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| 1 | +// MultiAttributeSize.js |
| 2 | +// 顶点着色器 |
| 3 | +var VSHADER_SOURCE = |
| 4 | + 'attribute vec4 a_Position;\n' + |
| 5 | + 'attribute float a_PointSize;\n' + |
| 6 | + 'void main() {\n' + |
| 7 | + ' gl_Position = a_Position;\n' + |
| 8 | + ' gl_PointSize = a_PointSize;\n' + |
| 9 | + '}\n'; |
| 10 | + |
| 11 | +// 片源着色器 |
| 12 | +var FSHADER_SOURCE = |
| 13 | + 'precision mediump float;\n' + |
| 14 | + 'uniform vec4 u_FragColor;\n' + // uniform变量 |
| 15 | + 'void main() {\n' + |
| 16 | + ' gl_FragColor = u_FragColor;\n' + |
| 17 | + '}\n'; |
| 18 | + |
| 19 | +function main() { |
| 20 | + // 获取<canvas>元素 |
| 21 | + var canvas = document.getElementById('webgl'); |
| 22 | + |
| 23 | + // 获取webGL上下文 |
| 24 | + var gl =getWebGLContext(canvas); |
| 25 | + |
| 26 | + if(!gl) { |
| 27 | + console.log('Failed to get the rendering context for WebGL'); |
| 28 | + return; |
| 29 | + } |
| 30 | + |
| 31 | + // 初始化着色器 |
| 32 | + if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) { |
| 33 | + console.log('Failed to initialize shaders'); |
| 34 | + return; |
| 35 | + } |
| 36 | + |
| 37 | + // 设置顶点位置 |
| 38 | + var n = initVertexBuffers(gl); |
| 39 | + if (n < 0) { |
| 40 | + console.log('Failed to set the positions of the vertices'); |
| 41 | + return; |
| 42 | + } |
| 43 | + |
| 44 | + // 清空<canvas>的背景色 |
| 45 | + gl.clearColor(0.0, 0.0, 0.0, 1.0); |
| 46 | + |
| 47 | + gl.clear(gl.COLOR_BUFFER_BIT); |
| 48 | + |
| 49 | + // 绘制三个点 |
| 50 | + gl.drawArrays(gl.POINTS, 0, n); // n is 3 |
| 51 | +} |
| 52 | + |
| 53 | +function initVertexBuffers(gl) { |
| 54 | + var vertices = new Float32Array([ |
| 55 | + 0.0, 0.5, -0.5, -0.5, 0.5, -0.5 |
| 56 | + ]); |
| 57 | + var n = 3; //点的个数 |
| 58 | + |
| 59 | + var sizes = new Float32Array([ |
| 60 | + 10.0, 20.0, 30.0 // 点的尺寸 |
| 61 | + ]); |
| 62 | + // 创建缓冲区对象 |
| 63 | + var vertexBuffer = gl.createBuffer(); |
| 64 | + if (!vertexBuffer) { |
| 65 | + console.log('Failed to create the vertexBuffer object '); |
| 66 | + return -1; |
| 67 | + } |
| 68 | + |
| 69 | + var sizeBuffer = gl.createBuffer(); |
| 70 | + if (!sizeBuffer) { |
| 71 | + console.log('Failed to create the sizeBuffer object '); |
| 72 | + return -1; |
| 73 | + } |
| 74 | + |
| 75 | + // 将缓冲区对象绑定到目标 |
| 76 | + gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer); |
| 77 | + |
| 78 | + //向缓冲区对象写入数据 |
| 79 | + gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW); |
| 80 | + |
| 81 | + var a_Position = gl.getAttribLocation(gl.program, 'a_Position'); |
| 82 | + |
| 83 | + if (a_Position < 0) { |
| 84 | + console.log('Failed to get the storage location of a_Position'); |
| 85 | + return a_Position; |
| 86 | + } |
| 87 | + |
| 88 | + // 将缓冲区对象分配给a_Position变量 |
| 89 | + gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0); |
| 90 | + |
| 91 | + // 连接a_Poisition变量与分配给它的缓冲区对象 |
| 92 | + gl.enableVertexAttribArray(a_Position); |
| 93 | + |
| 94 | + // 将顶点尺寸写入缓冲区对象并开启 |
| 95 | + gl.bindBuffer(gl.ARRAY_BUFFER, sizeBuffer); |
| 96 | + gl.bufferData(gl.ARRAY_BUFFER, sizes, gl.STATIC_DRAW); |
| 97 | + |
| 98 | + var a_PointSize = gl.getAttribLocation(gl.program, 'a_PointSize'); |
| 99 | + |
| 100 | + if (a_PointSize < 0) { |
| 101 | + console.log('Failed to get the storage location of a_PointSize'); |
| 102 | + return a_PointSize; |
| 103 | + } |
| 104 | + gl.vertexAttribPointer(a_PointSize, 1, gl.FLOAT, false, 0, 0); |
| 105 | + gl.enableVertexAttribArray(a_PointSize); |
| 106 | + |
| 107 | + return n |
| 108 | +} |
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