Canvas动画转视频-前段框架whammy

whammy是在前端将canvas动画转视频，它的github地址为：https://github.com/antimatter15/whammy
由于英文比较晦涩难懂，接下来就实践一下体会whammy的用法。

写一个时钟动画

我直接在官网的demo基础上改了一些。

<canvas id="canvas" width="150" height="150"></canvas>
<script>
    
    function clock(time){
        var now = new Date();
        now.setTime(time);
        var ctx = document.getElementById('canvas').getContext('2d');
        ctx.save();
        ctx.fillStyle = 'white'
        ctx.fillRect(0,0,150,150); // videos cant handle transprency
        ctx.translate(75,75);
        ctx.scale(0.4,0.4);
        ctx.rotate(-Math.PI/2);
        ctx.strokeStyle = "black";
        ctx.fillStyle = "white";
        ctx.lineWidth = 8;
        ctx.lineCap = "round";
        
        // Hour marks
        ctx.save();
        for (var i=0;i<12;i++){
            ctx.beginPath();
            ctx.rotate(Math.PI/6);
            ctx.moveTo(100,0);
            ctx.lineTo(120,0);
            ctx.stroke();
        }
        ctx.restore();
        
        // Minute marks
        ctx.save();
        ctx.lineWidth = 5;
        for (i=0;i<60;i++){
            if (i%5!=0) {
                ctx.beginPath();
                ctx.moveTo(117,0);
                ctx.lineTo(120,0);
                ctx.stroke();
            }
            ctx.rotate(Math.PI/30);
        }
        ctx.restore();
        
        var sec = now.getSeconds();
        var min = now.getMinutes();
        var hr  = now.getHours();
        hr = hr>=12 ? hr-12 : hr;
        
        ctx.fillStyle = "black";
        
        // write Hours
        ctx.save();
        ctx.rotate( hr*(Math.PI/6) + (Math.PI/360)*min + (Math.PI/21600)*sec )
        ctx.lineWidth = 14;
        ctx.beginPath();
        ctx.moveTo(-20,0);
        ctx.lineTo(80,0);
        ctx.stroke();
        ctx.restore();
        
        // write Minutes
        ctx.save();
        ctx.rotate( (Math.PI/30)*min + (Math.PI/1800)*sec )
        ctx.lineWidth = 10;
        ctx.beginPath();
        ctx.moveTo(-28,0);
        ctx.lineTo(112,0);
        ctx.stroke();
        ctx.restore();
        
        // Write seconds
        ctx.save();
        ctx.rotate(sec * Math.PI/30);
        ctx.strokeStyle = "#D40000";
        ctx.fillStyle = "#D40000";
        ctx.lineWidth = 6;
        ctx.beginPath();
        ctx.moveTo(-30,0);
        ctx.lineTo(83,0);
        ctx.stroke();
        ctx.beginPath();
        ctx.arc(0,0,10,0,Math.PI*2,true);
        ctx.fill();
        ctx.beginPath();
        ctx.arc(95,0,10,0,Math.PI*2,true);
        ctx.stroke();
        ctx.fillStyle = "#555";
        ctx.arc(0,0,3,0,Math.PI*2,true);
        ctx.fill();
        ctx.restore();
        
        ctx.beginPath();
        ctx.lineWidth = 14;
        ctx.strokeStyle = '#325FA2';
        ctx.arc(0,0,142,0,Math.PI*2,true);
        ctx.stroke();
        
        ctx.restore();
        
        return ctx;
    }

var last_time = +new Date;


var progress = 1;

function next(){
    progress++;
    clock(last_time += 1000);
    if(progress<100){
<!--        setTimeout(function (){-->
<!--                   console.log("<<<");-->
<!--<!--                   next();-->-->
<!--                   // 更好的动画方式-->
<!--                   requestAnimationFrame(next);-->
<!--                   }, 1000);-->

requestAnimationFrame(next);
    }else{
      
    }
}

next();
    
</script>

如何转视频

1. 引入whammy.js的库，下载whammy.js，路径需要在同一级。 <script src="whammy.js"></script>
2. 引入Whammy的viedo对象 var video = new Whammy.Video(15);
3. 每一个画布对象添加进来 video.add(context);
4. 动画结束时生成视频，交给框架requestAnimationFrame(finalizeVideo);

