Snappping the 3D cursor to the surface and find the surface's face it was snapped to

Question

To snap the 3D cursor to the surface of my object, I set the "Cursor Depth" to True in the interface user preferences. How can I know exactly to which face/vertice the cursor was snapped (in code)? Do I need to use object.closest_point_on_mesh?

object.closest_point_on_mesh(bpy.context.scene.cursor_location)

Or maybe this data is stored somewhere? Isn't is the whole purpose of Cursor Depth? Also, how can I know which object was it snapped to, in the case of multiple objects in the scene? Thanks!

Answer 1

Using Scene.ray_cast

---

Can shoot a ray into the scene using Scene.ray_cast from the cursor location, in the direction of the converted view matrix's z axis. Test code, prints the ray hit (if hit) of each 3d view in the context screen.

import bpy
from mathutils import Vector
context = bpy.context
screen = context.screen
scene = context.scene
areas3d = [a for a in screen.areas if a.type == 'VIEW_3D']
for a in areas3d:
    r3d = a.spaces.active.region_3d
    vm = r3d.view_matrix.transposed().to_3x3().to_4x4()
    norm = vm * Vector((0, 0, 1))
    norm.normalize() 
    ray = scene.ray_cast(scene.cursor_location, norm)
    hit, loc, norm, face, obj, matrix = ray
    if hit:
        print("hit object", obj, "on face:", face)