WebGL——水波纹特效

　　大家好，今天我ccentry要做一个水波纹特效，我们来看看水波纹特效的做法。首先我们来看一下水波纹特效的效果是怎么样的，请看下图。

　　我们要做的就是类似这种纹理特效，那么我们来看看是如何制作的吧。首先鲫鱼我新建一个空项目，来编写这个demo，项目结构如下图所示。

img文件夹中存放的是uv贴图和底图，js文件夹下存放的是jquery和我的水波纹效果的js文件，还有就是展示页面index.html。很简单，没什么东西了，接下来就来看鲫鱼我是怎么实现上面这个水波纹特效的吧。我们先开始编辑ripples.js，这就是这个特效的核心功能。再来看一遍工程结构。

且看鲫鱼我怎么写这个ripple.js。首先我们检查浏览器是否支持webgl的api，这是一个浏览器校验功能函数，代码块如下。

var gl;

function hasWebGLSupport() {
        var canvas = document.createElement('canvas');
        var context = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
        var result = context && context.getExtension('OES_texture_float') && context.getExtension('OES_texture_float_linear');
        return result;
    }

这里先是创建了一个canvas标签，然后由这个canvas中拿到context('webgl')对象，我们所有做webgl的api都由此而来。这里只是校验并获取gl对象的动作，然后我们来看函数的返回值，这里有个js的&&运算符的妙用，result = context && context.getExtension('OES_texture_float') && context.getExtension('OES_texture_float_linear');这句话是指context存在，就取context.getExtension('OES_texture_float')，而且context.getExtension('OES_texture_float')存在，就取context.getExtension('OES_texture_float_linear')，这是递进式的取值方式，我们最终通过了前两个的校验获取到了'OES_texture_float_linear'对象，鲫鱼相信大家也都看得懂，我们就不在这里浪费时间了，继续往下看。

var supportsWebGL = hasWebGLSupport();

这句就一目了然了，我们调用了hasWebGLSupport函数，从而获取到了'OES_texture_float_linear'线性浮点数的材质处理对象。这个对象我们后面要使用到，现在这里拿到手再说。我们接下去看。

function createProgram(vertexSource, fragmentSource, uniformValues)
    {
        function compileSource(type, source) {
            var shader = gl.createShader(type);
            gl.shaderSource(shader, source);
            gl.compileShader(shader);
            if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
                throw new Error('compile error: ' + gl.getShaderInfoLog(shader));
            }
            return shader;
        }

        var program = {};

        program.id = gl.createProgram();
        gl.attachShader(program.id, compileSource(gl.VERTEX_SHADER, vertexSource));
        gl.attachShader(program.id, compileSource(gl.FRAGMENT_SHADER, fragmentSource));
        gl.linkProgram(program.id);
        if (!gl.getProgramParameter(program.id, gl.LINK_STATUS)) {
            throw new Error('link error: ' + gl.getProgramInfoLog(program.id));
        }

        // Fetch the uniform and attribute locations
        program.uniforms = {};
        program.locations = {};
        gl.useProgram(program.id);
        gl.enableVertexAttribArray(0);
        var name, type, regex = /uniform (\w+) (\w+)/g, shaderCode = vertexSource + fragmentSource;
        while ((match = regex.exec(shaderCode)) != null) {
            name = match[2];
            program.locations[name] = gl.getUniformLocation(program.id, name);
        }

        return program;
    }

这一个功能自然不必再解释了，这是gl对象绑定shader的工具，参数为vertexSource顶点着色器字符串，fragmentSource片段着色器字符串，uniformValues向着色器传递的参数，如果读者对这个函数存在疑问，鲫鱼建议读者先学习《webgl编程指南》和阅读鲫鱼之前的博客https://www.cnblogs.com/ccentry/p/9864847.html，这里不再赘述。我们再往下看。

function bindTexture(texture, unit) {
        gl.activeTexture(gl.TEXTURE0 + (unit || 0));
        gl.bindTexture(gl.TEXTURE_2D, texture);
    }

