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

[amulenkov]

I had the same problem and ended up encoding world space normals as RGB values, storing them in vertex colors, and rendering the mesh with pyrender.RenderFlags.FLAT flag. After that you can transform the world space normal maps to screen space. Alternatively you can extract normal maps directly from depth maps.

Although, it is possible that there is an easier solution already implemented in pyrender, in which case I would be interested to know it too.