Method CreateBitmapInfoStruct

ColorCop/ColorCopDlg.cpp:3173–3235

PBITMAPINFO CColorCopDlg::CreateBitmapInfoStruct(HWND /*hwnd*/, HBITMAP hBmp) {
    BITMAP bmp = {};
    if (!GetObject(hBmp, sizeof(bmp), &bmp)) {
        AfxMessageBox(_T("Unable to receive bitmap information"));
        return nullptr;
    }

    // Compute effective color depth (clamped to standard buckets)
    WORD cClrBits = static_cast<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 <= 16)
        cClrBits = 16;
    else if (cClrBits <= 24)
        cClrBits = 24;
    else
        cClrBits = 32;

    // Compute palette size safely (avoid 1 << cClrBits overflow)
    DWORD clrUsed = 0;
    if (cClrBits < 24) {
        // max palette entries for <= 8bpp is 256; for 16/32bpp it's 0
        clrUsed = (cClrBits <= 8) ? (1u << cClrBits) : 0u;
    }

    // Compute allocation size
    const SIZE_T headerSize = sizeof(BITMAPINFOHEADER);
    const SIZE_T paletteSize = clrUsed * sizeof(RGBQUAD);

    // Overflow check (defensive)
    if (paletteSize / sizeof(RGBQUAD) != clrUsed) {
        return nullptr;  // overflow detected
    }

    const SIZE_T totalSize = headerSize + paletteSize;

    PBITMAPINFO pbmi = static_cast<PBITMAPINFO>(LocalAlloc(LPTR, totalSize));
    if (!pbmi) {
        return nullptr;
    }

    // Initialize 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;
    pbmi->bmiHeader.biCompression = BI_RGB;
    pbmi->bmiHeader.biClrUsed = clrUsed;

    // Compute image size (DWORD-aligned scanlines)
    const DWORD bitsPerLine = bmp.bmWidth * cClrBits;
    const DWORD alignedBits = (bitsPerLine + 31u) & ~31u;
    pbmi->bmiHeader.biSizeImage = (alignedBits / 8u) * bmp.bmHeight;