混合 2 个位图

Question

我有 2 个缓冲区指向不同大小的 RGB32 图像，所以我的想法是缩放一个缓冲区以匹配另一个缓冲区并对这些图像进行 alphablend。

目前，我能够将 StretchBlt（用于缩放性能）和 GDI+ drawimage 函数与用于 alphablending 的颜色矩阵混合。这似乎有点慢，而且使用 DirectX 的不同组件使用缓冲区也存在问题。对于缓冲区问题，我尝试以相反的顺序复制行，但它在 DirectX 相关组件中除外。

Bitmap bmp1(width, height, 4bytesperpixel, RGB32, bufferpointer1);
Bitmap blend(width, height, 4bytesperpixel);
Graphics g(&newbmp)

using GDI function
Bitmap bmp2(scaleWidth, scaleHeight, 4bytesperpixel, RGB32, bufferpointer2)
HDC memdc = g.GetHDC();

////  scaling the bufferpointer2 to actual width & height
StretchDIBits(memdc, x,y, width, height, 0, 0,scaleWidth, scaleHeight, bufferpointer2,..)
g.ReleaseDC(memdc); // so that content is copied to the bitmap

//// Then alphablending bmp1 on top of the scaled imaged bmp2
//// Using lockbits to copy the bitmap bytes and unlocking it.

所以我需要替换 GDI+ 函数并为此使用像 AlphaBlend 这样的 Win32 函数。我试过这样的东西，它显示一个黑屏

    BITMAPINFO bminfo1 = {};
    bminfo1.bmiHeader.biSize = sizeof( BITMAPINFO );
    bminfo1.bmiHeader.biWidth = w;
    bminfo1.bmiHeader.biHeight = h;
    bminfo1.bmiHeader.biBitCount = m_nBytesPerPixel * 8;
    bminfo1.bmiHeader.biCompression = BI_RGB;
    bminfo1.bmiHeader.biPlanes = 1;

    BITMAPINFO bminfo2 = {};
    bminfo2.bmiHeader.biSize = sizeof( BITMAPINFO );
    bminfo2.bmiHeader.biWidth = sW;
    bminfo2.bmiHeader.biHeight = sH;
    bminfo2.bmiHeader.biBitCount = m_nBytesPerPixel * 8;
    bminfo2.bmiHeader.biCompression = BI_RGB;
    bminfo2.bmiHeader.biPlanes = 1;

    char* pBytes1, *pBytes2;

    HDC hmemdc1 = CreateCompatibleDC(GetDC(0));
    HDC hmemdc2 = CreateCompatibleDC(GetDC(0));

    HBITMAP hBitmap1 = CreateDIBSection(hmemdc1, &bminfo1, DIB_RGB_COLORS, (void**) &pBytes1, NULL, 0);
    SetDIBits(hmemdc1, hBitmap1, 0, bminfo1.bmiHeader.bih, pBuffer[0], &bminfo1, DIB_RGB_COLORS);

    HBITMAP hBitmap2 = CreateDIBSection(hmemdc2, &bminfo2, DIB_RGB_COLORS, (void**) &pBytes2, NULL, 0);
    SelectObject(hmemdc2,hBitmap2);
    StretchDIBits(hmemdc2, 0, 0, w, h, 0, 0,
        sW, sH, pBuffer[1], &bminfo2, DIB_RGB_COLORS, SRCCOPY );

    BLENDFUNCTION bStruct; 
    bStruct.BlendOp = AC_SRC_OVER;
    bStruct.BlendFlags = 0;
    bStruct.SourceConstantAlpha = 255;
    bStruct.AlphaFormat = AC_SRC_ALPHA;

    SelectObject(hmemdc1,hBitmap1);
    SelectObject(hmemdc2,hBitmap2);

    //blend bmp2 on bmp1
    BOOL res = AlphaBlend(hmemdc1, 0, 0, w, h, hmemdc2, 0, 0, w, h, bStruct);

    //for testing output
    SelectObject(hmemdc1,hBitmap1);
    BitBlt(GetDC(0),0,0,width,height,hmemdc1,100,100,SRCCOPY);


    //copy the bitmap buffer
    memcpy(out, pBytes1, (w * m_nBytesPerPixel) * h);

我不确定是否可以使用 AlphaBlend 函数来混合基于 2 个内存 DC 的每个像素的位图。任何帮助将不胜感激。

Answer 1

这部分错了：

bminfo1.bmiHeader.biSize = sizeof( BITMAPINFO );

它应该是 sizeof(BITMAPINFOHEADER) 否则它会毁了一切。您也不能使用GetDC(0) 进行任何适当的绘画。改为使用：

HDC hdc = GetDC(hwnd);
...
ReleaseDC(hwnd, hdc);

或使用来自BeginPaint 的HDC。由于您使用的是 GDI+，那么您必须拥有来自 bmp->GetHBITMAP() 的 HBITMAP 句柄，没有理由转换为内存并返回到 HBITMAP

对于AlphaBlend 设置SourceConstantAlpha = 128;，以防 Alpha 通道未设置。

void blend(HDC hdc, RECT rc, HBITMAP hbitmap1, HBITMAP hbitmap2)
{
    HDC memdc1 = CreateCompatibleDC(hdc);
    HDC memdc2 = CreateCompatibleDC(hdc);

