Incoherent face index result of ray_cast

Question

I do a ray_cast from the camera along its direction to get the hit face:

def find_hit_face(camera, direction):
    _, _, _, hit_face_index, hit_object, _ = (
        scene.ray_cast(
            depsgraph=context.view_layer.depsgraph,
            origin=camera.location,
            direction=direction,
            distance=camera.data.clip_end,
        )
    )
    polygons = hit_object.data.polygons()
    return polygons[hit_face_index]

But I got the error IndexError: bpy_prop_collection[index]: index 5544 out of range, size 2224.

How can I get the hit face from the hit face index?

Answer 1

You need to query the evaluated object. By default raycasting acts on the evaluated scene so you want to query the evaluated object's polygons.

import bpy

def find_hit_face(camera, direction):
    _, _, _, hit_face_index, hit_object, _ = (
        scene.ray_cast(
            depsgraph=context.view_layer.depsgraph,
            origin=camera.location,
            direction=direction,
            distance=camera.data.clip_end,
        )
    )
    polygons = hit_object.evaluated_get(bpy.context.view_layer.depsgraph).data.polygons
    return polygons[hit_face_index]

Link to bpy.types.ID.evaluated_get docs