WebGL入门指南：探索3D图形编程

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"WebGL入门教程，面向初学者的HTML5和WebGL图书" 这本《WebGL for Beginning》是一本面向初学者的指南，旨在教授读者如何利用WebGL和HTML5进行网页图形编程。WebGL是一种基于OpenGL标准的JavaScript API，它允许在任何兼容的Web浏览器中实现硬件加速的3D图形渲染，无需插件。以下是本书的主要内容概览： 1. **设置场景(Chapter 1: Setting the Scene)**：这部分会介绍WebGL的基本概念，包括如何在HTML5 canvas元素中设置WebGL上下文，以及绘制基本的3D几何形状。 2. **着色器基础(Chapter 2: Shaders 101)**：着色器是WebGL的核心，用于计算每个像素的颜色。这一章将讲解顶点着色器和片段着色器的工作原理，以及如何编写GLSL（OpenGL Shading Language）代码。 3. **纹理与光照(Chapter 3: Textures and Lighting)**：这部分会介绍如何应用纹理到3D模型上，增加视觉真实感，并讲解不同的光照模型，如环境光、点光源和方向光。 4. **增强现实感(Chapter 4: Increasing Realism)**：本章可能涉及更高级的技术，如法线贴图、镜面高光、深度测试等，用于进一步提升3D场景的真实感。 5. **物理模拟(Chapter 5: Physics)**：探讨如何在WebGL中实现简单的物理引擎，如碰撞检测和刚体动力学，为3D交互提供更真实的行为。 6. **分形、高度图和粒子系统(Chapter 6: Fractals, Height Maps, and Particle Systems)**：这部分可能会介绍如何使用分形创建复杂的几何结构，使用高度图创建地形，以及如何创建动态的粒子效果，如烟雾、火花或水流。 7. **Three.js框架(Chapter 7: Three.js Framework)**：Three.js是一个流行的JavaScript库，简化了WebGL的使用。本章将介绍如何利用Three.js进行3D开发，包括对象管理、动画和相机控制等。 8. **生产力工具(Chapter 8: Productivity Tools)**：讲解有助于提高开发效率的工具和技巧，如调试器、性能优化方法，以及代码组织策略。 9. **调试与性能(Chapter 9: Debugging and Performance)**：介绍如何调试WebGL代码，找出性能瓶颈，并提供优化建议以确保流畅的用户体验。 10. **特效、技巧和窍门(Chapter 10: Effects, Tips, and Tricks)**：分享一些高级技巧，如后期处理效果、阴影投射等，以及如何通过WebGL实现创意视觉效果。 11. **WebGL的未来(Afterword: The Future of WebGL)**：作者将对WebGL技术的未来发展进行展望，可能包括新特性的讨论和行业趋势分析。 12. **附录**：附录部分提供了HTML5和JavaScript的基础知识回顾，图形学复习，WebGL规范的补充信息，以及更多资源的链接，方便读者深入学习。这本书不仅适合WebGL新手，也适合有一定基础的开发者，它将引导读者逐步掌握3D图形编程，实现互动丰富的Web应用程序。通过学习，读者将能够创建出令人惊叹的3D Web内容，充分利用现代浏览器的能力。

CHAPTER 1 ■ SETTING THE SCENE

var myBuffer = gl.createBuffer();

gl.bindBuffer(gl.ARRAY_BUFFER, myBuffer);

gl.bufferData(gl.ARRAY_BUFFER, data, STATIC_DRAW);

Notice that in the gl.bufferData line, we do not explicitly specify the buer to place the data into. WebGL

implicitly uses the currently bound buer.

When you are done with a buer you can delete it with a call to this:

void deleteBuffer(WebGLBuffer buffer);

As the chapter progresses, we will show how to setup a shader program and pass VBO data into it.

