WebGL基础（四）

内容简介：WebGL基础（四）

本节主要讲解一下颜色的设置。1、WebGL可以使用多个多个缓冲器对象向顶点着色器传输数据。

使用两个缓冲器对象传输数据

看一个示例程序

// MultiAttributeColor.js (c) 2012 matsuda // Vertex shader program var VSHADER_SOURCE =   'attribute vec4 a_Position;\n' +   'attribute vec4 a_Color;\n' +   'varying vec4 v_Color;\n' + // varying 变量   'void main() {\n' +   '  gl_Position = a_Position;\n' +   '  gl_PointSize = 10.0;\n' +   '  v_Color = a_Color;\n' +  // 将数据传输给片元着色器   '}\n';  // Fragment shader program var FSHADER_SOURCE =   '#ifdef GL_ES\n' +   'precision mediump float;\n' + // Precision qualifier (See Chapter 6)   '#endif GL_ES\n' +   'varying vec4 v_Color;\n' +    // Receive the data from the vertex shader   'void main() {\n' +   '  gl_FragColor = v_Color;\n' +   '}\n';  function main() {   // Retrieve <canvas> element   var canvas = document.getElementById('webgl');    // Get the rendering context for WebGL   var gl = getWebGLContext(canvas);   if (!gl) {     console.log('Failed to get the rendering context for WebGL');     return;   }    // Initialize shaders   if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {     console.log('Failed to intialize shaders.');     return;   }    //    var n = initVertexBuffers(gl);   if (n < 0) {     console.log('Failed to set the vertex information');     return;   }    // Specify the color for clearing <canvas>   gl.clearColor(0.0, 0.0, 0.0, 1.0);    // Clear <canvas>   gl.clear(gl.COLOR_BUFFER_BIT);    // Draw three points   gl.drawArrays(gl.POINTS, 0, n); }  function initVertexBuffers(gl) {   var verticesColors = new Float32Array([     // 顶点坐标和颜色      0.0,  0.5,  1.0,  0.0,  0.0,      -0.5, -0.5,  0.0,  1.0,  0.0,       0.5, -0.5,  0.0,  0.0,  1.0,    ]);   var n = 3; // The number of vertices    // Create a buffer object   var vertexColorBuffer = gl.createBuffer();     if (!vertexColorBuffer) {     console.log('Failed to create the buffer object');     return false;   }    // Write the vertex coordinates and colors to the buffer object   gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);   gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);    var FSIZE = verticesColors.BYTES_PER_ELEMENT;   //获取a_Position存储位置，分配缓冲区并开启   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 -1;   }   gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, FSIZE * 5, 0);   gl.enableVertexAttribArray(a_Position);  // Enable the assignment of the buffer object    // 获取a_Color存储位置，分配缓冲区并开启   var a_Color = gl.getAttribLocation(gl.program, 'a_Color');   if(a_Color < 0) {     console.log('Failed to get the storage location of a_Color');     return -1;   }   gl.vertexAttribPointer(a_Color, 3, gl.FLOAT, false, FSIZE * 5, FSIZE * 2);   gl.enableVertexAttribArray(a_Color);  // Enable the assignment of the buffer object   return n; }

程序中vertexAttribPointer函数：