Как использовать несколько текстур в WebGL?

Я хотел использовать 6 различных текстур на кубе, по одной на сторону, но не могу найти ошибку. Вот мой текущий код:

   var texturen = new Array();
function initTexture(sFilename,texturen)  
{
  var anz = texturen.length;
  texturen[anz] = gl.createTexture();
  texturen[anz].image = new Image();
  texturen[anz].image.onload = function()    
  {
  gl.bindTexture(gl.TEXTURE_2D, texturen[anz]);
  gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, false);
  gl.texImage2D
  (gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, texturen[anz].image);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
  gl.bindTexture(gl.TEXTURE_2D, null);
  }
  texturen[anz].image.src = sFilename;
} 


var mvMatrix = mat4.create();
var mvMatrixStack = [];
var pMatrix = mat4.create();

function mvPushMatrix() {
    var copy = mat4.create();
    mat4.set(mvMatrix, copy);
    mvMatrixStack.push(copy);
}

function mvPopMatrix() {
    if (mvMatrixStack.length == 0) {
        throw "Invalid popMatrix!";
    }
    mvMatrix = mvMatrixStack.pop();
}


function setMatrixUniforms() {
    gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
    gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}


function degToRad(degrees) {
    return degrees * Math.PI / 180;
}

var cubeVertexPositionBuffer;
var cubeVertexTextureCoordBuffer;
var cubeVertexIndexBuffer;
var cubeVertexPositionBuffer1;
var cubeVertexTextureCoordBuffer1;
var cubeVertexIndexBuffer1;


function initBuffers() {
    cubeVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
    vertices = [
        // Front face
        -1.0, -1.0,  1.0,
         1.0, -1.0,  1.0,
         1.0,  1.0,  1.0,
        -1.0,  1.0,  1.0,

        // Back face
        -1.0, -1.0, -1.0,
        -1.0,  1.0, -1.0,
         1.0,  1.0, -1.0,
         1.0, -1.0, -1.0,

        // Top face
        -1.0,  1.0, -1.0,
        -1.0,  1.0,  1.0,
         1.0,  1.0,  1.0,
         1.0,  1.0, -1.0,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    cubeVertexPositionBuffer.itemSize = 3;
    cubeVertexPositionBuffer.numItems = 12;

cubeVertexPositionBuffer1 = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer1);
    vertices = [
       // Bottom face
        -1.0, -1.0, -1.0,
         1.0, -1.0, -1.0,
         1.0, -1.0,  1.0,
        -1.0, -1.0,  1.0,

        // Right face
         1.0, -1.0, -1.0,
         1.0,  1.0, -1.0,
         1.0,  1.0,  1.0,
         1.0, -1.0,  1.0,

        // Left face
        -1.0, -1.0, -1.0,
        -1.0, -1.0,  1.0,
        -1.0,  1.0,  1.0,
        -1.0,  1.0, -1.0,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    cubeVertexPositionBuffer1.itemSize = 3;
    cubeVertexPositionBuffer1.numItems = 12;


    cubeVertexTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexTextureCoordBuffer);
    var textureCoords = [
      // Front face
      0.0, 0.0,
      1.0, 0.0,
      1.0, 1.0,
      0.0, 1.0,

      // Back face
      1.0, 0.0,
      1.0, 1.0,
      0.0, 1.0,
      0.0, 0.0,

      // Top face
      0.0, 1.0,
      0.0, 0.0,
      1.0, 0.0,
      1.0, 1.0,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), gl.STATIC_DRAW);
    cubeVertexTextureCoordBuffer.itemSize = 2;
    cubeVertexTextureCoordBuffer.numItems = 12;



cubeVertexTextureCoordBuffer1 = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexTextureCoordBuffer1);
    var textureCoords = [
   // Bottom face
      1.0, 1.0,
      0.0, 1.0,
      0.0, 0.0,
      1.0, 0.0,

      // Right face
      1.0, 0.0,
      1.0, 1.0,
      0.0, 1.0,
      0.0, 0.0,

      // Left face
      0.0, 0.0,
      1.0, 0.0,
      1.0, 1.0,
      0.0, 1.0,
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoords), gl.STATIC_DRAW);
    cubeVertexTextureCoordBuffer1.itemSize = 2;
    cubeVertexTextureCoordBuffer1.numItems = 12;

cubeVertexIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);
    var cubeVertexIndices = [
        0, 1, 2,      0, 2, 3,    // Front face
        4, 5, 6,      4, 6, 7,    // Back face
        8, 9, 10,     8, 10, 11,  // Top face
    ];
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
    cubeVertexIndexBuffer.itemSize = 1;
    cubeVertexIndexBuffer.numItems = 18;

cubeVertexIndexBuffer1 = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer1);
    var cubeVertexIndices = [
        12, 13, 14,   12, 14, 15, // Bottom face
        16, 17, 18,   16, 18, 19, // Right face
        20, 21, 22,   20, 22, 23  // Left face
    ];
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
    cubeVertexIndexBuffer1.itemSize = 1;
    cubeVertexIndexBuffer1.numItems = 18;



}


var xRot = 0;
var yRot = 0;
var zRot = 0;

function drawScene() {
    gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    mat4.perspective(45, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0, pMatrix);

    mat4.identity(mvMatrix);

    mat4.translate(mvMatrix, [0.0, 0.0, -5.0]);

    mat4.rotate(mvMatrix, degToRad(xRot), [1, 0, 0]);
    mat4.rotate(mvMatrix, degToRad(yRot), [0, 1, 0]);
    mat4.rotate(mvMatrix, degToRad(zRot), [0, 0, 0]);
    setMatrixUniforms();

 gl.activeTexture(gl.TEXTURE0);
 gl.bindTexture(gl.TEXTURE_2D, texturen[0]); 
 gl.vertexAttribPointer
 (textureCoordAttribute, cubeVertexTextureCoordBuffer.itemSize,  gl.FLOAT, false, 0,  0);
   gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer);
  gl.vertexAttribPointer
  (shaderProgram.vertexPositionAttribute,cubeVertexPositionBuffer.itemSize, 
  gl.FLOAT, false, 0, 0);

  gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer);

    gl.drawElements(gl.TRIANGLES, cubeVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);


 gl.activeTexture(gl.TEXTURE1);
 gl.bindTexture(gl.TEXTURE_2D, texturen[1]); 
 gl.vertexAttribPointer
 (textureCoordAttribute, cubeVertexTextureCoordBuffer1.itemSize,  gl.FLOAT, false, 0, 0);
 gl.bindBuffer(gl.ARRAY_BUFFER, cubeVertexPositionBuffer1);
 gl.vertexAttribPointer
 (shaderProgram.vertexPositionAttribute,cubeVertexPositionBuffer1.itemSize, 
  gl.FLOAT, false, 0, 0);


    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVertexIndexBuffer1);

    gl.drawElements(gl.TRIANGLES, cubeVertexIndexBuffer1.numItems, gl.UNSIGNED_SHORT, 0);


}

Я просто разделил его на две части, пытаясь сделать тест с двумя разными картинками. И для чего нужны cubeVertexIndexBuffers?

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