今天是2014年的最后一天，这个时刻总会让人想起时钟，再过几个小时地球人都要再老了一岁，于是搞个HTML5版的时钟就是我们今天要完成的任务，实现HTML5的时钟绘制一般会采用三种方式，第一种采用CSS的实现方式，例如 http://www.css-tricks.com/examples/CSS3Clock/ ；第二种采用SVG的实现方式，例如 http://www.css-tricks.com/examples/CSS3Clock/；第三种采用Cavnas的2D绘制方式，如HT for Web中《矢量手册》中自定义绘制的clock例子，HT的例子的实现效果如下，其实现代码附在本文的最后部分。
以上三种方式都是较容易理解的实现方式，今天我们将采用的则是较为少见的WebGL纯Shading Language实现方式，这种方式极其高效，毕竟我们采用的是可利用GPU硬件加速的WebGL技术，CPU代码角度看仅有两个三角形的绘制，真正表盘的绘制逻辑完全在GPU对两个三角形进行Fragment Shading时实现。
可通过这里 http://js.do/hightopo/glsl-clock 玩玩最后的实现效果以及实现代码，采用GLSL的实现最重要的就是决定当前坐标位置的gl_FragColor的颜色，我们将始终分为表盘、外圈、刻度、时针、分针和秒针几个部分，代码后部分的留个连续Blend代码相当于逐层绘制的逻辑，以下几个函数技术点说明：
- Rect函数中的clamp(uv, -size/2.0, size/2.0))是我们决定点是否在矩形区域的技巧
- 函数Rotate(vec2 uv,float angle)将坐标点旋转到水平或垂直位置方便我们确定Rect和Line参数进行对比
- Blend函数mix(shapeColor, backColor, smoothstep(0.0, 0.005, shape))是常用的混合mix和smoothstep达到更好处理边缘平滑效果GLSL常用技巧
为了说明mix和smoothstep的融合效果，我搞了个 http://js.do/hightopo/glsl-smooth-clrcle 的例子，你可以尝试去掉#define SMOOTH后边缘锯齿较明显的问题，也可以调节smoothstep(0.49, 0.5, d)的0.49为0.3等较小的参数体验渐进的效果，以下为几种效果的综合对比
GLSL的Fragment Shader实现代码如下：
#ifdef GL_ES precision mediump float; #endif uniform float time; uniform vec2 resolution; float pi = 3.1415926; float tau = pi * 2.0; vec2 Rotate(vec2 uv,float angle); float Circle(vec2 uv,float r); float Rect(vec2 uv,vec2 size,float r); float Line(vec2 uv,vec2 start,vec2 end,float r); float Merge(float a,float b); float Outline(float a,float r); vec3 Blend(vec3 backColor, vec3 shapeColor, float shape); float SecStep(float x); void main( void ) { vec2 res = resolution / resolution.y; vec2 uv = ( gl_FragCoord.xy / resolution.y ); uv -= res / 2.0; float secAng = (SecStep(time) / 60.0) * tau; float minAng = (time / 3600.0) * tau; float hourAng = (time / 43200.0) * tau; float clockFace = Circle(uv, 0.45); float clockTrim = Outline(clockFace, 0.01); vec2 secDomain = Rotate(uv, secAng); float clockSec = Line(secDomain, vec2(0.0, -0.15), vec2(0.0, 0.35), 0.001); clockSec = Merge(clockSec, Circle(uv, 0.01)); clockSec = Merge(clockSec, Rect(secDomain - vec2(0.0, -0.08), vec2(0.012, 0.07), 0.0)); float clockMin = Line(Rotate(uv, minAng), vec2(0.0,-0.08), vec2(0.0, 0.35), 0.005); float clockHour = Line(Rotate(uv, hourAng), vec2(0.0,-0.05), vec2(0.0,0.3), 0.007); clockHour = Merge(clockHour, Circle(uv, 0.02)); float tickMarks = 1.0; vec2 tickDomain = uv; for(int i = 0;i < 60;i++) { tickDomain = Rotate(tickDomain, tau / 60.0); vec2 size = (mod(float(i + 1), 5.0) == 0.0) ? vec2(0.08, 0.01) : vec2(0.04, 0.002); tickMarks = Merge(tickMarks, Rect(tickDomain - vec2(0.38, 0.0), size, 0.0)); } vec3 faceColor = mix(vec3(1.0, 1.0, 0.0), vec3(1.0, 1.0, 1.0), uv.x+0.5); vec3 trimColor = mix(vec3(0.0, 1.0, 0.0), vec3(0.0, 0.0, 1.0), uv.y + 0.5); vec3 secColor = vec3(1.0, 0.0, 0.0); vec3 handColor = vec3(0.0, 0.0, 0.0); vec3 color = mix(vec3(1.0, 0.0, 0.0), vec3(1.0, 1.0, 1.0), uv.y+0.5); color = Blend(color, faceColor, clockFace); color = Blend(color, trimColor, clockTrim); color = Blend(color, trimColor, tickMarks); color = Blend(color, handColor, clockHour); color = Blend(color, handColor, clockMin); color = Blend(color, secColor, clockSec); gl_FragColor = vec4(color, 1.0); } float SecStep(float x) { float interp = smoothstep(0.80, 1.0, mod(x, 1.0)); return floor(x) + interp + (sin(interp * pi)) ; } float Line(vec2 uv,vec2 start,vec2 end,float