SUMMARY
This article describes the steps that are necessary to programmatically create a cursor or icon that contains alpha bits. For the purposes of this article, these types of cursors or icons are referred to as "alpha blended cursors" or "alpha blended icons." Alpha blended cursors and alpha blended icons are only supported on Microsoft Windows XP.
MORE INFORMATION
To create an alpha blended cursor or icon, create a DIB section that contains alpha values, and call the
CreateIconIndirect function with that DIB section. Although the Mask bitmap in the ICONINFO structure is not necessary, you must create an empty monochrome bitmap to send to the
CreateIconIndirect function as the Mask bitmap. The alpha bits for each pixel in the DIB section bitmap determines the visibility for each pixel in the cursor or icon that is created.
Follow these steps to create an alpha blended cursor or icon:
- Complete aBITMAPV5HEADER structure, as in the code example following these steps, to define a 32 bits per pixel (BPP) alpha blended DIB.
- Call theCreateDIBSection function to create a DIB section based on theBITMAPV5HEADER structure that you completed.
- Use the bitmap and alpha information that you want for your alpha blended cursor or icon to complete the DIB section.
- Complete anICONINFO structure.
- Place an empty monochrome bitmap in thehbmMask field, and then place the alpha blended DIB section in thehbmColor field.
- Call theCreateIconIndirect function to create the alpha blended cursor or icon.
The following Microsoft Visual C++ code demonstrates how to create an alpha blended cursor. You can use the same code to create an alpha blended icon by changing the
fIcon member of the
ICONINFO structure to TRUE:
HCURSOR CreateAlphaCursor(void){ HDC hMemDC; DWORD dwWidth, dwHeight; BITMAPV5HEADER bi; HBITMAP hBitmap, hOldBitmap; void *lpBits; DWORD x,y; HCURSOR hAlphaCursor = NULL; dwWidth = 32; // width of cursor dwHeight = 32; // height of cursor ZeroMemory(&bi,sizeof(BITMAPV5HEADER)); bi.bV5Size = sizeof(BITMAPV5HEADER); bi.bV5Width = dwWidth; bi.bV5Height = dwHeight; bi.bV5Planes = 1; bi.bV5BitCount = 32; bi.bV5Compression = BI_BITFIELDS; // The following mask specification specifies a supported 32 BPP // alpha format for Windows XP. bi.bV5RedMask = 0x00FF0000; bi.bV5GreenMask = 0x0000FF00; bi.bV5BlueMask = 0x000000FF; bi.bV5AlphaMask = 0xFF000000; HDC hdc; hdc = GetDC(NULL); // Create the DIB section with an alpha channel. hBitmap = CreateDIBSection(hdc, (BITMAPINFO *)&bi, DIB_RGB_COLORS, (void **)&lpBits, NULL, (DWORD)0); hMemDC = CreateCompatibleDC(hdc); ReleaseDC(NULL,hdc); // Draw something on the DIB section. hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap); PatBlt(hMemDC,0,0,dwWidth,dwHeight,WHITENESS); SetTextColor(hMemDC,RGB(0,0,0)); SetBkMode(hMemDC,TRANSPARENT); TextOut(hMemDC,0,9,"rgba",4); SelectObject(hMemDC, hOldBitmap); DeleteDC(hMemDC); // Create an empty mask bitmap. HBITMAP hMonoBitmap = CreateBitmap(dwWidth,dwHeight,1,1,NULL); // Set the alpha values for each pixel in the cursor so that // the complete cursor is semi-transparent. DWORD *lpdwPixel; lpdwPixel = (DWORD *)lpBits; for (x=0;x<dwWidth;x++) for (y=0;y<dwHeight;y++) { // Clear the alpha bits *lpdwPixel &= 0x00FFFFFF; // Set the alpha bits to 0x9F (semi-transparent) *lpdwPixel |= 0x9F000000; lpdwPixel++; } ICONINFO ii; ii.fIcon = FALSE; // Change fIcon to TRUE to create an alpha icon ii.xHotspot = 0; ii.yHotspot = 0; ii.hbmMask = hMonoBitmap; ii.hbmColor = hBitmap; // Create the alpha cursor with the alpha DIB section. hAlphaCursor = CreateIconIndirect(&ii); DeleteObject(hBitmap); DeleteObject(hMonoBitmap); return hAlphaCursor;}
