How to capture the screen of a window that contains transparency?

Jack 21 Reputation points
2022-01-20T04:31:04.493+00:00

Trying to find a way to capture a window that contains transparency that also works when the window is covered by another.

I tried the function [PrintWindow][1] but it doesn't store the transparency information in the hdc.
If possible using gdi+.

Windows API - Win32
Windows API - Win32
A core set of Windows application programming interfaces (APIs) for desktop and server applications. Previously known as Win32 API.
2,411 questions
C++
C++
A high-level, general-purpose programming language, created as an extension of the C programming language, that has object-oriented, generic, and functional features in addition to facilities for low-level memory manipulation.
3,516 questions

4 answers

Sort by: Most helpful
Most helpful Newest Oldest
  1. Junjie Zhu - MSFT 14,136 Reputation points Microsoft Vendor
    2022-01-27T07:54:08.103+00:00

    Hello,
    Welcome to Microsoft Q&A!

    I used GetSystemMetrics(SM_CYCAPTION) to get the title bar height and got a full screenshot. I made these changes in the following code.(Attached is the complete code)
    based on code sample: https://learn.microsoft.com/en-us/windows/win32/gdi/capturing-an-image#code-example
    In the screenshot, the transparent area of the original window turned green area.
    Find this FindWindow(NULL, L" untitled-notepad "); Then change the name of the window you want to capture.

    168961-gdi-capture.txt
    Thank you.

    If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

    2 people found this answer helpful.
    0 comments
  2. Jack 21 Reputation points
    2022-01-21T17:55:02.093+00:00

    @Junjie Zhu - MSFT In the saved image its missing the window titlebar, also how i could capture the window when its covered by another? 

    int CaptureAnImage(HWND hWnd)  
{  
 HDC hdcScreen;  
 HDC hdcWindow;  
 HDC hdcMemDC = NULL;  
 HBITMAP hbmScreen = NULL;  
 BITMAP bmpScreen;  
 DWORD dwBytesWritten = 0;  
 DWORD dwSizeofDIB = 0;  
 HANDLE hFile = NULL;  
 char* lpbitmap = NULL;  
 HANDLE hDIB = NULL;  
 DWORD dwBmpSize = 0;  
  
 // Retrieve the handle to a display device context for the client   
 // area of the window.   
 hdcScreen = GetDC(hWnd); // GetDC(NULL);  
 hdcWindow = GetDC(hWnd);  
  
 // Create a compatible DC, which is used in a BitBlt from the window DC.  
 hdcMemDC = CreateCompatibleDC(hdcWindow);  
  
 if (!hdcMemDC)  
 {  
 MessageBox(hWnd, L"CreateCompatibleDC has failed", L"Failed", MB_OK);  
 goto done;  
 }  
  
 // Get the client area for size calculation.  
 RECT rcClient;  
 GetClientRect(hWnd, &rcClient);  
  
 // This is the best stretch mode.  
 SetStretchBltMode(hdcWindow, HALFTONE);  
  
 // The source DC is the entire screen, and the destination DC is the current window (HWND).  
 if (!StretchBlt(hdcWindow,  
 0, 0,  
 rcClient.right, rcClient.bottom,  
 hdcScreen,  
 0, 0,  
 rcClient.right, //GetSystemMetrics(SM_CXSCREEN),  
 rcClient.bottom, //GetSystemMetrics(SM_CYSCREEN),  
 SRCCOPY | CAPTUREBLT))  
 {  
 MessageBox(hWnd, L"StretchBlt has failed", L"Failed", MB_OK);  
 goto done;  
 }  
  
 // Create a compatible bitmap from the Window DC.  
 hbmScreen = CreateCompatibleBitmap(hdcWindow, rcClient.right - rcClient.left, rcClient.bottom - rcClient.top);  
  
 if (!hbmScreen)  
 {  
 MessageBox(hWnd, L"CreateCompatibleBitmap Failed", L"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,  
 rcClient.right - rcClient.left, rcClient.bottom - rcClient.top,  
 hdcWindow,  
 0, 0,  
 SRCCOPY | CAPTUREBLT))  
 {  
 MessageBox(hWnd, L"BitBlt has failed", L"Failed", MB_OK);  
 goto done;  
 }  
  
 // Get the BITMAP from the HBITMAP.  
 GetObject(hbmScreen, sizeof(BITMAP), &bmpScreen);  
  
