Loop

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:

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;
                        }

                        }

---

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.

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

It's because of this line:

Code:

---

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?

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

Code:

---

if (randomcol=2)

---

should be:

Code:

---

if (randomcol == 2)

---

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

Code:

---

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.

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.....

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

Code:

---

bool bVal = true;

while(bVal) {

}

---

Quote:

---

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.

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....

It still stops responding....

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

Code:

---

        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);
                        }

---

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()

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:

Code:

---


#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);
        }

---

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....

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:

Code:

---

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

That is right!

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.

Put it into a thread will be better :)

PHP Code:

---

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,

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

Code:

---

randomcol = rand()%1;

---

but it should be this:

Code:

---

randomcol = rand()%2;

---

The rest of the code will work fine.

Thanks for all your replies guys! :) I really appriciate it! ;)