Vertex colouring on a plane (moving plane)

Questions & Answers
1

In my scene I have a plane with a sphere resting on it. I have the vertices changing colour as the sphere moves across the plane. As soon as I try to move the plane instead of moving the sphere it stops working (I need it this way for a different project). Even moving the plane a tiny amount stops the vertices changing colour. I suspect its something to do with the vertex locations being different when the plane is moved. Heres the code I’m using:

using UnityEngine;
using System.Collections;

//[ExecuteInEditMode]

public class Plane : MonoBehaviour {

	public Vector3 contactPoint;
	public Vector3 nearestVert;
	
	float h, v;


	Mesh mesh;
	Vector3[] verts;
	Vector3 vertPos;
	Color[] colors;
	
	// Use this for initialization
	void Start () {

		mesh = GetComponent<MeshFilter>().mesh;

	}
	
	// Update is called once per frame
	void Update () {

		verts = mesh.vertices;
		colors = mesh.colors;
		
		//v = Input.GetAxis("Vertical");
		//h = Input.GetAxis("Horizontal");

		//transform.Translate(h*0.2f, 0, v*0.2f);

		nearestVert = NearestVertexTo(contactPoint);
		Debug.Log("NearestVert: " + nearestVert);

		for( int i = 0; i < verts.Length; i++)
		{
			if(verts *== nearestVert)*

  •  	{*

  •  		Debug.Log("Collision Yo");*

_ colors = Color.red;_
* }*
* }*

* mesh.colors = colors;*
* mesh.vertices = verts;*
* mesh.RecalculateBounds();*
* mesh.RecalculateNormals();*

* }*

* public Vector3 NearestVertexTo(Vector3 point)*
* {*
* // convert point to local space*
* point = transform.InverseTransformPoint(point);*

* float minDistanceSqr = Mathf.Infinity;*
* Vector3 nearestVertex = Vector3.zero;*

* // scan all vertices to find nearest*
* foreach (Vector3 vertex in mesh.vertices)*
* {*
* Vector3 diff = point-vertex;*
* float distSqr = diff.sqrMagnitude;*

* if (distSqr < minDistanceSqr)*
* {*
* minDistanceSqr = distSqr;*
* nearestVertex = vertex;*
* }*
* }*

* // convert nearest vertex back to world space*
* return transform.TransformPoint(nearestVertex);*

* }*

* void OnCollisionStay(Collision collision) {*
* foreach (ContactPoint contact in collision.contacts) {*
* Debug.DrawRay(contact.point, Vector3.up, Color.green, 4, false);*
* contactPoint = contact.point;*
* }*
* }*
}
Any pointers on how I could move forward from here? What I need is the plane to move, the sphere to be stationary and the vertices to still change colour.
Thanks

2

I believe line 79 is your issue. You are converting the point found back into world space, but you are using in a comparison of local coordinates on line 42. The only way I can see this code working is if the plane is at (0,0,0) and scaled (1,1,1). Rewrite line 79 to:

return nearestVertex;

But there are some other things here that you should consider changing. There is no reason to go through the vertices twice. You go through them once in NearestVertexTo() then again on 40. Instead, rewrite NearestVertexTo() so that it uses a for() loop instead of a foreach() loop, and then return the index of the closest vertex. You also don’t need to reset the vertices or recalculate the bounds or recalculate the normals. Here is a quick, untested rewrite:

using UnityEngine;
using System.Collections;

public class Plane : MonoBehaviour {
	
	public Vector3 contactPoint;
	public Vector3 nearestVert;
	
	Mesh mesh;
	Vector3[] verts;
	Vector3 vertPos;
	Color[] colors;
	
	void Start () {
		mesh = GetComponent<MeshFilter>().mesh;
		verts = mesh.vertices;
		colors = mesh.colors;
	}
	
	void Update () {
		colors[NearestVertexTo(contactPoint)] = Color.red;
		mesh.colors = colors;
	}
	
	int NearestVertexTo(Vector3 point) {
		point = transform.InverseTransformPoint(point);
		
		float minDistanceSqr = Mathf.Infinity;
		int nearestVertex = -1; 

		// scan all vertices to find nearest
		for (int i = 0; i < verts.Length; i++) {
			float distSqr = (point - verts*).sqrMagnitude;*

  •  	if (distSqr < minDistanceSqr) {*

  •  		minDistanceSqr = distSqr;*

  •  		nearestVertex = i;*

  •  	}*

  •  }*

  •  return nearestVertex;*

  • }*

  • void OnCollisionStay(Collision collision) {*

  •  foreach (ContactPoint contact in collision.contacts) {*

  •  	Debug.DrawRay(contact.point, Vector3.up, Color.green, 4, false);*

  •  	contactPoint = contact.point;*

  •  }*

  • }*
    }