-----------------------------------

Anon

Sat Mar 24, 2007 10:20 pm


event driven programming in C++

-----------------------------------

I was just wondering what the best way was to implement event driven programming in C++ with the SDL. Right now I'm using a while loop that continously checks a boolean flag, and that flag is set when the user X's out the window, signalling the program to terminate. However, in Java, all I had to do was to implement a listener and write the event handler. Is there anything like that in C++/SDL? If not, is there a better way to handle events then what I'm doing now?

heres a snippet from my code that might better show what I mean.
This is what I'm doing right now:

while (qflag) {
  while (SDL_PollEvent(&evt)) {
    if (evt.type == SDL_QUIT) {qflag = false;}
  }


}


This is the sort of thing I'd do in Java(note: I believe the example code is deprecated, but I just want to show how I could streamline detection/handling of events in Java):

public class ExampleApp extends Frame
{
	//other stuff
	
	public boolean handleEvent(Event evt)
	{
		if (evt.id == Event.WINDOW_DESTROY)
		{
			System.exit(0);
		}
                return false;
	}
	
}



-----------------------------------

abcdefghijklmnopqrstuvwxy

Sat Mar 24, 2007 10:47 pm


RE:event driven programming in C++

-----------------------------------

I too am using c++ with sdl and was wondering if the top example you posted is actually an example of "event driven programming".  Cause all it is is a big while loop with a bunch of conditional statements - seems kind of blande to me.  

About your java code, if all you want is a function handEvents() than why don't you just write a c++ function called handle events and sub it in your while loop.


-----------------------------------

Anon

Sat Mar 24, 2007 10:58 pm


RE:event driven programming in C++

-----------------------------------

I agree, the C++ stuff I wrote doesnt really seem like 'proper' event driven stuff to me.

The thing with the java code is, that in the java example above, the handleEvent Method was all that was needed. Whenever the user closed the window, handleEvent was automatically called, ie there was no need to continously check to see if an event had been fired.

Thats what I'd like to do with C++ and the SDL.


-----------------------------------

ericfourfour

Sun Mar 25, 2007 1:12 am


RE:event driven programming in C++

-----------------------------------

Some of the more experienced c++ users may be able to help you, but I'm going to suggest callback functions.

Although, if you want to make it work like Java (I assume you were working with Swing), you are going to have to do some research into Swing. It doesn't quite "automatically" call the handleEvent method and it does consistently check if an event has occurred. If you want to get the same effect in your c++ program, you are going to have to do a lot of work.


-----------------------------------

abcdefghijklmnopqrstuvwxy

Sun Mar 25, 2007 6:03 am


RE:event driven programming in C++

-----------------------------------

Anon I was also asking if it was "proper" cause I honestly don't know that's just how I'm doing it.  So far I haven't come across a better way.  

About handleEvents() I don't get how it would "automatically" get called.

Your code could look something like this though, incase you don't already know...



while (qflag) {
  while (SDL_PollEvent(&evt)) {
     handleEvents(evt);
  }
}   



I guess it makes the main() smaller to make a handleEvent function, but other than that I don't see a benifit.


-----------------------------------

md

Sun Mar 25, 2007 10:35 am


RE:event driven programming in C++

-----------------------------------

If SDL supports callback functions you can use those, but in the end you'll have a while loop somewhere that just just as you've already got.

Java hides all the looping and polling from you so you don't have to worry about it. In C++ there is no such abstraction, so you need to either write an extensive class system to create it; or just get used to the idea of having a central while loop that controls everything.


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Mazer

Sun Mar 25, 2007 12:51 pm


RE:event driven programming in C++

-----------------------------------

It might also be worth knowing that none of that was actually C++. You can use it with C++, but SDL is written in C.


-----------------------------------

Anon

Mon Mar 26, 2007 10:07 am


Re: RE:event driven programming in C++

-----------------------------------

It might also be worth knowing that none of that was actually C++. You can use it with C++, but SDL is written in C.

really? thats interesting,
 I was compiling with g++, all this time, but after reading this I used gcc to compile my program, and it worked just fine, since I had no OOP stuff, and I stuck to c strings. Thanks.

I have another question though. When I compile/run my program, (entire code below), it seems to use a lot of CPU power, according to the windows task manager. have I done something wrong?
I apologise in advance for the lack of good commenting




#include 
#include 

#include "SDL.h"
#include "SDL_Image.h"
#include "SDL_ttf.h"


//define screen constants
#define SCRN_WDTH 640
#define SCRN_HGHT 480
#define SCRN_RS 32

//declare SDL surfaces globally
SDL_Surface *image = NULL;
SDL_Surface *msg = NULL;
SDL_Surface *screen = NULL;

//declare SDL_Event var
SDL_Event evt;
//declare an array of rectangles that will define where on the sprite sheet we clip the image
SDL_Rect clips[4];
//declare a fontface & color
TTF_Font *font = NULL;
SDL_Color textColor = { 0, 255, 255 };

//initialise SDL
int init() {
	if (SDL_Init(SDL_INIT_EVERYTHING) w;
		tmp.h = img->h;
	}

	off.x = x;
	off.y = y;

	SDL_BlitSurface(img, clip, scrn, &off);

}


int main(int argc, char *argv[]) {
//init the quit flag, and the clps array
	int qflag = 0;
	clips[0].x = 0;
	clips[0].y = 0;
	clips[0].w = 50;
	clips[0].h = 50;

	clips[1].x = 50;
	clips[1].y = 0;
	clips[1].w = 50;
	clips[1].h = 50;

	clips[2].x = 0;
	clips[2].y = 50;
	clips[2].w = 50;
	clips[2].h = 50;

	clips[3].x = 50;
	clips[3].y = 50;
	clips[3].w = 50;
	clips[3].h = 50;
//initialise
	if (init() == 1) {return 1;}
	atexit(SDL_Quit);

	screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
	if (screen == NULL) {return 1;}
	SDL_WM_SetCaption("TEST",NULL);
//wipe the screen blank
	SDL_FillRect( screen, &screen->clip_rect, SDL_MapRGB( screen->format, 0xFF, 0xFF, 0xFF ) );
//load necessary files
	image = safeLoadImage("image.bmp");
	font = safeLoadFont("maneater.ttf", 20);

	if (image == NULL || font == NULL) {return 1;}
//paint the stuff to screen
	applyToScreen( 0, 0, image, screen, &clips[ 0 ] );
	applyToScreen( 540, 0, image, screen, &clips[ 1 ] );
	applyToScreen( 0, 380, image, screen, &clips[ 2 ] );
	applyToScreen( 540, 380, image, screen, &clips[ 3 ] );


	if (SDL_Flip(screen) clip_rect, SDL_MapRGB( screen->format, 0xFF, 0xFF, 0xFF ) );
					applyToScreen( 0, 0, image, screen, &clips[ 0 ] );
					applyToScreen( 540, 0, image, screen, &clips[ 1 ] );
					applyToScreen( 0, 380, image, screen, &clips[ 2 ] );
					applyToScreen( 540, 380, image, screen, &clips[ 3 ] );
				applyToScreen(100,100, msg, screen, NULL);
				if (SDL_Flip(screen)