Qt Scripting Potentialities (ProcessingJS+QT)

[gabon]

Hi guys, I am very interested in the potentialities of QT Scripting. I used rapid prototyping platforms like Processing in the past. Its recent online version ProcessingJS seems to be pretty popular and proved Processing to be a good language for visualizations. I am very interested to see if QT could be used to build more performant visualisations than the Java Processing itself. I presume it shouldn't be hard to build a javascript middle layer to communicate to OpenGL, I am just a bit concerned about the javascript execution speed (since big part of the logic, the user code, could still be there).

What do you reckon? Does it worth investigating? Is there anyone who wants to be involved?

Thanks for any info/opinion, cheers, chr

[gabon]

I made a test with random() and when Javascript and Processing Java take around 5ms to generate 100,000 numbers, QT engine takes > 20 ms. I am not particularly surprised, but this seems to be a show stopper for my purposes

Clearly QT Script hasn't been created to compute demanding operations, and this is totally understandable.


Thanks, chr

[tbscope]

Well, did you try creating a script function that calls a C++ function to generate those numbers?

You can create wrapper functions for your scripts. Keep performance demanding functions in C++ and provide wrapper or access functions in your scripts.

[gabon]

// .cpp
QScriptValue random(QScriptContext *context, QScriptEngine *engine)
{
    float r = (float) rand()/RAND_MAX;
    int len = context->argumentCount();
    if(len == 0){
        return r;
    }
    QScriptValue a = context->argument(0);
    if(len == 1){
        return r * a.toNumber();
    }
    Q_ASSERT(len < 3);
    QScriptValue b = context->argument(1);
    return a.toNumber() + (b.toNumber() - a.toNumber()) * r;
}

// .cpp
QScriptValue random(QScriptContext *context, QScriptEngine *engine)
{
    float r = (float) rand()/RAND_MAX;
    int len = context->argumentCount();
    if(len == 0){
        return r;
    }
    QScriptValue a = context->argument(0);
    if(len == 1){
        return r * a.toNumber();
    }
    Q_ASSERT(len < 3);
    QScriptValue b = context->argument(1);
    return a.toNumber() + (b.toNumber() - a.toNumber()) * r;
}

To copy to clipboard, switch view to plain text mode 

linked

engine.globalObject().setProperty("random", engine.newFunction(random));

engine.globalObject().setProperty("random", engine.newFunction(random));

To copy to clipboard, switch view to plain text mode 

// .js
var m = new Date().getTime();
var num;
for(var i=0; i<100000; i++){
	num = random(10,200);
}
println("qt processed in " + (new Date().getTime() - m));

// .js
var m = new Date().getTime();
var num;
for(var i=0; i<100000; i++){
	num = random(10,200);
}
println("qt processed in " + (new Date().getTime() - m));

To copy to clipboard, switch view to plain text mode 

Cheers, chr

[gabon]

You can create wrapper functions for your scripts. Keep performance demanding functions in C++ and provide wrapper or access functions in your scripts.

Sure, but the purpose of the experiment was to let the user write the whole application in js and just provide some global functions for the OpenGL rendering.

Cheers, chr