AlphaBlend返回'false'的原因可能是什么

Question

我想用alpha来拉伸HBITMAP并将其绘制到另一个hdc。

我正在使用StretchDIBits，然后是AlphaBlend，如下面的代码所示。

问题是AlphaBlend失败并返回false。
1.有谁知道可能是什么原因？ 2.是否有更好的为什么拉伸和绘制透明图像？

void AnimationManager::Draw(HDC hBBDC, Instance sInstance,RECT sClientRect) 
{ 
    // sClientRect is the hwnd rect 

    int nID = GetId(sInstance.nAnemationId); 
    int nFrameindex = sInstance.nFrameIndexs; 

    HDC hdcScreen = GetDC(NULL); 
    HDC hdcMem = CreateCompatibleDC(hdcScreen); 

    BITMAP bmp; 
    PBITMAPINFO pbmi; 
    WORD cClrBits; 

    ///******************* create PBITMAPINFO *********************/// 

    GetObject(m_pAnimations[nID]->m_pFramesArray[nFrameindex]->hBmp, sizeof(bmp), &bmp); 
    cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel); 
    if(cClrBits == 1) 
     cClrBits = 1; 
    else if(cClrBits <= 4) 
      cClrBits = 4; 
    else if(cClrBits <= 8) 
      cClrBits = 8; 
    else if(cClrBits <= 24) 
      cClrBits = 24; 
    else cClrBits = 32; 

    if(cClrBits != 24) 
     pbmi = (PBITMAPINFO)LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER)+sizeof(RGBQUAD)*(1<<cClrBits)); 
    else 
     pbmi = (PBITMAPINFO)LocalAlloc(LPTR, sizeof(BITMAPINFOHEADER)); 

    pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER); 
    pbmi->bmiHeader.biWidth = bmp.bmWidth; 
    pbmi->bmiHeader.biHeight = bmp.bmHeight; 
    pbmi->bmiHeader.biPlanes = bmp.bmPlanes; 
    pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel; 
    if(cClrBits < 24) 
     pbmi->bmiHeader.biClrUsed = (1<<cClrBits); 

    pbmi->bmiHeader.biCompression = BI_RGB; 

    pbmi->bmiHeader.biSizeImage = ((pbmi->bmiHeader.biWidth * cClrBits + 31)& ~31)/8 * pbmi->bmiHeader.biHeight; 
    pbmi->bmiHeader.biClrImportant = 0; 


    ///**************************end PBITMAPINFO creation *****************************************/// 


    // I checked the code to this point and it seems to be fine. The problem stasrts here: 

    ///create a pointer to the image bits 
    LPVOID lpvBits = (LPVOID)LocalAlloc(GPTR,pbmi->bmiHeader.biSizeImage); 
    GetBitmapBits(m_pAnimations[nID]->m_pFramesArray[nFrameindex]->hBmp, pbmi->bmiHeader.biSizeImage, lpvBits); 

    ///stretch 
    bool test = StretchDIBits(hdcMem,0,sClientRect.bottom,sClientRect.right, -1*sClientRect.bottom,0,0,pbmi->bmiHeader.biWidth,pbmi->bmiHeader.biHeight, lpvBits,pbmi,DIB_RGB_COLORS, SRCCOPY); 

    ///blend 
    test = AlphaBlend(hBBDC,0,0,sClientRect.right, sClientRect.bottom,hdcMem,0,0,sClientRect.right,sClientRect.bottom,m_sBlendfunc); 


    test = DeleteDC(hdcMem); // after CreateCompatibleDC 
    test = ReleaseDC(NULL, hdcScreen); // after GetDC 

    LocalFree(pbmi); 
    LocalFree(lpvBits); 
} 

Answer 1

为什么使用StretchDIBits如果AlphaBlend也能拉伸？

Answer 2

我不能准确地说出代码失败的原因，但是我从最近的经验中知道AlphaBlend对它所接受的位图格式非常挑剔。幸运的是，我可以提供一些工作代码，这些代码应该适用于其他情况。

static void DrawBitmapWithAlpha(HDC aDeviceContext,const CartoType::TBitmap* aBitmap,const CartoType::TRect& aDestRect,const CartoType::TRect& aSourceRect) 
{ 
HDC hdc = CreateCompatibleDC(aDeviceContext); 
BITMAPINFOHEADER bitmap_header; 
memset(&bitmap_header,0,sizeof(bitmap_header)); 
bitmap_header.biSize = sizeof(BITMAPINFOHEADER); 
bitmap_header.biWidth = aBitmap->Width(); 
bitmap_header.biHeight = aBitmap->Height(); 
bitmap_header.biPlanes = 1; 
bitmap_header.biBitCount = 32; 
bitmap_header.biCompression = BI_RGB; 
bitmap_header.biSizeImage = 0; 
bitmap_header.biXPelsPerMeter = 1000; 
bitmap_header.biYPelsPerMeter = 1000; 
bitmap_header.biClrUsed = 0; 
bitmap_header.biClrImportant = 0; 

void* bitmap_data = NULL; 
HBITMAP hbitmap = CreateDIBSection(hdc,(const BITMAPINFO*)&bitmap_header,DIB_RGB_COLORS,&bitmap_data,NULL,0); 

// Reflect the data vertically and change from ABGR to BGRA. 
unsigned char* dest_row = (unsigned char*)bitmap_data; 
const unsigned char* source_row = aBitmap->Data() + (aBitmap->Height() - 1) * aBitmap->RowBytes(); 
for (int y = 0; y < aBitmap->Height(); y++, dest_row += aBitmap->RowBytes(), source_row -= aBitmap->RowBytes()) 
    { 
    const unsigned char* p = source_row; 
    unsigned char* q = dest_row; 
    unsigned char* end = q + aBitmap->RowBytes(); 
    while (q < end) 
     { 
     *q++ = p[1]; 
     *q++ = p[2]; 
     *q++ = p[3]; 
     *q++ = p[0]; 
     p += 4; 
     } 
    } 
SelectObject(hdc,hbitmap); 

BLENDFUNCTION bf; 
bf.BlendOp = AC_SRC_OVER; 
bf.BlendFlags = 0; 
bf.SourceConstantAlpha = 0xFF; 
bf.AlphaFormat = AC_SRC_ALPHA; 

AlphaBlend(aDeviceContext,aDestRect.Left(),aDestRect.Top(),aDestRect.Width(),aDestRect.Height(), 
      hdc,aSourceRect.Left(),aSourceRect.Top(),aSourceRect.Width(),aSourceRect.Height(), 
      bf); 

DeleteObject(hbitmap); 
DeleteDC(hdc); 
} 

开始的部分“反映数据垂直”可以很容易地改变采取一切必要的位图数据复制到由CreateDIBSection创建位图。

我的位图格式与Windows兼容，因为它的行字节数始终相同;如果您的位图格式没有该属性，则需要更改代码以相应地复制数据。

另一个有用的观点：我无法得到这与bitfields工作;我进一步怀疑你必须提供一个压缩比为32bpp的位图，设置为BI_RGB。