这个函数是绑定材质的函数，参数texture是材质，unit是偏移量，这个函数只有两步操作，启用gl.TEXTURE0材质类型，将传入的材质按照该类型去绑定到gl程序对象上。该函数做到这件事，我们看下去。

//Ripples构造函数
    var Ripples = function (el, options) {
        var that = this;

        this.$el = $(el);
        this.$el.addClass('jquery-ripples');

        // If this element doesn't have a background image, don't apply this effect to it
        var backgroundUrl = (/url\(["']?([^"']*)["']?\)/.exec(this.$el.css('background-image')));
        if (backgroundUrl == null) return;
        backgroundUrl = backgroundUrl[1];

        this.interactive = options.interactive;
        this.resolution = options.resolution || 256;
        this.textureDelta = new Float32Array([1 / this.resolution, 1 / this.resolution]);

        this.perturbance = options.perturbance;
        this.dropRadius = options.dropRadius;

        var canvas = document.createElement('canvas');
        canvas.width = this.$el.innerWidth();
        canvas.height = this.$el.innerHeight();
        this.canvas = canvas;
        this.$canvas = $(canvas);
        this.$canvas.css({
            position: 'absolute',
            left: 0,
            top: 0,
            right: 0,
            bottom: 0,
            zIndex: -1
        });

        this.$el.append(canvas);
        this.context = gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');

        // Load extensions
        gl.getExtension('OES_texture_float');
        gl.getExtension('OES_texture_float_linear');

        // Init events
        $(window).on('resize', function() {
            if (that.$el.innerWidth() != that.canvas.width || that.$el.innerHeight() != that.canvas.height) {
                canvas.width = that.$el.innerWidth();
                canvas.height = that.$el.innerHeight();
            }
        });

        this.$el.on('mousemove.ripples', function(e) {
            if (that.visible && that.running && that.interactive) that.dropAtMouse(e, that.dropRadius, 0.01);
        }).on('mousedown.ripples', function(e) {
            if (that.visible && that.running && that.interactive) that.dropAtMouse(e, that.dropRadius * 1.5, 0.14);
        });

        this.textures = [];
        this.framebuffers = [];

        for (var i = 0; i < 2; i++) {
            var texture = gl.createTexture();
            var framebuffer = gl.createFramebuffer();

            gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
            framebuffer.width = this.resolution;
            framebuffer.height = this.resolution;

            gl.bindTexture(gl.TEXTURE_2D, texture);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
            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);
            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, this.resolution, this.resolution, 0, gl.RGBA, gl.FLOAT, null);

            gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
            if (gl.checkFramebufferStatus(gl.FRAMEBUFFER) != gl.FRAMEBUFFER_COMPLETE) {
                throw new Error('Rendering to this texture is not supported (incomplete framebuffer)');
            }

            gl.bindTexture(gl.TEXTURE_2D, null);
            gl.bindFramebuffer(gl.FRAMEBUFFER, null);

            this.textures.push(texture);
            this.framebuffers.push(framebuffer);
        }

        this.running = true;

        // Init GL stuff
        this.quad = gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER, this.quad);
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
            -1, -1,
            +1, -1,
            +1, +1,
            -1, +1
        ]), gl.STATIC_DRAW);

        this.initShaders();

        // Init textures
        var image = new Image;
        image.crossOrigin = '';
        image.onload = function() {
            gl = that.context;

            function isPowerOfTwo(x) {
                return (x & (x - 1)) == 0;
            }

            var wrapping = (isPowerOfTwo(image.width) && isPowerOfTwo(image.height)) ? gl.REPEAT : gl.CLAMP_TO_EDGE;

            that.backgroundWidth = image.width;
            that.backgroundHeight = image.height;

            var texture = gl.createTexture();

            gl.bindTexture(gl.TEXTURE_2D, texture);
            gl.pixelStorei(gl.UNPACK_FLIP_Y_WEBGL, 1);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, wrapping);
            gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, wrapping);
            gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);

            that.backgroundTexture = texture;

