Need some help with this code because I can't see what's wrong with it

[Finchie_88]

Here is some code that I've written, the idea is that i'm going to make a simple 2 player pong game. The problem is that the circle isn't drawn on the screen and it doesn't move. Thanks in advance...

while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    // MAIN PROGRAMMING ////////////////////////////////////////////////////////

    hdc = GetDC(hwnd);
    
    rect.left  = ball_x - BALL_RADIUS;
    rect.right = ball_x + BALL_RADIUS;
    rect.top   = ball_y - BALL_RADIUS;
    rect.bottom= ball_y + BALL_RADIUS;
        // erase the ball /////////////////////////////////////
    SelectObject(hdc, GetStockObject(BLACK_BRUSH));
    SelectObject(hdc, black_pen);
    Ellipse(hdc, rect.left, rect.top, rect.right, rect.bottom);

    // move the ball //////////////////////////////////////
    ball_x += x;
    ball_y += y;
                    // fill in rect structure with new position
    rect.left  = ball_x - BALL_RADIUS;
    rect.right = ball_x + BALL_RADIUS;
    rect.top   = ball_y - BALL_RADIUS;
    rect.bottom= ball_y + BALL_RADIUS;
        Ellipse(hdc, rect.left, rect.top, rect.right, rect.bottom);
    
    // draw the ball
    SelectObject(hdc, red_pen);
    Ellipse(hdc, rect.left, rect.top, rect.right, rect.bottom);
    
    // TEST TO SEE IF AT THE EDGE OF THE WINDOW ////
    if(x == a||b){
        x = -x;
    }
    else if(x == a||b){
        y = -y;
    }        
    
    // release the device context
    ReleaseDC(hwnd,hdc);
            Sleep(40);

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}

[Salem]

1. your while loop loops until the program exits - by then it's all too late.
Study how normal windows programs are structured.

2. if(x == a||b){
This isn't what you meant, I'm pretty sure.
Perhaps if ( x == a || x == b )

[zcot]

yes, if you just expanded the while block to include the graphics code then at least something would happen. However I would also suggest a study of windows main loops. The structure you have will not be set up for a nicely timed drawing scheme since it will be strictly controlled by the message pump there. You could dig into the ON_PAINT message perhaps...

here's a few out of context mainloops though:

	//do this for a while
	while(GetMessage(&msg, NULL, 0, 0))
	{
		if(!TranslateAccelerator(hwndApp, hacc, &msg))
		{
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}

		PlaySound(snd, hinst, SND_ASYNC | SND_NODEFAULT | SND_RESOURCE);
	}

or...

while(1)
{
	startime = GetTickCount();

	if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
	{ 
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
	else
	{
		// do something here
		anothertime = GetTickCount();
	}
}

and..

while(1)
{
	if (PeekMessage(&msg, NULL, 0, 0, PM_NOREMOVE))
	{
		if (!GetMessage(&msg, NULL, 0, 0))
			return msg.wParam;
		TranslateMessage(&msg);
		DispatchMessage(&msg);
	}
	else if(!paused)
	{
		//go to town
	}
	else WaitMessage();
}

So if you did an index search in the MS SDK for 'WaitMessage', for example, then you would be all around that mainloop functionality. Also, if I'm not mistaken there is some good example code for some GDI bouncing ball thing as well.

keep me posted on your progress I'd be interested to see this.