JS-CTYPES Status

// define the struct
var POINT = [{"x": INT32}, {"y": INT32}];

// use the struct when declaring the function call
var pointsEqual = library.declare("PointsEqual", STDCALL, BOOLEAN, POINT, POINT);

// initialize objects that looks like POINT
var pt1 = {"x": 10, "y": 20};
var pt2 = {"x": 20, "y": 20};
var result = pointsEqual(pt1, pt2);

// "result" should be false :)

4 Replies to “JS-CTYPES Status”

1. From the example I’m confused, should the first line be:
   var POINT = {“x”: INT32, “y”: INT32};
   XOR the pt1 line be like:
   var pt1 = [{“x”: 10}, {“y”: 20}];
   ?

2. sky – well, I was originally thinking it would work that way, but just like in Python, JavaScript object properties are stored in a hash and when iterating over the properties, order is not guaranteed (in SpiderMonkey). So, we use an array, just like Python ctypes, to define the struct.

   However, when actually using an object (pt1 for example) it is more “normal” for a JavaScript developer to use an object, not an array. Since the struct is defined in an indexed manner (using array), we can allow the use of objects for passing data.

   We could merge the concepts of defining the struct and using the struct as well.
   
function POINT(x, y) {
this.x = x; this.y = y;
}

   POINT.prototype = {
   _fields_ : [{"x": INT32}, {"y": INT32}]
   }

   // _fields_ will be used internally to get the primitives
   var pointsEqual = library.declare("PointsEqual", STDCALL, BOOLEAN, POINT, POINT);

   var pt1 = new POINT(10, 20);
var pt2 = new POINT(20, 20);
var result = pointsEqual(pt1, pt2);

   Then the POINT object could be used for both defining and using POINTs

3. Pingback: Christopher Blizzard » Blog Archive » mozilla embedding overview & meetup notes
4. Pingback: Bridging the gap between native functions and Active Scripting with a COM-based FFI wrapper « KK’s Blog

Comments are closed.