            // Everything loaded successfully - hide the CSS background image
            that.$el.css('backgroundImage', 'none');
        };
        image.src = backgroundUrl;

        this.visible = true;

        // Init animation
        function step() {
            that.step();
            requestAnimationFrame(step);
        }

        requestAnimationFrame(step);
    };

    Ripples.DEFAULTS = {
        resolution: 256,
        dropRadius: 20,
        perturbance: 0.03,
        interactive: true
    };

以上就是Ripples的构造函数，我们看到这个构造函数非常的冗长，而且其中一些函数还是调用的Ripples原型对象的api，所以我们赶快再把Ripples的原型对象也一起贴出，以下是鲫鱼对Ripples原型对象的定义，我们来看代码。

Ripples.prototype = {

        step: function() {
            gl = this.context;

            if (!this.visible || !this.backgroundTexture) return;

            this.computeTextureBoundaries();

            if (this.running) {
                this.update();
            }

            this.render();
        },

        drawQuad: function() {
            gl.bindBuffer(gl.ARRAY_BUFFER, this.quad);
            gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
            gl.drawArrays(gl.TRIANGLE_FAN, 0, 4);
        },

        render: function() {
            gl.viewport(0, 0, this.canvas.width, this.canvas.height);
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

            gl.useProgram(this.renderProgram.id);

            bindTexture(this.backgroundTexture, 0);
            bindTexture(this.textures[0], 1);

            gl.uniform2fv(this.renderProgram.locations.topLeft, this.renderProgram.uniforms.topLeft);
            gl.uniform2fv(this.renderProgram.locations.bottomRight, this.renderProgram.uniforms.bottomRight);
            gl.uniform2fv(this.renderProgram.locations.containerRatio, this.renderProgram.uniforms.containerRatio);
            gl.uniform1i(this.renderProgram.locations.samplerBackground, 0);
            gl.uniform1i(this.renderProgram.locations.samplerRipples, 1);

            this.drawQuad();
        },

        update: function() {
            gl.viewport(0, 0, this.resolution, this.resolution);

            for (var i = 0; i < 2; i++) {
                gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffers[i]);
                bindTexture(this.textures[1-i]);
                gl.useProgram(this.updateProgram[i].id);

                this.drawQuad();
            }

            gl.bindFramebuffer(gl.FRAMEBUFFER, null);
        },

        computeTextureBoundaries: function() {
            var backgroundSize = this.$el.css('background-size');
            var backgroundAttachment = this.$el.css('background-attachment');
            var backgroundPosition = this.$el.css('background-position').split(' ');

            // Here the 'window' is the element which the background adapts to
            // (either the chrome window or some element, depending on attachment)
            var parElement = backgroundAttachment == 'fixed' ? $window : this.$el;
            var winOffset = parElement.offset() || {left: pageXOffset, top: pageYOffset};
            var winWidth = parElement.innerWidth();
            var winHeight = parElement.innerHeight();

            // TODO: background-clip
            if (backgroundSize == 'cover') {
                var scale = Math.max(winWidth / this.backgroundWidth, winHeight / this.backgroundHeight);

                var backgroundWidth = this.backgroundWidth * scale;
                var backgroundHeight = this.backgroundHeight * scale;
            }
            else if (backgroundSize == 'contain') {
                var scale = Math.min(winWidth / this.backgroundWidth, winHeight / this.backgroundHeight);

                var backgroundWidth = this.backgroundWidth * scale;
                var backgroundHeight = this.backgroundHeight * scale;
            }
            else {
                backgroundSize = backgroundSize.split(' ');
                var backgroundWidth = backgroundSize[0] || '';
                var backgroundHeight = backgroundSize[1] || backgroundWidth;

                if (isPercentage(backgroundWidth)) backgroundWidth = winWidth * parseFloat(backgroundWidth) / 100;
                else if (backgroundWidth != 'auto') backgroundWidth = parseFloat(backgroundWidth);

