Finding closest distance from point to mesh in BGE

Question

In BGE, I have a simple mesh, say, a cube that has been subdivided a few times to give it more than 8 vertices, like so:

What I'd like to do, generically speaking, is find the shortest distance from the surface, or alternately the bounding box, of that mesh a given location.

To be more specific, I want to find the distance from the camera (player) to the mesh. I would then pass that information into a text field on a HUD (which I already know how to do). Think of it like a range-finder, where the player always sees the distance from him/herself to the target object. I've found a few methods that work using the object's origin, but that doesn't work for me. I need the distance to the closest vertex on the object's mesh. Or alternately, at least the closest point on the object's bounding box.

I know how to get the camera's current location with object.worldPosition. I've tested that successfully.

Here's what else I've found so far, none of which works for me:

• closest_point_on_mesh, an object property in BPY. This seems like it would work perfectly - I'd find the closest point, and find the distance from that point to the camera's location. Except that it's only for BPY, which doesn't help me for BGE.
• Ray casting in BGE, from this similar object property list for BGE. I'm not quite understanding how ray casting works here or how I would use it to find the nearest point to my origin point (the camera location). Note, I already know what mesh I want to "hit" (the cube), I just need to find the closest vertex or closest point on its surface.
• This StackExchange answer that relates to BPY. Again, I need a BGE-workable solution.
• This other StackExchange answer that is in BGE, but it is only for the distance between two objects' origins. I need the distance from one point, to the closest point on the object. Not the origin-to-origin distance.

Finally, here's what I've tried to implement. Since object.closest_point_on_mesh from the first bullet above seems to be the closest to what I want, I decided why not try it in BGE and see if it works after all. It didn't.

import bge
from math import sqrt

#There's a bunch of other code in here that I won't repeat,
#but one of them is getHUDfield(), which retrieves the text
#objects in the HUD scene so that their text can be updated

def RangeUpdate():
    #Have this actuated by "Always" and reside on the camera
    #Find camera location
    cam_loc = bge.logic.getCurrentController().owner.worldPosition
    print(cam_loc) #for debugging - this works, successfully gives me the cam's location in the console
    #Find the cube object and find the closest point on its mesh
    objects = bge.logic.getCurrentScene().objects
    bounding_cube = objects["Cube_00"]
    loc, norm, idx = bounding_cube.closest_point_on_mesh(cam_loc)
    #^^^Right now the problem is here: closest_point_on_mesh might not work in BGE?

    #Find the distance between cam's location and this location
    dist = sqrt((loc[0]-cam_loc[0])**2 + (loc[1]-cam_loc[1])**2 + (loc[2]-cam_loc[2])**2)

    #Display it on the HUDfield called RangeLabel
    allhudfields = getHUDfield()
    hudfield = allhudfields["RangeLabel"]
    hudfield["Text"] = str(dist) + " blender units"

The code fails at bounding_cube.closest_point_on_mesh(cam_loc). The console output says AttributeError: 'KX_GameObject' object has no attribute 'closest_point_on_mesh' For the curious or skeptical, the part where it updates the hud field's text DOES work (if I feed it a dummy value). Clearly the failure is in finding the point on the mesh closest to the given location.

So does anyone know either how I can do something similar to calling the property closest_point_on_mesh, but in BGE instead of BPY? Or, is there a totally different method or a work-around that works in BGE? To reiterate, my objective is to find the shortest possible distance from an arbitrary point (the camera's location), to the surface of a specified object/mesh (or at least the nearest vertex on the mesh, or the closest point on its bounding box).

Answer 1

If it's just the distance to the Bound Box, does not require any complex function for this.

I do not usually use bge, but you can take advantage of this code to get the nearest point of a Bound_Box.

#bound.min: smaller coordinates x, y, z of Bound Box
#bound.max: greater coordinates x, y, z of Bound Box
#co coordinate of the point to test the nearest
from math import sqrt
def find_nearest_t_AABB(bound, co):
    nearest = [0.,0.,0.]
    dist = 0.
    for i in range(3):
        if (bounds.min[i] > co[i]):
            nearest[i] = bounds.min[i]
        elif (bounds.max[i] < co[i]):
            nearest[i] = bounds.max[i]
        else:
            nearest[i] = co[i]

        dist += (co[i] - nearest[i])**2
    return sqrt(dist), nearest

Answer 2

To get the closest vertex to a mesh you can build a kdtree and check a point to get the closest vertex, but be aware, any time the object moves you will need to build a new tree.