WEBGL学习【七】画布绘图

主要是对WEBGL的绘图部分进行了进一步加强的认识和理解

<!DOCTYPE HTML>
<html lang="en">
<head>
    <title>WEBGL高级编程----绘制六边形</title>
    <meta charset="utf-8">
    <script id="shader-vs" type="x-shader/x-vertex">
      attribute vec3 aVertexPosition;
      attribute vec4 aVertexColor;
      varying vec4 vColor;

      void main() {
        vColor = aVertexColor;
        gl_Position = vec4(aVertexPosition, 1.0);
      }

    </script>

    <script id="shader-fs" type="x-shader/x-fragment">
      precision mediump float;

      varying vec4 vColor;
      void main() {
        gl_FragColor = vColor;
      }

    </script>

    <!--引入我的库文件-->
    <script src="./lib/webgl-debug.js"></script>

    <script type="text/javascript">
        var gl;
        var canvas;
        var shaderProgram;
        //六边形顶点缓冲区
        var hexagonVertexBuffer;
        //坐标系缓冲区
        var xyCordBuffer;
        //三角形顶点位置缓冲区
        var triangleVertexBuffer;
        var triangleVertexBufferTwo;
        //三角形颜色缓冲区
        var triangleVertexColorBuffer;
        //三角形带1
        var stripVertexBuffer;

        //创建我的上下文句柄
        function createGLContext(canvas) {
            var names = ["webgl", "experimental-webgl"];
            var context = null;
            for (var i = 0; i < names.length; i++) {
                try {
                    context = canvas.getContext(names[i]);
                } catch (e) {
                }
                if (context) {
                    break;
                }
            }
            if (context) {
                context.viewportWidth = canvas.width;
                context.viewportHeight = canvas.height;
            } else {
                alert("Failed to create WebGL context!");
            }
            return context;
        }

        //从JavaScript代码中通过DOM加载着色器
        function loadShaderFromDOM(id) {
            var shaderScript = document.getElementById(id);

            // If we don't find an element with the specified id
            // we do an early exit
            if (!shaderScript) {
                return null;
            }

            // Loop through the children for the found DOM element and
            // build up the shader source code as a string
            var shaderSource = "";
            var currentChild = shaderScript.firstChild;
            while (currentChild) {
                if (currentChild.nodeType == 3) { // 3 corresponds to TEXT_NODE
                    shaderSource += currentChild.textContent;
                }
                currentChild = currentChild.nextSibling;
            }

            var shader;
            if (shaderScript.type == "x-shader/x-fragment") {
                shader = gl.createShader(gl.FRAGMENT_SHADER);
            } else if (shaderScript.type == "x-shader/x-vertex") {
                shader = gl.createShader(gl.VERTEX_SHADER);
            } else {
                return null;
            }

            gl.shaderSource(shader, shaderSource);
            gl.compileShader(shader);

            if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
                alert(gl.getShaderInfoLog(shader));
                return null;
            }
            return shader;
        }

        //设置我的着色器
        function setupShaders() {
            var vertexShader = loadShaderFromDOM("shader-vs");
            var fragmentShader = loadShaderFromDOM("shader-fs");

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

            if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
                alert("Failed to setup shaders");
            }

            gl.useProgram(shaderProgram);

            shaderProgram.vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
            shaderProgram.vertexColorAttribute = gl.getAttribLocation(shaderProgram, "aVertexColor");

            gl.enableVertexAttribArray(shaderProgram.vertexPositionAttribute);
        }

        //设置我的缓冲区
        function setupBuffers() {
            //创建六边形
            hexagonVertexBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, hexagonVertexBuffer);
            var hexagonVertices = [
                -0.3, 0.6, 0.0, //v0
                -0.4, 0.8, 0.0, //v1
                -0.6, 0.8, 0.0, //v2
                -0.7, 0.6, 0.0, //v3
                -0.6, 0.4, 0.0, //v4
                -0.4, 0.4, 0.0, //v5
                -0.3, 0.6, 0.0, //v6
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(hexagonVertices), gl.STATIC_DRAW);
            hexagonVertexBuffer.itemSize = 3;
            hexagonVertexBuffer.numberOfItems = 7;



