[solved] adding Qt to existing program

mzimmers

OK, I'm back. (Had to chase down some bugs for a couple of days.)

So, regarding this "event loop" -- it seems to be a member function of QWidget, right? I'm curious...what throttles it? I assume it doesn't just run open loop.

Also...what happens to my main()? In my main, besides initializing some variables, I have a loop that calls a function. Does this functionality become a function that is passed to the event loop by a connect()?

Let's say I just want to imbed my current program into a Qt application. For right now, I don't even need to create a GUI; I just want to get my program logic contained within the Qt constructs. Do I create a loop function, and use a connect() call to access it?

And...what's the best source of online documentation for this? The help stuff in Creator seems to have some dead links.

Thanks.

goetz

It's always the same answer: It depends :-)

If it is a program without GUI components and if you do not use signal/slot connections within the existing code, it is very likely that you do not need an event loop.

It would be helpful if you could describe what you want to do by embedding the existing code into a Qt application environment.

Some reading about events and the event loop is in:

"QCoreApplication Class Reference":http://doc.qt.nokia.com/4.7/qcoreapplication.html#exec
"QEventLoop Class Reference":http://doc.qt.nokia.com/4.7/qeventloop.html
"The Event System":http://doc.qt.nokia.com/4.7/eventsandfilters.html

Signals/slots need a running event loop to work reliably.

PS: If you stumble over dead links, please open a bug report, so that the Trolls can fix them for the next release.

giesbert

Hi Volker,

one correction regarding signals/slots:

Afaik, they also work without an event loop, if you only use direct connections. This means in fact a syncronous execution of everything, nothing asynchronous, no user input (only via command line).

mzimmers

It would be helpful if you could describe what you want to do by embedding the existing code into a Qt application environment.

I thought it might be a good first step, to help me understand the control flow of a Qt application, and where application code is supposed to "live," without actually getting into the nuts and bolts of the GUI yet. The long term plan is definitely to have an event loop.

ZapB

[quote author="mzimmers" date="1301086103"]OK, I'm back. (Had to chase down some bugs for a couple of days.)
[/quote]

I'm back too now. Been offline whilst decorating...

[quote author="mzimmers" date="1301086103"]
So, regarding this "event loop" -- it seems to be a member function of QWidget, right? I'm curious...what throttles it? I assume it doesn't just run open loop.
[/quote]

exec() is a function of QCoreApplication (plus a few other classes QEventLoop, QDialog etc). The purpose of the event loop is to notice "events" (keypresses, mouse moves, window system damage events, network socket or file descriptor events) and translate these into events that can be handled within your Qt application. You normally do this by either overriding a virtual function such as QWidget::resizeEvent( QResizeEvent* e ) or by connecting to a convenient signal from a Qt class such as QIODevice::readyRead(). It depends upon what you are trying to do.

[quote author="mzimmers" date="1301086103"]
Also...what happens to my main()? In my main, besides initializing some variables, I have a loop that calls a function. Does this functionality become a function that is passed to the event loop by a connect()?
[/quote]

Not normally. There are a few approaches you can take. If the work can easily be split into small packages then you can simply use a timer to do a little bit of work at a time. A similar approach is to not use a timer bu tinstead call QCoreApplication::processEvents() every so often in your loop. Both of these approaches allow control to return to the event loop so that your GUI does not appear to freeze. Remember, whilst the main thread is busy doing your calculations it is not available to paint the screen or handle any other types of events.

If you work is not easily broken up, or if you want to take advantage of multiple cores or processors then you should take a look at QThread or QtConcurrent. These allow you to move your heavy work to a separate thread (or threads) of execution, leaving the main thread free to update the GUI and handle other events in the event loop. Come back with more questions if you need help with this.

[quote author="mzimmers" date="1301086103"]
Let's say I just want to imbed my current program into a Qt application. For right now, I don't even need to create a GUI; I just want to get my program logic contained within the Qt constructs. Do I create a loop function, and use a connect() call to access it?
[/quote]

Take a look at the above options and this "Qt Quarterly article":http://doc.qt.nokia.com/qq/qq27-responsive-guis.html.

[quote author="mzimmers" date="1301086103"]
And...what's the best source of online documentation for this? The help stuff in Creator seems to have some dead links.
[/quote]

The "online documentation":http://doc.qt.nokia.com/latest/.

Good luck!

mzimmers

exec() is a function of QCoreApplication (plus a few other classes QEventLoop, QDialog etc). The purpose of the event loop is to notice “events” (keypresses, mouse moves, window system damage events, network socket or file descriptor events) and translate these into events that can be handled within your Qt application. You normally do this by either overriding a virtual function such as QWidget::resizeEvent( QResizeEvent* e ) or by connecting to a convenient signal from a Qt class such as QIODevice::readyRead(). It depends upon what you are trying to do.

