WebGL-无法读取null的属性createShader
WebGL - cannot reader property createShader of null
我正在关注一本名为专业WebGL的书，我正在手写一些东西以确保我的理解，我有这样的代码：
<!DOCTYPE HTML>
<html lang="en">
<head>
<title>2-1 A first WebGL example</title>
<meta charset="utf-8">
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;
void main() {
gl_Position = vec4(aVertexPosition, 1.0);
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
void main() {
gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}
</script>
<script type="text/javascript">
var gl;
var canvas;
var shaderProgram;
var vertexBuffer;
/*Function to create the webgl context*/
function createGLContext(canvas) {
var names = ["webgl", "experimental-webgl"];
var context = null;
for(var i = 0; i < names.length; i++) {
try {
context = canvas.getContext(names[i]);
} catch(e) {
if(context) {
break;
}
}
}
if(context) {
context.viewportWidth = canvas.width;
context.viewportHeight = canvas.height;
} else {
alert("Failed to create webgl context");
}
return context;
}
function loadShaderFromDOM(id) {
var shaderScript = document.getElementById(id);
//if we don't find an element with the specified id
//we do an early exit
if(!shaderScript) {
return null;
}
//loop through the children for the found DOM element and
//build up the shader source code as a string.
var shaderSource = "";
var currentChild = shaderScript.firstChild;
while(currentChild) {
if(currentChild.nodeType == 3) {
//3 corresponds to TEXT_NODE
shaderSource += currentChild.textContent;
}
currentChild = currentChild.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, shaderSource);
gl.compileShader(shader);
if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
/*Function to setup the shaders*/
function setupShaders() {
var vertexShader = loadShaderFromDOM("shader-vs");
var fragmentShader = loadShaderFromDOM("shader-fs");
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
if(!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Failed toe setup shaders");
}
gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
}
/*Function to setup the buffers*/
function setupBuffers() {
vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
var triangleVertices = [
0.0, 0.5, 0.0,
-0.5, -0.5, 0.0,
0.5, -0.5, 0.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
vertexBuffer.itemSize = 3;
vertexBuffer.numberOfItems = 3;
}
/*Function to draw the triangle*/
function draw() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.celar(gl.COLOR_BUFFER_BIT);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, vertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.numberOfItems);
}
/*Function to kick everything off*/
function startup() {
canvas = document.getElementById("myGLCanvas");
gl = createGLContext(canvas);
setupShaders();
setupBuffers();
gl.clearColor(0.0, 0.0, 0.0, 0.1);
draw();
}
</script>
</head>
<body onload="startup()">
<canvas id="myGLCnvas" width="500" height="300"></canvas>
</body>
</html>
出于某种原因，它表示无法在此处读取createShader的属性null：shader = gl.createShader(gl.VERTEX_SHADER);
但是，对于相同的声明，它一点也不抱怨，而是使用片段着色器。
版本略有更改。gl.celar是错误的，并且是获取上下文的主循环。
<!DOCTYPE HTML>
<html lang="en">
<head>
<title>2-1 A first WebGL example</title>
<meta charset="utf-8">
<script id="shader-vs" type="x-shader/x-vertex">
attribute vec3 aVertexPosition;
void main() {
gl_Position = vec4(aVertexPosition, 1.0);
}
</script>
<script id="shader-fs" type="x-shader/x-fragment">
precision mediump float;
void main() {
gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);
}
</script>
<script type="text/javascript">
var gl;
var canvas;
var shaderProgram;
var vertexBuffer;
/*Function to create the webgl context*/
function createGLContext(canvas) {
var names = ["webgl", "experimental-webgl"];
gl = null;
for(var i = 0; i < names.length; i++) {
gl = canvas.getContext(names[i]);
if(gl)
break;
}
if(gl) {
gl.viewportWidth = canvas.width;
gl.viewportHeight = canvas.height;
} else {
console.log("Failed to create webgl context");
}
}
function loadShaderFromDOM(id) {
var shaderScript = document.getElementById(id);
//if we don't find an element with the specified id
//we do an early exit
if(!shaderScript) {
return null;
}
//loop through the children for the found DOM element and
//build up the shader source code as a string.
var shaderSource = "";
var currentChild = shaderScript.firstChild;
while(currentChild) {
if(currentChild.nodeType == 3) {
//3 corresponds to TEXT_NODE
shaderSource += currentChild.textContent;
}
currentChild = currentChild.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, shaderSource);
gl.compileShader(shader);
if(!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
alert(gl.getShaderInfoLog(shader));
return null;
}
return shader;
}
/*Function to setup the shaders*/
function setupShaders() {
var vertexShader = loadShaderFromDOM("shader-vs");
var fragmentShader = loadShaderFromDOM("shader-fs");
shaderProgram = gl.createProgram();
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
if(!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
alert("Failed toe setup shaders");
}
gl.useProgram(shaderProgram);
shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
}
/*Function to setup the buffers*/
function setupBuffers() {
vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
var triangleVertices = [
0.0, 0.5, 0.0,
-0.5, -0.5, 0.0,
0.5, -0.5, 0.0
];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
vertexBuffer.itemSize = 3;
vertexBuffer.numberOfItems = 3;
}
/*Function to draw the triangle*/
function draw() {
gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute, vertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
gl.drawArrays(gl.TRIANGLES, 0, vertexBuffer.numberOfItems);
}
/*Function to kick everything off*/
function startup() {
canvas = document.getElementById("myGLCnvas");
createGLContext(canvas);
setupShaders();
setupBuffers();
gl.clearColor(0.0, 0.0, 0.0, 0.1);
draw();
}
</script>
</head>
<body onload="startup()">
<canvas id="myGLCnvas" width="500" height="300"></canvas>
</body>
</html>
我也遇到了同样的问题，其中一个页面是一个打开的场景，以一个可以工作的html开始，而另一个页面则是一个死亡匹配，使用外部主文件和map和unitsize，并且没有硬编码，因此不起作用。两个页面的代码相同
CCD_ 4与CCD_。.min文件有效。
相关文章：
- RegEx删除空属性?例如，如果(class=“”||class=“”）移除;否则就下课
- 全局变量和全局对象的属性之间有什么区别吗
- 如果使用 lodash 将属性存在于另一个对象中，则向对象添加属性
- 如何在Bootstrap Modal中为动态点击生成的变量设置jade属性
- 序列化数据属性中对象的最可靠方法
- 分析高度属性时出现意外值｛｛specs.height｝｝.index.html
- TypeError:无法读取属性'推'未定义的JavaScript
- 同样，同样的错误'ahorcado.js:26未捕获类型错误:无法读取属性'beginPath'
- AngularJS-使用'true'属性
- 可以't使用JavaScript获取width属性
- 未捕获的TypeError无法读取未定义的属性socialsharing
- 如何使用javascript获取嵌套对象中所有子对象的单个属性
- JavaScript Pub/Sub属性访问问题
- 从JavaScript访问struts操作中的属性
- 是否可以从父类访问子类的属性
- 如何更改reactjs中外部/独立组件的状态或属性
- 如何在选项卡上定义属性'的主窗口对象
- 锚点元素的href属性自动更改
- jQuery最近父级的数据属性选择器
- WebGL-无法读取null的属性createShader
