Where is a way to apply a filter in the overlayImage?

问题

I would like to apply a filter in the overlayImage. the only way to do it, is appling the filter in the whole canvas after render?

回答1:

There's no built-in support for this, but it's fairly easy to "hack".

var overlayImageUrl = '...';

// load overlay image first
fabric.Image.fromURL(overlayImageUrl, function(oImg) {

  // add and apply filter to overlay image 
  oImg.filters.push(new fabric.Image.filters.Grayscale());
  oImg.applyFilters();

  // set <img> element of fabric.Image instance 
  // and assign it directly to canvas' "overlayImage"
  canvas.overlayImage = oImg.getElement();

  // render canvas for overlayImage to appear
  canvas.renderAll();
});

来源：https://stackoverflow.com/questions/13538460/where-is-a-way-to-apply-a-filter-in-the-overlayimage