gradually changing opacity

[Ael_]

API function SetLayeredWindowAttributes sets the opacity for a window. Is it possible (and how) to make the window opacity level gradually change from the centre to the borders. For instance, can i set the opacity 95 percent for the centre and make it go down to 10% to the borders?
Thanks!

[sephiroth2m]

I dont know if there's a function like that. How about imitate it by making ur own 'alpha-blitting' function? There're alot of 'alpha-blitting' algorithms on Google.

[usman999_1]

Originally posted by sephiroth2m
I dont know if there's a function like that. How about imitate it by making ur own 'alpha-blitting' function? There're alot of 'alpha-blitting' algorithms on Google.

Hi sephiroth2m,
Can you please post some URLs, I tired alpha-belneding on google it but it didnt return anything useful.
Thanks in advance,
Regards,
Usman.

[Marc G]

How would you imitate it?
I mean, that can't possible work always correctly.
What happens when the window in the back is changed? You should somehow capture that and re-blit your window?

Or am I missing something?

[Ael_]

Thanks for your replies. I go the solution (with some help )
Have a look:

#define _WIN32_WINNT 0x0500
#define UNICODE
#include <windows.h>
#include <gdiplus.h>
using namespace Gdiplus;

const INT iWidth=400,iHeight=700;
HBITMAP hBitmap;

VOID OnPaint(HDC hdc){
HDC hDC_BMP=CreateCompatibleDC(hdc);
SelectObject(hDC_BMP,hBitmap);
BitBlt(hdc,0,0,iWidth,iHeight,hDC_BMP,0,0,SRCCOPY);
DeleteObject(hDC_BMP);
}


VOID CreateTrBitmap(HDC hdc){

HDC hDC_BMP=CreateCompatibleDC(hdc);
Bitmap *bmp=new Bitmap(iWidth,iHeight);
Graphics gr(bmp);
gr.Clear(Color(0,255,255,255));
GraphicsPath path;
path.AddEllipse(0, 0, iWidth, iHeight);
PathGradientBrush pthGrBrush(&path);
pthGrBrush.SetCenterColor(Color(0, 0, 0, 255));
Color colors[] = {Color(255, 100,100,0)};
int count = 1;
pthGrBrush.SetSurroundColors(colors, &count);
gr.FillEllipse(&pthGrBrush, 0, 0, iWidth, iHeight);
bmp->GetHBITMAP(Color(0,0,0,0),&hBitmap);
delete bmp;
DeleteObject(hDC_BMP);

}

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

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, PSTR, INT iCmdShow)
{
	
   HWND                hWnd;
   MSG                 msg;
   WNDCLASS            wndClass;
   GdiplusStartupInput gdiplusStartupInput;
   ULONG_PTR           gdiplusToken;
   
   // Initialize GDI+.
   GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
   
   wndClass.style          = CS_HREDRAW | CS_VREDRAW;
   wndClass.lpfnWndProc    = WndProc;
   wndClass.cbClsExtra     = 0;
   wndClass.cbWndExtra     = 0;
   wndClass.hInstance      = hInstance;
   wndClass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
   wndClass.hCursor        = LoadCursor(NULL, IDC_ARROW);
   wndClass.hbrBackground  = (HBRUSH)GetStockObject(NULL_BRUSH);
   wndClass.lpszMenuName   = NULL;
   wndClass.lpszClassName  = TEXT("GettingStarted");
   
   RegisterClass(&wndClass);
   hWnd = CreateWindowEx(
	   WS_EX_LAYERED,
      TEXT("GettingStarted"),   // window class name
      TEXT("Getting Started"),  // window caption
      WS_OVERLAPPEDWINDOW,      // window style
      CW_USEDEFAULT,            // initial x position
      CW_USEDEFAULT,            // initial y position
     iWidth,            // initial x size
      iHeight,            // initial y size
      NULL,                     // parent window handle
      NULL,                     // window menu handle
      hInstance,                // program instance handle
      NULL);                    // creation parameters
	  
   ShowWindow(hWnd, iCmdShow);
   UpdateWindow(hWnd);
   
   while(GetMessage(&msg, NULL, 0, 0))
   {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
   }
   
   GdiplusShutdown(gdiplusToken);
   return msg.wParam;
}  // WinMain

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, 
   WPARAM wParam, LPARAM lParam)
{
	HDC          hdc=NULL;
   PAINTSTRUCT  ps;
    BLENDFUNCTION blend;
	POINT ptSrc={0,0};HDC hDC_BMP;
	SIZE szDefault;
	szDefault.cx=iWidth;
	szDefault.cy=iHeight;
   switch(message)
   {

   case WM_CREATE:
       CreateTrBitmap(GetDC(hWnd));
       hDC_BMP=CreateCompatibleDC(hdc);
      SelectObject(hDC_BMP,hBitmap);
	   blend.BlendOp=AC_SRC_OVER;
	   blend.BlendFlags=0;
	   blend.SourceConstantAlpha=255;
	   blend.AlphaFormat=AC_SRC_ALPHA;
	  if( UpdateLayeredWindow(hWnd,
		NULL,&ptSrc,&szDefault,hDC_BMP,&ptSrc,NULL,&blend,
       ULW_ALPHA)==0)
	   MessageBox(NULL,TEXT("Update failed!"),TEXT(""),MB_OK);
	   DeleteObject(hDC_BMP);
	   break;
/*****************************************
WM_PAINT NEVER GETS CALLED
   case WM_PAINT:
      hdc = BeginPaint(hWnd, &ps);
     OnPaint(hdc);
      EndPaint(hWnd, &ps);
      return 0;
	  ************************/
   case WM_DESTROY:
      PostQuitMessage(0);
      return 0;
   default:
      return DefWindowProc(hWnd, message, wParam, lParam);
   }
} // WndProc

[Marc G]

Yes, UpdateLayeredWindow is a solution, but it makes it a lot more difficult to display standard windows objects etc...