code: function initCanvas() {
      var containerData = this.containerData,
          imageData = this.imageData;
      var viewMode = this.options.viewMode;
      var rotated = Math.abs(imageData.rotate) % 180 === 90;
      var naturalWidth = rotated ? imageData.naturalHeight : imageData.naturalWidth;
      var naturalHeight = rotated ? imageData.naturalWidth : imageData.naturalHeight;
      var aspectRatio = naturalWidth / naturalHeight;
      var canvasWidth = containerData.width;
      var canvasHeight = containerData.height;
  
      if (containerData.height * aspectRatio > containerData.width) {
        if (viewMode === 3) {
          canvasWidth = containerData.height * aspectRatio;
        } else {
          canvasHeight = containerData.width / aspectRatio;
        }
      } else if (viewMode === 3) {
        canvasHeight = containerData.width / aspectRatio;
      } else {
        canvasWidth = containerData.height * aspectRatio;
      }
  
      var canvasData = {
        aspectRatio: aspectRatio,
        naturalWidth: naturalWidth,
        naturalHeight: naturalHeight,
        width: canvasWidth,
        height: canvasHeight
      };
      canvasData.left = (containerData.width - canvasWidth) / 2;
      canvasData.top = (containerData.height - canvasHeight) / 2;
      canvasData.oldLeft = canvasData.left;
      canvasData.oldTop = canvasData.top;
      this.canvasData = canvasData;
      this.limited = viewMode === 1 || viewMode === 2;
      this.limitCanvas(true, true);
      this.initialImageData = assign({}, imageData);
      this.initialCanvasData = assign({}, canvasData);
    }
docs: Canvas (image wrapper)