DC not working

[Bv202]

Hey,

I'm having a strange issue with these DC's. This is my code:

LRESULT CALLBACK
WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	HDC hdc = 0;
	HDC tHDC = 0;
	HWND hWndApp = 0;

	switch(msg)
	{
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

	case WM_PAINT:
		hWndApp = FindWindow(0,"Test");

		hdc = BeginPaint(hWnd, &ps);
		tHDC = GetDC(hWndApp);
		
		BitBlt(hdc, 0, 0, 500, 500, tHDC, 0, 0, SRCCOPY);

		ReleaseDC(hWndApp, tHDC);
		EndPaint(hWnd, &ps);

		return 0;
	}
	return DefWindowProc(hWnd, msg, wParam, lParam);
}

I just get a white screen (I want a screenshot of the window with the caption "Test"). The strange thing is that, when I put tHDC INSIDE the case, it works.

This code works:

LRESULT CALLBACK
WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	HDC hdc = 0;
	HWND hWndApp = 0;

	switch(msg)
	{
	case WM_DESTROY:
		PostQuitMessage(0);
		return 0;

	case WM_PAINT:
                HDC tHDC = 0;
		hWndApp = FindWindow(0,"Test");

		hdc = BeginPaint(hWnd, &ps);
		tHDC = GetDC(hWndApp);
		
		BitBlt(hdc, 0, 0, 500, 500, tHDC, 0, 0, SRCCOPY);

		ReleaseDC(hWndApp, tHDC);
		EndPaint(hWnd, &ps);

		return 0;
	}
	return DefWindowProc(hWnd, msg, wParam, lParam);
}

Is there any reason why I should put it there and not global, like the other HDC's? I was thinking about DC leaks, but can't think of any here..

Thanks

[freddie1]

I'm not that familiar with what you are doing, but it wouldn't surprise me if there were multiple invocations of WM_PAINT or other WNDPROC messages on the stack, causing rentrancy or variable scoping issues. With tHDC as a non-static global, each invocation of the WNDPROC will get a new one.

[Bv202]

Hey,

But the strange this is: it works with all the other HDC's. Only this one can't be declared in the case part...

[guestgulkan]

The original code - works for me.