            //绘制一个坐标系
            xyCordBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, xyCordBuffer);
            var xyCordVertices = [
                -1.0, 0.0, 0.0,
                1.0, 0.0, 0.0,
                0.0, -1.0, 0.0,
                0.0, 1.0, 0.0
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(xyCordVertices), gl.STATIC_DRAW);
            xyCordBuffer.itemSize = 3;
            xyCordBuffer.numberOfItems = 4;


            //绘制一个三角形
            triangleVertexBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexBuffer);
            var triangleVertices = [
                0.3, 0.4, 0.0, //v0
                0.7, 0.4, 0.0, //v1
                0.5, 0.8, 0.0, //v2
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVertices), gl.STATIC_DRAW);
            triangleVertexBuffer.itemSize = 3;
            triangleVertexBuffer.numberOfItems = 3;

            //绘制一个三角形
            triangleVertexBufferTwo = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexBufferTwo);
            var triangleVerticesTwo = [
                0.0, 0.2, 0.0, //v0
                -0.2, -0.2, 0.0, //v1
                0.2, -0.2, 0.0, //v2
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(triangleVerticesTwo), gl.STATIC_DRAW);
            triangleVertexBufferTwo.itemSize = 3;
            triangleVertexBufferTwo.numberOfItems = 3;

            //创建三角形颜色数组
            triangleVertexColorBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexColorBuffer);
            var colors = [
                1.0, 0.0, 0.0, 1.0, //v0
                0.0, 1.0, 0.0, 1.0, //v1
                0.0, 0.0, 1.0, 1.0  //v2
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(colors), gl.STATIC_DRAW);
            triangleVertexColorBuffer.itemSize = 4;
            triangleVertexColorBuffer.numberOfItems = 3;

            //绘制一个三角形带1
            stripVertexBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ARRAY_BUFFER, stripVertexBuffer);
            //绘制两条
            var stripVertices = [
                -0.5, 0.2, 0.0, //v0
                -0.4, 0.0, 0.0, //v1
                -0.3, 0.2, 0.0, //v2
                -0.2, 0.0, 0.0, //v3
                -0.1, 0.2, 0.0, //v4
                0.0, 0.0, 0.0, //v5
                0.1, 0.2, 0.0, //v6
                0.2, 0.0, 0.0, //v7
                0.3, 0.2, 0.0, //v8
                0.4, 0.0, 0.0, //v9
                0.5, 0.2, 0.0, //v10

                // start second strip
                -0.5, -0.3, 0.0, //v11
                -0.4, -0.5, 0.0, //v12
                -0.3, -0.3, 0.0, //v13
                -0.2, -0.5, 0.0, //v14
                -0.1, -0.3, 0.0, //v15
                0.0, -0.5, 0.0, //v16
                0.1, -0.3, 0.0, //v17
                0.2, -0.5, 0.0, //v18
                0.3, -0.3, 0.0, //v19
                0.4, -0.5, 0.0, //v20
                0.5, -0.3, 0.0  //v21
            ];
            gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(stripVertices), gl.STATIC_DRAW);
            stripVertexBuffer.itemSize = 3;
            stripVertexBuffer.numberOfItems = 22;

            //创建三角形条带缓冲区（元素数组缓冲）
            stripElementBuffer = gl.createBuffer();
            gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, stripElementBuffer);
            //注意顶点索引的数量与【组绕顺序】有关，默认是逆时针方向为正方向
            //【记住：如果三角形数量为奇数，就必须增加三个索引，从而会出现5个退化三角形；
            //      如果三角形数量为偶数，就必须增加两个索引， 从而会出现4个退化三角形；
            //      否则，就会出现组绕三角形的逆时针/顺时针混乱的问题【记住了嘛？】
            // 】
            var indices = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
                10, 11, 11,// 3 extra indices for the degenerate triangles（这里共计有五个退化了的三角形）
                11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21];

            gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(indices), gl.STATIC_DRAW);

            stripElementBuffer.numberOfItems = 25;
        }



        //绘图函数
        function draw() {
            //设置视口，清空深度缓存
            gl.viewport(0, 0, gl.viewportWidth, gl.viewportHeight);
            gl.clear(gl.COLOR_BUFFER_BIT);

