Loop

[CyberCarsten]

I'm using the following loop to draw random pixels on the screen, but the loop makes the application freeze....anyone know how to avoid this...

Code:

int index;
		 for (index = 0;index<512; index++)
		 {
			int randomcol= 0;
			randomcol = rand()%2;
			if (randomcol == 1)
			{
				SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT,
					RGB(0,0,0));
			}

			if (randomcol=2)
			{
				SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT,
				RGB(255,255,255));
				Sleep(2);
			if (index >510)
			{
				index = 0;
			}

			}

[HarryW]

Are you sure it's freezing? It looks like it's just drawing black pixels to me.

rand()%2 will return either 0 or 1, not 1 or 2. The modulus operator is like a remainder. An even number divided by 2 will always give remainder 0, and an odd number will always give remainder 1.

In your loop, if it's a 0 you don't draw anything, if it's a 1 you draw a black pixel, and if it's a 2 you draw a white pixel. Since it's never a 2, you will never draw a white pixel.

I suspect your application is running fine, it's just only drawing black pixels.

[CyberCarsten]

It's drawing both white and black pixels, but when I run the taskman, it's not responding....

[Megatron]

It's because of this line:

if (index >510)
{
    index = 0;
}

Anytime your loop reaches 510, it's automatically reset to 0, hence your loop never ends. Did you intend for this?

[HarryW]

Ahh I see why it's still drawing white pixels, even though rand()%2 is never 2. You have made the classic mistake of using assignment when you meant to use equality.

The line

if (randomcol=2)

should be:

if (randomcol == 2)

only it shouldn't, because then it will never work. What it really ought to be is this:

if (randomcol == 0)

.

Of course, you do have an infinite loop there as Megatron mentioned, but it was pretty blindingly obvious so I figured you would have known that.

[CyberCarsten]

Hi guys!
There is nothing wrong with the drawing section, the problem is that, I wan't to make the section loop forever......how can I do that without freezing the program.....

[Megatron]

If you want to make your loop infinit, why not just use a blank for loop or a while loop? e.g:

bool bVal = true;

while(bVal) {

}

[HarryW]

There is nothing wrong with the drawing section

That depends on what you think of as 'wrong'. It draws a white pixel every iteration, and a black one every other iteration, so you have a black to white pixel ratio of 1:2.

If that's what you intended then fine, but I doubt if it was. I did explain it but if you want to ignore me that's your choice.

Megatron is right though, this is a slightly silly way to implement an infinite loop.

[CyberCarsten]

Thanks for the replies guys!
Harry>> Ofcourse I don't want to ignore you!
In fact, I want to draw white/black 1:1....but there is still more whites....

I'll try the loop megatron....

[CyberCarsten]

It still stops responding....

If I use the code you suggested Harry, it won't draw the pixels...

	int randomcol= 0;
			randomcol = rand()%1;
			if (randomcol == 0 )
			{
				SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT,
					RGB(0,0,0));
				Sleep(2);
			}

			if (randomcol== 1)
			{
				SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT,
				RGB(255,255,255));
				Sleep(2);
			}

[unformed]

if you want to make an infinite loop, you'll need to create a new thread...see a few posts down, there was another post about CreateThread()

[abdul]

Here is a little code that draws random rectangles (size of pixels) forever but when you want to do anything like move a window, it stops and then starts again. You may need change the code a little for your need:

#include <windows.h>
#include <stdlib.h>
static char g_szClassName[] = "MyWindowClass";
static HINSTANCE hinst = NULL;

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

void DrawRectangle(HWND hwnd);

int cxclient, cyclient;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
   LPSTR lpCmdLine, int nCmdShow)
{
   WNDCLASSEX WndClass;
   MSG msg;
   HWND hwnd;

   hinst = hInstance;

   WndClass.cbSize        = sizeof(WNDCLASSEX);
   WndClass.style         = CS_HREDRAW | CS_VREDRAW;
   WndClass.lpfnWndProc   = WndProc;
   WndClass.cbClsExtra    = 0;
   WndClass.cbWndExtra    = 0;
   WndClass.hInstance     = hinst;
   WndClass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
   WndClass.hCursor       = LoadCursor(NULL, IDC_ARROW);
   WndClass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
   WndClass.lpszMenuName  = NULL;
   WndClass.lpszClassName = g_szClassName;
   WndClass.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

   if(!RegisterClassEx(&WndClass))
   {
      MessageBox(0, "Window Registration Failed! :(", "Error!",
         MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL);
      return 0;
   }

   hwnd = CreateWindowEx(
      NULL,
      g_szClassName,
      "Coloured Shapes Generator",
      WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT, 500, 500,
      NULL, NULL, hinst, NULL);

   if(hwnd == NULL)
   {
      MessageBox(0, "Window Creation Failed! :(", "Error!",
         MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL);
      return 0;
   }