完整代码如下

<canvas id="canvas" width="150" height="150"></canvas>
<a style="display:none" id="download" download="clock.webm">Download video</a>
<script src="whammy.js"></script>
<!--1. 引入whammy.js的库-->
<script>
    
    function clock(time){
        var now = new Date();
        now.setTime(time);
        var ctx = document.getElementById('canvas').getContext('2d');
        ctx.save();
        ctx.fillStyle = 'white'
        ctx.fillRect(0,0,150,150); // videos cant handle transprency
        ctx.translate(75,75);
        ctx.scale(0.4,0.4);
        ctx.rotate(-Math.PI/2);
        ctx.strokeStyle = "black";
        ctx.fillStyle = "white";
        ctx.lineWidth = 8;
        ctx.lineCap = "round";
        
        // Hour marks
        ctx.save();
        for (var i=0;i<12;i++){
            ctx.beginPath();
            ctx.rotate(Math.PI/6);
            ctx.moveTo(100,0);
            ctx.lineTo(120,0);
            ctx.stroke();
        }
        ctx.restore();
        
        // Minute marks
        ctx.save();
        ctx.lineWidth = 5;
        for (i=0;i<60;i++){
            if (i%5!=0) {
                ctx.beginPath();
                ctx.moveTo(117,0);
                ctx.lineTo(120,0);
                ctx.stroke();
            }
            ctx.rotate(Math.PI/30);
        }
        ctx.restore();
        
        var sec = now.getSeconds();
        var min = now.getMinutes();
        var hr  = now.getHours();
        hr = hr>=12 ? hr-12 : hr;
        
        ctx.fillStyle = "black";
        
        // write Hours
        ctx.save();
        ctx.rotate( hr*(Math.PI/6) + (Math.PI/360)*min + (Math.PI/21600)*sec )
        ctx.lineWidth = 14;
        ctx.beginPath();
        ctx.moveTo(-20,0);
        ctx.lineTo(80,0);
        ctx.stroke();
        ctx.restore();
        
        // write Minutes
        ctx.save();
        ctx.rotate( (Math.PI/30)*min + (Math.PI/1800)*sec )
        ctx.lineWidth = 10;
        ctx.beginPath();
        ctx.moveTo(-28,0);
        ctx.lineTo(112,0);
        ctx.stroke();
        ctx.restore();
        
        // Write seconds
        ctx.save();
        ctx.rotate(sec * Math.PI/30);
        ctx.strokeStyle = "#D40000";
        ctx.fillStyle = "#D40000";
        ctx.lineWidth = 6;
        ctx.beginPath();
        ctx.moveTo(-30,0);
        ctx.lineTo(83,0);
        ctx.stroke();
        ctx.beginPath();
        ctx.arc(0,0,10,0,Math.PI*2,true);
        ctx.fill();
        ctx.beginPath();
        ctx.arc(95,0,10,0,Math.PI*2,true);
        ctx.stroke();
        ctx.fillStyle = "#555";
        ctx.arc(0,0,3,0,Math.PI*2,true);
        ctx.fill();
        ctx.restore();
        
        ctx.beginPath();
        ctx.lineWidth = 14;
        ctx.strokeStyle = '#325FA2';
        ctx.arc(0,0,142,0,Math.PI*2,true);
        ctx.stroke();
        
        ctx.restore();
        
        return ctx;
    }

<!-- 2. 引入Whammy的viedo -->
var video = new Whammy.Video(15);

var last_time = +new Date;

var progress = 1;

function next(){
    progress++;
    var context = clock(last_time += 1000);
<!-- 3. 每一个画布对象添加进来 -->
    video.add(context);
    if(progress<100){
<!--        setTimeout(function (){-->
<!--                   console.log("<<<");-->
<!--<!--                   next();-->-->
<!--                   // 更好的动画方式-->
<!--                   requestAnimationFrame(next);-->
<!--                   }, 1000);-->

requestAnimationFrame(next);
    }else{
<!--  4. 结束动画时，生成视频 -->
      requestAnimationFrame(finalizeVideo);
    }
}

function finalizeVideo(){
    var start_time = +new Date;
    video.compile(false, function(output){
                  
                  var end_time = +new Date;
                  var url = webkitURL.createObjectURL(output);
                  console.log("url:"+url);
                  document.getElementById('download').style.display = '';
                  document.getElementById('download').href = url;
                  });
}

next();
    
</script>