SOURCE

/**
 * Created by hebo on 2017/12/26.
 */
main();

function main() {
    const canvas = document.querySelector("#glcanvas");
    // Initialize the GL context
    const gl = canvas.getContext("webgl");

    // Only continue if WebGL is available and working
    if (!gl) {
        alert("Unable to initialize WebGL. Your browser or machine may not support it.");
        return;
    }

    // 顶点着色器  glsl-es语言编写
    let vertexSource = `
		attribute vec4 a_Position;
    void main(){
    	gl_Position = a_Position;
      gl_PointSize = 5.0;
    }`;
    // 片元着色器  glsl-es语言编写
    let fragmentSource = `
    void main(){
    	gl_FragColor = vec4(1.0,0.0,0.0,1.0);
    }`;
	
  	// 创建着色器程序
  	let shaderProgram = initShaderProgram(gl, vertexSource, fragmentSource);
		// 创建顶点缓冲区对象，将多个点数据存储进去 交给着色器渲染，
	  // 因为有多个点，我们需要将点的数量交给gl.drawArrays
	  let len = initBuffers(gl, shaderProgram)
		
		// 绘制
		draw(gl, shaderProgram, len)
}

function initBuffers(gl, shaderProgram){
	// 定义了3个点(x,y) vec2
	let vertices = new Float32Array([
		0.0, 0.5,   -0.5, -0.5,   0.5, -0.5
	]);
	// 表达点的数量
	let len = 3;
	// 创建缓冲区
	let vertexBuffer = gl.createBuffer();
	let a_pos = gl.getAttribLocation(shaderProgram,'a_Position');
	// 
	gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
  gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
  
  gl.vertexAttribPointer(a_pos, 2, gl.FLOAT, false, 0, 0);
  gl.enableVertexAttribArray(a_pos);
	return len;
}

function draw(gl,program, pointLength){
		gl.useProgram(program);
      // Set clear color to black, fully opaque
    // 指定绘图区背景色  arg: r,g,b,a
    gl.clearColor(0.0, 0.0, 0.0, 1.0);
    // Clear the color buffer with specified clear color
    // 清空绘图区域，用设定的背景色填充绘图区域
    gl.clear(gl.COLOR_BUFFER_BIT);
    
	  // 执行顶点着色器， 
		//args: mode 绘制模式，接受的是gl常量 比如 gl.LINES 
		//     first 指定从哪个顶点开始绘制
		//     count 指定绘制需要用多少个顶点
    gl.drawArrays(gl.POINTS, 0, pointLength);
}

function initShaderProgram(gl, vsSource, fsSource) {
    let vertexShader = loadShader(gl, gl.VERTEX_SHADER, vsSource);
    let fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fsSource);

    const shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);

    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
        alert('Unable to initialize the shader program: ' + gl.getProgramInfoLog(shaderProgram));
        return null;
    }

    return shaderProgram;
}

function loadShader(gl, type, source) {
    // 依据type创建着色器
    const shader = gl.createShader(type);

    // Send the source to the shader object

    gl.shaderSource(shader, source);

    // Compile the shader program

    gl.compileShader(shader);

    // See if it compiled successfully

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        alert('An error occurred compiling the shaders: ' + gl.getShaderInfoLog(shader));
        gl.deleteShader(shader);
        return null;
    }

    return shader;
}

<h3>WebGL Demo</h3>
<canvas id="glcanvas" width="640" height="480"></canvas>