Plane.Raycast

Description

Intersects a ray with the plane.

This function sets enter to the distance along the ray, where it intersects the plane. If the ray is parallel to the plane, function returns false and sets enter to zero. If the ray is pointing in the opposite direction than the plane, function returns false/ and sets enter to the distance along the ray (negative value).

// Position a marker object at the point on the "ground" where the
// mouse is clicked. The ground is represented by a Plane object.
var groundPlane: Plane;
var markerObject: Transform;

function Update() {
    // If the mouse button is clicked...
    if (Input.GetMouseButtonDown(0)) {
        // Get a ray corresponding to the screen position of the mouse.
        var ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        var rayDistance: float;

        // If the ray makes contact with the ground plane then
        // position the marker at the distance along the ray where it
        // crosses the plane.
        if (groundPlane.Raycast(ray, rayDistance)) {
            markerObject.position = ray.GetPoint(rayDistance);
        }
    }
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Plane groundPlane;
    public Transform markerObject;
    void Update() {
        if (Input.GetMouseButtonDown(0)) {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            float rayDistance;
            if (groundPlane.Raycast(ray, out rayDistance))
                markerObject.position = ray.GetPoint(rayDistance);
            
        }
    }
}

See Also: Physics.Raycast.