WebGL - 试图为正方形设置纹理，但由于某种原因它不起作用

所以我非常需要一个通读代码，如果有人这么善良的话-我不知道故障可能来自哪里-我一直在将此代码与教程中的代码进行比较：

http://learningwebgl.com/lessons/lesson05/index.html

我已经看了大约10遍了——我只是不知道。。。需要专业人士的帮助。。。只是试图纹理一个正方形，没有任何我现在不喜欢的3d东西-

    <script id="shader-fs" type="x-shader/x-fragment">
    precision mediump float;
    varying vec2 vTextureCoord;
    uniform sampler2D uSampler;
    void main(void) {
        gl_FragColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
       // gl_FragColor= vec4(0.0, 1.0, 0.0, 1.0);
    }
    </script>
<script id="shader-vs" type="x-shader/x-vertex">
    attribute vec3 aVertexPosition;
    attribute vec2 aTextureCoord;
    uniform mat4 uMVMatrix;
    uniform mat4 uPMatrix;
    varying vec2 vTextureCoord;

    void main(void) {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
        vTextureCoord = aTextureCoord;
    }
    </script>
<script type="text/javascript">
var gl;
function initGL(canvas) {
    try {
        gl = canvas.getContext("experimental-webgl");
        gl.viewportWidth = canvas.width;
        gl.viewportHeight = canvas.height;
    } catch (e) {
    }
    if (!gl) {
        alert("Could not initialise WebGL, sorry :-(");
    }
}

function getShader(gl, id) {
    var shaderScript = document.getElementById(id);
    if (!shaderScript) {
        return null;
    }
    var str = "";
    var k = shaderScript.firstChild;
    while (k) {
        if (k.nodeType == 3) {
            str += k.textContent;
        }
        k = k.nextSibling;
    }
    var shader;
    if (shaderScript.type == "x-shader/x-fragment") {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == "x-shader/x-vertex") {
        shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
        return null;
    }
    gl.shaderSource(shader, str);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        alert(gl.getShaderInfoLog(shader));
        return null;
    }
    return shader;
}

var shaderProgram;
function initShaders() {
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");
    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);
    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
        alert("Could not initialise shaders");
    }
    gl.useProgram(shaderProgram);
    shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);

    shaderProgram.textureCoordAttribute=gl.getAttribLocation(shaderProgram, "aTextureCoord");
    gl.enableVertexAttribArray(shaderProgram.textureCoordAttribute); //**
    shaderProgram.samplerUniform= gl.getUniformLocation(shaderProgram, "uSampler");

    shaderProgram.pMatrixUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
    shaderProgram.mvMatrixUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
}

var mvMatrix = mat4.create();
var pMatrix = mat4.create();
function setMatrixUniforms() {
    gl.uniformMatrix4fv(shaderProgram.pMatrixUniform, false, pMatrix);
    gl.uniformMatrix4fv(shaderProgram.mvMatrixUniform, false, mvMatrix);
}

var triangleVertexPositionBuffer;
var squareVertexPositionBuffer;
function initBuffers() {

    squareVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    vertices = [
         1.0,  1.0,  0.0,
        -1.0,  1.0,  0.0,
         1.0, -1.0,  0.0,
        -1.0, -1.0,  0.0
    ];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
    squareVertexPositionBuffer.itemSize = 3;
    squareVertexPositionBuffer.numItems = 4;

    squareTexPositionBuffer=gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, squareTexPositionBuffer);
    texvert= [1.0, 0.0,
              0.0, 0.0,
              1.0, 1.0,
              0.0, 1.0];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(texvert), gl.STATIC_DRAW);
    squareTexPositionBuffer.itemSize=2;
    squareTexPositionBuffer.numItems=4;


}

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, [-2.0, 0.0, -7.0]);

    mat4.translate(mvMatrix, [3.0, 0.0, 0.0]);
    gl.bindBuffer(gl.ARRAY_BUFFER, squareVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, squareVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    gl.bindBuffer(gl.ARRAY_BUFFER, squareTexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.textureCoordAttribute, squareTexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);
    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, neheTexture);
    gl.uniform1i(shaderProgram.samplerUniform, 0);



    setMatrixUniforms();
    gl.drawArrays(gl.TRIANGLE_STRIP, 0, squareVertexPositionBuffer.numItems);

}

function handleLoadedTexture(texture) {
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, texture.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);
}

var neheTexture;
function initTexture(){

    neheTexture = gl.createTexture();
    neheTexture.image = new Image();
    neheTexture.image.onload = function() {
        handleLoadedTexture(neheTexture)
    }
    neheTexture.image.src = "nehe.gif";
}

function webGLStart() {
    var canvas = document.getElementById("lesson01-canvas");
    initGL(canvas);
    initShaders();
    initBuffers();
    initTexture();
    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    gl.enable(gl.DEPTH_TEST);
    drawScene();
}

</script>