Thread: transparent windows - SetLayeredWindowAttributes

Originally posted by Sorensen
This should be in the Windows forum. Try placing

#define _WIN32_WINNT 0x0500

in the file, before you include windows.h.

That wont do the job if he/she has an older version of the SDK....

There is a work around that involves getting a pointer to the API function at runtime yourself. Also you must declare all the macros as well as your heders will not have them declared

Try this for size

Code:

#include <windows.h>

/* Declare Macros*/
#ifndef WS_EX_LAYERED
#define WS_EX_LAYERED           0x00080000
#define LWA_COLORKEY            0x00000001
#define LWA_ALPHA               0x00000002
#endif 

/*typedef a pointer to the API function*/
typedef BOOL (WINAPI *lpfnSetLayeredWindowAttributes)(HWND hWnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags);

lpfnSetLayeredWindowAttributes m_pSetLayeredWindowAttributes;



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

char szClassName[] = "WindowsApp";
HINSTANCE g_hInst;


int WINAPI WinMain(HINSTANCE hThisInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int nFunsterStil)

{
    HWND hwnd;               
	MSG messages;            
	WNDCLASSEX wincl; 

            /*Load dll that holds the API func*/
	HMODULE hUser32 = GetModuleHandle("USER32.DLL");
	
            /*Grab pointer to API*/
            m_pSetLayeredWindowAttributes = (lpfnSetLayeredWindowAttributes)GetProcAddress(hUser32, "SetLayeredWindowAttributes");


	if (NULL == m_pSetLayeredWindowAttributes)
	MessageBox(NULL,"Error!","",MB_OK);
            return 1;

	g_hInst = hThisInstance;

    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProc;      
    wincl.style = CS_DBLCLKS;               
    wincl.cbSize = sizeof(WNDCLASSEX);
    wincl.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor(NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;
    wincl.cbClsExtra = 0; 
    wincl.cbWndExtra = 0; 
	wincl.hbrBackground = (HBRUSH) GetStockObject(LTGRAY_BRUSH);

    
    if(!RegisterClassEx(&wincl)) return 0;

   
    hwnd = CreateWindowEx(0,szClassName, "Windows App",
		WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,CW_USEDEFAULT,
		CW_USEDEFAULT,CW_USEDEFAULT, HWND_DESKTOP,NULL,            
           hThisInstance,NULL );    

   
    ShowWindow(hwnd, nFunsterStil);
	UpdateWindow(hwnd);
   
    while(GetMessage(&messages, NULL, 0, 0))
    {
          TranslateMessage(&messages);
          DispatchMessage(&messages);
    }

    return messages.wParam;
}


LRESULT CALLBACK WindowProc(HWND hwnd, UINT message, 
							WPARAM wParam, LPARAM lParam)
{
    switch (message)                
    {
           case WM_CREATE: 
			SetWindowLong(hwnd, GWL_EXSTYLE,
				GetWindowLong(hwnd, GWL_EXSTYLE) | WS_EX_LAYERED);
                                    /*Use pointer to function*/
			m_pSetLayeredWindowAttributes(hwnd, 0, 
				(255 * 70) / 100, LWA_ALPHA);
           
           break;
           
           case WM_PAINT:
           
           break;
           
           case WM_DESTROY:
           PostQuitMessage(0);        
           break;
           default:                   
           return DefWindowProc(hwnd, message, wParam, lParam);
    }
    return 0;
}

Originally posted by codec

If possible could you explain why i had to put that directive in my code so I can understand why I have done it, it would be very helpful.

Which?

Code:

#define _WIN32_WINNT 0x0500

- this tells the compiler that the target platform will at least be Win2000......this is because transparent layering did not exist in any of the Win95 family or WinNT 4 and below...

Code:

#ifndef WS_EX_LAYERED
#define WS_EX_LAYERED           0x00080000
#define LWA_COLORKEY            0x00000001
#define LWA_ALPHA               0x00000002
#endif

/*typedef a pointer to the API function*/
typedef BOOL (WINAPI *lpfnSetLayeredWindowAttributes)(HWND hWnd, COLORREF crKey, BYTE bAlpha, DWORD dwFlags);

lpfnSetLayeredWindowAttributes m_pSetLayeredWindowAttributes;

This first of all defined the macros as the hexadecimal values that the functions would expect......it first checks to see if the definition is already there....if not it declares them.....

The typedef is simply declaring a pointer to a function......it says what params the function will recieve and what return value it will return...