Need help understanding GUI event functions

EvilNoodle · 02-11-2010 11:04 PM

Hi,

I downloaded this engine yesterday and having looked through the tutorial source I am very impressed but there are one or two things I don't understand.

In the GameMenu GUI example there is code like...

Code:

struct MenuLoad // load-game menu

{

   Window window;

   Text   text;

   Button close;

   static void Close(Ptr){Ml.window.fadeOut();}

   void create()

   {

      Gui   +=window.create(Rect_C(0,0,0.9,0.5)).barVisible(false).hide();

      window+=text  .create(Vec2  (window.crect.w()/2,-0.15),"Load Game");

      window+=close .create(Rect_C(window.crect.w()/2,-window.crect.h()/2-0.1,0.4,0.08),"Close").func(Close);

   }

}Ml;

My main question is what does "Ptr" correspond to in the Close function arguments? When I run this with the debugger it shows in the watch list as "Ptr CXX0030: Error: expression cannot be evaluated".

The logical guess would be a reference to the control that was activated.

My second question is suppose I wanted to define a class that implements a GUI window for a console like...

Code:

class Console

{

private:

    Window mWnd;

    Button mBtnClose;

    //Other components...

    void Close();

public:

    void create();

};

and implemented like

Code:

void Console::create()

{

    Gui += mWnd.create(Rect_C(0,0,0.9,0.5)).barVisible(false).hide();

    mWnd += mBtnClose.create(Rect_C(mWnd.crect.w()/2,-mWnd.crect.h()/2-0.1,0.4,0.08),"Close").func(Close);

    //Init other controls and add...

}

void Console::Close()

{

    this->mWnd.fadeOut();

}

So I could have two instances like...

Code:

//...

Console mainConsole;

mainConsole.create();

Console altConsole;

altConsole.create();

//...

Can I do this? and if so what would I need to change about the code above to facilitate it?

Any help on this greatly appreciated.

EvilNoodle

OK I have looked at this a bit more and it seems that user data for the callback is passed through using the "func(void(*func)(TYPE *), TYPE *user)" function assuming that TYPE can be an arbitrary struct. Am I right on this and if so does anybody have an example?

If this is correct then the missing link in what I want to do is what is required to use a non-static function for the button callback.

Any ideas?

**Esenthel** · 02-12-2010 12:08 AM

yes, Ptr in this case is a custom pointer to custom user data (set by 'user')

EvilNoodle · 02-12-2010 12:28 AM

Thanks for that.

How is this data passed and what, if any, format does it need to be in?

Do you have an example of using this with custom data?

Cheers

EvilNoodle

Masterxilo · 02-12-2010 12:36 AM

Code:

#include "stdafx.h"

Button button_a;

void InitPre() {

    App.name("Buttons"); App.flag=APP_NO_FX;

    Paks.add("../data/engine.pak"); D.mode(800,600);

}

void Func(Ptr userdata) {

    Int* pValue = static_cast<Int*>(userdata);

    *pValue += 1;

}

Bool Init() {

    Text_ds.color =BLACK;

    Text_ds.shadow=0;

    Gui+=button_a.create(Rect_C( 0.0,0, 0.45,0.08),"Button Func").func(Func);

    button_a.user = new Int; *static_cast<Int*>(button_a.user) = 0; 

    return true;

}

void Shut() {

    delete button_a.user;

}

Bool Update() {

    if(Kb.bp(KB_ESC))return false;

    Gui.update();

    return true;

}

void Draw() {

    D  .clear(WHITE);

    Gui.draw ();

    Int* pValue = static_cast<Int*>(button_a.user);

    D.text(0,0.6,S+"value = "     + *pValue);

}

EvilNoodle · 02-12-2010 01:32 AM

Thank you for that, that is absolutley brilliant!!

Will it work with anything that can be static cast back to the right type or does it need to be a primitive?

EvilNoodle

**Esenthel** · 02-12-2010 02:31 AM

actually please don't allocate memory and set the pointer to 'user' as it may cause errors in a rare situtation when copying 1 object to another

it should be done other way:

Code:

struct Struct

{

 ...

}Object;

static void Func(Struct &obj)

{

}

button.func(Func,Object); // 'user' must point to constant memory address

Masterxilo · 02-12-2010 02:58 AM

Quote:Will it work with anything that can be static cast back to the right type or does it need to be a primitive?

With anything, since you can get a pointer to anything and convert pointers back to pointers to anything.

@Esenthel
Ah ok, so you suggest to use it only to point to memory that will be freed by itself.

I didn't know that you can cast:
void (*func)(TYPE&)
into
void (*func)(Ptr )

Never seen that before. Are pointers and references in c++ about the same? Is there any reason to "still" use pointers instead of references?

Need help understanding GUI event functions
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