混合2位图

Question

我有两个缓冲器指向不同大小的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，并将这些图像进行字母混合。

目前，我能够将StretchBlt (用于缩放性能)和GDI+绘图图像函数与用于字母混合的colormatrix混合。这似乎有点慢，而且使用DirectX的其他组件使用缓冲区也有问题。对于缓冲区问题，我试图以相反的顺序复制行，除了在DirectX相关组件中，它可以工作。

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.

因此，我需要替换GDI+函数，并为此使用类似于AlphaBlend的Win32函数。我试过这样的方法，它显示了一个黑色的屏幕

    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功能来混合基于2个内存DC的每像素位图。任何帮助都将不胜感激。

Answer 1

这部分是错误的：

bminfo1.bmiHeader.biSize = sizeof( BITMAPINFO );

它应该是sizeof(BITMAPINFOHEADER)，否则它会破坏一切。此外，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);

或者使用来自BeginPaint的BeginPaint。由于您使用的是GDI+，所以必须有来自bmp->GetHBITMAP()的HBITMAP句柄，因此没有理由将其转换为内存并返回到HBITMAP。

对于AlphaBlend集，在没有设置alpha通道的情况下，SourceConstantAlpha = 128;。

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，那么不要使用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:这个方法应该更快，因为它使用一个StretchBlt和一个AlphaBlend。通过这种方式，您可以使用预先计算的alphas，尽管它不是必要的。

只有当您想要将两个图像与背景混合时，才使用2 AlphaBlend的另一种方法。

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);
}