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

Question

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

Jack 21

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+.

Junjie Zhu - MSFT 6,716 Reputation points Microsoft Vendor

2022-01-20T06:22:43.07+00:00

Is your transparent window form regular or irregular?
Jack 21 Reputation points

2022-01-20T14:49:28.773+00:00

@Junjie Zhu - MSFT
Sorry i dont understand what you mean by window form regular or irregular?
Do you mean the window shape? its a rect window.
Castorix31 68,306 Reputation points

2022-01-21T18:20:56.07+00:00

Have you tested with Windows.Graphics.Capture ( New Ways to do Screen Capture )
Jack 21 Reputation points

2022-01-21T23:08:05.757+00:00

@Castorix31 no, had never heard about it, but i was trying to get this using Gdi+
Junjie Zhu - MSFT 6,716 Reputation points Microsoft Vendor

2022-02-16T06:50:19.263+00:00

It has been a long time. Have you solved your problem？

Junjie Zhu - MSFT 6,716 Reputation points Microsoft Vendor

2022-01-20T06:22:43.07+00:00

Is your transparent window form regular or irregular?
Jack 21 Reputation points

2022-01-20T14:49:28.773+00:00

@Junjie Zhu - MSFT
Sorry i dont understand what you mean by window form regular or irregular?
Do you mean the window shape? its a rect window.
Castorix31 68,306 Reputation points

2022-01-21T18:20:56.07+00:00

Have you tested with Windows.Graphics.Capture ( New Ways to do Screen Capture )
Jack 21 Reputation points

2022-01-21T23:08:05.757+00:00

@Castorix31 no, had never heard about it, but i was trying to get this using Gdi+
Junjie Zhu - MSFT 6,716 Reputation points Microsoft Vendor

2022-02-16T06:50:19.263+00:00

It has been a long time. Have you solved your problem？

Answer 1

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.

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Answer 2

@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);  
              
}

Junjie Zhu - MSFT 6,716 Reputation points Microsoft Vendor

2022-01-24T01:59:34.017+00:00

You can use ShowWindow and SetForegroundWindow to top the covered window.

ShowWindow(hWnd, SW_SHOW); SetForegroundWindow(hWnd); //then get the screenshots

1 https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-showwindow
2 https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setforegroundwindow

Answer 3

Castorix31 68,306

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)

Jack 21 Reputation points

2022-01-23T14:29:47.09+00:00

@Castorix31 can you share the code? tried to find something similar but i couldn't find such examples.
Castorix31 68,306 Reputation points

2022-01-23T15:04:26.197+00:00

It was a "draft" code I had done in C# to capture hidden windows
I converted into C++ the part with DWM (just from a given window to simplify, instead of the list of top windows that I had added in a combobox)
I can add the part to convert the DWM "window" to a HBITMAP with D3D9, but what do you need exactly ?
Jack 21 Reputation points

2022-01-23T15:30:18.623+00:00

I can add the part to convert the DWM "window" to a HBITMAP with D3D9

This could help.
I can use this HBITMAP with D3D9 as a normal GDI+ hBitmap?

but what do you need exactly ?

Be able to save the bitmap to disk containing the same transparency as the target window.
Castorix31 68,306 Reputation points

2022-01-23T15:40:49.26+00:00

I can use this HBITMAP with D3D9 as a normal GDI+ hBitmap?

Yes, with Bitmap::FromHBITMAP (btw, the code you posted is GDI, not GDI+)

Be able to save the bitmap to disk containing the same transparency as the target window.

Ok, I did not try that yet (atm I have a bitmap with the transparent color identified by the color I have set as background (so I think I must convert this known RGB to ARGB...))
Castorix31 68,306 Reputation points

2022-01-23T19:17:53.473+00:00

I could save the transparent part with ImageAttributes::SetColorKey (there is just a rectangle around which probably could be fixed...)
Jack 21 Reputation points

2022-01-23T19:50:41.987+00:00

Share code please, maybe i or someone else could help fix it.
Jack 21 Reputation points

2022-01-26T00:37:28.393+00:00

@Castorix31 you gave up?

Answer 4

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;  
}

Jack 21 Reputation points

2022-01-26T13:10:51.627+00:00

Why you didnt post the full code? the same with Castorix, you always need to ask him to post the code, what will help posting here that you got it and didn't show the code used for that?

When i copy your code with the rest of the function in the link you post, it saved a invalid bitmap, and when i copy your code with my previous, it save an empty png file.

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

4 answers

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