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一个域名一个ip做多个网站,seo推广培训费用,网站功能建设中,做网站需要买多大空间案例查看地址：点击这里问题原因我公司里有一个项目，需要能够一个矩形的四个顶点能够随意移动，而且上面还绘制的纹理。然后，我按照以前的方式书写，问题来了，由于一个矩形是由两个三角形组成的&#xff0…

案例查看地址：点击这里

问题原因

我公司里有一个项目，需要能够一个矩形的四个顶点能够随意移动，而且上面还绘制的纹理。然后，我按照以前的方式书写，问题来了，由于一个矩形是由两个三角形组成的，然后就出现下面喜闻乐见的效果：
这里写图片描述
我们会发现，两个三角形的交汇处，有一道折线，所以比较尴尬了。
而我们需要的是什么呢：

我们需要的是上面这种，具有透视效果，而且图形不会有折线的效果。
即使是随意的扭曲，也不会出现折线，这就是所谓的透视纹理绘制。
这里写图片描述

思路

首先，我需要先获取到当前绘制的那一点的坐标x，y两个轴的，然后计算这一个点和四个矩形顶点的位置关系，计算出这个点需要绘制的纹理图片的位置。关系图如下：

查看图形，其实我们唯一不知道的就是过图形的线和两个点切割获得的比例，通过高中的学的图形知识，将五个点代进去，计算一下，最后出来的就是这个点。
由于(c1-v1)/(v0-v1) = (c2-v3)/(v2-v3)这个比例保证每一个点在纹理坐标中确定需要绘制的纹理。
然后通过两个点确定一条直线，根据两点方程(x-c1.x)/(c2.x-c1.x) = (y-c1.y)/(c2.y-c1.y)然后将所有的值代入进入，再通过一元二次方程的解析，最后得出比例。
以下是js版本的代码：

function  calc(p1,p2,p3,p4,p0) {/**   p1-------p3*   |         |*   |         |*   |         |*   p2-------p4*假设四个点的坐标分别是(x1,y1)、(x2,y2)、(x3,y3)、(x4,y4)* 则下式成立平行* （x1-x2)/(y1-y2)=(x3-x4)/(y3-y4)**//** 根据两点式方程* (y-y1)/(y2-y1) = (x-x1)/(x2-x1)* 得出* (y-y1)(x2-x1) = (y2-y1)(x-x1)* yx2-yx1-y1x2+y1x1 = y2x-y2x1-y1x+y1x1* yx2-yx1-y1x2+y1x1-(y2x-y2x1-y1x+y1x1) = 0;* yx2-yx1-y1x2+y1x1-y2x+y2x1+y1x-y1x1 = 0;* yx2-yx1-y1x2-y2x+y2x1+y1x = 0;\* x2(y-y1)+x1(y2-y)+x(y1-y2)=0** //两个点的位置为* p12Xlen = p2.x-p1.x;* p12Ylen = p2.y-p1.y;* p34Xlen = p4.x-p3.x;* p34Ylen = p4.y-p3.y;* p12.x = x1 = p1.x+p12Xlen*s;* p12.y = y1 = p1.y+p12Ylen*s;* p34.x = x2 = p3.x+p34Xlen*s;* p34.y = y2 = p3.y+p34Ylen*s;* x = p0.x;* y = p0.y;** 由此得出* x2(y-y1) = (p3.x+p34Xlen*s)(p0.y-(p1.y+p12Ylen*s));* x2(y-y1) = (p3.x + p34Xlen*s)(p0.y - p1.y - p12Ylen*s);* x2(y-y1) = p3.x*p0.y-p3.x*p1.y-p3.x*p12Ylen*s+p0.y*p34Xlen*s-p1.y*p34Xlen*s-p12Ylen*p34Xlen*s*s;* x2(y-y1) = p3.x*p0.y-p3.x*p1.y+(-p3.x*p12Ylen+p0.y*p34Xlen-p1.y*p34Xlen)*s-p12Ylen*p34Xlen*s*s;** x1(y2-y) = (p1.x+p12Xlen*s)*(p3.y+p34Ylen*s-p0.y);* x1(y2-y) = (p1.x+p12Xlen*s)*(p3.y-p0.y+p34Ylen*s);* x1(y2-y) = p1.x*p3.y-p1.x*p0.y+p1.x*p34Ylen*s+p3.y*p12Xlen*s-p0.y*p12Xlen*s+p12Xlen*p34Ylen*s*s;* x1(y2-y) = p1.x*p3.y-p1.x*p0.y+(p1.x*p34Ylen+p3.y*p12Xlen-p0.y*p12Xlen)*s+p12Xlen*p34Ylen*s*s;** x(y1-y2) = p0.x(p1.y+p12Ylen*s-(p3.y+p34Ylen*s));* x(y1-y2) = p0.x(p1.y+p12Ylen*s-p3.y-p34Ylen*s);* x(y1-y2) = p0.x(p1.y-p3.y+p12Ylen*s-p34Ylen*s);* x(y1-y2) = p0.x(p1.y-p3.y)+p0.x(p12Ylen-p34Ylen)*s;** 得出** A = p12Xlen*p34Ylen-p12Ylen*p34Xlen;** B = p1.x*p34Ylen+p3.y*p12Xlen-p0.y*p12Xlen-p3.x*p12Ylen+p0.y*p34Xlen-p1.y*p34Xlen+p0.x(p12Ylen-p34Ylen);** C = p3.x*p0.y-p3.x*p1.y+p1.x*p3.y-p1.x*p0.y+p0.x(p1.y-p3.y)** Ass + Bs +C = 0;* */var p12Xlen = p2.x-p1.x;var p12Ylen = p2.y-p1.y;var p34Xlen = p4.x-p3.x;var p34Ylen = p4.y-p3.y;var a = p12Xlen*p34Ylen-p12Ylen*p34Xlen;var b = p1.x*p34Ylen+p3.y*p12Xlen-p0.y*p12Xlen-p3.x*p12Ylen+p0.y*p34Xlen-p1.y*p34Xlen+p0.x*(p12Ylen-p34Ylen);var c = p3.x*p0.y-p3.x*p1.y+p1.x*p3.y-p1.x*p0.y+p0.x*(p1.y-p3.y);//在两条线平行的情况下if(a === 0){return -c/b;}//在两条线不平行的情况下 获取数组里面再0到1范围内的return [(-b+Math.sqrt(b*b-4.0*a*c))/(2*a),(-b-Math.sqrt(b*b-4.0*a*c))/(2*a)];}

