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