如何在MFC中绘制Alpha Blended位图？ [英] How to draw Alpha Blended bitmap in MFC?

问题描述

任何人都有Alpha Blended位图图像绘制的例子吗？





提前谢谢。

Any one have the example for Alpha Blended bitmap image drawing?


Thanks in advance.

推荐答案

要绘制以DIB（设备独立位图）提供的位图，必须将其转换为设备（通常为：屏幕）兼容的DDB（设备相关位图）。这可以使用 CreateDIBitmap（） [ ^ ] GDI功能：

To draw a bitmap that is provided as DIB (Device Independant Bitmap), it must be converted to a device (usually: screen) compatible DDB (Device Dependant Bitmap). This can be done using the CreateDIBitmap()[^] GDI function:

// LPCVOID lpData points to a DIB
LPBITMAPINFOHEADER lpBIH = static_cast<LPBITMAPINFOHEADER>(lpData);
unsigned nColorSize = lpBIH->biClrUsed * sizeof(RGBQUAD);
if (lpBIH->biBitCount <= 8)
{
    // If lpBIH->bmiHeader.biClrUsed is non zero it specifies the number of colors.
    // If it is zero, all colors are used.
    if (0 == nColorSize)
        nColorSize = (lpBIH->biBitCount << 1) * sizeof(RGBQUAD);
}
// With BI_BITFIELDS compression, use 3 DWORDs.
else if (BI_BITFIELDS == lpBIH->biCompression)
    nColorSize = 3 * sizeof(DWORD);

// Create a BITMAPINFO structure.
LPBYTE lpBiBuf[sizeof(BITMAPINFO) + 255 * sizeof(RGBQUAD)];
LPBITMAPINFO = lpBI reinterpret_cast<LPBITMAPINFO>(lpBiBuf);
// Copy the common content with V4 and V5 headers
::CopyMemory(lpBI, lpBIH, sizeof(BITMAPINFO));
// Adjust the size member
lpBI->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
// Copy the color table
if (nColorSize)
    ::CopyMemory(lpBI->bmiColors, static_cast<LPBYTE>(lpData) + lpBIH->biSize, nColorSize);

HDC hScreen = ::GetDC(NULL);
HBITMAP hBitmap = ::CreateDIBitmap(
    hScreen,              // Create screen compatible bitmap
    lpBIH,                // BITMAPINFOHEADER, BITMAPV4HEADER, or BITMAPV5HEADER
    CBM_INIT,             // Initialize bitmap with data from next parameters
    static_cast<LPBYTE>(lpData) + lpBIH->biSize + nColorSize,
    lpBI,                 // BITMAPINFO (BITMAPINFOHEADER followed by color table)
    DIB_RGB_COLORS);      // Color table uses RGB values
::ReleaseDC(NULL, hScreen);

现在可以将创建的位图选择到设备上下文中，并使用其中一个阻塞函数绘制。

The created bitmap can be now be selected into a device context and drawn using one of the blitter functions.

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