WebGL绘制正方体

时间 2020-05-19
标签 webgl 绘制正方体繁體版
原文原文链接
<!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 οnlοad="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须要的相关变量
    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("没法初始化着色器");
            return;
        }
 
        var n = initVertexBuffers(gl);
        if (n < 0) {
            console.log("没法建立缓冲区");
            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("没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)至关于在着色器里面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) {
        // 建立一个立方体
        //    v6----- v5
        //   /|      /|
        //  v1------v0|
        //  | |     | |
        //  | |v7---|-|v4
        //  |/      |/
        //  v2------v3
        var verticesColors = new Float32Array([
            // 设置顶点和颜色（偷的顶点代码位置）
            1.0,  1.0,  1.0,     1.0,  1.0,  1.0,  // v0 White
            -1.0,  1.0,  1.0,     1.0,  0.0,  1.0,  // v1 Magenta
            -1.0, -1.0,  1.0,     1.0,  0.0,  0.0,  // v2 Red
            1.0, -1.0,  1.0,     1.0,  1.0,  0.0,  // v3 Yellow
            1.0, -1.0, -1.0,     0.0,  1.0,  0.0,  // v4 Green
            1.0,  1.0, -1.0,     0.0,  1.0,  1.0,  // v5 Cyan
            -1.0,  1.0, -1.0,     0.0,  0.0,  1.0,  // v6 Blue
            -1.0, -1.0, -1.0,     0.0,  0.0,  0.0   // v7 Black
        ]);
 
        //顶点索引
        var indices = new Uint8Array([
            0, 1, 2,   0, 2, 3,    // 前
            0, 3, 4,   0, 4, 5,    // 右
            0, 5, 6,   0, 6, 1,    // 上
            1, 6, 7,   1, 7, 2,    // 左
            7, 4, 3,   7, 3, 2,    // 下
            4, 7, 6,   4, 6, 5     // 后
        ]);
 
        //建立缓冲区对象
        var vertexColorBuffer = gl.createBuffer();
        var indexBuffer = gl.createBuffer();
        if (!vertexColorBuffer || !indexBuffer) {
            console.log("没法建立缓冲区对象");
            return -1;
        }
 
        //绑定缓冲区对象并写入数据
        gl.bindBuffer(gl.ARRAY_BUFFER, vertexColorBuffer);
        gl.bufferData(gl.ARRAY_BUFFER, verticesColors, gl.STATIC_DRAW);
 
        //获取数组中一个元素所占的字节数
        var fsize = verticesColors.BYTES_PER_ELEMENT;
 
        //获取顶点位置变量位置
        var a_Position = gl.getAttribLocation(gl.program, "a_Position");
        if (a_Position < 0) {
            console.log("没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_Position, 3, gl.FLOAT, false, fsize * 6, 0);
        gl.enableVertexAttribArray(a_Position);
 
        //获取顶点颜色的变量
        var a_Color = gl.getAttribLocation(gl.program, "a_Color");
        if (a_Color < 0) {
            console.log("没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_Color, 3, gl.FLOAT, false, fsize * 6, fsize * 3);
        gl.enableVertexAttribArray(a_Color);
 
        //将顶点索引数据写入缓冲区对象
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER,indexBuffer);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,indices,gl.STATIC_DRAW);
 
        return indices.length;
    }
</script>
</html>