【WebGL】《WebGL编程指南》读书笔记—

【WebGL】《WebGL编程指南》读书笔记——第2章

一、前言

最近看了《WebGL编程指南》这本书，发现还是很有意思的，故每章阅读后做个笔记。

二、正文

Example1：在canvas中绘制2D矩形

<!DOCTYPE html>
<html lang="en"><head><meta charset="utf-8" /><title>Draw a blue rectangle (canvas version)</title></head><body onload="main()"><canvas id="example" width="400" height="400">Please use a browser that supports "canvas"</canvas><script src="DrawRectangle.js"></script></body>

</html>

function main() {  var canvas = document.getElementById('example');  if (!canvas) { console.log('Failed to retrieve the <canvas> element');return false; } var ctx = canvas.getContext('2d');  //获取绘图上下文ctx.fillStyle = 'rgba(0, 0, 255, 1.0)'; //设置颜色，rgb为三原色通道，a为alphaa透明度ctx.fillRect(120, 10, 350, 150); //设置矩形的位置及大小，margin-left为120，margin-top为10；绘制长350px，宽为150px的矩形
}

Example2：清空canvas

function main() {var canvas = document.getElementById('webgl');var gl = getWebGLContext(canvas); //获取webgl绘图上下文if (!gl) {console.log('Failed to get the rendering context for WebGL');return;}gl.clearColor(0.0, 0.0, 0.0, 1.0); //设置清空颜色，颜色值都是0-1之间！不是0-255！！！gl.clear(gl.COLOR_BUFFER_BIT); //清空颜色缓存
}

Example3：在canvas中绘制一个红点

//顶点着色器数据源
var VSHADER_SOURCE = 'void main() {\n'  '  gl_Position = vec4(0.0, 0.0, 0.0, 1.0);\n'    //位置，vec4由四个浮点型数据组成，即(float,float,float,float)'  gl_PointSize = 10.0;\n'                       //点的大小'}\n';//片元着色器数据源
var FSHADER_SOURCE ='void main() {\n'  '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n'   //颜色rgba'}\n';function main() {var canvas = document.getElementById('webgl');var gl = getWebGLContext(canvas);if (!gl) {console.log('Failed to get the rendering context for WebGL');return;}// Step1：初始化着色器if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {console.log('Failed to intialize shaders.');return;}
  // Step2:清空背景色及canvas颜色缓存gl.clearColor(0.0, 0.0, 0.0, 1.0);gl.clear(gl.COLOR_BUFFER_BIT);// 画点gl.drawArrays(gl.POINTS, 0, 1); //（mode，first，count）；
}

function initShaders(gl, vshader, fshader) {
  // Step1：创建程序对象var program = createProgram(gl, vshader, fshader);if (!program) {console.log('Failed to create program');return false;}

  // Step2：设置用于渲染的程序对象 链接地址：https://msdn.microsoft.com/library/dn302459(v=vs.85).aspxgl.useProgram(program); gl.program = program;return true;
}
//********************************以上为主程序************************************


function createProgram(gl, vshader, fshader) {
  // Step1：加载着色器
  var vertexShader = loadShader(gl, gl.VERTEX_SHADER, vshader);
  var fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fshader);

  if (!vertexShader || !fragmentShader) 
  {
    return null;
  }

  // Step2：创建空程序对象 链接地址： https://msdn.microsoft.com/library/Dn302384
  var program = gl.createProgram();
  if (!program) 
  {
    return null;
  }


  // Step3：着色器附着至程序对象 链接地址：https://msdn.microsoft.com/library/Dn302364
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);

  // Step4：链接上程序对象
  gl.linkProgram(program);

 // Step5：检查链接结果
  var linked = gl.getProgramParameterprogram, gl.LINK_STATUS);
  if (!linked) {
    var error = gl.getProgramInfoLog(program);
    console.log('Failed to link program: '   error);
    gl.deleteProgram(program);
    gl.deleteShader(fragmentShader);
    gl.deleteShader(vertexShader);
    return null;
  }
  return program;
}


function loadShader(gl, type, source) {

  // Step1：创建着色器对象（依据着色器类型）
  var shader = gl.createShader(type);
  if (shader == null) {
    console.log('unable to create shader');
    return null;
  }

  // Step2： 设置着色器数据源（着色器对象，数据源）
  gl.shaderSource(shader, source);

  // Step3： 编译着色器
  gl.compileShader(shader);

  // Step4： 检查编译结果
  var compiled = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if (!compiled) {
    var error = gl.getShaderInfoLog(shader);
    console.log('Failed to compile shader: '   error);
    gl.deleteShader(shader);
    return null;
  }
  return shader;
}

Example4：使用attribute变量在canvas中绘制一个红点


var VSHADER_SOURCE = 'attribute vec4 a_Position;\n'   //限定符，类型，变量名称 attribute变量传输与顶点有关的数据
'void main() {\n'  '  gl_Position = a_Position;\n'  '  gl_PointSize = 10.0;\n'  '}\n'; 

var FSHADER_SOURCE = 'void main() {\n'  '  gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n'  '}\n';function main() {var canvas = document.getElementById('webgl');var gl = getWebGLContext(canvas);if (!gl) {console.log('Failed to get the rendering context for WebGL');return;}
if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {console.log('Failed to intialize shaders.');return;}// 获取attribute变量的存储位置（程序对象，attribute变量名称）var a_Position = gl.getAttribLocation(gl.program, 'a_Position');if (a_Position < 0) {console.log('Failed to get the storage location of a_Position');return;}// 将顶点位置赋给attribute变量的存储位置，3f表述3个float型参数gl.vertexAttrib3f(a_Position, 0.0, 0.0, 0.0);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
  gl.clear(gl.COLOR_BUFFER_BIT);gl.drawArrays(gl.POINTS, 0, 1);
}

Example5：浏览器坐标->Canvas坐标->webgl坐标

  var x = ev.clientX; // x coordinate of a mouse pointervar y = ev.clientY; // y coordinate of a mouse pointervar rect = ev.target.getBoundingClientRect() ;x = ((x - rect.left) - canvas.width/2)/(canvas.width/2);y = (canvas.height/2 - (y - rect.top))/(canvas.height/2);