抜き文字（メモ）

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
#define	PROC_NAME	L"ProcSample04"

//----------------------------------------------------------------
int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPreInst, LPWSTR lpszCmdLine, int nCmdShow )
{
	HWND	hwnd;
	MSG		msg;
	WNDCLASS myProg;

	if (!hPreInst) {
		myProg.style			= CS_HREDRAW | CS_VREDRAW;
		myProg.lpfnWndProc		= WndProc;
		myProg.cbClsExtra		= 0;
		myProg.cbWndExtra		= 0;
		myProg.hInstance		= hInstance;
		myProg.hIcon			= NULL;
		myProg.hCursor			= NULL;
		myProg.hbrBackground	= (HBRUSH)DKGRAY_BRUSH;
		myProg.lpszMenuName		= NULL;
		myProg.lpszClassName	= PROC_NAME;		
		if (!RegisterClass( &myProg )){
			return FALSE;
		}
	}
	hwnd = CreateWindow( PROC_NAME,
		L"Sample04",
		WS_OVERLAPPED | WS_SYSMENU | WS_CAPTION,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		CW_USEDEFAULT,
		NULL,
		NULL,
		hInstance,
		NULL);
	ShowWindow( hwnd, nCmdShow );
	UpdateWindow( hwnd );

	do{
		if(PeekMessage( &msg, NULL, 0U, 0U, PM_REMOVE )) {
			TranslateMessage( &msg );
			DispatchMessage( &msg );
		}
	} while(msg.message != WM_QUIT);
	return (int)( msg.wParam );
}

//----------------------------------------------------------------
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
	HDC hdc;
	PAINTSTRUCT paintSt;
	size_t size;
	LPTSTR str = _T("TestSample04"); 

	switch (msg) {
		case WM_PAINT:
			hdc = BeginPaint( hwnd, &paintSt );

			StringCchLength( str, STRSAFE_MAX_CCH, &size ); 
			ExtTextOut( hdc, 10, 10, NULL, NULL, str, size, NULL ); 

			EndPaint( hwnd, &paintSt );
			break;
		case WM_DESTROY:
			PostQuitMessage( 0 );
			break;
		default:
		return(DefWindowProc( hwnd, msg, wParam, lParam ));
	}
	return (0L);
}

このプログラムを実行すると、文字の周りに白い帯がつきます。

この部分を抜き状態にしたい場合

	hdc = BeginPaint( hwnd, &paintSt );

	SetBkMode(hdc, TRANSPARENT);

	StringCchLength( str, STRSAFE_MAX_CCH, &size ); 
	ExtTextOut( hdc, 10, 10, NULL, NULL, str, size, NULL ); 

	EndPaint( hwnd, &paintSt );

というように「SetBkMode」を１行たせば