   ShowWindow(hwnd, nCmdShow);
   UpdateWindow(hwnd);

  while(TRUE)
  {
   if (PeekMessage(&msg, NULL,0,0, PM_REMOVE))
         {
           if(msg.message == WM_QUIT)
                 break;

	   TranslateMessage(&msg);
       DispatchMessage(&msg);
		 }
   else
	   DrawRectangle(hwnd);
  }
return msg.wParam;
    
  }

LRESULT CALLBACK WndProc(HWND hwnd, UINT Message, WPARAM wparam, LPARAM lparam)
{

   switch(Message)
   {
   case WM_SIZE:
	   cxclient = LOWORD(wparam);
	   cyclient = HIWORD(wparam);
	   return 0;
 
      case WM_DESTROY:
         PostQuitMessage(0);
		return 0;
   }
         return DefWindowProc(hwnd, Message, wparam, lparam);
}


void DrawRectangle(HWND hwnd)
	{

	HDC hdc;
	RECT rect;
	HBRUSH hbrush;


		   SetRect(&rect, rand () % 2, rand () % 2,
						  rand () % 2, rand () % 2);

		   hbrush = CreateSolidBrush( RGB(rand () % 256,
										  rand()  % 256,
										  rand () % 256));

		    OffsetRect(&rect, rand() % 800, rand() % 800);


	   hdc = GetDC(hwnd);

	   FillRect(hdc, &rect, hbrush);

	   ReleaseDC(hwnd, hdc);

	   DeleteObject(hbrush);
	}

[CyberCarsten]

abdul, thanks for the code
But, the only thing I want, is to make a loop that runs over and over again without freezing my program....

[kedaman]

your app "freezes" because it's not responding to the window messages the system is sending it. In abdul's code the part that responds to them is:

while(TRUE) 
{ 
if (PeekMessage(&msg, NULL,0,0, PM_REMOVE)) 
{ 
if(msg.message == WM_QUIT) 
break; 

TranslateMessage(&msg); 
DispatchMessage(&msg); 
} 
else 
DrawRectangle(hwnd); 
}

letting it for instance close when WM_QUIT is sent to it. If you want your app to extend this functionality, put your loop contents instead of the Drawrectangle call

[abdul]

That is right!

[Zaei]

Abdul got it. Just like DoEvents in VB. Although I usually have WM_QUIT in the MsgProc function, and draw regardless of a message being in the queue.

Z.

[Chris]

Put it into a thread will be better

HANDLE hThread=NULL;
DWORD WINAPI RndPixels(LPVOID pParam);

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    DWORD        dwThreadID=0;

    switch (message) 
    {
        case WM_CREATE:
            if (hThread != NULL)
                TerminateThread(hThread, WM_QUIT);

            hThread = CreateThread(NULL, 0, RndPixels, hWnd, 0, &dwThreadID);
            return true;
        case WM_DESTROY:
            TerminateThread(hThread, WM_QUIT);
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}

DWORD WINAPI RndPixels(LPVOID pParam)
{
    BOOL    b=true;
    DWORD    dwRes=0;
    RECT    rc;
    long    WINDOW_WIDTH=0;
    long    WINDOW_HEIGHT=0;

    HWND hWnd = (HWND)pParam;
    HDC  hdc  = GetDC(hWnd);
    
    do
    {
        GetClientRect(hWnd, &rc);
        WINDOW_WIDTH = rc.right - rc.left;
        WINDOW_HEIGHT = rc.bottom - rc.top; 

        switch (rand()%5)
        {
        case 0:
            SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT, RGB(0,0,0));
            break;
        case 1:
            SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT, RGB(255,0,0));
            break;
        case 2:
            SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT, RGB(0,255,0));
            break;
        case 3:
            SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT, RGB(0,0,255));
            break;
        case 4:
            SetPixel(hdc,rand()%WINDOW_WIDTH,rand()%WINDOW_HEIGHT, RGB(255,255,255));
            break;
        }

    } while (b);    

    return 1;
} 

regards,

[HarryW]

CyberCarsten, the code doesn't work because you changed it wrong You changed it to this:

randomcol = rand()%1;

but it should be this:

randomcol = rand()%2;

The rest of the code will work fine.

[CyberCarsten]

Thanks for all your replies guys! I really appriciate it!