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Lägg till en AlphaBlend-effekt
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Kategori: Grafik
Inlagt: 2004-12-17
Läst: 1355
Inlagt av: Staffan Berg
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Beskrivning |
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AlphaBlend har till uppgift att visa bilder som har transparenta eller halvtransparenta pixlar. Observera att det inte finns stöd för AlphaBlend i Windowsversioner tidigare än Windows 2000.
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Kod |
const
AC_SRC_ALPHA = $1;
procedure DrawAlphaBlend (hWnd : HWND; hdcwnd : HDC);
var
Ahdc : HDC; // handle of the DC we will create
bf : BLENDFUNCTION; // structure for alpha blending
Ahbitmap : HBITMAP; // bitmap handle
bmi : BITMAPINFO; // bitmap header
pvBits : pointer; // pointer to DIB section
ulWindowWidth,
ulWindowHeight : ULONG; // window width/height
ulBitmapWidth,
ulBitmapHeight : ULONG; // bitmap width/height
rt : TRect; // used for getting window dimensions
begin
// get window dimensions
GetClientRect(hWnd, rt);
// calculate window width/height
ulWindowWidth := rt.right - rt.left;
ulWindowHeight := rt.bottom - rt.top;
// make sure we have at least some window size
if ((ulWindowWidth = 0 ) and (ulWindowHeight=0)) then
exit;
// divide the window into 3 horizontal areas
ulWindowHeight := trunc(ulWindowHeight / 3);
// create a DC for our bitmap -- the source DC for AlphaBlend
Ahdc := CreateCompatibleDC(hdcwnd);
// zero the memory for the bitmap info
ZeroMemory(@bmi, sizeof(BITMAPINFO));
// setup bitmap info
bmi.bmiHeader.biSize := sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth := trunc(ulWindowWidth - (ulWindowWidth/5)*2);
ulBitmapWidth := trunc(ulWindowWidth - (ulWindowWidth/5)*2);
bmi.bmiHeader.biHeight := trunc(ulWindowHeight - (ulWindowHeight/5)*2);
ulBitmapHeight := trunc(ulWindowHeight - (ulWindowHeight/5)*2);
bmi.bmiHeader.biPlanes := 1;
bmi.bmiHeader.biBitCount := 32; // four 8-bit components
bmi.bmiHeader.biCompression := BI_RGB;
bmi.bmiHeader.biSizeImage := ulBitmapWidth * ulBitmapHeight * 4;
// create our DIB section and select the bitmap into the dc
Ahbitmap := CreateDIBSection(Ahdc, bmi, DIB_RGB_COLORS, pvBits, 0, 0);
SelectObject(Ahdc, Ahbitmap);
bf.BlendOp := AC_SRC_OVER;
bf.BlendFlags := 0;
bf.SourceConstantAlpha := $7f; // half of 0xff = 50% transparency
bf.AlphaFormat := 0; // ignore source alpha channel
AlphaBlend(hdcwnd, trunc(ulWindowWidth/5), trunc(ulWindowHeight/5),
ulBitmapWidth, ulBitmapHeight,
Ahdc, 0, 0, ulBitmapWidth, ulBitmapHeight, bf);
bf.BlendOp := AC_SRC_OVER;
bf.BlendFlags := 0;
bf.AlphaFormat := AC_SRC_ALPHA; // use source alpha
bf.SourceConstantAlpha := $ff; // opaque (disable constant alpha)
AlphaBlend(hdcwnd, trunc(ulWindowWidth/5),
trunc(ulWindowHeight/5+ulWindowHeight), ulBitmapWidth, ulBitmapHeight,
Ahdc, 0, 0, ulBitmapWidth, ulBitmapHeight, bf);
bf.BlendOp := AC_SRC_OVER;
bf.BlendFlags := 0;
bf.AlphaFormat := 0;
bf.SourceConstantAlpha := $3A;
AlphaBlend(hdcwnd, trunc(ulWindowWidth/5),
trunc(ulWindowHeight/5+2*ulWindowHeight), ulBitmapWidth,
ulBitmapHeight, Ahdc, 0, 0, ulBitmapWidth,
ulBitmapHeight, bf);
// do cleanup
DeleteObject(Ahbitmap);
DeleteDC(Ahdc);
end;
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