            // Draw the hexagon
            // We disable the vertex attrib array since we want to use a
            // constant color for all vertices in the hexagon
            //将顶点的颜色设置为一个常量
            gl.disableVertexAttribArray(shaderProgram.vertexColorAttribute);
            //将顶点颜色设置为黑色
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 0.0, 0.0, 1.0, 1.0);
            //把六边形的坐标传给顶点着色器
            gl.bindBuffer(gl.ARRAY_BUFFER, hexagonVertexBuffer);
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                hexagonVertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
            //绘制首尾相连的图形
            gl.drawArrays(gl.LINE_STRIP, 0, hexagonVertexBuffer.numberOfItems);


            //开始传值到顶点着色器
            gl.disableVertexAttribArray(shaderProgram.vertexColorAttribute);
            //这里可以给我的坐标系指定一个常量颜色（红色）
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 1.0, 0.0, 0.0, 1.0);
            gl.bindBuffer(gl.ARRAY_BUFFER, xyCordBuffer);
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                xyCordBuffer.itemSize, gl.FLOAT, false, 0, 0);
            gl.drawArrays(gl.LINES, 0, xyCordBuffer.numberOfItems);


            //绘制三角形(如果要从一个颜色数组去设置顶点的颜色这里需要开启，如果要通过常量去设置颜色，这里就需要关闭)
            gl.disableVertexAttribArray(shaderProgram.vertexColorAttribute);
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 0.0, 1.0, 0.0, 1.0);
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexBuffer);
            //每一个位置信息需要triangleVertexBuffer.itemSize个参数信息来表示
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                triangleVertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
            gl.drawArrays(gl.TRIANGLES, 0, triangleVertexBuffer.numberOfItems);

            //再次绘制一个三角形（用颜色数组来绘制）
            gl.enableVertexAttribArray(shaderProgram.vertexColorAttribute);
            //传递顶点位置
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexBufferTwo);
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                triangleVertexBufferTwo.itemSize, gl.FLOAT, false, 0, 0);
            //传递顶点颜色
            gl.bindBuffer(gl.ARRAY_BUFFER, triangleVertexColorBuffer);
            gl.vertexAttribPointer(shaderProgram.vertexColorAttribute,
                triangleVertexColorBuffer.itemSize, gl.FLOAT, false, 0, 0);
            gl.drawArrays(gl.TRIANGLES, 0, triangleVertexBuffer.numberOfItems);

            //开始绘制三角形带1
            /*gl.disableVertexAttribArray(shaderProgram.vertexColorAttribute);
            gl.bindBuffer(gl.ARRAY_BUFFER, stripVertexBuffer);
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                stripVertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 1.0, 1.0, 0.0, 1.0);
            gl.drawArrays(gl.TRIANGLES, 0, stripVertexBuffer.numberOfItems);*/

            //begin to drawElements()
            //first put the vertexBuffer to the shader
            gl.disableVertexAttribArray(shaderProgram.vertexColorAttribute);
            gl.bindBuffer(gl.ARRAY_BUFFER, stripVertexBuffer);
            gl.vertexAttribPointer(shaderProgram.vertexPositionAttribute,
                stripVertexBuffer.itemSize, gl.FLOAT, false, 0, 0);
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 1.0, 1.0, 0.0, 1.0);
            gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, stripElementBuffer);
            gl.drawElements(gl.TRIANGLE_STRIP, stripElementBuffer.numberOfItems, gl.UNSIGNED_SHORT, 0);


            //set the color of help line(black color )
            gl.vertexAttrib4f(shaderProgram.vertexColorAttribute, 1.0, 0.0, 0.0, 1.0);
            // Draw help lines to easier see the triangles
            // that build up the triangle-strip
            gl.drawArrays(gl.LINE_STRIP, 0, 11);
            gl.drawArrays(gl.LINE_STRIP, 11, 11);
        }

        function startup() {
            canvas = document.getElementById("myGLCanvas");
            gl = WebGLDebugUtils.makeDebugContext(createGLContext(canvas));
            setupShaders();
            setupBuffers();
            gl.clearColor(1.0, 1.0, 1.0, 1.0);


            //逆时针方向是前面
            gl.frontFace(gl.CW);
            //激活背面剔除功能
            gl.enable(gl.CULL_FACE);
            //WEBGL剔除背面三角形
            gl.cullFace(gl.FRONT);

            draw();
        }
    </script>

</head>

<body onload="startup();">
<canvas id="myGLCanvas" width="500" height="500" style="border: 2px solid springgreen;"></canvas>
</body>

</html>

【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/52tech/p/9325118.html