案例代码

以下是可以运行的案例代码，把文件放到服务里面，设置好图片，就可以直接查看效果：

<!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 {display: block;}#div{width:800px;height:800px;position: relative;margin: 0 auto;}</style>
</head>
<body onload="main()">
<div id="div"><canvas id="canvas" height="800" width="800"></canvas>
</div>
</body>
<script src="https://johnson2heng.github.io/webgl-demo/lib/webgl-utils.js"></script>
<script src="https://johnson2heng.github.io/webgl-demo/lib/webgl-debug.js"></script>
<script src="https://johnson2heng.github.io/webgl-demo/lib/cuon-utils.js"></script>
<script src="https://johnson2heng.github.io/webgl-demo/lib/cuon-matrix.js"></script>
<script>/*第一部分顶点着色器接收顶点的纹理坐标，传递给片元着色器*/var VSHADER_SOURCE = "" +"attribute vec4 a_Position;\n" +//"varying vec2 v_Position;\n" +"void main(){\n" +"   gl_Position = a_Position;\n" +"   v_Position = vec2(a_Position);\n" +"}\n";var FSHADER_SOURCE = "" +"precision mediump float;\n" +//"uniform sampler2D u_Sampler;\n" +//"varying vec2 v_Position;\n" +"uniform vec2 u_point0;\n" +"uniform vec2 u_point1;\n" +"uniform vec2 u_point2;\n" +"uniform vec2 u_point3;\n"  +"float calc(vec2 p1,vec2 p2,vec2 p3,vec2 p4,vec2 p0){\n" +//如果不是平行的两条直线"   float p12Xlen = p2.x-p1.x;\n" +"   float p12Ylen = p2.y-p1.y;\n" +"   float p34Xlen = p4.x-p3.x;\n" +"   float p34Ylen = p4.y-p3.y;\n" +"   float a = p12Xlen*p34Ylen-p12Ylen*p34Xlen;\n" +"   float b = p1.x*p34Ylen+p3.y*p12Xlen-p0.y*p12Xlen-p3.x*p12Ylen+p0.y*p34Xlen-p1.y*p34Xlen+p0.x*(p12Ylen-p34Ylen);\n" +"   float c = p3.x*p0.y-p3.x*p1.y+p1.x*p3.y-p1.x*p0.y+p0.x*(p1.y-p3.y);\n" +//两条线都垂直于x轴或者y轴的情况下"   if(a == 0.0){\n" +"       return -c/b;\n" +"   }\n" +//两条线不平行的情况下"   float endA = (-b+sqrt(b*b-4.0*a*c))/(2.0*a);\n" +"   float endB = (-b-sqrt(b*b-4.0*a*c))/(2.0*a);\n" +"   if(endA > 0.0 && endA < 1.0){\n" +"       return endA;\n" +"   }\n" +"   if(endB > 0.0 && endB < 1.0){\n" +"       return endB;\n" +"   }\n" +"   else {\n" +"       return -c/b;\n" +"   }\n" +"}\n" +""+//两个点的位置，第一个calc（v0,v2,v1,v3,p0） 第二个calc(v1,v0,v3,v2,p0)"void main(){\n" +"   gl_FragColor = texture2D(u_Sampler,vec2(calc(u_point0,u_point2,u_point1,u_point3,v_Position),calc(u_point1,u_point0,u_point3,u_point2,v_Position)));\n" +//"}\n";//四个顶点的位置var v0 = {x:-0.5,y:0.5};var v1 = {x:-0.5,y:-0.5};var v2 = {x:0.5,y:0.5};var v3 = {x:0.5,y:-0.5};//图片的地址设置var imgSrc = "../image/door/001.png";var gl;/*第二部分 main()方法 初始化着色器，设置顶点信息，调用配置纹理方法*/function main() {var canvas = document.getElementById("canvas");gl = getWebGLContext(canvas);if(!gl){console.log("你的电脑不支持WebGL！");return;}if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){console.log("初始化着色器失败！");return;}//设置顶点的相关信息var n = initVertexBuffers(gl);if(n < 0){console.log("无法获取到点的数据");return;}//配置纹理if(!initTextures(gl,n)){console.log("无法配置纹理");return;}}/*第三部分 initVertexBuffers() 设置顶点坐标和纹理坐标 调用initTextures()进行下一步处理*/function initVertexBuffers(gl) {/**   v0-------v2*   |         |*   |         |*   |         |*   v1-------v3**   [v0.x,v0.y,v1.x,v1.y,v2.x,v2.y,v3.x,v3.y]*   config.Positions[0].Config 数组由八个数据组成，代表四个点的位置，距离中心点的偏移量* */var verticesSizes = new Float32Array([//四个顶点的位置v0.x,v0.y,v1.x,v1.y,v2.x,v2.y,v3.x,v3.y]);initArrayBuffer(gl, verticesSizes, 