OK, my main program is pretty simple. It initializes a few variables, and then goes into a loop. The loop will probably be infinite in production mode, but each instance should complete in well under a second.

Let's say that I'd like to build a GUI for this that displays two values after each loop iteration. I'd probably put a minor delay in, just to prevent the GUI from updating so rapidly that it's hard to read. So...how do I go about this? Each variable needs its own widget, right? With most of the stuff that you have in widget.cpp above?

Thanks.

EDIT:

Also...I've been looking through the online docs, and don't find an entry for emit. I also don't find an entry for dataChanged() which looks right for how you're using it. I DID find an entry for emitDataChanged(). Is the code you used pre 4.7?

ZapB

[quote author="mzimmers" date="1301337361"]
OK, my main program is pretty simple. It initializes a few variables, and then goes into a loop. The loop will probably be infinite in production mode, but each instance should complete in well under a second.

Let's say that I'd like to build a GUI for this that displays two values after each loop iteration. I'd probably put a minor delay in, just to prevent the GUI from updating so rapidly that it's hard to read. So...how do I go about this? Each variable needs its own widget, right? With most of the stuff that you have in widget.cpp above?
[/quote]

As a first pass, I would try simply putting your existing code into the Generator class that we made earlier. In the calculateNextValue() function would be a good place. Refactor it so that this function only contains the body of your loop. We alreayd have this function being called in response to a timer.

You can build up in complexity from there using one of the techniques that I described earlier. From what you have described, putting your infinite loop into a worker thread could well be the best approach. Then you can just emit your calculated values in a signal after a certain amount of time has elapsed (you can use QTime::start() and QTime::elapsed() to measure this).

The way in which you display the results of your calculations is entirely up to you. If you just have a pair of doubles, then using a couple of QLabels would be a reasonable approach. If you had 1000 doubles then I would look at using something else, a QTableView for e.g.

If you would like some more help in getting any of this to work then feel free to come back with more questions and we'll do what we can to help you. It doesn't sound like it will be particularly complicated.

[quote author="mzimmers" date="1301337361"]
EDIT:

Also...I've been looking through the online docs, and don't find an entry for emit. I also don't find an entry for dataChanged() which looks right for how you're using it. I DID find an entry for emitDataChanged(). Is the code you used pre 4.7?[/quote]

The "emit" keyword is just a macro that expands to nothing. It is just semantic sugar to make you think that a signal really is broadcast. In reality, the moc implements the body of the signal function for you.

As for our signal, dataChanged(), this is just a signal that we invented for our custom Widget class so you will not find anything about it in the Qt docs.

mzimmers

OK, I'm going to start on this in a bit. My goal is to get something working today.

Newbie question: what does refactoring do?

ZapB

Refactoring just means modifying your existing code so that it works in a different context or is organised differently. In this case moving your loop code and adjusting it as described above.

mzimmers

OK, thanks. So, if I:

bring generator and widget files into my existing project

take all my stuff out of my main and put it into generator

replace my main with the one you posted

do the refactor thingie

Is that on the right track?

mzimmers

OK, I've changed my approach slightly. I decided to create a class to contain all the stuff for my main routine. I've called this class Soc, and its only data members are an object of another class (Filter), and some control variables.

Now I'm having some trouble getting the Soc constructor right. The Soc constructor needs to pass an argument to the Filter constructor. The problem is, Soc (like generator) inherits its constructor from the QObject class. As such, it isn't prepared to take any additional parameters (like the argument I want to pass).

How can I form the Soc constructor so that I can pass an argument to the Filter constructor? Or, is there a better way of doing this?

Thanks.

EDIT:

I think I resolved this problem by adding the Filter initialization to the Soc parameter initialization (did I word that correctly?):

@#include "Soc.h"
const int resetValue = 55;

using namespace std;

Soc::Soc(QObject *parent) :
QObject(parent), filter(resetValue)
{
}
@

Now, I'm getting a symbol not found error:

bq. Undefined symbols:
"Soc::getCoeffs(int*, int*)", referenced from:
Soc::runOneCycle() in Soc.o
Soc::qt_metacall(QMetaObject::Call, int, void**)in moc_Soc.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Is this somehow related to the fact that the calling routine (I've named it Soc::runOneCycle()) is defined as a public slot, and not an "ordinary" member function?

