How to render normal maps?

[dqj5182]

I wish to render normal maps based on this code. For different trials, I have done changing flags from "flags=pyrender.RenderFlags.RGBA" to "pyrender.RenderFlags.VERTEX_NORMALS". Could you give recommendations on how to render normal maps with Pyrender?

def render_mesh(img, mesh, face, cam_param):
    # mesh
    mesh = trimesh.Trimesh(mesh, face)
    rot = trimesh.transformations.rotation_matrix(
	np.radians(180), [1, 0, 0])
    mesh.apply_transform(rot)
    material = pyrender.MetallicRoughnessMaterial(metallicFactor=0.0, alphaMode='OPAQUE', baseColorFactor=(1.0, 1.0, 0.9, 1.0))
    mesh = pyrender.Mesh.from_trimesh(mesh, material=material, smooth=False)
    scene = pyrender.Scene(ambient_light=(0.3, 0.3, 0.3))
    scene.add(mesh, 'mesh')
    
    focal, princpt = cam_param['focal'], cam_param['princpt']
    camera = pyrender.IntrinsicsCamera(fx=focal[0], fy=focal[1], cx=princpt[0], cy=princpt[1])
    scene.add(camera)
 
    # renderer
    renderer = pyrender.OffscreenRenderer(viewport_width=img.shape[1], viewport_height=img.shape[0], point_size=1.0)
   
    # light
    light = pyrender.DirectionalLight(color=[1.0, 1.0, 1.0], intensity=0.8)
    light_pose = np.eye(4)
    light_pose[:3, 3] = np.array([0, -1, 1])
    scene.add(light, pose=light_pose)
    light_pose[:3, 3] = np.array([0, 1, 1])
    scene.add(light, pose=light_pose)
    light_pose[:3, 3] = np.array([1, 1, 2])
    scene.add(light, pose=light_pose)

    # render
    rgb, depth = renderer.render(scene, flags=pyrender.RenderFlags.RGBA)
    rgb = rgb[:,:,:3].astype(np.float32)
    valid_mask = (depth > 0)[:,:,None]

    # save to image
    img = rgb * valid_mask + img * (1-valid_mask)
    return img