片元着色器精度声明不可或缺

function main(){
    var canvas = document.getElementById("webgl");
    var gl = getWebGLContext(canvas);
    var VSHADER_SOURCE = function(){
        /*
         attribute vec4 a_Position;
         attribute float a_PointSize;
         void main(){
         gl_Position = a_Position;
         gl_PointSize = a_PointSize;
         }
         */
    }.toString().match(/\/\*([^]*)\*\//)[1];

    var FSHADER_SOURCE = function(){
        /*
      precision lowp float;
         uniform vec4 u_FragColor;
         void main(){
         gl_FragColor = u_FragColor;
         }
         */
    }.toString().match(/\/\*([^]*)\*\//)[1];

    initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE);
    var a_Position = gl.getAttribLocation(gl.program,"a_Position");
    var a_PointSize = gl.getAttribLocation(gl.program,"a_PointSize");
    var u_FragColor = gl.getUniformLocation(gl.program,"u_FragColor");
    gl.clearColor(0.0,0.0,0.0,0.8);
    gl.clear(gl.COLOR_BUFFER_BIT);
    gl.uniform4f(u_FragColor, 0.1,1.0,1.0,1.0);
    for (var i=0;i<10;i++){
        gl.vertexAttrib3f(a_Position,(i+1)*0.1,(i+1)*0.1,0.0);
        gl.vertexAttrib1f(a_PointSize, 10.0);
        gl.drawArrays(gl.POINTS, 0, 1);
    }
}

如果：

Failed to compile shader: ERROR: 0:3: ‘‘ : No precision specified for (float)

解决办法：

在片元着色器里面加上浮点数精度声明（事实上，片元着色器支持所有3种精度，并不是精度不支持，只是需要声明而已）