前提条件和预期结果
目前只有少数的浏览器支持 WebGL ,请看我的另外一篇文章:Can I use WebGL?.
下面的例子是在 Windows 下的 Chrome 16/23 以及 Android 下的 Firefox 17 进行测试。如果你使用的是非兼容浏览器访问则会弹出一个警告。
图1:包含 Hello world 文本的动画的 WebGL 立方体
在兼容 HTML5 的浏览器上,你将会看到如下图所示的带动画效果的立方体:
图2: 示例运行的屏幕截图
该代码基于 Lighting in WebGL - How to simulate lighting effects in your WebGL context - 非常感谢这篇教程。在该实例初始运行时,动画的立方体是通过一个静态的 Bitmap 图形对象渲染的。
下面的代码演示如何在程序中动态的渲染文本:
XML/HTML Code复制内容到剪贴板
- // TODO #1 New method to create a texture
- function createCubeTexture(text) {
- ...
- }
在这里使用 gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true); 是非常重要的,用来确保写文本时不会前后颠倒。剩下的就很容易理解了:
XML/HTML Code复制内容到剪贴板
- // TODO #2 Assign the created texture for display
- cubeTexture = createCubeTexture(\"Hello World!\");
源码
// File #1: webgl-demo.htm
XML/HTML Code复制内容到剪贴板
- <html>
- <head>
- <title>WebGL - Hello World!</title>
- <meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\">
- <script src=\"sylvester.js\" type=\"text/javascript\"></script>
- <script src=\"glUtils.js\" type=\"text/javascript\"></script>
- <script src=\"webgl-demo.js\" type=\"text/javascript\"></script>
-
-
- <script id=\"shader-fs\" type=\"x-shader/x-fragment\">
- varying highp vec2 vTextureCoord;
- varying highp vec3 vLighting;
-
- uniform sampler2D uSampler;
-
- void main(void) {
- highp vec4 texelColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
-
- gl_FragColor = vec4(texelColor.rgb * vLighting, texelColor.a);
- }
- </script>
-
-
- <script id=\"shader-vs\" type=\"x-shader/x-vertex\">
- attribute highp vec3 aVertexNormal;
- attribute highp vec3 aVertexPosition;
- attribute highp vec2 aTextureCoord;
-
- uniform highp mat4 uNormalMatrix;
- uniform highp mat4 uMVMatrix;
- uniform highp mat4 uPMatrix;
-
- varying highp vec2 vTextureCoord;
- varying highp vec3 vLighting;
-
- void main(void) {
- gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
- vTextureCoord = aTextureCoord;
-
- // Apply lighting effect
-
- highp vec3 ambientLight = vec3(0.6, 0.6, 0.6);
- highp vec3 directionalLightColor = vec3(0.5, 0.5, 0.75);
- highp vec3 directionalVector = vec3(0.85, 0.8, 0.75);
- highp vec4 transformedNormal = uNormalMatrix * vec4(aVertexNormal, 1.0);
-
- highp float directional = max(dot(transformedNormal.xyz, directionalVector), 0.0);
- vLighting = ambientLight + (directionalLightColor * directional);
- }
- </script>
- </head>
-
- <body onload=\"start()\">
- <canvas id=\"glcanvas\" width=\"640\" height=\"480\">
- Your browser doesn\'t appear to support the HTML5 <code><canvas></code> element.
- </canvas>
- </body>
- </html>
// File #02: webgl-demo.js
XML/HTML Code复制内容到剪贴板
- var canvas;
- var gl;
-
- var cubeVerticesBuffer;
- var cubeVerticesTextureCoordBuffer;
- var cubeVerticesIndexBuffer;
- var cubeVerticesIndexBuffer;
- var cubeRotation = 0.0;
- var lastCubeUpdateTime = 0;
-
- var cubeImage;
- var cubeTexture;
-
- var mvMatrix;
- var shaderProgram;
- var vertexPositionAttribute;
- var vertexNormalAttribute;
- var textureCoordAttribute;
- var perspectiveMatrix;
-
- //
- // start
- //
- // Called when the canvas is created to get the ball rolling.
- //
- function start() {
- canvas = document.getElementById(\"glcanvas\");
-
- initWebGL(canvas); // Initialize the GL context
-
- // Only continue if WebGL is available and working
-
- if (gl) {
- gl.clearColor(0.0, 0.0, 0.0, 1.0); // Clear to black, fully opaque
- gl.clearDepth(1.0); // Clear everything
- gl.enable(gl.DEPTH_TEST); // Enable depth testing
- gl.depthFunc(gl.LEQUAL); // Near things obscure far things
-
- // Initialize the shaders; this is where all the lighting for the
- // vertices and so forth is established.
-
- initShaders();
-
- // Here\'s where we call the routine that builds all the objects
- // we\'ll be drawing.
-
- initBuffers();
-
- // Next, load and set up the textures we\'ll be using.
-
- // TODO#2 Start
- cubeTexture = createCubeTexture(\"Hello World!\");
- // TODO#2 End
-
- // Set up to draw the scene periodically.
