Analysing an icon editor application

J.Hilk

@mrjj Wait, what !? I wasn't aware of that! Very very handy!

Thankfully with 4.4.1 my Creator doesnt bug out any longer when i have more than one window open. Previously any and all popups would no longer be shown. Aggravating but made me lookup and learn more shortcuts...

mrjj

@J.Hilk
Yep, now i only wish for a key that can open/close all comment sections in a file :)

tomy

Guys, I don't need these (I knew F2). I don't want to know where such a function is written or not, it's like ctrl+F. I want the sequence of the statements which are executed from the beginning of the program until end. You can also read prior posts as well.

In Visual Studio 2017 when I code in C++, I put the cursor on the first statement of the main function and press Ctrl + F10 (Run to Cursor). And by pressing F10 (for executing a statement) and F11 (for going into the body of a function), it goes through the statements in the same way as they are executed by the compiler. So I will be aware of the process being done from start (where I pressed ctrl + F10) until end.

Since I'm rather new in Qt, for being able to understand the program correctly, I need to know how the whole program runs.
I hope I've made it clear now what I'm looking for.

J.Hilk

@tomy mmh, ist that just a fancy way of setting a breakpoint and hitting F5 ? That you can do in QtCreator as well as in VS, even same short cuts.

mrjj

Ah you ment while debugging.
Just place break point and the call trace window will show the complete call tree.
http://doc.qt.io/qtcreator/creator-debug-mode.html
section Viewing Call Stack Trace

tomy

OK, I want to go through a program line-by-line or instruction-by-instruction. For that apparently I can use the debugger. For that the first thing is I think going to Window > Views. But Views is grayed out there!

I also went to main.cpp and tried to trace the instructions by F10 and F11. This way, I only could go into the constructor by F11 on IconEditor iconEditor;. I still don't know how those several functions in iconeditor.cpp are called/used!

mrjj

@tomy

I still don't know how those several functions in iconeditor.cpp are called/used!

Place break points in them and do the actions that triggers them.
Then use F10/F11 to step around.
Or use the Find Usage functions to see all places used.

The debugger wont show you the functions call before they are actually executed.

Charlie_Hdz

@tomy for your last comment.

I think that you might want to study the Qt Debugger a little longer.

Set breakpoints.
Press F5 to go directly to the breakpoint.
If the breakpoint is not entering, then the app flow won't arrive there.
You can enter you OWN function directly by using F11.
Somewhat, rebuild and build your solution.

Kind Regards

Enrique

tomy

I put a break point on the first instruction of each function in iconeditor.cpp. Then went back to main.cpp on the line IconEditor iconEditor;, pressed F10.

The result: It goes to the break point of the constructor and after returning from that by iconEditor.setIconImage(QImage(":/images/mouse.png"));it goes to the void IconEditor::setIconImage(const QImage &newImage) function body. And then after returning from that to main.cpp, by iconEditor.show();
to QSize IconEditor::sizeHint() const function body. after that it returns to main.cpp and then neither F10 nor F11 does any action. By now I know how these two above functions are called but what about other functions!? :(

Charlie_Hdz

@tomy

show function is the last function that you're calling...

Don't know your implementation, but there is the possibility to have cascade calls from function. Use only F11 to see all the called functions.

Kind Regards,

Enrique

tomy

I've provided all three files contents in the first post here. Please copy and paste them onto a project on your Qt Creator to see whether it's possible to know how other functions are called.

mrjj

@tomy
Hi
It always possible.
But a function like setWindowsTitle are from Qt and it wont step into that code as
the actual code is not included in the installation. only the binary result.

Maybe that is what confusing you ?

Also as @Charlie_Hdz says, you are only calling
iconEditor.setWindowTitle(QObject::tr("Icon Editor"));
iconEditor.setIconImage(QImage(":/images/mouse.png"));

so none of the other function are called, except those use by the 2 functions.

tomy

@mrjj
Hi,
Please take a look at the functions below. When I press ctrl+R, the programs starts and execute all functions including these ones too. Do you know how and where in the code the following functions are called?

   QColor penColor() const { return curColor; }
   QImage iconImage() const { return image; }
   int zoomFactor() const { return zoom; }
   void setPenColor(const QColor &newColor);
   void setZoomFactor(int newZoom);

   ~IconEditor();

protected:
   void mousePressEvent(QMouseEvent *event);
   void mouseMoveEvent(QMouseEvent *event);
   void paintEvent(QPaintEvent *event);

private:
   void setImagePixel(const QPoint &pos, bool opaque);
   QRect pixelRect(int i, int j) const;

mrjj

@tomy said in Analysing an icon editor application:

ctrl+R,

That is normal run. Not debug so no stepping or breakpoint active.

QColor penColor() const { return curColor; } // called when setting property
QImage iconImage() const { return image; } // called when asking for image
int zoomFactor() const { return zoom; } // called when u click stuff
void setPenColor(const QColor &newColor); / called when setting property
void setZoomFactor(int newZoom); // called when u click stuff

protected: // called on mouse use
void mousePressEvent(QMouseEvent *event); // called by qt
void mouseMoveEvent(QMouseEvent *event); // called by qt
void paintEvent(QPaintEvent *event);// called by qt

tomy

@mrjj

That is normal run. Not debug so no stepping or breakpoint active.

I know that. Just said that to make the issue clear, as a bigger shape.
I got the point for the functions except:

QColor penColor() const { return curColor; } // called when setting property
void setPenColor(const QColor &newColor); / called when setting property
QImage iconImage() const { return image; } // called when asking for image

Do you mean the three Q_PROPERTY used in the header file by "called when setting property"? If so, then how are they called when I don't use those Q_PROPERTYes? Because they seem useless, that is either I use or remove them the program runs and works well.

And about "called when asking for image", in what line is there an instruction that asks for the image?

mrjj

@tomy
well its part of a larger system and are very usefull with rest of Qt
http://doc.qt.io/qt-5/properties.html

iconImage() is an access function and it seem its not used.
Its normal to make access function for data user might want to read.
One could also make the image variable public but that is bad design.

tomy

@mrjj
Thanks.

very useful with rest of Qt

I saw the page and found it a little advanced for me. In the case of this example, it's simply redundant but it's surely useful for the next stages of Qt when I study, if I've understood your talk above, correctly.

That function is also useless here as of a few before-mentioned functions. I think the author has founded a right structure for uses like that but here has used only the needed functions.

One question in this end, how do you know a method is called by Qt itself? By your experience or is there any clue?

mrjj

@tomy
Yes, its not always you use all access function at once but its part of the design
to better to cope with changes later on.

Well when i dont know a function , i press F1 on it (help) and if there is help
its Qt function.
Also, you can ask Creator to show all functions in a file and its then easy to see if part of
an object or must come from other place.

tomy

@mrjj

and if there is help
its Qt function.

And no need for our calling; it's called by the system (Qt). Yeah?

Also, you can ask Creator to show all functions in a file and its then easy to see if part of
an object or must come from other place.

Did you mean again, using 'Find Usages' which is another appearance of ctrl+F to me?

jsulm

@tomy said in Analysing an icon editor application:

how do you know a method is called by Qt itself?

Well, it depends on the method. If you for example override an event handler in your own class derived from QWidget then it will be called by Qt. There is no simple answer to this question. Read Qt documentation and try to understand how Qt works. In general Qt can only call something it knows about (what belongs to Qt, like event handler) or what you connect to signals.