扩展

用你自定义的方法扩展 gm 是很容易的. 所有必要的是将你的方法添加到 gm.prototype. 例如, 让我们写一个棕褐色的扩展名，它会给任何图像一个很好的“sepia”.

var gm = require("gm")
gm.prototype.sepia = function(){
  this.modulate(115, 0, 100).colorize(7, 21, 50)
  return this
}

嘿，看起来很简单吧？ 你可以这样使用它：

gm("path/to/img.png")
  .sepia()
  .write("iLoveSepiaAndSoShouldYou.png", function(err){ ... })

So let's take a looky at what's going on here. Within the sepia method, this refers to the current instance of gm so you have access to all of the other gm methods and extensions. We're just utilizing two built in gm methods here to get the effect we want. Notice also that we return this, which let's us retain the ability to continue chaining methods. We could return a little more elegantly too since, by convention, every method returns this:

var gm = require("gm")
gm.prototype.sepia = function(){
  return this.modulate(115, 0, 100).colorize(7, 21, 50)
}