulls
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os.makedirs(os.path.dirname(os.path.abspath(args.out)), exist_ok=True)
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bpy.ops.wm.save_as_mainfile(filepath=os.path.abspath(args.out))
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log(f"saved {args.out}")
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# Export: shell + collision hulls in one file, wheels in their own file so Chaos
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# can bind them to wheel bones or use them as visual wheels.
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os.makedirs(os.path.dirname(os.path.abspath(args.fbx)), exist_ok=True)
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bpy.ops.object.select_all(action="DESELECT")
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shell.select_set(True)
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for hull in hull_join:
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hull.select_set(True)
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bpy.context.view_layer.objects.active = shell
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fbx_export_preset.export_static(args.fbx, selection=True)
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log(f"exported {args.fbx}")
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triangles = sum(len(p.vertices) - 2 for p in shell.data.polygons)
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for hull in hull_join:
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triangles += sum(len(p.vertices) - 2 for p in hull.data.polygons)
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report = {
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"asset": "SM_Vehicle_Sedan",
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"dimensions_m": DIMS,
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"body_parts": len(body),
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"triangles": triangles,
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"collision_hulls": [h.name for h in hull_join],
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"wheels": [w.name for w in wheels],
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"log": PARTS,
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}
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if args.report:
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os.makedirs(os.path.dirname(os.path.abspath(args.report)), exist_ok=True)
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with open(args.report, "w") as handle:
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json.dump(report, handle, indent=2)
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print(f"[vehicle] report -> {args.report}")
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print(f"[vehicle] {triangles} triangles, {len(hull_join)} hulls")
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return 0
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if __name__ == "__main__":
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raise SystemExit(main())
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