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HTML

              
                <canvas id="cvs" width="680px" height="500px" style="background-color:#000;"></canvas>

              
            
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CSS

              
                
              
            
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JS

              
                var canvas = document.getElementById("cvs");
var ctx = canvas.getContext("2d");
var imgCnt = 25;          // 描画する画像の数
var aryImg = [];          // 画像の情報を格納
var cvsw = 680;           // canvasタグに指定したwidth
var cvsh = 500;           // canvasタグに指定したheight
var imgBaseSizeW = 15;    // 画像の基本サイズ横幅
var imgBaseSizeH = 18.5;  // 画像の基本サイズ立幅
var aspectMax = 1.5;      // アスペクト比計算時の最大値
var aspectMin = 0.5;      // アスペクト比計算時の最小値
var speedMax = 2;         // 落下速度の最大値
var speedMin = 0.5;       // 落下速度の最小値
var angleAdd = 4;         // 画像角度への加算値

// 画像の読み込み
var img = new Image();
img.src = "http://www.otwo.jp/blog/demo/canvas/images/sakura.png";
img.onload = flow_start;

// 画像のパラメーターを設定
function setImagas(){
  var aspect = 0;
  for(var i = 0;i < imgCnt;i++){
    // 画像サイズに掛けるアスペクト比を0.5~1.5倍でランダムで生成
    aspect = Math.random()*(aspectMax-aspectMin)+aspectMin;
    aryImg.push({
      "posx": Math.random()*cvsw,   // 初期表示位置x
      "posy": Math.random()*cvsh,   // 初期表示位置y
      "sizew": imgBaseSizeW*aspect, // 画像の横幅
      "sizeh": imgBaseSizeH*aspect, // 画像の縦幅
      "speedy": Math.random()*(speedMax-speedMin)+speedMin, // 画像が落ちていく速度
      "angle": Math.random()*360,   // 角度
    });
  }
}

// 描画、パラメーターの更新
var idx = 0;
var cos = 0;
var sin = 0;
var rad = Math.PI / 180;
function flow(){
  ctx.clearRect(0,0,cvsw,cvsh);
  for(idx = 0;idx < imgCnt;idx++){
    aryImg[idx].posy += aryImg[idx].speedy;
    aryImg[idx].angle += Math.random()*angleAdd;
    cos = Math.cos(aryImg[idx].angle * rad);
    sin = Math.sin(aryImg[idx].angle * rad);
    ctx.setTransform(cos, sin, sin, cos, aryImg[idx].posx, aryImg[idx].posy);
    ctx.drawImage(img, 0, 0 , aryImg[idx].sizew , aryImg[idx].sizeh);
    ctx.setTransform(1, 0, 0, 1, 0, 0);
    // 範囲外に描画された画像を上に戻す
    if(aryImg[idx].posy >= cvsh){
      aryImg[idx].posy = -aryImg[idx].sizeh;
    }
  }
}

function flow_start(){
  setImagas();
  setInterval(flow,10);
}
              
            
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999px

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