c++ - 如何仅使用直接 WinAPI 将与设备无关的位图放入 Windows 剪贴板？ (没有 MFC 或其他包装器)

Question

一段时间以来，我一直在努力让它发挥作用，但我似乎无法弄清楚，谷歌搜索了几个小时也没有显示任何有用的结果。

我有一个 RGBA 顺序的 32 位像素数组，我想从它们创建一个与设备无关的位图，并使用 SetClipboardData(CF_DIBV5, dib) 或类似的方法将其放在剪贴板上(理想情况下，我想保留 alpha channel )。注册自定义剪贴板类型不是一种选择，因为将它放在剪贴板上的目的是为了将其粘贴到另一个程序中。如果我不必手动将我的像素数据转换为其他格式(例如平面 BGRA)，则可加分。

我当前的代码是这样的(都在 set_clipboard_img 函数中):

if(!OpenClipboard(hwnd)) return;
BITMAPV5HEADER* info = (BITMAPV5HEADER*) GlobalAlloc(GMEM_MOVEABLE, sizeof(BITMAPV5HEADER));
info->bV5Size = sizeof(BITMAPV5HEADER);
info->bV5Width = img_width;
info->bV5Height = -img_height;
info->bV5Planes = 1; // The docs say this is the only valid value here.
info->bV5BitCount = 32;
info->bV5Compression = BI_BITFIELDS;
info->bV5SizeImage = img_width * img_height * 4;
info->bV5RedMask   = 0xff000000;
info->bV5GreenMask = 0x00ff0000;
info->bV5BlueMask  = 0x0000ff00;
info->bV5AlphaMask = 0x000000ff;
unsigned char* buf;
// One of the sources I found said that I can pass a BITMAPV5HEADER in place of the BITMAPINFO, hence the first reinterpret_cast.
HBITMAP dib = CreateDIBSection(NULL, reinterpret_cast<BITMAPINFO*>(info), DIB_RGB_COLORS, reinterpret_cast<void**>(&buf), NULL, 0);
if(dib == NULL) {
    CloseClipboard();
    return;
}
// img_pixels_ptr is a unsigned char* to the pixels in non-planar RGBA format
std::copy_n(img_pixels_ptr, info->bV5SizeImage, buf);
EmptyClipboard();
auto result = SetClipboardData(CF_DIBV5, dib);
if(result == NULL) {
    char str[256];
    str[255] = 0;
    FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM, NULL, GetLastError(), 0, str, 255, NULL);
    std::cerr << "Error setting clipboard: " << str << std::endl;
    // Here I get "handle not valid". I have no idea _why_ it's not valid, though.
}
CloseClipboard();

最终，我还需要能够逆转该过程(从剪贴板中获取可能透明的位图)，但一次做一件事。

Answer 1

您不能将 HBITMAP 传递给 SetClipboardData()。它需要来自 GlobalAlloc() 的 HGLOBAL。这就是 SetClipboardData() 因 ERROR_INVALID_HANDLE 错误而失败的原因。

您需要将BITMAPV5HEADER 和像素数据直接放入分配的HGLOBAL 并将其按原样放到剪贴板上，忘记使用CreateDIBSection() 全部:

Standard Clipboard Formats

CF_DIBV5
17
A memory object containing a BITMAPV5HEADER structure followed by the bitmap color space information and the bitmap bits.

尝试更像这样的东西:

void printErr(const char *msg)
{
    char str[256] = {0};
    FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM, NULL, GetLastError(), 0, str, 255, NULL);
    std::cerr << msg << ": " << str << std::endl;
}

...

DWORD size_pixels = img_width * img_height * 4;

HGLOBAL hMem = GlobalAlloc(GHND, sizeof(BITMAPV5HEADER) + size_pixels);
if (!hMem)
{
    printErr("Error allocating memory for bitmap data");
    return;
}

BITMAPV5HEADER* hdr = (BITMAPV5HEADER*) GlobalLock(hMem);
if (!hdr)
{
    printErr("Error accessing memory for bitmap data");
    GlobalFree(hMem);
    return;
}

hdr->bV5Size = sizeof(BITMAPV5HEADER);
hdr->bV5Width = img_width;
hdr->bV5Height = -img_height;
hdr->bV5Planes = 1;
hdr->bV5BitCount = 32;
hdr->bV5Compression = BI_BITFIELDS;
hdr->bV5SizeImage = size_pixels;
hdr->bV5RedMask   = 0xff000000;
hdr->bV5GreenMask = 0x00ff0000;
hdr->bV5BlueMask  = 0x0000ff00;
hdr->bV5AlphaMask = 0x000000ff;

// img_pixels_ptr is a unsigned char* to the pixels in non-planar RGBA format
CopyMemory(hdr+1, img_pixels_ptr, size_pixels);
GlobalUnlock(hMem);

if (!OpenClipboard(hwnd))
{
    printErr("Error opening clipboard");
}
else
{
    if (!EmptyClipboard())
        printErr("Error emptying clipboard");

    else if (!SetClipboardData(CF_DIBV5, hMem))
        printErr("Error setting bitmap on clipboard");

    else
        hMem = NULL; // clipboard now owns the memory

    CloseClipboard();
}

if (hMem)
    GlobalFree(hMem);