Native codes call Function of javascript is slower than javascript?

[Feng Wang]

I have an image (1024x1024x3) that needs to be process pixel-by-pixel. The per-pixel processing code is written using javascript. I've found that it takes 277ms to loop through this handler in c++ code, and only 10ms to loop in javascript code. I want to know how to make the c++ call javascript function as fast as possible.

//javascript per-pixel processing function
var pixelfunction=function( rgb , index )
{
  var outval = (rgb[0]-rgb[1]/(rgb[0]+rgb[1]) ;
  return outval;
}

//c++ codes loop call pixelfunction
...
v8::Function* pixelFunc = ...; // this Function pointer is pixelfunction in javascript.
v8::Local<v8::Uint8Array> vals = ...; //
v8::Local<Value> targs[2] ;
for(int it = 0 ;it<1024*1024;++it)
{
  vals = ...; // get r,g,b values from image ;
  targs[0] = vals;
  targs[1] = v8::Integer::New( global , it );
  pixelFunc->Call( context , context->Global() , 2 , targs);//For convenience, I'm giving up the return value.
}
...

-

//javascript loop call:
var vals=new Uint8Array(3);
for(var it = 0 ; it < 1024*1024 ; ++it )
{
  vals=...; //get r,g,b values from image
  pixelfunction( vals , it );//For convenience, I'm giving up the return value.
}

[Yang Guo]

Put everything into an ArrayBuffer and call C++ just once.

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[Feng Wang]

Thanks Yang. But I have to define the processing algorithm in javascript.

	Feng Wang
邮箱：jfwf...@gmail.com

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[Jakob Kummerow]

Use the JavaScript version of the loop, and call that just once from C++. 

If it's convenient from a packaging point of view, you can put it into a string literal in your C++ source, and compile/run it from there.

Calls between C++ and JavaScript (in both directions) are always going to have quite a bit of overhead; the best way to speed them up is to avoid doing too many of them.

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[Feng Wang]

Thanks, Kummerow. I use js loop.

	Feng Wang
邮箱：jfwf...@gmail.com

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