-
- setInterval(drawScene, 15);
- }
- }
-
- //
- // initWebGL
- //
- // Initialize WebGL, returning the GL context or null if
- // WebGL isn\'t available or could not be initialized.
- //
- function initWebGL() {
- gl = null;
-
- try {
- gl = canvas.getContext(\"experimental-webgl\");
- }
- catch(e) {
- }
-
- // If we don\'t have a GL context, give up now
-
- if (!gl) {
- alert(\"Unable to initialize WebGL. Your browser may not support it.\");
- }
- }
-
- //
- // initBuffers
- //
- // Initialize the buffers we\'ll need. For this demo, we just have
- // one object -- a simple two-dimensional cube.
- //
- function initBuffers() {
-
- // Create a buffer for the cube\'s vertices.
-
- cubeVerticesBuffer = gl.createBuffer();
-
- // Select the cubeVerticesBuffer as the one to apply vertex
- // operations to from here out.
-
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesBuffer);
-
- // Now create an array of vertices for the cube.
-
- var 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,
-
- // 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
- ];
-
- // Now pass the list of vertices into WebGL to build the shape. We
- // do this by creating a Float32Array from the JavaScript array,
- // then use it to fill the current vertex buffer.
-
- gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);
-
- // Set up the normals for the vertices, so that we can compute lighting.
-
- cubeVerticesNormalBuffer = gl.createBuffer();
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesNormalBuffer);
-
- var vertexNormals = [
- // Front
- 0.0, 0.0, 1.0,
- 0.0, 0.0, 1.0,
- 0.0, 0.0, 1.0,
- 0.0, 0.0, 1.0,
-
- // Back
- 0.0, 0.0, -1.0,
- 0.0, 0.0, -1.0,
- 0.0, 0.0, -1.0,
- 0.0, 0.0, -1.0,
-
- // Top
- 0.0, 1.0, 0.0,
- 0.0, 1.0, 0.0,
- 0.0, 1.0, 0.0,
- 0.0, 1.0, 0.0,
-
- // Bottom
- 0.0, -1.0, 0.0,
- 0.0, -1.0, 0.0,
- 0.0, -1.0, 0.0,
- 0.0, -1.0, 0.0,
-
- // Right
- 1.0, 0.0, 0.0,
- 1.0, 0.0, 0.0,
- 1.0, 0.0, 0.0,
- 1.0, 0.0, 0.0,
-
- // Left
- -1.0, 0.0, 0.0,
- -1.0, 0.0, 0.0,
- -1.0, 0.0, 0.0,
- -1.0, 0.0, 0.0
- ];
-
- gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertexNormals),
- gl.STATIC_DRAW);
-
- // Map the texture onto the cube\'s faces.
-
- cubeVerticesTextureCoordBuffer = gl.createBuffer();
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesTextureCoordBuffer);
-
- var textureCoordinates = [
- // Front
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0,
- // Back
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0,
- // Top
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0,
- // Bottom
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0,
- // Right
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0,
- // Left
- 0.0, 0.0,
- 1.0, 0.0,
- 1.0, 1.0,
- 0.0, 1.0
- ];
-
- gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoordinates),
- gl.STATIC_DRAW);
-
- // Build the element array buffer; this specifies the indices
- // into the vertex array for each face\'s vertices.
-
- cubeVerticesIndexBuffer = gl.createBuffer();
- gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVerticesIndexBuffer);
-
- // This array defines each face as two triangles, using the
- // indices into the vertex array to specify each triangle\'s
- // position.
-
- var cubeVertexIndices = [
- 0, 1, 2, 0, 2, 3, // front
- 4, 5, 6, 4, 6, 7, // back
- 8, 9, 10, 8, 10, 11, // top
- 12, 13, 14, 12, 14, 15, // bottom
- 16, 17, 18, 16, 18, 19, // right
- 20, 21, 22, 20, 22, 23 // left
- ]
-
- // Now send the element array to GL
-
- gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,
- new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
- }
-
- //
- // initTextures
- //
- // Initialize the textures we\'ll be using, then initiate a load of
- // the texture images. The handleTextureLoaded() callback will finish
- // the job; it gets called each time a texture finishes loading.
- //
- // TODO#1 Start
- function createCubeTexture(text) {
-
- // create a hidden canvas to draw the texture
- var canvas = document.createElement(\'canvas\');
- canvas.id = \"hiddenCanvas\";
- canvas.width = 512;
- canvas.height = 512;
- canvas.style.display = \"none\";
- var body = document.getElementsByTagName(\"body\")[0];
- body.appendChild(canvas);
-
- // draw texture
- var cubeImage = document.getElementById(\'hiddenCanvas\');
- var ctx = cubeImage.getContext(\'2d\');
- ctx.beginPath();
- ctx.rect(0, 0, ctx.canvas.width, ctx.canvas.height);
- ctx.fillStyle = \'white\';
- ctx.fill();
- ctx.fillStyle = \'black\';
- ctx.font = \"65px Arial\";
- ctx.textAlign = \'center\';
- ctx.fillText(text, ctx.canvas.width / 2, ctx.canvas.height / 2);
- ctx.restore();
-
- // create new texture
- var texture = gl.createTexture();
- gl.bindTexture(gl.TEXTURE_2D, texture);
- gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
- gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
- gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, true);
- handleTextureLoaded(cubeImage, texture)
-
- return texture;
- }
- // TODO#1 End
-
- function handleTextureLoaded(image, texture) {
- gl.bindTexture(gl.TEXTURE_2D, texture);
- gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);
- gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
- gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
- gl.generateMipmap(gl.TEXTURE_2D);
- gl.bindTexture(gl.TEXTURE_2D, null);
- }
-
- //
- // drawScene
- //
- // Draw the scene.