2, gl.FLOAT, "a_Position");//将四个顶点位置传入var point0 = gl.getUniformLocation(gl.program, "u_point0");var point1 = gl.getUniformLocation(gl.program, "u_point1");var point2 = gl.getUniformLocation(gl.program, "u_point2");var point3 = gl.getUniformLocation(gl.program, "u_point3");if(point0 < 0){alert("无法获取到存储的位置");}gl.uniform2f(point0,v0.x,v0.y);gl.uniform2f(point1,v1.x,v1.y);gl.uniform2f(point2,v2.x,v2.y);gl.uniform2f(point3,v3.x,v3.y);var indexSize = new Uint8Array([0,1,3,0,2,3]);//将索引写入缓冲区对象var indexBuffer = gl.createBuffer();gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER,indexBuffer);gl.bufferData(gl.ELEMENT_ARRAY_BUFFER,indexSize, gl.STATIC_DRAW);return indexSize.length;}//创建变量缓冲区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);}/*第四部分 initTextures() 创建纹理对象 并调用纹理绘制方法*/function initTextures(gl,n) {var texture = gl.createTexture();//创建纹理对象if(!texture){console.log("无法创建纹理对象");return;}//获取u_Sampler的存储位置var u_Sampler = gl.getUniformLocation(gl.program,"u_Sampler");if(u_Sampler < 0){console.log("无法获取变量的存储位置");return;}//创建Image对象，并绑定加载完成事件var image = new Image();image.onload = function () {loadTexture(gl,n,texture,u_Sampler,image);//初始化交互事件initMoveBtn();};image.src = imgSrc;return true;}function initMoveBtn() {var canvas = document.querySelector("#canvas");var div = document.querySelector("#div");var canvasWidth = canvas.width;var canvasHeight = canvas.height;addBtn(v0);addBtn(v1);addBtn(v2);addBtn(v3);function addBtn(obj) {var x = (obj.x+1)/2;var y = 1-(obj.y+1)/2;var btn = document.createElement("div");btn.style.cssText = "height:10px; width:10px; transform:translate(-50%,-50%); position:absolute; background:green; cursor:pointer;";btn.style.left = x *canvasWidth+"px";btn.style.top = y * canvasHeight +"px";div.appendChild(btn);var downX,downY,btnX,btnY;btn.addEventListener("mousedown",function (event) {//鼠标按下时的位置downX = event.clientX;downY = event.clientY;//按下时btn的位置btnX = parseFloat(btn.style.left);btnY = parseFloat(btn.style.top);document.addEventListener("mousemove",move,true);document.addEventListener("mouseup",up,true);},true);function move(event) {event.preventDefault();var moveX = event.clientX;var moveY = event.clientY;var x = moveX-downX + btnX;var y = moveY - downY + btnY;btn.style.left = x+"px";btn.style.top = y + "px";obj.x = x/canvasWidth*2-1;obj.y = (1-y/canvasHeight)*2-1;//重新绘制reload();}function up() {document.removeEventListener("mousemove",move,true);document.removeEventListener("mouseup",up,true);}}}/*第五部分 设置纹理相关信息供WebGL使用，并进行绘制*/function loadTexture(gl,n,texture,u_Sampler,image) {//对纹理图像进行y轴反转gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL,1);//开启0号纹理单元gl.activeTexture(gl.TEXTURE0);//向target绑定纹理对象gl.bindTexture(gl.TEXTURE_2D,texture);//配置纹理参数gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);//配置纹理图像gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);//将0号纹理传递给着色器gl.uniform1i(u_Sampler,0);draw(n);}//重新绘制的方法function reload(){var n = initVertexBuffers(gl);//绘制draw(n);}function draw(n) {//绘制gl.clearColor(0.0,0.0,0.0,1.0);gl.clear(gl.COLOR_BUFFER_BIT);gl.drawElements(gl.TRIANGLES, n, gl.UNSIGNED_BYTE, 0);}</script>
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