将Alpha通道添加到位图或将位图转换为32位

Adding Alpha channel to bitmap or converting bitmap to 32bit

本文关键字：位图转换 32位 Alpha 通道添加更新时间：2023-10-16

已解决：当前代码示例：

HBITMAP TwoBitmap(HDC &hdc, RECT &rc)
{
    HDC hdcmem = CreateCompatibleDC(hdc);
    HBITMAP hbitmap = CreateCompatibleBitmap(hdc, rc.right-rc.left, rc.bottom-rc.top);
    SelectObject(hdcmem, hbitmap);
    HBRUSH hBrush = GetSysColorBrush(2);
    FillRect(hdcmem, &rc, hBrush);
    DeleteObject((HBRUSH)hBrush);
    DeleteDC(hdcmem);
    return hbitmap;
}
void CreateTransparentBitmap(HBITMAP &hBitmap)
{
    BITMAP TemporaryBitmap;
    GetObject(hBitmap, sizeof(BITMAP), &TemporaryBitmap);
    HDC MemoryDC = CreateCompatibleDC(NULL);
    BITMAPINFO BitmapInfo;
    ZeroMemory(&BitmapInfo,sizeof(BITMAPINFO));
    BitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    BitmapInfo.bmiHeader.biWidth = TemporaryBitmap.bmWidth;
    BitmapInfo.bmiHeader.biHeight = TemporaryBitmap.bmHeight;
    BitmapInfo.bmiHeader.biPlanes = 1;
    BitmapInfo.bmiHeader.biBitCount = 32;
    BitmapInfo.bmiHeader.biCompression = BI_RGB;
    RGBQUAD* pArgb = NULL;
    HBITMAP hTemporaryBitmap = CreateDIBSection(MemoryDC, &BitmapInfo, DIB_RGB_COLORS, (void**)&pArgb, NULL, 0);
    GetDIBits(MemoryDC, hBitmap, 0, BitmapInfo.bmiHeader.biHeight, pArgb, &BitmapInfo, DIB_RGB_COLORS);
    for (int i = 0; i < BitmapInfo.bmiHeader.biWidth * BitmapInfo.bmiHeader.biHeight; i++)
        pArgb[i].rgbReserved = 255;
    DeleteDC(MemoryDC);
    DeleteObject(hBitmap);
    hBitmap = hTemporaryBitmap;
}
case WM_PAINT:
    {
        PAINTSTRUCT p;
        HDC hDC = BeginPaint(hWnd, &p);
        HDC hdcmem = CreateCompatibleDC(hDC);
        HBITMAP hImage = TwoBitmap(hDC, p.rcPaint);
        CreateTransparentBitmap(hImage);
        SelectObject(hdcmem, hImage);
        BLENDFUNCTION bfn;
        bfn.BlendOp = AC_SRC_OVER;
        bfn.BlendFlags = 0;
        bfn.SourceConstantAlpha = 10;
        bfn.AlphaFormat = AC_SRC_ALPHA;
        AlphaBlend(hDC, 0, 0, 100, 64, hdcmem, 0, 0, 100, 64, bfn);
        bfn.SourceConstantAlpha = 80;
        AlphaBlend(hDC, 200, 0, 100, 64, hdcmem, 0, 0, 100, 64, bfn);
        bfn.SourceConstantAlpha = 255;
        AlphaBlend(hDC, 400, 0, 100, 64, hdcmem, 0, 0, 100, 64, bfn);
        BitBlt(hDC, 0, 100, 100, 64, hdcmem, 0, 0, SRCCOPY);
        DeleteDC(hdcmem);
        DeleteObject(hImage);
        EndPaint(hWnd, &p);
    }
    break;

对于这个例子，我有一个使用CreateCompatibleBitmap（）创建的简单位图：

HBITMAP TwoBitmap(HDC &hdc, RECT &rc)
{
    HDC hdcmem = CreateCompatibleDC(hdc);
    HBITMAP hbitmap = CreateCompatibleBitmap(hdc, rc.right-rc.left, 
                                             rc.bottom-rc.top);
    SelectObject(hdcmem, hbitmap);
    HBRUSH hBrush = GetSysColorBrush(3);
    FillRect(hdcmem, &rc, hBrush);
    DeleteObject((HBRUSH)hBrush);
    DeleteDC(hdcmem);
    return hbitmap;
}

