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win32 api problem

Started by perrywky Oct 29, 2005 at 9:18 AM 4 replies 700+ views

Original Post

Oct 29, 2005 at 9:18 AM

I've got a problem in one of my win32 application, case WM_PAINT: hdc = BeginPaint (hwnd, &ps); while (i < 20){ SelectObject (hdc, CreateSolidBrush (RGB(rand () % 256, rand () % 256, rand () % 256))); Rectangle (hdc, 3 * cxClient / 8, i * cyClient / 20, 5 * cxClient / 8, (i + 1)*cyClient / 20) ; i++; } when i resize the window,the blocks i drawed just disappeared,left only a blank in the client area,but if i don't use the loop,like SelectObject (hdc, CreateSolidBrush (RGB (rand () % 256, rand () % 256, rand () % 256))) ; Rectangle (hdc, 3 * cxClient / 8, 0 * cyClient / 20, 5 * cxClient / 8, 1 * cyClient / 20) ; SelectObject (hdc, CreateSolidBrush (RGB (rand () % 256, rand () % 256, rand () % 256))) ; Rectangle (hdc, 3 * cxClient / 8, 1 * cyClient / 20, 5 * cxClient / 8, 2 * cyClient / 20) ; SelectObject (hdc, CreateSolidBrush (RGB (rand () % 256, rand () % 256, rand () % 256))) ; Rectangle (hdc, 3 * cxClient / 8, 2 * cyClient / 20, 5 * cxClient / 8, 3 * cyClient / 20) ; draw each block manually,it shows what should be when i resize the window,i don't why,could someone kind tell me why and how i can slove this problem?

PantherBoy

Oct 29, 2005 at 9:24 AM

You sure the WM_PAINT message is called when the window is maximised? It sounds like something that should be called but you might want to check or remove it as a test

Kippesoep

Oct 29, 2005 at 9:44 AM

Wow, there's an awful lot wrong with that code. Let's see if I can sum it all up:

Cause of your problem: i is not initialised. Add an "i = 0;" first, or use a for loop.

Where's the EndPaint?

Continued calls to CreateSolidBrush without calling DeleteObject on the created handle -- this will exhaust the GDI pool after a whle.

You're not catching the result of the SelectObject and restoring it afterwards, leaving the DC in a bad state and leaking even more GDI objects

To do it right:

case WM_PAINT:   hdc = BeginPaint (hwnd, &ps);   for (i = 0; i < 20; ++i)   {      HBRUSH hbr = CreateSolidBrush (RGB(rand () % 256, rand () % 256, rand () % 256));      HGDIOBJ hold = SelectObject (hdc, hbr);      Rectangle (hdc, 3 * cxClient / 8, i * cyClient / 20, 5 * cxClient / 8, (i + 1)*cyClient / 20);      SelectObject (hdc, hold);      DeleteObject (hbr);   }   EndPaint (hwnd, &ps);   break;

Edit: added EndPaint (thanks CTar).

[Edited by - Kippesoep on October 29, 2005 10:44:13 AM]

CTar

Oct 29, 2005 at 9:54 AM

Kippesoep: In your example you are still missing EndPaint.

perrywky

Oct 30, 2005 at 1:05 AM

thank you very much,it's really helpful
in fact i have declared and initialised the i at the begin of the function WinProc(),but i don't know why i should initialised it in the PAINT case,
and how could i paste my code the way like yours?

Ravuya

Oct 30, 2005 at 1:48 AM

Please do not double post. The original thread is here.

Thanks for the replies so far, but please take it to the other thread.

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