    BITMAP bmp1, bmp2;
    GetObject(hbitmap1, sizeof(BITMAP), &bmp1);
    GetObject(hbitmap2, sizeof(BITMAP), &bmp2);

    SelectObject(memdc1, hbitmap1);
    SelectObject(memdc2, hbitmap2);

    BLENDFUNCTION blend = { 0 };
    blend.SourceConstantAlpha = 128;

    SetStretchBltMode(hdc, COLORONCOLOR);
    AlphaBlend(memdc2, 0, 0, bmp2.bmWidth, bmp2.bmHeight, memdc1, 0, 0, bmp1.bmWidth, bmp1.bmHeight, blend);
    StretchBlt(hdc, 0, 0, rc.right, rc.bottom, memdc2, 0, 0, bmp2.bmWidth, bmp2.bmHeight, SRCCOPY);

    //or create another memdc to get dibs

    DeleteDC(memdc1);
    DeleteDC(memdc2);
}

如果您想获得 dib，则不要使用 hdc，而是创建第三个 memdc 和另一个 HBITMAP，然后使用 GetDIBits

HDC memdc = CreateCompatibleDC(hdc);
HBITMAP hbmp = CreateCompatibleBitmap(hdc, rc.right, rc.bottom);
SelectObject(memdc, hbmp);
SetStretchBltMode(memdc, COLORONCOLOR);
StretchBlt(memdc, 0, 0, rc.right, rc.bottom, 
    memdc2, 0, 0, bmp2.bmWidth, bmp2.bmHeight, SRCCOPY);

int w = rc.right;
int h = rc.bottom;
BITMAPINFOHEADER bmpInfoHeader = { sizeof(BITMAPINFOHEADER) };
bmpInfoHeader.biWidth = w;
bmpInfoHeader.biHeight = h;
bmpInfoHeader.biBitCount = 32;
bmpInfoHeader.biCompression = BI_RGB;
bmpInfoHeader.biPlanes = 1;

DWORD size = w * 4 * h;
char *dib = new char[size];
GetDIBits(hdc, hbmp, 0, h, dib, (BITMAPINFO*)&bmpInfoHeader, DIB_RGB_COLORS);
...
DeleteDC(memdc);
DeleteObject(hbitmap);
delete[]dib;

---

编辑

方法 2：此方法应该更快，因为它使用一个StretchBlt 和一个AlphaBlend。这样您就可以使用预先计算的 alpha，尽管这不是必需的。

仅当您想将两个图像与背景混合时，才使用带有 2 AlphaBlend 的其他方法。

void modify_bits(HDC hdc, HBITMAP hbitmap) 
{   //expecting 32-bit bitmap
    BITMAP bm = { 0 };
    GetObject(hbitmap, sizeof(bm), &bm);
    int w = bm.bmWidth;
    int h = bm.bmHeight;
    BITMAPINFOHEADER bmpInfoHeader = { sizeof(BITMAPINFOHEADER),
        w, h, 1, 32, BI_RGB, 0, 0, 0, 0, 0 };
    BYTE* bits = new BYTE[w * h * 4];
    if (GetDIBits(hdc, hbitmap, 0, h, bits, (BITMAPINFO*)&bmpInfoHeader, DIB_RGB_COLORS)) {
        BYTE* p = bits;
        for (int x = 0; x < w; x++) {
            for (int y = 0; y < h; y++) {
                p[3] = 128;
                p[0] = p[0] * p[3] / 255;
                p[1] = p[1] * p[3] / 255;
                p[2] = p[2] * p[3] / 255;
                p += 4;
            }
        }
        SetDIBits(hdc, hbitmap, 0, h, bits, (BITMAPINFO*)&bmpInfoHeader, DIB_RGB_COLORS);
    }
    delete[] bits;
}

void blend2(HDC hdc, RECT rc, HBITMAP hbitmap1, HBITMAP hbitmap2)
{
    int w = rc.right;
    int h = rc.bottom;

    modify_bits(hdc, hbitmap2);

    HDC memdc1 = CreateCompatibleDC(hdc);
    HDC memdc2 = CreateCompatibleDC(hdc);

    BITMAP bmp1, bmp2;
    GetObject(hbitmap1, sizeof(BITMAP), &bmp1);
    GetObject(hbitmap2, sizeof(BITMAP), &bmp2);
    int w1 = bmp1.bmWidth;
    int h1 = bmp1.bmHeight;
    int w2 = bmp2.bmWidth;
    int h2 = bmp2.bmHeight;

    SelectObject(memdc1, hbitmap1);
    SelectObject(memdc2, hbitmap2);

    BLENDFUNCTION blend = { 0 };
    blend.BlendOp = AC_SRC_OVER;
    blend.BlendFlags = 0;
    blend.SourceConstantAlpha = 255;
    blend.AlphaFormat = AC_SRC_ALPHA;

    SetStretchBltMode(hdc, COLORONCOLOR);

    //draw first image normally:
    StretchBlt(hdc, 0, 0, w, h, memdc1, 0, 0, w1, h1, SRCCOPY);

    //AlphaBlend the second image:
    AlphaBlend(hdc, 0, 0, w, h, memdc2, 0, 0, w2, h2, blend);

    DeleteDC(memdc1);
    DeleteDC(memdc2);
}