                if (isPercentage(backgroundHeight)) backgroundHeight = winHeight * parseFloat(backgroundHeight) / 100;
                else if (backgroundHeight != 'auto') backgroundHeight = parseFloat(backgroundHeight);

                if (backgroundWidth == 'auto' && backgroundHeight == 'auto') {
                    backgroundWidth = this.backgroundWidth;
                    backgroundHeight = this.backgroundHeight;
                }
                else {
                    if (backgroundWidth == 'auto') backgroundWidth = this.backgroundWidth * (backgroundHeight / this.backgroundHeight);
                    if (backgroundHeight == 'auto') backgroundHeight = this.backgroundHeight * (backgroundWidth / this.backgroundWidth);
                }
            }

            // Compute backgroundX and backgroundY in page coordinates
            var backgroundX = backgroundPosition[0] || '';
            var backgroundY = backgroundPosition[1] || backgroundX;

            if (backgroundX == 'left') backgroundX = winOffset.left;
            else if (backgroundX == 'center') backgroundX = winOffset.left + winWidth / 2 - backgroundWidth / 2;
            else if (backgroundX == 'right') backgroundX = winOffset.left + winWidth - backgroundWidth;
            else if (isPercentage(backgroundX)) {
                backgroundX = winOffset.left + (winWidth - backgroundWidth) * parseFloat(backgroundX) / 100;
            }
            else {
                backgroundX = parseFloat(backgroundX);
            }

            if (backgroundY == 'top') backgroundY = winOffset.top;
            else if (backgroundY == 'center') backgroundY = winOffset.top + winHeight / 2 - backgroundHeight / 2;
            else if (backgroundY == 'bottom') backgroundY = winOffset.top + winHeight - backgroundHeight;
            else if (isPercentage(backgroundY)) {
                backgroundY = winOffset.top + (winHeight - backgroundHeight) * parseFloat(backgroundY) / 100;
            }
            else {
                backgroundY = parseFloat(backgroundY);
            }

            var elementOffset = this.$el.offset();

            this.renderProgram.uniforms.topLeft = new Float32Array([
                (elementOffset.left - backgroundX) / backgroundWidth,
                (elementOffset.top - backgroundY) / backgroundHeight
            ]);
            this.renderProgram.uniforms.bottomRight = new Float32Array([
                this.renderProgram.uniforms.topLeft[0] + this.$el.innerWidth() / backgroundWidth,
                this.renderProgram.uniforms.topLeft[1] + this.$el.innerHeight() / backgroundHeight
            ]);

            var maxSide = Math.max(this.canvas.width, this.canvas.height);

            this.renderProgram.uniforms.containerRatio = new Float32Array([
                this.canvas.width / maxSide,
                this.canvas.height / maxSide
            ]);
        },

        initShaders: function() {
            var vertexShader = [
                'attribute vec2 vertex;',
                'varying vec2 coord;',
                'void main() {',
                    'coord = vertex * 0.5 + 0.5;',
                    'gl_Position = vec4(vertex, 0.0, 1.0);',
                '}'
            ].join('\n');

            this.dropProgram = createProgram(vertexShader, [
                'precision highp float;',

                'const float PI = 3.141592653589793;',
                'uniform sampler2D texture;',
                'uniform vec2 center;',
                'uniform float radius;',
                'uniform float strength;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'float drop = max(0.0, 1.0 - length(center * 0.5 + 0.5 - coord) / radius);',
                    'drop = 0.5 - cos(drop * PI) * 0.5;',

                    'info.r += drop * strength;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));

            this.updateProgram = [0,0];
            this.updateProgram[0] = createProgram(vertexShader, [
                'precision highp float;',

                'uniform sampler2D texture;',
                'uniform vec2 delta;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'vec2 dx = vec2(delta.x, 0.0);',
                    'vec2 dy = vec2(0.0, delta.y);',