r) { return Rect(uv-(end+start)/2.0, vec2(r, end.y - start.y), r); } float Rect(vec2 uv,vec2 size,float r) { return length(uv - clamp(uv, -size/2.0, size/2.0)) - r; } vec2 Rotate(vec2 uv,float angle) { return mat2(cos(angle), sin(angle),-sin(angle), cos(angle)) * uv; } float Circle(vec2 uv,float r) { return length(uv) - r; } float Merge(float a,float b) { return min(a, b); } float Outline(float a,float r) { return abs(a) - r; } vec3 Blend(vec3 backColor, vec3 shapeColor, float shape) { return mix(shapeColor, backColor, smoothstep(0.0, 0.005, shape)); }
HT for Web中《矢量手册》中自定义绘制的clock例子实现代码如下：
function init() { dataModel = new ht.DataModel(); graphView = new ht.graph.GraphView(dataModel); view = graphView.getView(); view.className = 'main'; document.body.appendChild(view); window.addEventListener('resize', function(e) { graphView.invalidate(); }, false); ht.Default.setCompType('clock-face', function(g, rect, comp, data, view) { var cx = rect.x + rect.width / 2; var cy = rect.y + rect.height / 2; var theta = 0; var r = Math.min(rect.width, rect.height)/2 * 0.92; g.strokeStyle = "#137"; for (var i = 0; i < 60; i++) { g.beginPath(); g.arc( cx + Math.cos(theta) * r, cy + Math.sin(theta) * r, i % 5 === 0 ? 4 : 1, 0, Math.PI * 2, true); g.closePath(); g.lineWidth = i % 5 === 0 ? 2 : 1; g.stroke(); theta = theta + (6 * Math.PI / 180); } }); ht.Default.setImage('clock', { width: 500, height: 500, comps: [ { type: 'circle', relative: true, rect: [0, 0, 1, 1], background: 'yellow', gradient: 'linear.northeast' }, { type: 'clock-face', relative: true, rect: [0, 0, 1, 1] }, { type: function(g, rect, comp, data, view) { // get current time var date = data.a('date'); if(!date){ return; } var hours = date.getHours(); var minutes = date.getMinutes(); var seconds = date.getSeconds(); hours = hours > 12 ? hours - 12 : hours; var hour = hours + minutes / 60; var minute = minutes + seconds / 60; var clockRadius = 250; // save current context g.save(); g.translate(clockRadius, clockRadius); g.beginPath(); // draw numbers g.font = '36px Arial'; g.fillStyle = '#000'; g.textAlign = 'center'; g.textBaseline = 'middle'; for (var n = 1; n <= 12; n++) { var theta = (n - 3) * (Math.PI * 2) / 12; var x = clockRadius * 0.75 * Math.cos(theta); var y = clockRadius * 0.75 * Math.sin(theta); g.fillText(n, x, y); } // draw hour g.save(); var theta = (hour - 3) * 2 * Math.PI / 12; g.rotate(theta); g.beginPath(); g.moveTo(-15, -5); g.lineTo(-15, 5); g.lineTo(clockRadius * 0.5, 1); g.lineTo(clockRadius * 0.5, -1); g.fill(); g.restore(); // draw minute g.save(); var theta = (minute - 15) * 2 * Math.PI / 60; g.rotate(theta); g.beginPath(); g.moveTo(-15, -4); g.lineTo(-15, 4); g.lineTo(clockRadius * 0.8, 1); g.lineTo(clockRadius * 0.8, -1); g.fill(); g.restore(); // draw second g.save(); var theta = (seconds - 15) * 2 * Math.PI / 60; g.rotate(theta); g.beginPath(); g.moveTo(-15, -3); g.lineTo(-15, 3); g.lineTo(clockRadius * 0.9, 1); g.lineTo(clockRadius * 0.9, -1); g.fillStyle = '#0f0'; g.fill(); g.restore(); g.restore(); } } ] }); var node = new ht.Node(); node.setPosition(150, 150); node.setSize(250, 250); node.setImage('clock'); node.a('date', new Date()); node.s('image.stretch', 'centerUniform'); dataModel.add(node); graphView.setEditable(true); setInterval(function(){ node.a('date', new Date()); }, 1000); }
