2021-10-09---绘制立方体var VSHADER_SOURCE = "" + "attribute vec4

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Title</title>
    <style>
        body {
            margin: 0;
            text-align: center;
        }

        #canvas {
            margin: 0;
        }
    </style>
</head>
<body onload="main()">
<canvas id="canvas" height="800" width="1200"></canvas>
</body>
<script src="/lib/webgl-utils.js"></script>
<script src="/lib/webgl-debug.js"></script>
<script src="/lib/cuon-utils.js"></script>
<script src="/lib/cuon-matrix.js"></script>
<script>
    //顶点着色器
    var VSHADER_SOURCE = "" +
        "attribute vec4 a_Position;\n" +
        "attribute vec4 a_Color;\n" +
        "uniform mat4 u_ModelViewMatrix;\n" +
        "varying vec4 v_Color;\n" +
        "void main(){" +
        "   gl_Position = u_ModelViewMatrix * a_Position;\n" +
        "   v_Color = a_Color;\n" +
        "}\n";

    //片元着色器
    var FSHADER_SOURCE = "" +
        "#ifdef GL_ES\n" +
        "precision mediump float;\n" +
        "#endif\n" +
        "varying vec4 v_Color;\n" +
        "void main(){" +
        "   gl_FragColor = v_Color;\n" +
        "}\n";

    //声明js需要的相关变量
    var canvas = document.getElementById("canvas");
    var gl = getWebGLContext(canvas);

    function main() {
        if (!gl) {
            console.log("你的浏览器不支持WebGL");
            return;
        }

        //初始化着色器
        if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
            console.log("无法初始化着色器");
            return;
        }

        var n = initVertexBuffers(gl);
        if (n < 0) {
            console.log("无法创建缓冲区");
            return;
        }

        //设置视角矩阵的相关信息
        var u_ModelViewMatrix = gl.getUniformLocation(gl.program, "u_ModelViewMatrix");
        if (u_ModelViewMatrix < 0) {
            console.log("无法获取矩阵变量的存储位置");
            return;
        }

        //设置底色
        gl.clearColor(0.0, 0.0, 0.0, 1.0);

        //进入场景初始化
        draw(gl, n, u_ModelViewMatrix);
    }

    function draw(gl, n, u_ModelViewMatrix) {
        //设置视角矩阵的相关信息（视点，视线，上方向）
        var viewMatrix = new Matrix4();
        viewMatrix.setLookAt(3,3,7,0,0,0,0,1,0);

        //设置模型矩阵的相关信息
        var modelMatrix = new Matrix4();
        modelMatrix.setRotate(0, 0, 0, 1);

        //设置透视投影矩阵
        var projMatrix = new Matrix4();
        projMatrix.setPerspective(30,canvas.width/canvas.height,1,100);

        //计算出模型视图矩阵 viewMatrix.multiply(modelMatrix)相当于在着色器里面u_ViewMatrix * u_ModelMatrix
        var modeViewMatrix = projMatrix.multiply(viewMatrix.multiply(modelMatrix));

        //将试图矩阵传给u_ViewMatrix变量
        gl.uniformMatrix4fv(u_ModelViewMatrix, false, modeViewMatrix.elements);

        //开启隐藏面清除
        gl.enable(gl.DEPTH_TEST);

        //清空颜色和深度缓冲区
        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

        //绘制图形
        gl.drawElements(gl.TRIANGLES,n,gl.UNSIGNED_BYTE,0);

    }

    function initVertexBuffers(gl) {
        // 创建一个立方体
        //    v6----- v5
        //   /|      /|
        //  v1------v0|
        //  | |     | |
        //  | |v7---|-|v4
        //  |/      |/
        //  v2------v3

        var vertices = new Float32Array([   // 顶点的位置坐标数据
            1.0, 1.0, 1.0,  -1.0, 1.0, 1.0,  -1.0,-1.0, 1.0,   1.0,-1.0, 1.0,  // v0-v1-v2-v3 front
            1.0, 1.0, 1.0,   1.0,-1.0, 1.0,   1.0,-1.0,-1.0,   1.0, 1.0,-1.0,  // v0-v3-v4-v5 right
            1.0, 1.0, 1.0,   1.0, 1.0,-1.0,  -1.0, 1.0,-1.0,  -1.0, 1.0, 1.0,  // v0-v5-v6-v1 up
            -1.0, 1.0, 1.0,  -1.0, 1.0,-1.0,  -1.0,-1.0,-1.0,  -1.0,-1.0, 1.0,  // v1-v6-v7-v2 left
            -1.0,-1.0,-1.0,   1.0,-1.0,-1.0,   1.0,-1.0, 1.0,  -1.0,-1.0, 1.0,  // v7-v4-v3-v2 down
            1.0,-1.0,-1.0,  -1.0,-1.0,-1.0,  -1.0, 1.0,-1.0,   1.0, 1.0,-1.0   // v4-v7-v6-v5 back
        ]);

        var colors = new Float32Array([     // 顶点的颜色
            0.4, 0.4, 0.4,  0.4, 0.4, 0.4,  0.4, 0.4, 0.4,  0.4, 0.4, 0.4,  // v0-v1-v2-v3 front(blue)
            0.9, 0.9, 0.9,  0.9, 0.9, 0.9,  0.9, 0.9, 0.9,  0.9, 0.9, 0.9,  // v0-v3-v4-v5 right(green)
            0.6, 0.6, 0.6,  0.6, 0.6, 0.6,  0.6, 0.6, 0.6,  0.6, 0.6, 0.6,  // v0-v5-v6-v1 up(red)
            0.1, 0.1, 0.1,  0.1, 0.1, 0.1,  0.1, 0.1, 0.1,  0.1, 0.1, 0.1,  // v1-v6-v7-v2 left
            0.5, 0.5, 0.5,  0.5, 0.5, 0.5,  0.5, 0.5, 0.5,  0.5, 0.5, 0.5,  // v7-v4-v3-v2 down
            0.8, 0.8, 0.8,  0.8, 0.8, 0.8,  0.8, 0.8, 0.8,  0.8, 0.8, 0.8   // v4-v7-v6-v5 back
        ]);

        var indices = new Uint8Array([       // 绘制的索引
            0, 1, 2,   0, 2, 3,    // front
            4, 5, 6,   4, 6, 7,    // right
            8, 9,10,   8,10,11,    // up
            12,13,14,  12,14,15,    // left
            16,17,18,  16,18,19,    // down
            20,21,22,  20,22,23     // back
        ]);

        //创建缓冲区对象
        initArrayBuffer(gl,vertices,3,gl.FLOAT,"a_Position");

        initArrayBuffer(gl,colors,3,gl.FLOAT,"a_Color");

        //将顶点索引数据写入缓冲区对象
        var indexBuffer = gl.createBuffer();
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER,indexBuffer);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,indices,gl.STATIC_DRAW);

        return indices.length;
    }

    function initArrayBuffer(gl,data,num,type,attribute) {
        //创建缓冲区对象
        var buffer = gl.createBuffer();
        if (!buffer) {
            console.log("无法创建缓冲区对象");
            return -1;
        }

        //绑定缓冲区对象并写入数据
        gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
        gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);

        //获取顶点位置变量位置
        var a_attribue = gl.getAttribLocation(gl.program, attribute);
        if (a_attribue < 0) {
            console.log("无法获取顶点位置的存储变量");
            return -1;
        }

        //对位置的顶点数据进行分配，并开启
        gl.vertexAttribPointer(a_attribue, num, type, false, 0, 0);
        gl.enableVertexAttribArray(a_attribue);
    }
</script>
</html>