                    'float average = (',
                        'texture2D(texture, coord - dx).r +',
                        'texture2D(texture, coord - dy).r +',
                        'texture2D(texture, coord + dx).r +',
                        'texture2D(texture, coord + dy).r',
                    ') * 0.25;',

                    'info.g += (average - info.r) * 2.0;',
                    'info.g *= 0.995;',
                    'info.r += info.g;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));
            gl.uniform2fv(this.updateProgram[0].locations.delta, this.textureDelta);

            this.updateProgram[1] = createProgram(vertexShader, [
                'precision highp float;',

                'uniform sampler2D texture;',
                'uniform vec2 delta;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'vec3 dx = vec3(delta.x, texture2D(texture, vec2(coord.x + delta.x, coord.y)).r - info.r, 0.0);',
                    'vec3 dy = vec3(0.0, texture2D(texture, vec2(coord.x, coord.y + delta.y)).r - info.r, delta.y);',
                    'info.ba = normalize(cross(dy, dx)).xz;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));
            gl.uniform2fv(this.updateProgram[1].locations.delta, this.textureDelta);

            this.renderProgram = createProgram([
                'precision highp float;',

                'attribute vec2 vertex;',
                'uniform vec2 topLeft;',
                'uniform vec2 bottomRight;',
                'uniform vec2 containerRatio;',
                'varying vec2 ripplesCoord;',
                'varying vec2 backgroundCoord;',
                'void main() {',
                    'backgroundCoord = mix(topLeft, bottomRight, vertex * 0.5 + 0.5);',
                    'backgroundCoord.y = 1.0 - backgroundCoord.y;',
                    'ripplesCoord = vec2(vertex.x, -vertex.y) * containerRatio * 0.5 + 0.5;',
                    'gl_Position = vec4(vertex.x, -vertex.y, 0.0, 1.0);',
                '}'
            ].join('\n'), [
                'precision highp float;',

                'uniform sampler2D samplerBackground;',
                'uniform sampler2D samplerRipples;',
                'uniform float perturbance;',
                'varying vec2 ripplesCoord;',
                'varying vec2 backgroundCoord;',

                'void main() {',
                    'vec2 offset = -texture2D(samplerRipples, ripplesCoord).ba;',
                    'float specular = pow(max(0.0, dot(offset, normalize(vec2(-0.6, 1.0)))), 4.0);',
                    'gl_FragColor = texture2D(samplerBackground, backgroundCoord + offset * perturbance) + specular;',
                '}'
            ].join('\n'));
            gl.uniform1f(this.renderProgram.locations.perturbance, this.perturbance);
        },

        dropAtMouse: function(e, radius, strength) {
            this.drop(
                e.pageX - this.$el.offset().left,
                e.pageY - this.$el.offset().top,
                radius,
                strength
            );
        },

        drop: function(x, y, radius, strength) {
            var that = this;

            gl = this.context;

            var elWidth = this.$el.outerWidth();
            var elHeight = this.$el.outerHeight();
            var longestSide = Math.max(elWidth, elHeight);

            radius = radius / longestSide;

            var dropPosition = new Float32Array([
                (2 * x - elWidth) / longestSide,
                (elHeight - 2 * y) / longestSide
            ]);

            gl.viewport(0, 0, this.resolution, this.resolution);

            // Render onto texture/framebuffer 0
            gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffers[0]);

            // Using texture 1
            bindTexture(this.textures[1]);

            gl.useProgram(this.dropProgram.id);
            gl.uniform2fv(this.dropProgram.locations.center, dropPosition);
            gl.uniform1f(this.dropProgram.locations.radius, radius);
            gl.uniform1f(this.dropProgram.locations.strength, strength);

            this.drawQuad();

