Function cuboid_cuboid_find_local_separating_normal_oneway

pub fn cuboid_cuboid_find_local_separating_normal_oneway(
    cuboid1: &Cuboid,
    cuboid2: &Cuboid,
    pos12: &Isometry<f32>,
) -> (f32, Vector<f32>)

Finds the best separating axis by testing the face normals of the first cuboid.

This function tests the face normals (X, Y, Z axes in 2D/3D) of cuboid1 to find which direction gives the maximum separation between the two cuboids. This is the “one-way” test that only considers faces from one cuboid.

Why “One-Way”?

For a complete SAT test between two cuboids, you need to test:

1. Face normals from cuboid1 (this function)
2. Face normals from cuboid2 (call this function again with swapped arguments)
3. Edge-edge cross products in 3D (cuboid_cuboid_find_local_separating_edge_twoway)

By testing only one shape’s normals at a time, the implementation can be more efficient and reusable.

Parameters

• cuboid1: The cuboid whose face normals will be tested
• cuboid2: The other cuboid
• pos12: The position of cuboid2 relative to cuboid1

Returns

A tuple containing:

• Real: The maximum separation found among cuboid1’s face normals
  • Positive: Shapes are separated by at least this distance
  • Negative: Shapes are overlapping (penetration)
• Vector<Real>: The face normal direction that gives this separation

Example

use parry2d::shape::Cuboid;
use parry2d::query::sat::cuboid_cuboid_find_local_separating_normal_oneway;
use nalgebra::{Isometry2, Vector2};

let rect1 = Cuboid::new(Vector2::new(1.0, 1.0));
let rect2 = Cuboid::new(Vector2::new(0.5, 0.5));

// Position rect2 to the right of rect1
let pos12 = Isometry2::translation(2.5, 0.0);

// Test rect1's face normals (X and Y axes)
let (sep1, normal1) = cuboid_cuboid_find_local_separating_normal_oneway(
    &rect1, &rect2, &pos12
);

// Test rect2's face normals by swapping arguments and inverting the transform
let (sep2, normal2) = cuboid_cuboid_find_local_separating_normal_oneway(
    &rect2, &rect1, &pos12.inverse()
);

// The maximum separation indicates if shapes collide
let max_separation = sep1.max(sep2);
if max_separation > 0.0 {
    println!("Shapes are separated!");
}

Algorithm Details

For each axis (X, Y, and Z in 3D):

1. Computes the support point on cuboid2 in the negative axis direction
2. Transforms it to cuboid1’s space
3. Measures the signed distance from cuboid1’s boundary
4. Tracks the axis with maximum separation