 BITMAPFILEHEADER   bmfHeader;  
 BITMAPINFOHEADER   bi;  
  
 bi.biSize = sizeof(BITMAPINFOHEADER);  
 bi.biWidth = bmpScreen.bmWidth;  
 bi.biHeight = bmpScreen.bmHeight;  
 bi.biPlanes = 1;  
 bi.biBitCount = 32;  
 bi.biCompression = BI_RGB;  
 bi.biSizeImage = 0;  
 bi.biXPelsPerMeter = 0;  
 bi.biYPelsPerMeter = 0;  
 bi.biClrUsed = 0;  
 bi.biClrImportant = 0;  
  
 dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpScreen.bmHeight;  
  
 // 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   
 // that's pointed to by lpbitmap.  
 GetDIBits(hdcWindow, hbmScreen, 0,  
 (UINT)bmpScreen.bmHeight,  
 lpbitmap,  
 (BITMAPINFO*)&bi, DIB_RGB_COLORS);  
  
 // A file is created, this is where we will save the screen capture.  
 hFile = CreateFile(L"captureqwsx.png",  
 GENERIC_WRITE,  
 0,  
 NULL,  
 CREATE_ALWAYS,  
 FILE_ATTRIBUTE_NORMAL, NULL);  
  
 // Add the size of the headers to the size of the bitmap to get the total file size.  
 dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);  
  
 // Offset to where the actual bitmap bits start.  
 bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);  
  
 // Size of the file.  
 bmfHeader.bfSize = dwSizeofDIB;  
  
 // bfType must always be BM for Bitmaps.  
 bmfHeader.bfType = 0x4D42; // BM.  
  
 WriteFile(hFile, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);  
 WriteFile(hFile, (LPSTR)&bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);  
 WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);  
  
 // Unlock and Free the DIB from the heap.  
 GlobalUnlock(hDIB);  
 GlobalFree(hDIB);  
  
 // Close the handle for the file that was created.  
 CloseHandle(hFile);  
  
 // Clean up.  
done:  
 DeleteObject(hbmScreen);  
 DeleteObject(hdcMemDC);  
 ReleaseDC(NULL, hdcScreen);  
 ReleaseDC(hWnd, hdcWindow);  
  
 return 0;  
}  
  
  
          
          
int _tmain(int argc, _TCHAR* argv[])  
{  
              
    HWND hWnd = FindWindow(NULL, L"Untitled - Notepad");  
              
              
    DWORD exstyle = GetWindowLong(hWnd, GWL_EXSTYLE);  
    SetWindowLong(hWnd, GWL_EXSTYLE, exstyle | WS_EX_LAYERED);  
    SetLayeredWindowAttributes(hWnd, 0, 100, LWA_ALPHA);  
              
    CaptureAnImage(hWnd);  
              
}
  3. Castorix31 81,446 Reputation points
    2022-01-22T09:38:33.77+00:00

    I tested with DwmRegisterThumbnail and it detects transparent regions
    For example, the third PictureBox in this Form with 3 PictureBoxes is transparent, then I set background to light green and the Picture Box rectangle is drawn with transparency in light green
    (then I used D3DXSaveSurfaceToFileInMemory to get the HBITMAP)

    167336-dwmregisterthumbnail.jpg

  4. Junjie Zhu - MSFT 14,136 Reputation points Microsoft Vendor
    2022-01-26T03:08:13.867+00:00

    I used GetSystemMetrics(SM_CYCAPTION) to get the title bar height and got a full screenshot. I made these changes in the following code.
    based on code sample: https://learn.microsoft.com/en-us/windows/win32/gdi/capturing-an-image#code-example
    In the screenshot, the transparent area of the original window turned green area. 

    int CaptureAnImage(HWND hWnd)  
{  
HDC hdcScreen;  
HDC hdcWindow;  
HDC hdcMemDC = NULL;  
HBITMAP hbmScreen = NULL;  
BITMAP bmpScreen;  
DWORD dwBytesWritten = 0;  
DWORD dwSizeofDIB = 0;  
HANDLE hFile = NULL;  
char* lpbitmap = NULL;  
HANDLE hDIB = NULL;  
DWORD dwBmpSize = 0;  
  
// Retrieve the handle to a display device context for the client   
// area of the window.   
HWND mhWnd = FindWindow(NULL, L"GifCam 1000x639");  
hdcScreen = GetDC(mhWnd);  
hdcWindow = GetDC(hWnd);  
  