            // Switch textures
            var t = this.framebuffers[0]; this.framebuffers[0] = this.framebuffers[1]; this.framebuffers[1] = t;
            t = this.textures[0]; this.textures[0] = this.textures[1]; this.textures[1] = t;

            gl.bindFramebuffer(gl.FRAMEBUFFER, null);
        },

        // Actions
        destroy: function() {
            this.canvas.remove();
            this.$el.off('.ripples');
            this.$el.css('backgroundImage', '');
            this.$el.removeClass('jquery-ripples').removeData('ripples');
        },

        show: function() {
            this.$canvas.show();
            this.$el.css('backgroundImage', 'none');
            this.visible = true;
        },

        hide: function() {
            this.$canvas.hide();
            this.$el.css('backgroundImage', '');
            this.visible = false;
        },

        pause: function() {
            this.running = false;
        },

        play: function() {
            this.running = true;
        },

        set: function(property, value)
        {
            switch (property)
            {
                case 'interactive':
                    this.interactive = value;
                    break;
            }
        }
    };

这就是Ripple的原型，我们一个一个函数来过，第一个函数step

step: function() {
            gl = this.context;

            if (!this.visible || !this.backgroundTexture) return;

            this.computeTextureBoundaries();

            if (this.running) {
                this.update();
            }

            this.render();
        },

这是下一帧的渲染函数，(1)创建gl对象，(2)判断视图可见，背景纹理可见，不可见即返回，(3)计算纹理边界，(4)如果this.running，就更新视图，(5)渲染，先这样解释，读者接着看第二个函数。

drawQuad: function() {
            gl.bindBuffer(gl.ARRAY_BUFFER, this.quad);
            gl.vertexAttribPointer(0, 2, gl.FLOAT, false, 0, 0);
            gl.drawArrays(gl.TRIANGLE_FAN, 0, 4);
        },

这是绘制三角扇图元。(1)传入顶点this.quad，(2)绑定vertex-shader顶点着色器，底0个参数，数组节点跨度2，浮点类型，(3)使用drawArrays绘制四边形，从第0个点开始绘制，4个点一个图元四边形。我们通过drawQuad就能画四边形，没什么难的，我们继续看下一个函数。

render: function() {
            gl.viewport(0, 0, this.canvas.width, this.canvas.height);
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

            gl.useProgram(this.renderProgram.id);

            bindTexture(this.backgroundTexture, 0);
            bindTexture(this.textures[0], 1);

            gl.uniform2fv(this.renderProgram.locations.topLeft, this.renderProgram.uniforms.topLeft);
            gl.uniform2fv(this.renderProgram.locations.bottomRight, this.renderProgram.uniforms.bottomRight);
            gl.uniform2fv(this.renderProgram.locations.containerRatio, this.renderProgram.uniforms.containerRatio);
            gl.uniform1i(this.renderProgram.locations.samplerBackground, 0);
            gl.uniform1i(this.renderProgram.locations.samplerRipples, 1);

            this.drawQuad();
        },

这是渲染，我们遵循的就是向renderProgram着色器中传uniform参数。我们一起来看看下一个向着色器传参的函数。

update: function() {
            gl.viewport(0, 0, this.resolution, this.resolution);

            for (var i = 0; i < 2; i++) {
                gl.bindFramebuffer(gl.FRAMEBUFFER, this.framebuffers[i]);
                bindTexture(this.textures[1-i]);
                gl.useProgram(this.updateProgram[i].id);

                this.drawQuad();
            }

            gl.bindFramebuffer(gl.FRAMEBUFFER, null);
        },

这就是刷新，遵循向updateProgram着色器中传uniform参数。看到这里，我们马上把着色器函数都扒出来看一下。

initShaders: function() {
            var vertexShader = [
                'attribute vec2 vertex;',
                'varying vec2 coord;',
                'void main() {',
                    'coord = vertex * 0.5 + 0.5;',
                    'gl_Position = vec4(vertex, 0.0, 1.0);',
                '}'
            ].join('\n');

            this.dropProgram = createProgram(vertexShader, [
                'precision highp float;',

