多个滤镜叠加

给图片添加滤镜前，我们必须先使用cache()方法将它缓存起来，然后使用filter()方法添加多个滤镜。
Konva Multiple Filters Image Demoview raw
<!DOCTYPE html>
<html>
  <head>
    <script src="https://unpkg.com/konva@4.0.18/konva.min.js"></script>
    <meta charset="utf-8" />
    <title>Konva Multiple Filters Demo</title>
    <style>
      body {
        margin: 0;
        padding: 0;
        overflow: hidden;
        background-color: #f0f0f0;
      }

      #slider {
        position: absolute;
        top: 20px;
        left: 20px;
      }
    </style>
  </head>

  <body>
    <div id="container"></div>
    <input id="slider" type="range" min="0" max="40" step="0.05" value="20" />
    <script>
      function loadImages(sources, callback) {
        var images = {};
        var loadedImages = 0;
        var numImages = 0;
        for (var src in sources) {
          numImages++;
        }
        for (var src in sources) {
          images[src] = new Image();
          images[src].onload = function() {
            if (++loadedImages >= numImages) {
              callback(images);
            }
          };
          images[src].src = sources[src];
        }
      }
      function buildStage(images) {
        var stage = new Konva.Stage({
          container: 'container',
          width: window.innerWidth,
          height: window.innerHeight
        });

        var layer = new Konva.Layer();

        var lion = new Konva.Image({
          image: images.lion,
          x: 80,
          y: 30,
          blurRadius: 20,
          draggable: true
        });

        lion.cache();
        lion.filters([Konva.Filters.Blur, Konva.Filters.Invert]);
        layer.add(lion);
        stage.add(layer);
        var slider = document.getElementById('slider');
        slider.oninput = function() {
          lion.blurRadius(slider.value);
          layer.batchDraw();
        };
      }

      var sources = {
        lion: '/assets/lion.png'
      };

      loadImages(sources, buildStage);
    </script>
  </body>
</html>