Attributes and Uniforms

As mentioned, vertices have attributes which can be passed to shaders. We can also pass uniform values to

the shader which will be constant for each vertex. Shader attributes and uniforms can get complex and will be

covered in more depth in the next chapter but touched upon here. As the shader is a compiled external program,

we need to be able to reference the location of all variables within the program. Once we obtain the location of a

variable, we can send data to the shader from our web application. To get the location of an attribute or uniform

within the WebGL program, we use these API calls:

GLint getAttribLocation(WebGLProgram program, DOMString name)

WebGLUniformLocation getUniformLocation(WebGLProgram program, DOMString name)

e GLint and WebGLUniformLocation return values are references to the location of the attribute or uniform

within the shader program. e ﬁrst parameter is our WebGLProgram object and the second parameter is the

attribute name as found in the vertex or fragment shader source. If we have an attribute in a shader by the name

of "aVertexPosition", we obtain its position within our JavaScript like this:

var vertexPositionAttribute = gl.getAttribLocation(glProgram, "aVertexPosition");

If we are sending an array of data to an attribute, we have to enable array data with a call to this:

void enableVertexAttribArray(GLuint index)

Here, the index is the attribute location that we previously obtained and stored. e return value is void

because the function returns no value.

With our previously deﬁned attribute location, this call looks like the following:

gl.enableVertexAttribArray(vertexPositionAttribute);

Now that we have the location of an attribute and have told our shader that we will be using an array of

values, we assign the currently bound ARRAY_BUFFER target to this vertex attribute as we have demonstrated in the

previous section:

gl.bindBuffer(gl.ARRAY_BUFFER, myBuffer);

Finally, we let our shader know how to interpret our data. We need to remember that the shader knows nothing

about the incoming data. Just because we name an array to help us understand what data it contains, such as

myColorData, the shader just sees data without any context. e API call to explain our data format is as follows:

void vertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei

stride, GLintptr offset)

size is the number of components per attribute. For example, with RGB colors, it would be 3; and with an

alpha channel, RGBA, it would be 4. If we have location data with (x,y,z) attributes, it would be 3; and if we

had a fourth parameter w, (x,y,z,w), it would be 4. Texture parameters (s,t) would be 2. type is the datatype,

stride and offset can be set to the default of 0 for now and will be reexamined in Chapter 9 when we discuss

interleaved arrays.

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CHAPTER 1 ■ SETTING THE SCENE

Eventually, we will pass in vertex points that correspond to the two triangles that we are rendering, but right

now nothing is passed in and so we still see only the green clear color. In Listing 1-3 we have also added new

variables that will store our WebGL shading language program, fragment and vertex shaders, vertex position

attribute that will be passed to the vertex shader, and the vertex buer object that will store our triangle vertices

as shown in this code:

var gl = null,

canvas = null,

glProgram = null,

fragmentShader = null,

vertexShader = null;

var vertexPositionAttribute = null,

trianglesVerticeBuffer = null;

Note ■ Our modiﬁed line in Listing 1-3 to get the WebGL context is future compatible. It will check for the “webgl”

context ﬁrst. If this is not supported, it will try the “experimental-webgl” context next, as shown in the following

code:

gl = canvas.getContext("webgl") || canvas.getContext("experimental-webgl");

Once we successfully obtain a WebGL context, we call four functions:

setupWebGL();

initShaders();

setupBuffers();

drawScene();

We currently have these functions deﬁned as follows:

function setupWebGL()

{

//set the clear color to a shade of green

gl.clearColor(0.1, 0.5, 0.1, 1.0);

gl.clear(gl.COLOR_BUFFER_BIT);

}

function initShaders(){}

function setupBuffers(){}

function drawScene(){}

e ﬁrst function sets the clear color to green, and the other three at this point are stub functions so that

the program runs without error. e next bit of functionality that we will implement is the creation of the shader

program and shaders. is involves using several functions to set up each shader and the program.

For each shader, we call the API function createShader to create a WebGLShader object, in which the type

parameter is either VERTEX_SHADER or FRAGMENT_SHADER for the vertex and fragment shaders, respectively:

WebGLShader createShader(GLenum type)

ese calls look like this:

var vertexShader = gl.createShader(gl.VERTEX_SHADER);

var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);

Next we attach the source to each shader with API calls to:

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