[css-paint-api] Add inputArguments to paint API

[bfgeek]

Syntax...

registerPaint('foo', class {
  static get inputArguments() { return ['<length>', '<number>']; }

  paint(ctx, geom, styleMap, args) {
    args[0] instanceof CSSLengthValue; // true
    args[1] instanceof CSSNumberValue;  // true
  }
});

[bfgeek]

background-image: paint(foo, 2px, 42);

[dmvaldman]

If this notation is adopted, is the inputArguments getter still necessary?

If that method is for caching purposes, it seems it wouldn't be necessary as you'd know when the cache is busted because this new notation explicitly defines the input arguments.

[tabatkins]

I'm confused by your question - did you mean to refer to something else?

The inputArguments getter specifies the types of the arguments, so we know how to parse and expose them to the paint() function.