我有一个将 hwnd 保存到 ppm 文件中的功能。这个函数的灵感来自一个 msdn 示例。msdn 示例和我的函数都可以工作，但是......我有一个问题......
但首先，这是功能。
int CaptureAnImage(HWND hWnd)
{
HDC hdcWindow;
HDC hdcMemDC = NULL;
HBITMAP hbmScreen = NULL;
RECT rc;
BITMAPINFOHEADER bi;
DWORD dwBmpSize;
HANDLE hDIB;
char *lpbitmap;
int w, h;
FILE *f;
// Retrieve the handle to a display device context for the client
// area of the window.
hdcWindow = GetDC(hWnd);
// Create a compatible DC which is used in a BitBlt from the window DC
hdcMemDC = CreateCompatibleDC(hdcWindow);
if(!hdcMemDC) {
MessageBox(hWnd, "CreateCompatibleDC has failed","Failed", MB_OK);
goto done;
}
// Get the client area for size calculation
GetClientRect(hWnd, &rc);
w = rc.right - rc.left;
h=rc.bottom-rc.top;
// Create a compatible bitmap from the Window DC
hbmScreen = CreateCompatibleBitmap(hdcWindow, w, h);
if(!hbmScreen) {
MessageBox(hWnd, "CreateCompatibleBitmap Failed","Failed", MB_OK);
goto done;
}
// Select the compatible bitmap into the compatible memory DC.
SelectObject(hdcMemDC,hbmScreen);
// Bit block transfer into our compatible memory DC.
if(!BitBlt(hdcMemDC,
0,0,
w, h,
hdcWindow,
0,0,
SRCCOPY)) {
MessageBox(hWnd, "BitBlt has failed", "Failed", MB_OK);
goto done;
}
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = w;
bi.biHeight = h;
bi.biPlanes = 1;
bi.biBitCount = 24;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;
dwBmpSize = w*bi.biBitCount*h;
// Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper functions that
// call HeapAlloc using a handle to the process's default heap. Therefore, GlobalAlloc and LocalAlloc
// have greater overhead than HeapAlloc.
hDIB = GlobalAlloc(GHND,dwBmpSize);
lpbitmap = (char *)GlobalLock(hDIB);
// Gets the "bits" from the bitmap and copies them into a buffer
// which is pointed to by lpbitmap.
GetDIBits(hdcWindow, hbmScreen, 0,
(UINT)h,
lpbitmap,
(BITMAPINFO *)&bi, DIB_RGB_COLORS);
f = fopen("./test.ppm", "wb");
if (!f) {
fprintf(stderr, "cannot create ppm file\n");
goto done;
}
fprintf(f, "P6\n%d %d\n255\n", w, h);
fwrite((LPSTR)lpbitmap, dwBmpSize, 1, f);
fclose(f);
//Unlock and Free the DIB from the heap
GlobalUnlock(hDIB);
GlobalFree(hDIB);
//Clean up
done:
DeleteObject(hbmScreen);
DeleteObject(hdcMemDC);
ReleaseDC(hWnd,hdcWindow);
return 0;
}
所以这是生成的图像：
http://imageshack.us/photo/my-images/853/test2ne.jpg/
如您所见，宽度大小存在问题。也许是因为窗口的边框？如果在代码中，我更改“w = rc.right - rc.left;” 变成“w = rc.right - rc.left - 10;”，这样更好。但我不明白为什么我必须放“-10”并且......图片右侧缺少一些像素（可能是10像素？）
http://imageshack.us/photo/my-images/207/test3jq.jpg
最后一个问题：有什么方法可以要求 GetDIBits 函数将我的字节倒序排列？我不想逐个像素地复制，因为它会花费一些 cpu 时间。（好吧，你可能会说，既然我将这个文件保存到磁盘，那么我不应该担心cpu时间，但我的目标不是将这张图片保存到磁盘。我这样做只是为了调试）
提前感谢您的帮助