This is a tricky code example showing the simplest method to have a window with transparent areas (using alpha channel).
The main window is layered (WS_EX_LAYERED), and opaque (alpha=255). The WS_EX_LAYERED extended styles makes possible to copy pixels from the desktop, but not including our window.
We copy the desktop pixels from a rectangle where our window resides into temporary device context, per pixel alpha-blend it with previously saved window pixels, and then the result is copied on main window.
If you add a grow (caption text) and blur (caption) effects, it will be a real aero
$include "windowssdk.inc"
$use "msimg32.lib"
$define CLIENT_ALPHA 255
$define NONCLIENT_ALPHA 128
main()
end
sub width(pointer rc),int
settype rc,WINRECT
return *rc.right - *rc.left
endsub
sub height(pointer rc),int
settype rc,WINRECT
return *rc.bottom - *rc.top
endsub
sub DrawMe(HWND hwnd, HDC hdcOrigin, HDC hdcTemp)
WINRECT rc
BLENDFUNCTION bf
HDC hdcDesktop = GetDC(0)
HDC hdcWindow = GetWindowDC(hwnd)
bf.BlendOp = AC_SRC_OVER
bf.BlendFlags = 0
bf.AlphaFormat = AC_SRC_ALPHA
bf.SourceConstantAlpha = 255
GetWindowRect(hwnd, &rc)
int w = width(&rc)
int h = height(&rc)
' copy from desktop bitmap to temporary bitmap
BitBlt(hdcTemp, 0, 0, w, h, hdcDesktop, rc.left, rc.top, SRCCOPY)
' blend the original window bitmap onto temporary bitmap
AlphaBlend(hdcTemp, 0, 0, w, h, hdcOrigin, 0, 0, w, h, bf)
' show the result
BitBlt(hdcWindow, 0, 0, w, h, hdcTemp, 0, 0, SRCCOPY)
ReleaseDC(hwnd, hdcWindow)
ReleaseDC(0, hdcDesktop)
endsub
sub MyWndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam),BOOL
HDC _hdcOrigin = GetProp(hwnd, "_hdcOrigin")' window bitmap with alpha pixels
HDC _hdcTemp = GetProp(hwnd, "_hdcTemp")
select (uMsg)
case WM_WINDOWPOSCHANGED:
pointer pos = *<WINDOWPOS>lParam
settype pos,WINDOWPOS
' if the window is showing and the variables are not initialized yet
if ((*pos.flags & SWP_SHOWWINDOW) and !_hdcOrigin)
WINDOWINFO wi
BITMAPINFOHEADER bh
pointer pixels
settype pixels, RGBQUAD
POINT pt
HDC hdc = GetWindowDC(hwnd)
wi.cbSize = len(wi)
GetWindowInfo(hwnd, wi)
ZeroMemory(&bh, len(bh))
bh.biSize = len(bh)
bh.biWidth = width(&wi.rcWindow)
bh.biHeight = height(&wi.rcWindow)
bh.biPlanes = 1
bh.biBitCount = 32
' create window bitmap
_hdcOrigin = CreateCompatibleDC(hdc)
DeleteObject(SelectObject(_hdcOrigin, CreateDIBSection(_
hdc, &bh, DIB_RGB_COLORS, &pixels, 0, 0)))
' remember current window bits
BitBlt(_hdcOrigin, 0, 0, width(&wi.rcWindow), height(&wi.rcWindow), hdc, 0, 0, SRCCOPY)
' temporary bitmap for drawing
_hdcTemp = CreateCompatibleDC(hdc)
DeleteObject(SelectObject(_hdcTemp, CreateCompatibleBitmap(_
hdc, width(&wi.rcWindow), height(&wi.rcWindow))))
ReleaseDC(0, hdc)
SetProp(hwnd, "_hdcOrigin", _hdcOrigin)
SetProp(hwnd, "_hdcTemp", _hdcTemp)
' initialize alpha pixels
int left = wi.rcClient.left - wi.rcWindow.left
int top = wi.rcClient.top - wi.rcWindow.top
SetRect(&wi.rcClient, left, top, left+width(&wi.rcClient), top+height(&wi.rcClient))
for pt.y=0 to bh.biHeight-1
int y = bh.biHeight - pt.y - 1
pointer lineptr = &*pixels[y * bh.biWidth]
settype lineptr, RGBQUAD
for pt.x=0 to bh.biWidth-1
*lineptr[pt.x].rgbReserved = IIF(PtInRect(&wi.rcClient, pt), CLIENT_ALPHA, NONCLIENT_ALPHA)
next pt.x
next pt.y
endif
DrawMe(hwnd, _hdcOrigin, _hdcTemp)
case WM_CLOSE
DestroyWindow(hwnd)
case WM_DESTROY:
if (_hdcOrigin)
DeleteDC(_hdcOrigin)
DeleteDC(_hdcTemp)
RemoveProp(hwnd, "_hdcOrigin")
RemoveProp(hwnd, "_hdcTemp")
endif
PostQuitMessage(0)
case WM_MOVE
case& WM_NCACTIVATE
case& WM_ACTIVATE
case& WM_ACTIVATEAPP
case& WM_MOUSEACTIVATE
case& WM_NCLBUTTONDOWN
case& 0x02A2
case& WM_SIZING
DrawMe(hwnd, _hdcOrigin, _hdcTemp)
endselect
return FALSE
endsub
sub main()
MSG msg
' open invisible dialog
HWND hwnd = CreateWindowExA(WS_EX_LAYERED, WC_DIALOG, "Transparent Caption", WS_CAPTION|WS_SYSMENU|WS_BORDER,0,0,0,0,0,0,0,0)
' make it opaque
SetLayeredWindowAttributes(hwnd, 0, 255, LWA_ALPHA)
' set message callback function
SetWindowLong(hwnd, DWL_DLGPROC, &MyWndProc)
' show it
SetWindowPos(hwnd,0,200,200,400,300,SWP_NOZORDER|SWP_SHOWWINDOW)
while (GetMessage(&msg, 0, 0, 0))
TranslateMessage(&msg)
DispatchMessage(&msg)
endwhile
return 0
endsub
