"""Preview scene for the kit: a top-down orthographic camera framing the whole sheet (2000 x 1000 px = 6 x 3 m), a light
grey floor and soft light, in collection '_preview' (not exported). render(path, engine) writes one picture."""
import bpy, math

def setup():
    sc = bpy.context.scene
    c = bpy.data.collections.get("_preview") or bpy.data.collections.new("_preview")
    if c.name not in sc.collection.children:
        sc.collection.children.link(c)
    cam = bpy.data.objects.get("PV_Camera")
    if cam is None:
        cam = bpy.data.objects.new("PV_Camera", bpy.data.cameras.new("PV_Camera")); c.objects.link(cam)
    cam.data.type = 'ORTHO'; cam.data.ortho_scale = 6.0
    cam.location = (0.0, -(500 - 470) * 0.003, 8.0); cam.rotation_euler = (0, 0, 0)
    cam.data.clip_end = 50
    sc.camera = cam
    fl = bpy.data.objects.get("PV_Floor")
    if fl is None:
        me = bpy.data.meshes.new("PV_Floor")
        me.from_pydata([(-6, -4, 0), (6, -4, 0), (6, 4, 0), (-6, 4, 0)], [], [(0, 1, 2, 3)])
        fl = bpy.data.objects.new("PV_Floor", me); c.objects.link(fl)
        m = bpy.data.materials.new("PV_Floor"); m.use_nodes = True
        b = m.node_tree.nodes["Principled BSDF"]; b.inputs["Base Color"].default_value = (0.8, 0.8, 0.82, 1)
        b.inputs["Roughness"].default_value = 0.8
        me.materials.append(m)
    sun = bpy.data.objects.get("PV_Sun")
    if sun is None:
        sun = bpy.data.objects.new("PV_Sun", bpy.data.lights.new("PV_Sun", 'SUN')); c.objects.link(sun)
    sun.data.energy = 2.2; sun.data.angle = math.radians(25)
    sun.rotation_euler = (math.radians(28), math.radians(-12), math.radians(20))
    w = sc.world or bpy.data.worlds.new("World"); sc.world = w; w.use_nodes = True
    w.node_tree.nodes["Background"].inputs[0].default_value = (0.9, 0.9, 0.92, 1)
    w.node_tree.nodes["Background"].inputs[1].default_value = 0.9
    sc.render.resolution_x, sc.render.resolution_y, sc.render.resolution_percentage = 2000, 1000, 100
    sc.view_settings.view_transform = 'AgX'
    return cam

def render(path, engine='BLENDER_EEVEE', samples=32):
    sc = bpy.context.scene
    setup()
    sc.render.engine = engine
    if engine == 'CYCLES':
        sc.cycles.samples = samples; sc.cycles.use_denoising = True
        try:
            sc.cycles.device = 'GPU'
        except Exception:
            pass
    sc.render.filepath = path
    bpy.ops.render.render(write_still=True)
    return path