extensible packages

[Henri Tuhola]

I teamed up with author of node-openvg, and we need to make a shared API for videocontext handling. I'd like to keep it open as possible, so people could extend it with their own renderers later.

surface.getContext("webgl", options) - this should grab API that's currently given by node-video.

surface.getContext("2d", options) - this should grab API that's provided by node-openvg-canvas

How to package it such that it's simple and easy to handle? Is it possible without changing the API?

[Henri Tuhola]

To make it clear, it's that extensibility property I'm looking for, without immediate need to insert anything into the library that takes care of implementing getContext -method.

[Bradley Meck]

This sounds like a shared state lookup. Document and specify an interface for the renderers ("webgl" and "2d" in this case). Once you have done that, in getContext

Surface.prototype.getContext = function (name, options) {

  var renderer = this._renderers[name] // _ prefix is for implementation detail

  if (!renderer) {

    throw ...

  }

  renderer.getContext(this, options) // or similar api

}

And then developers could extend the surface with a different api, it could require direct access to _renderers or some helper function like surface._addRenderer(name, interface).

[Henri Tuhola]

Sounds good except to the fact that it's better to not preload all those renderers. I don't know which ones will be used by the process and which not. Somehow I still feel this presents challenges to npm. I'll write some doodles today to study it out.

[Henri Tuhola]

var renderers = require("./renderers.json");

Surface.prototype.getContext = function(name, options) {

    var renderer = renderers[name];

    if (!renderer) {

        throw "no renderer found";

    }

    var api = require(renderer);

    return vc.createContext(this, api, options);

};

I could let a build script generate the renderers.json, and mark all those libraries dependencies.

[greelgorke]

instead of relying on a config file, i would implement a register function for renderers, so the user can decide, install and register the renderer she want to use. i.E:

 

Surface.prototype.registerContext = function(name, packageIdent /*could be name or relativ path*/) {

    renderers[name] = packageIdent;

};