                'const float PI = 3.141592653589793;',
                'uniform sampler2D texture;',
                'uniform vec2 center;',
                'uniform float radius;',
                'uniform float strength;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'float drop = max(0.0, 1.0 - length(center * 0.5 + 0.5 - coord) / radius);',
                    'drop = 0.5 - cos(drop * PI) * 0.5;',

                    'info.r += drop * strength;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));

            this.updateProgram = [0,0];
            this.updateProgram[0] = createProgram(vertexShader, [
                'precision highp float;',

                'uniform sampler2D texture;',
                'uniform vec2 delta;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'vec2 dx = vec2(delta.x, 0.0);',
                    'vec2 dy = vec2(0.0, delta.y);',

                    'float average = (',
                        'texture2D(texture, coord - dx).r +',
                        'texture2D(texture, coord - dy).r +',
                        'texture2D(texture, coord + dx).r +',
                        'texture2D(texture, coord + dy).r',
                    ') * 0.25;',

                    'info.g += (average - info.r) * 2.0;',
                    'info.g *= 0.995;',
                    'info.r += info.g;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));
            gl.uniform2fv(this.updateProgram[0].locations.delta, this.textureDelta);

            this.updateProgram[1] = createProgram(vertexShader, [
                'precision highp float;',

                'uniform sampler2D texture;',
                'uniform vec2 delta;',

                'varying vec2 coord;',

                'void main() {',
                    'vec4 info = texture2D(texture, coord);',

                    'vec3 dx = vec3(delta.x, texture2D(texture, vec2(coord.x + delta.x, coord.y)).r - info.r, 0.0);',
                    'vec3 dy = vec3(0.0, texture2D(texture, vec2(coord.x, coord.y + delta.y)).r - info.r, delta.y);',
                    'info.ba = normalize(cross(dy, dx)).xz;',

                    'gl_FragColor = info;',
                '}'
            ].join('\n'));
            gl.uniform2fv(this.updateProgram[1].locations.delta, this.textureDelta);

            this.renderProgram = createProgram([
                'precision highp float;',

                'attribute vec2 vertex;',
                'uniform vec2 topLeft;',
                'uniform vec2 bottomRight;',
                'uniform vec2 containerRatio;',
                'varying vec2 ripplesCoord;',
                'varying vec2 backgroundCoord;',
                'void main() {',
                    'backgroundCoord = mix(topLeft, bottomRight, vertex * 0.5 + 0.5);',
                    'backgroundCoord.y = 1.0 - backgroundCoord.y;',
                    'ripplesCoord = vec2(vertex.x, -vertex.y) * containerRatio * 0.5 + 0.5;',
                    'gl_Position = vec4(vertex.x, -vertex.y, 0.0, 1.0);',
                '}'
            ].join('\n'), [
                'precision highp float;',

                'uniform sampler2D samplerBackground;',
                'uniform sampler2D samplerRipples;',
                'uniform float perturbance;',
                'varying vec2 ripplesCoord;',
                'varying vec2 backgroundCoord;',

                'void main() {',
                    'vec2 offset = -texture2D(samplerRipples, ripplesCoord).ba;',
                    'float specular = pow(max(0.0, dot(offset, normalize(vec2(-0.6, 1.0)))), 4.0);',
                    'gl_FragColor = texture2D(samplerBackground, backgroundCoord + offset * perturbance) + specular;',
                '}'
            ].join('\n'));
            gl.uniform1f(this.renderProgram.locations.perturbance, this.perturbance);
        },

以上是着色器代码，我们看到shader中是通过修改texture纹理的uv坐标位置每次update纹理的最新位置，这就是水波扩散的原理。每次获取鼠标移动的最新位置，以此为圆心，固定半径确定uv的最新坐标，然后重新按变形的坐标贴图，就出现了水波扩散的特效。
以上就是水波特效的插件代码，有点复杂，纯属texture材质特效，希望读者能不吝斧正。今天先到这里，鲫鱼谢谢大家阅读。祝读者们周末愉快。

本文系原作，如需引用，请注明出处：https://www.cnblogs.com/ccentry/p/10087065.html