WebGL绘制三角形

本文程序实现绘制一个三角形的任务，如下图。

整个程序包含两个文件，分别是：

1. HelloTriangle.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

<html>

    <head>

        <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

        <title>画一个三角形</title>

    </head>

    <body onload="startup()">

        <canvas id="myGLCanvas" width="600" height="600">

        </canvas>

    </body>

    <script type="text/javascript" src="HelloTriangle.js">

    </script>

</html>

2. HelloTriangle.js

var gl;

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]); //获取webgl context绘图上下文

    } 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 loadShader(type, shaderSource) {

  var shader = gl.createShader(type);

  gl.shaderSource(shader, shaderSource);

  gl.compileShader(shader);

  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {

      alert("Error compiling shader" + gl.getShaderInfoLog(shader));

      gl.deleteShader(shader);

      return null;

  }

  return shader;

}

function setupShaders() {

    //顶点着色器程序

    var vertexShaderSource =

      'attribute vec4 a_Position;\n' +

      'void main() {\n' +

      '  gl_Position = a_Position;\n' +

      '  gl_PointSize = 10.0;\n' +

      '}\n';

    //片元着色器程序

    var fragmentShaderSource =

      'void main(){ \n' +

      '    gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); \n' + //gl_FragColor指定像素的颜色

      '} \n';                                         

  var vertexShader = loadShader(gl.VERTEX_SHADER, vertexShaderSource);

  var fragmentShader = loadShader(gl.FRAGMENT_SHADER, fragmentShaderSource);

  var shaderProgram = gl.createProgram();

  gl.attachShader(shaderProgram, vertexShader);

  gl.attachShader(shaderProgram, fragmentShader);

  gl.linkProgram(shaderProgram);

  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {

    alert("Failed to setup shaders");

  }

  gl.useProgram(shaderProgram);

  gl.program= shaderProgram;

}

function initVertexBuffers(gl) {

  var vertices = new Float32Array([

    0, 0.5,   -0.5, -0.5,   0.5, -0.5

  ]);

  var n = 3; // The number of vertices

  // Create a buffer object

  var vertexBuffer = gl.createBuffer();

  if (!vertexBuffer) {

    console.log('Failed to create the buffer object');

    return -1;

  }

  // Bind the buffer object to target

  gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);

  // Write date into the buffer object

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

  var a_PosLocation = gl.getAttribLocation(gl.program, 'a_Position');

  if (a_PosLocation < 0) {

    console.log('Failed to get the storage location of a_Position');

    return -1;

  }

  // Assign the buffer object to a_Position variable

  gl.vertexAttribPointer(a_PosLocation, 2, gl.FLOAT, false, 0, 0);

  // Enable the assignment to a_Position variable

  gl.enableVertexAttribArray(a_PosLocation);

  return n;

}

function startup(){

    var canvas = document.getElementById('myGLCanvas');//获取<canvas>元素

    gl = createGLContext(canvas);

    setupShaders(); 

  // Write the positions of vertices to a vertex shader

  var n = initVertexBuffers(gl);

  if (n < 0) {

    console.log('Failed to set the positions of the vertices');

    return;

  }

  // Specify the color for clearing <canvas>

  gl.clearColor(0, 0, 0, 1);

  // Clear <canvas>

  gl.clear(gl.COLOR_BUFFER_BIT);

  // Draw the rectangle

  gl.drawArrays(gl.TRIANGLES, 0, n);

 }

参考代码

Hello Point——WebGL, http://www.cnblogs.com/idealer3d/p/3513838.html
Professional WebGL Programming: Developing 3D Graphics for the Web,Listing 2-1,http://media.wiley.com/product_ancillary/60/11199688/DOWNLOAD/Listing-2-1.html
WebGL Programming Guide, https://sites.google.com/site/webglbook/

转载请注明出处：http://www.cnblogs.com/opengl/p/7274033.html

巴特西

WebGL绘制三角形

1. HelloTriangle.html

2. HelloTriangle.js

参考代码

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