How to change texture in Gera library?

attribute         vec4 position;
attribute mediump vec4 textureCoordinate;

varying   mediump vec2 coordinate;

void main()
{
  gl_Position = position;
  coordinate  = textureCoordinate.xy;
}

varying highp vec2      coordinate;

uniform       sampler2D texture;

void main()
{
  gl_FragColor = texture2D(texture, coordinate);
}

     #define GL_FRAGMENT_PRECISION_HIGH 1

//file ExtensionsHandy.cs
using UnityEngine;
using UnityEngine.UI;
using System.Collections;
public static class ExtensionsHandy
{
public static float OrthoScreenWidth(this Camera c)
    {
    return
        c.ViewportToWorldPoint(new Vector3(1,1,10)).x
        - c.ViewportToWorldPoint(new Vector3(0,1,10)).x;
    }

public static float OrthoScreenHeight(this Camera c)
    {
    return
        c.ViewportToWorldPoint(new Vector3(0,1,10)).y
        - c.ViewportToWorldPoint(new Vector3(0,0,10)).y;
    }

}

   void Start()
     {
     float w = Camera.main.OrthoScreenWidth();
     Debug.Log("w is " +w.ToString("f4");
     }

 transform.ScreenRight();
 transform.ScreenTop();

void Update()
  {
  transform.ScreenRight();
  }

public static Vector3 WP( this Camera c, float x, float y, float z)
    {
    return c.ViewportToWorldPoint(new Vector3(x,y,z));
    }

public static void ScreenLeft(this GameObject moveme)
    {
    Vector3 rr = moveme.transform.position;

    Vector3 leftTop = Camera.main.WP(0f,1f,0f);
    float leftX = leftTop.x;

    rr.x = leftX;

    moveme.transform.position = rr;
    }

public static void ScreenRight(this GameObject moveme)
    {
    Vector3 rr = moveme.transform.position;

    Vector3 rightTop = Camera.main.WP(1f,1f,0f);
    float rightX = rightTop.x;

    rr.x = rightX;

    moveme.transform.position = rr;
    }

public static void ScreenBottom(this GameObject moveme)
    {
    Vector3 rr = moveme.transform.position;

    Vector3 bottomLeft = Camera.main.WP(0f,0f,0f);
    float bottomY = bottomLeft.y;

    rr.y = bottomY;

    moveme.transform.position = rr;
    }

public static void ScreenTop(this GameObject moveme)
    {
    Vector3 rr = moveme.transform.position;

    Vector3 topLeft = Camera.main.WP(0f,1f,0f);
    float topY = topLeft.y;

    rr.y = topY;

    moveme.transform.position = rr;
    }

var Wall1: GameObject; \\Existing Game Object
var wall1TC: Texture; \\Texture to change Existing Game Object to.

function OnTriggerEnter() {

    Wall1.GetComponent.<Renderer>().material.mainTexture = wall1TC;

}

const gl = document.createElement("canvas").getContext("webgl2");

testAttachment(gl.COLOR_ATTACHMENT1);
testAttachment(gl.COLOR_ATTACHMENT0);

function testAttachment(attachmentPoint) {

  function createTexture() {
    var texture = gl.createTexture();

    gl.bindTexture(gl.TEXTURE_2D, texture);
    var level = 0;
    var internalFormat = gl.RGBA32UI;
    var border = 0;
    var format = gl.RGBA_INTEGER;
    var type = gl.UNSIGNED_INT;
    var data = null;
    gl.texImage2D(gl.TEXTURE_2D, level, internalFormat,
      1, 1, border, format, type, data);

    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);
    return texture;
  }
  
  var texture = createTexture();

  var fb = gl.createFramebuffer();
  gl.bindFramebuffer(gl.FRAMEBUFFER, fb);

  var level = 0;
  gl.framebufferTexture2D(gl.FRAMEBUFFER, attachmentPoint, gl.TEXTURE_2D, texture, level);

  const status = gl.checkFramebufferStatus(gl.FRAMEBUFFER);

  console.log(glEnumToString(gl, attachmentPoint), glEnumToString(gl, status));
  
  if (status !== gl.FRAMEBUFFER_COMPLETE) {
    return;
  }
  
  const vs = `#version 300 es
  void main() {
     gl_Position = vec4(0,0,0,1);
     gl_PointSize = 100.0;
  }
  `;
  const fs = `#version 300 es
  uniform highp usampler2D color;
  out uvec4 outColor;
  void main() {
    outColor = texture(color, gl_PointCoord);
  }
  `;
  
  const prg = twgl.createProgram(gl, [vs, fs]);
  gl.useProgram(prg);
  
  // need a different input texture than output texture
  const inTex = createTexture();
  
  // no need to set uniforms since they default to 0
  // so using texture unit 0
  gl.drawArrays(gl.POINTS, 0, 1);

  // check that it rendered without error
  console.log(glEnumToString(gl, gl.getError()));
}

function glEnumToString(gl, value) {
  if (value === 0) { 
    return "NONE";
  }
  for (let key in gl) {
    if (gl[key] === value) {
      return key;
    }
  }
  return "0x" + value.toString(16);
}

<script src="https://twgljs.org/dist/4.x/twgl.min.js"></script>

int width = 150;
int height = 150;
Texture2D secondTexture;
public Texture2D source; //texture for a test, add in inspector
public Renderer rend; //Object for a test, add in inspector

      void Start()

    {
      secondTexture = new Texture2D(width, height);

      var pixels = new Color[width * height];
for (var x = 0; x < width; x++)
{
   for (var y = 0; y < height; y++)
   {
            Color pixels2 = source.GetPixel(x, y);

            if(pixels2 == Color.white)
            {
              //Paint the pixels in secondTexture that match X and Y of sourceTexture with blue per example
              pixels[x + y * width] = Color.blue;
            }
            else
            {
             //Paint the rest of the pixels with black
             pixels[x + y * width] = Color.black;
            }
   }
}
secondTexture.SetPixels(pixels);
secondTexture.wrapMode = TextureWrapMode.Clamp;
secondTexture.Apply();

rend.material.mainTexture = secondTexture;
    }