EDIT 2:

Aargh. Please ignore previous lame question. My fault for trying to work too fast. I'll come back when I have something legit.

mzimmers

OK...I've cleared the decks of my dumb mistakes (I think). I believe that I have now correctly implemented a class Soc, which contains a routine called runOneCycle() that replaces most of the functionality in my original main(). I now need to "hook it up" so it gets called. I guess the next step is to implement a version of the widget software that Zap posted above. Right now, I'd be happy if it ran 100 times, and showed the results of two variables after each running. (I have lots of plans for enhancing this, but this will do for now.)

I won't need a timer (yet), so we can eliminate that part of the code. So...do I need just one connect statement? Or, do I need two, since I'm planning on displaying the values of two variables with the Soc class?

Thanks...I think I'm slowly getting closer...

ZapB

Are you able to post your code? If yes then please do, if not then we'll have to work with examples still. Not a problem either way...

mzimmers

I can post some extracts, which would hopefully be good enough. I removed some irrelevant stuff for brevity.

Here's Soc.h:

@#ifndef SOC_H
#define SOC_H

#include <QObject>
#include <iostream>
#include <fstream>
#include <iomanip>
#include "DemodShaperFilter.h"

class Soc : public QObject
{
Q_OBJECT
private:
Filter filter; // Soc contains one filter for now.
/*

clocks and resets.
/
bool clockEnable;
bool clockState;
// bool systemReset;
bool filterReset;
/
arguments to drive the filter processing.
*/

int shaperCoeffI[NBR_CELLS];
int shaperCoeffQ[NBR_CELLS];
int combGainI;
int combGainQ;
int shaperOutI, shaperOutQ;

public:
explicit Soc(QObject *parent = 0);
int getCoeffs(int *aI, int *aQ);

signals:
void dataChanged (double value);
public slots:
void runOneCycle();
};
#endif // SOC_H
@

And here's the .cpp file:

@#include "Soc.h"
const int resetValue = 55;

//Soc::Soc(QObject *parent) :
// QObject(parent)
Soc::Soc(QObject *parent) :
QObject(parent), filter(resetValue)
{
}

void Soc::runOneCycle()
{
static int i=0;
int rc;
/*

test a single filter.
*/

// temporarily use simple variables for comb stuff.

combGainI = i;
combGainQ = i*2;
i++;

systemClock.setClock(HIGH);
filter.cycle(combGainI, // run the high cycle.
shaperCoeffI,
combGainQ,
shaperCoeffQ,
shaperOutI,
shaperOutQ,
clockEnable,
filterReset);

return;
}
@

mzimmers

So...I've added the widget files from the example above to my program, and changed m_generator to a Soc variable called (creatively enough) soc. The program runs, and produces the correct output (as displayed on the console), but I'm not getting anything in my GUI window.

I believe I need to modify this line of code in widget.cpp:

@ connect (soc, SIGNAL(dataChanged(double)), this, SLOT(setValue(double)));
@

I imagine I'd have to modify the doubles to ints, but...I need to tell it to look at my two variables. Do I:

need two connect statements for this?
replace "this" with soc.member-name?

I guess I should also modify setValue to accept an int instead of a double, too.

Thanks.

giesbert

Thje connect is correct. But I fI look at your last code, where do you emit the signal?

mzimmers

Oops.

I guess I need a emit dataChanged() call, don't I?

So, my question now is...what do I put in as a parameter for this call? I guess this is the missing link to my understanding of how these signals work. (It also looks like I missed changing a double to int in the Soc.h file.)

Thanks.

giesbert

Hi,

you have to put a double in, as specified in the header.
Which one, I can't tell you, that's depending on your application.
Typically, the value you want to notify :-)

mzimmers

So, I use a double in the call even if the variable I want to display is an int? What exactly does that double represent: I thought it was the variable I wanted to display...

EDIT: I just put the dataChanged() call into my code, and it seems to work. Now, if I want to do this for two variables, what all do I have to duplicate? Obviously, I'll need two calls to dataChanged(), but what else do I have to do?

Thanks.

giesbert

Think a bit, how the Qt widgets to it.

Look at QSpineBox:

it has a signal valueChanged(int) and sends the changed value.

Look at QDoubleSpineBox:

it has a signal valueChanged(double) and sends the changed value.

Look at QComboBox:

void activated ( int index )
void activated ( const QString & text )
both signals are emitted, with different content.

The client can connect to the signal he wants and has to interpret the values.

You can do a dataChanged() signal and leave it to the client to query all values and check which ones are changed, or do a dataChanged1() and dataChanged2() so the client knows, which value but has to query the new value. or you do

dataChanged1(int)
dataChanged2(int)
and deliver the new values to the client.

But I would rename dataChanged1(int) to some senseful names.