// Create a compatible DC, which is used in a BitBlt from the window DC.  
hdcMemDC = CreateCompatibleDC(hdcWindow);  
  
if (!hdcMemDC)  
{  
MessageBox(hWnd, L"CreateCompatibleDC has failed", L"Failed", MB_OK);  
goto done;  
}  
  
// Get the client area for size calculation.  
RECT rcClient;  
GetClientRect(hWnd, &rcClient);  
RECT rcSrcWnd;  
GetClientRect(mhWnd, &rcSrcWnd);  
// This is the best stretch mode.  
SetStretchBltMode(hdcWindow, HALFTONE);  
  
// The source DC is the entire screen, and the destination DC is the current window (HWND).  
if (!StretchBlt(hdcWindow,  
rcClient.left, rcClient.top,  
rcClient.right, rcClient.bottom,  
hdcScreen,  
0, 0-2 * GetSystemMetrics(SM_CYCAPTION),  
rcSrcWnd.right- rcSrcWnd.left, rcSrcWnd.bottom- rcSrcWnd.top,  
/*GetSystemMetrics(SM_CXSCREEN),  
GetSystemMetrics(SM_CYSCREEN),*/  
SRCCOPY))  
{  
MessageBox(hWnd, L"StretchBlt has failed", L"Failed", MB_OK);  
goto done;  
}  
  
// Create a compatible bitmap from the Window DC.  
hbmScreen = CreateCompatibleBitmap(hdcWindow, rcClient.right - rcClient.left, rcClient.bottom - rcClient.top);  
  
if (!hbmScreen)  
{  
MessageBox(hWnd, L"CreateCompatibleBitmap Failed", L"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,  
rcClient.right - rcClient.left, rcClient.bottom - rcClient.top,  
hdcWindow,  
0, 0,  
SRCCOPY))  
{  
MessageBox(hWnd, L"BitBlt has failed", L"Failed", MB_OK);  
goto done;  
}  
  
// Get the BITMAP from the HBITMAP.  
GetObject(hbmScreen, sizeof(BITMAP), &bmpScreen);  
  
BITMAPFILEHEADER   bmfHeader;  
BITMAPINFOHEADER   bi;  
  
bi.biSize = sizeof(BITMAPINFOHEADER);  
bi.biWidth = bmpScreen.bmWidth;  
bi.biHeight = bmpScreen.bmHeight;  
bi.biPlanes = 1;  
bi.biBitCount = 32;  
bi.biCompression = BI_RGB;  
bi.biSizeImage = 0;  
bi.biXPelsPerMeter = 0;  
bi.biYPelsPerMeter = 0;  
bi.biClrUsed = 0;  
bi.biClrImportant = 0;  
  
dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpScreen.bmHeight;  
  
// 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   
// that's pointed to by lpbitmap.  
GetDIBits(hdcWindow, hbmScreen, 0,  
(UINT)bmpScreen.bmHeight,  
lpbitmap,  
(BITMAPINFO*)& bi, DIB_RGB_COLORS);  
  
// A file is created, this is where we will save the screen capture.  
hFile = CreateFile(L"captureqwsx.bmp",  
GENERIC_WRITE,  
0,  
NULL,  
CREATE_ALWAYS,  
FILE_ATTRIBUTE_NORMAL, NULL);  
  
// Add the size of the headers to the size of the bitmap to get the total file size.  
dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);  
  
// Offset to where the actual bitmap bits start.  
bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);  
  
// Size of the file.  
bmfHeader.bfSize = dwSizeofDIB;  
  
// bfType must always be BM for Bitmaps.  
bmfHeader.bfType = 0x4D42; // BM.  
  
WriteFile(hFile, (LPSTR)& bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);  
WriteFile(hFile, (LPSTR)& bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);  
WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);  
  
// Unlock and Free the DIB from the heap.  
GlobalUnlock(hDIB);  
GlobalFree(hDIB);  
  
// Close the handle for the file that was created.  
CloseHandle(hFile);  
  
// Clean up.  
done:  
DeleteObject(hbmScreen);  
DeleteObject(hdcMemDC);  
ReleaseDC(NULL, hdcScreen);  
ReleaseDC(hWnd, hdcWindow);  
  
return 0;  
}