44 WebGL通过点击获取到点击面的下标

来源：互联网发布：淘宝上传生产许可证编辑：程序博客网时间：2024/05/16 07:30

<!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;        }        #canvas {            margin: 0;            display: block;        }    </style></head><body onload="main()"><canvas id="canvas" height="800" width="1200"></canvas></body><script src="webgl/webgl-utils.js"></script><script src="webgl/webgl-debug.js"></script><script src="webgl/cuon-utils.js"></script><script src="webgl/cuon-matrix.js"></script><script>    //设置WebGL全屏显示    var canvas = document.getElementById("canvas");    canvas.width = window.innerWidth;    canvas.height = window.innerHeight;    //顶点着色器    var vertexShaderSource = "" +        "attribute vec4 a_Position;\n" +        "attribute vec4 a_Color;\n" +        "attribute float a_Face;\n" +//表面编号，不是用int类型        "uniform mat4 u_MvpMatrix;\n" +        "uniform int u_PickedFace;\n" + //被选中的表面编号        "varying vec4 v_Color;\n" +        "void main (){\n" +        "   gl_Position = u_MvpMatrix * a_Position;\n" +        "   int face = int(a_Face);\n" +        "   vec3 color = (face == u_PickedFace) ? vec3(1.0) : a_Color.rgb;\n" +        "   if(u_PickedFace == 0){\n" +        "       v_Color = vec4(color, a_Face/255.0);\n" +        "   }else{\n" +        "       v_Color = vec4(color, a_Color.a);\n" +        "   }\n" +        "}\n";    //片元着色器    var fragmentShaderSource = "" +        "#ifdef GL_ES\n" +        "precision mediump float;\n" +        "#endif\n" +        "varying vec4 v_Color;\n" +        "void main(){\n" +        "   gl_FragColor = v_Color;\n" +        "}\n";    function main() {        //获取WebGL对象        var gl = getWebGLContext(canvas);        //初始化着色器        initShaders(gl, vertexShaderSource, fragmentShaderSource);        //将数据存入缓冲区        var n = initVertexBuffers(gl);        if (n < 0) {            console.log("数据存入缓冲区失败");            return;        }        //设置背景色和开启层级关系        gl.clearColor(0.0, 0.0, 0.0, 1.0);        gl.enable(gl.DEPTH_TEST);        //获取uniform变量的存储位置        var u_MvpMatrix = gl.getUniformLocation(gl.program, "u_MvpMatrix");        var u_PickedFace = gl.getUniformLocation(gl.program, "u_PickedFace");        if (!u_MvpMatrix || !u_PickedFace) {            console.log("无法获取相关的存储位置");            return;        }        //设置视点和投影矩阵        var viewProjectionMatrix = new Matrix4();        viewProjectionMatrix.setPerspective(30.0, canvas.width / canvas.height, 1.0, 100.0);        viewProjectionMatrix.lookAt(0.0, 0.0, 7.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);        //设置一个自动转圈的变量        var currentAngle = 0.0;        // 初始化被选中的表面的变量        gl.uniform1i(u_PickedFace, -1);        canvas.onmousedown = function (e) {            //鼠标按下时，将u_PickedFace修改为0，然后重新绘制场景            gl.uniform1i(u_PickedFace, 0);            draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);            //因为绘制的场景将代表下标的存入了a的值内，所以需要获取颜色来获取下标            var pixels = new Uint8Array(4); //存储获取的颜色的变量            gl.readPixels(e.offsetX, window.innerHeight - e.offsetY, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixels);            //给u_PickedFace赋值然后交给顶点着色器判断是否相同            gl.uniform1i(u_PickedFace, pixels[3]);            draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);        };        //定时绘制页面        var tick = function () {            currentAngle = animate(currentAngle);            draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix);            requestAnimationFrame(tick);        };        tick();    }    //修改currentAngle的值    var last = +new Date();    var angleStep = 20.0;//每次旋转的速度    function animate(currentAngle) {        var now = +new Date();        var elapsed = now - last;        last = now;        //这里是为了保证旋转保证匀速旋转        var newAngle = currentAngle + (angleStep * elapsed) / 1000;        return newAngle % 360;    }    //设置顶点数据和将数据存入缓冲区    function initVertexBuffers(gl) {        // Create a cube        //    v6----- v5        //   /|      /|        //  v1------v0|        //  | |     | |        //  | |v7---|-|v4        //  |/      |/        //  v2------v3        var vertices = new Float32Array([   // Vertex coordinates 顶点的位置数据            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([   // Colors 顶点的颜色数据            0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, 0.32, 0.18, 0.56, // v0-v1-v2-v3 front            0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69, 0.5, 0.41, 0.69,  // v0-v3-v4-v5 right            0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, 0.78, 0.69, 0.84, // v0-v5-v6-v1 up            0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61, 0.0, 0.32, 0.61,  // v1-v6-v7-v2 left            0.27, 0.58, 0.82, 0.27, 0.58, 0.82, 0.27, 0.58, 0.82, 0.27, 0.58, 0.82, // v7-v4-v3-v2 down            0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93, 0.73, 0.82, 0.93 // v4-v7-v6-v5 back        ]);        var faces = new Uint8Array([   // Faces  顶点的面的数据            1, 1, 1, 1,     // v0-v1-v2-v3 front            2, 2, 2, 2,     // v0-v3-v4-v5 right            3, 3, 3, 3,     // v0-v5-v6-v1 up            4, 4, 4, 4,     // v1-v6-v7-v2 left            5, 5, 5, 5,     // v7-v4-v3-v2 down            6, 6, 6, 6     // v4-v7-v6-v5 back        ]);        var indices = new Uint8Array([   // Indices of the vertices 顶点的索引数据            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        ]);        //存入缓冲区        if (!initArrayBuffer(gl, vertices, gl.FLOAT, 3, "a_Position")) {            return -1;        }        if (!initArrayBuffer(gl, colors, gl.FLOAT, 3, "a_Color")) {            return -1;        }        if (!initArrayBuffer(gl, faces, gl.UNSIGNED_BYTE, 1, "a_Face")) {            return -1;        }        //创建索引缓冲区        var indexBuffer = gl.createBuffer();        if (indexBuffer < 0) {            console.log("无法创建缓冲区");            return -1;        }        //取消ARRAY_BUFFER中的绑定        gl.bindBuffer(gl.ARRAY_BUFFER, null);        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, indexBuffer);        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.STATIC_DRAW);        return indices.length;    }    function initArrayBuffer(gl, data, type, num, attribute) {        var buffer = gl.createBuffer();        if (!buffer) {            console.log("无法创建缓冲区对象");            return;        }        gl.bindBuffer(gl.ARRAY_BUFFER, buffer);        gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);        var a_attribute = gl.getAttribLocation(gl.program, attribute);        if (a_attribute < 0) {            console.log("无法获取变量的存储位置" + attribute);            return false;        }        gl.vertexAttribPointer(a_attribute, num, type, false, 0, 0);        gl.enableVertexAttribArray(a_attribute);        return true;    }    //绘制    var matrix = new Matrix4();    function draw(gl, n, currentAngle, viewProjectionMatrix, u_MvpMatrix) {        matrix.set(viewProjectionMatrix);        matrix.rotate(currentAngle, 1.0, 0.0, 0.0);        matrix.rotate(currentAngle, 0.0, 1.0, 0.0);        matrix.rotate(currentAngle, 0.0, 0.0, 1.0);        gl.uniformMatrix4fv(u_MvpMatrix, false, matrix.elements);        gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);        gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);    }</script></html>

这是教程里面的一个案例，里面就是交给我们如何通过点击实现获取到哪个面。里面有趣的是有一个判断。

这里与上一节的案例代码区别不大，别的不再讲解。

我们直接从mousedown事件里面说起来。

触发mousedown事件以后，我们就把u_PickedFace变量改为了0. 然后让WebGL重新绘制页面。到了这里我们就去看顶点着色器，会发现有个if else的判断，在那里对u_PickedFace进行了判断。也就是说，在点击第一次绘制的时候，会把我们设置的当前面的index作为颜色的第四项传入到视图当中。等绘制完成，然后调用获取颜色的方法获取了一下当前下标，再次将u_PickedFace修改掉。然后通过顶点着色器里面的三元运算符运算，将处于相同面的点的颜色全部绘制成了白色。

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