现在，我试图实现的是将alpha通道添加到这个位图中（如果它还没有的话）。使用下面的代码，我尝试创建一个32位位图，然后将旧位图复制到这个新位图中。最后，我使用AlphaBlend（）和BitBlt（）函数打印出新的位图到屏幕上，像往常一样，我得到了单色的alpha混合图像和完美的BitBlt图像。

所以我的问题来了——我错过了什么，做错了什么？我在这里迷路了。我的代码（不要介意GDI泄漏）：

编辑：

多亏了PhoenixX_2我才解开了这个谜团，我只需要将Alpha位设置为255。下面是我的代码，请记住它不是无泄漏的。

PAINTSTRUCT p;
HDC hDC = BeginPaint(hWnd, &p);
HDC BufferDC = CreateCompatibleDC(NULL);
BITMAPINFO BufferInfo;
ZeroMemory(&BufferInfo,sizeof(BITMAPINFO));
BufferInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
BufferInfo.bmiHeader.biWidth = p.rcPaint.right-p.rcPaint.left;
BufferInfo.bmiHeader.biHeight = p.rcPaint.bottom-p.rcPaint.top;
BufferInfo.bmiHeader.biPlanes = 1;
BufferInfo.bmiHeader.biBitCount = 32;
BufferInfo.bmiHeader.biCompression = BI_RGB;
RGBQUAD* pArgb;
HBITMAP BufferBitmap = CreateDIBSection(BufferDC, &BufferInfo, DIB_RGB_COLORS,
                                       (void**)&pArgb, NULL, 0);
HBITMAP hImage  =  TwoBitmap(hDC, p.rcPaint);
GetDIBits(BufferDC, hImage, 0, BufferInfo.bmiHeader.biHeight, pArgb, 
          &BufferInfo, DIB_RGB_COLORS);
//----------------------------------the part I was missing
for (int i = 0; i < BufferInfo.bmiHeader.biWidth 
     * BufferInfo.bmiHeader.biHeight; i++)
pArgb[i].rgbReserved = 255;
//----------------------------------
SelectObject(BufferDC, BufferBitmap);
BLENDFUNCTION bfn;
bfn.BlendOp = AC_SRC_OVER;
bfn.BlendFlags = 0;
bfn.SourceConstantAlpha = 10;
bfn.AlphaFormat = AC_SRC_ALPHA;
AlphaBlend(hDC, 0, 0, 100, 64, BufferDC, 0, 0, 100, 64, bfn);
bfn.SourceConstantAlpha = 80;
AlphaBlend(hDC, 200, 0, 100, 64, BufferDC, 0, 0, 100, 64, bfn);
bfn.SourceConstantAlpha = 255;
AlphaBlend(hDC, 400, 0, 100, 64, BufferDC, 0, 0, 100, 64, bfn);
BitBlt(hDC, 0, 100, 100, 64, BufferDC, 0, 0, SRCCOPY);
DeleteDC(BufferDC);
DeleteObject((HBITMAP)BufferBitmap);
EndPaint(hWnd, &p);

我真的建议您使用像FreeImage这样的库。该库的好处，除了它是相当轻量级和非常开放的许可证之外，还在于它可以轻松地处理所有图像类型。然后，从任何格式（包括不同的位图格式）转换为32位都是微不足道的。渲染和其他任务也是如此。

除此之外，如果你对使用库不感兴趣，只需自己操作像素数据即可。从24位转换为32位是相当琐碎的两点和铸造。应该这样做：

uint8_t* pArgb;
uint8_t* pRgb;
GetDIBits(BufferDC, hImage, 0, BufferInfo.bmiHeader.biHeight, pRgb, &BufferInfo, DIB_RGB_COLORS);
pArgb = (uint8_t*)malloc(4 * BufferInfo.bmiHeader.biWidth * BufferInfo.bmiHeader.biHeight);
for (int i = 0; i < BufferInfo.bmiHeader.biWidth * BufferInfo.bmiHeader.biHeight; ++i) {
    *(int*)pArgb = 0xff000000 | (*(int*)(pRgb) >> 8);
    pArgb += 4;
    pRgb += 3;
}