- //
- function drawScene() {
- // Clear the canvas before we start drawing on it.
-
- gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
-
- // Establish the perspective with which we want to view the
- // scene. Our field of view is 45 degrees, with a width/height
- // ratio of 640:480, and we only want to see objects between 0.1 units
- // and 100 units away from the camera.
-
- perspectiveMatrix = makePerspective(45, 640.0/480.0, 0.1, 100.0);
-
- // Set the drawing position to the \"identity\" point, which is
- // the center of the scene.
-
- loadIdentity();
-
- // Now move the drawing position a bit to where we want to start
- // drawing the cube.
-
- mvTranslate([0.0, 0.0, -6.0]);
-
- // Save the current matrix, then rotate before we draw.
-
- mvPushMatrix();
- mvRotate(cubeRotation, [1, 0, 1]);
-
- // Draw the cube by binding the array buffer to the cube\'s vertices
- // array, setting attributes, and pushing it to GL.
-
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesBuffer);
- gl.vertexAttribPointer(vertexPositionAttribute, 3, gl.FLOAT, false, 0, 0);
-
- // Set the texture coordinates attribute for the vertices.
-
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesTextureCoordBuffer);
- gl.vertexAttribPointer(textureCoordAttribute, 2, gl.FLOAT, false, 0, 0);
-
- // Bind the normals buffer to the shader attribute.
-
- gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesNormalBuffer);
- gl.vertexAttribPointer(vertexNormalAttribute, 3, gl.FLOAT, false, 0, 0);
-
- // Specify the texture to map onto the faces.
-
- gl.activeTexture(gl.TEXTURE0);
- gl.bindTexture(gl.TEXTURE_2D, cubeTexture);
- gl.uniform1i(gl.getUniformLocation(shaderProgram, \"uSampler\"), 0);
-
- // Draw the cube.
-
- gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVerticesIndexBuffer);
- setMatrixUniforms();
- gl.drawElements(gl.TRIANGLES, 36, gl.UNSIGNED_SHORT, 0);
-
- // Restore the original matrix
-
- mvPopMatrix();
-
- // Update the rotation for the next draw, if it\'s time to do so.
-
- var currentTime = (new Date).getTime();
- if (lastCubeUpdateTime) {
- var delta = currentTime - lastCubeUpdateTime;
-
- cubeRotation += (30 * delta) / 1000.0;
- }
-
- lastCubeUpdateTime = currentTime;
- }
-
- //
- // initShaders
- //
- // Initialize the shaders, so WebGL knows how to light our scene.
- //
- function initShaders() {
- var fragmentShader = getShader(gl, \"shader-fs\");
- var vertexShader = getShader(gl, \"shader-vs\");
-
- // Create the shader program
-
- shaderProgram = gl.createProgram();
- gl.attachShader(shaderProgram, vertexShader);
- gl.attachShader(shaderProgram, fragmentShader);
- gl.linkProgram(shaderProgram);
-
- // If creating the shader program failed, alert
-
- if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
- alert(\"Unable to initialize the shader program.\");
- }
-
- gl.useProgram(shaderProgram);
-
- vertexPositionAttribute = gl.getAttribLocation(shaderProgram, \"aVertexPosition\");
- gl.enableVertexAttribArray(vertexPositionAttribute);
-
- textureCoordAttribute = gl.getAttribLocation(shaderProgram, \"aTextureCoord\");
- gl.enableVertexAttribArray(textureCoordAttribute);
-
- vertexNormalAttribute = gl.getAttribLocation(shaderProgram, \"aVertexNormal\");
- gl.enableVertexAttribArray(vertexNormalAttribute);
- }
-
- //
- // getShader
- //
- // Loads a shader program by scouring the current document,
- // looking for a script with the specified ID.
- //
- function getShader(gl, id) {
- var shaderScript = document.getElementById(id);
-
- // Didn\'t find an element with the specified ID; abort.
-
- if (!shaderScript) {
- return null;
- }
-
- // Walk through the source element\'s children, building the
- // shader source string.
-
- var theSource = \"\";
- var currentChild = shaderScript.firstChild;
-
- while(currentChild) {
- if (currentChild.nodeType == 3) {
- theSource += currentChild.textContent;
- }
-
- currentChildcurrentChild = currentChild.nextSibling;
- }
-
- // Now figure out what type of shader script we have,
- // based on its MIME type.
-
- 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; // Unknown shader type
- }
-
- // Send the source to the shader object
-
- gl.shaderSou
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