Function triangle 

pub fn triangle(
    origin: [f32; 3],
    direction: [f32; 3],
    vertices: [[f32; 3]; 3],
    maximum: f32,
) -> Option<f32>

Test a ray against one triangle. Returns the distance along the ray when the ray hits the triangle no farther than maximum.

Only front faces count. A hit on an edge, at distance zero or exactly at the current maximum counts too, and an equal distance replaces the earlier hit, as in the original’s order.