在WebGL中呈现领域遇到困难

Question

我正在学习WebGL，并且正在尝试显示一个领域。没有纹理，只有每个顶点颜色，但是我在Opera和Chrome中收到以下错误消息：“ [.WebGlrenderingContext] GL错误：GL_INVALID_OPERATION：GLDRAWELEMENTS：尝试在属性1中访问范围顶点1”。

我不明白我在做什么错，因为代码对我来说看起来不错，但是我显然缺少一些东西。

谢谢！迈克尔

（它是根据课程4和11的改编 http://learningwebgl.com.)

    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.vertexColorAttribute = gl.getAttribLocation(shaderProgram, "aVertexColor");
    gl.enableVertexAttribArray(shaderProgram.vertexColorAttribute);

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


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

function mvPushMatrix() {
    var copy = mat4.create();
    mat4.copy(copy, mvMatrix);
    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 sphereVertexPositionBuffer;
var sphereVertexColorBuffer;
var sphereVertexIndexBuffer;

function initBuffers() {
    var latitudeBands = 10;
    var longitudeBands = 10;
    var radius = 2;

    sphereVertexPositionBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, sphereVertexPositionBuffer);
    sphereVertexColorBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, sphereVertexColorBuffer);
    sphereVertexIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, sphereVertexIndexBuffer);

    var vertexPositionData = [];
    var colors = [];
    var indexData = [];
    for (var latNumber=0; latNumber <= latitudeBands; latNumber++) {
        var theta = latNumber * Math.PI / latitudeBands;
        var sinTheta = Math.sin(theta);
        var cosTheta = Math.cos(theta);

        for (var longNumber=0; longNumber <= longitudeBands; longNumber++) {
            var phi = longNumber * 2 * Math.PI / longitudeBands;
            var sinPhi = Math.sin(phi);
            var cosPhi = Math.cos(phi);

            var x = cosPhi * sinTheta;
            var y = cosTheta;
            var z = sinPhi * sinTheta;

            colors = [[1.0, 1.0, 0.3, 1.0]];
            vertexPositionData.push(radius * x);
            vertexPositionData.push(radius * y);
            vertexPositionData.push(radius * z);

            var first = (latNumber * (longitudeBands + 1)) + longNumber;
            var second = first + longitudeBands + 1;
            indexData.push(first);
            indexData.push(second);
            indexData.push(first + 1);

            indexData.push(second);
            indexData.push(second + 1);
            indexData.push(first + 1);
        }
    }

    var unpackedColors = [];
    for (var i in colors) {
        var color = colors[i];
        for (var j=0; j < 4; j++) {
            unpackedColors = unpackedColors.concat(color);
        }
    }

    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertexPositionData), gl.STATIC_DRAW);
    sphereVertexPositionBuffer.itemSize = 3;
    sphereVertexPositionBuffer.numItems = vertexPositionData.length / 3;

    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(unpackedColors), gl.STATIC_DRAW);
    sphereVertexColorBuffer.itemSize = 4;
    sphereVertexColorBuffer.numItems = unpackedColors.length / 4;

    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indexData), gl.STATIC_DRAW);
    sphereVertexIndexBuffer.itemSize = 1;
    sphereVertexIndexBuffer.numItems = indexData.length;

}


var rSphere = 0;

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

    mat4.perspective(pMatrix, 60, gl.viewportWidth / gl.viewportHeight, 0.1, 100.0);

    mat4.identity(mvMatrix);

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

    mvPushMatrix();
    mat4.rotate(mvMatrix, mvMatrix, degToRad(rSphere), [1, 1, 1]);

    gl.bindBuffer(gl.ARRAY_BUFFER, sphereVertexPositionBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, sphereVertexPositionBuffer.itemSize, gl.FLOAT, false, 0, 0);

    gl.bindBuffer(gl.ARRAY_BUFFER, sphereVertexColorBuffer);
    gl.vertexAttribPointer(shaderProgram.vertexColorAttribute, sphereVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);

    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, sphereVertexIndexBuffer);
    setMatrixUniforms();
    gl.drawElements(gl.TRIANGLES, sphereVertexIndexBuffer.numItems, gl.UNSIGNED_SHORT, 0);

    mvPopMatrix();

}


var lastTime = 0;

function animate() {
    var timeNow = new Date().getTime();
    if (lastTime != 0) {
        var elapsed = timeNow - lastTime;

        rSphere -= (75 * elapsed) / 1000.0;
    }
    lastTime = timeNow;
}


function tick() {
    requestAnimFrame(tick);
    drawScene();
    animate();
}


function webGLStart() {
    var canvas = document.getElementById("lesson04-canvas");
    initGL(canvas);
    initShaders()
    initBuffers();

    gl.clearColor(0.0, 0.0, 0.1, 1.0);
    gl.enable(gl.DEPTH_TEST);

    tick();
}

Answer 1

我找到了问题！

我将索引创建包括在循环中（小于或等于）：

for (var latNumber=0; latNumber <= latitudeBands; latNumber++)
for (var longNumber=0; longNumber <= longitudeBands; longNumber++)

而不是自己的循环（小于）：

for (var latNumber=0; latNumber < latitudeBands; latNumber++) 
for (var longNumber=0; longNumber < longitudeBands; longNumber++)