Solved

Screen capture CreateDIBSection doesn't capture LayeredWindow

Posted on 2010-09-20
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2,132 Views
Last Modified: 2013-12-03
Hello, I am trying to capture a screen shot using this code:

...
HWND hwnd=0;
hdc = GetWindowDC(hwnd);
memdc = CreateCompatibleDC(hdc);
...
hbmp = CreateDIBSection(hdc, &bmpinfo, DIB_PAL_COLORS, &pBits, NULL, 0)
SelectObject(memdc, hbmp);
...

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But I layered windows doesn't appear inside the shot, it is like them were invisible, only the desktop and other windows are captured.

Using "print screen" I get a full screen shot including layered window, then how can I correct that ?

Thanks
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Comment
Question by:Greg2FS
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9 Comments
 
LVL 33

Expert Comment

by:pgnatyuk
ID: 33715237
The code you posted does not contain BitBlt call or any other operation that will copy the pixels. It is also not clear from where to where you copy.
CreateDIBSection creates a DIB section. It does not capture any screen. Mainly, it is a way to create HBITMAP. pBits - this is the array of the pixels.
Sorry if I simplified too much.
In this EE article "Win32: Capture an image" (http://www.experts-exchange.com/A_1739.html) you can find the code that works. There is an example that takes screenshots from the desktop.
About the layered window (if your need):
Win32: Semi-Transparent Window: http://www.experts-exchange.com/A_1783.html 
 (There is the screenshot as an evidence for you).
0
 

Author Comment

by:Greg2FS
ID: 33715824
Sorry I didn't know exactly what does the job of taking the screenshot, but my code was longer and it seems that the code you link does exactly the same: the screenshot is taken but my layered window is not captured...
0
 
LVL 33

Expert Comment

by:pgnatyuk
ID: 33716098
No problem.
If you need the screenshots, you need to take the code from the article:
Win32: Capture an image
http://www.experts-exchange.com/A_1739.html 
 
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Author Comment

by:Greg2FS
ID: 33716244
I tried this code and said it does the same thing as mine.
0
 
LVL 33

Expert Comment

by:pgnatyuk
ID: 33716358
Yes. You are right. GetDC from the desktp does not help for the window with the WS_EX_LAYERED.
For a test, I took the screenshot of the layered window itself.

#include <Windows.h>

BOOL Capture(HDC, LPRECT, LPCWSTR);

int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, 
                      LPWSTR lpCmdLine, int nCmdShow)
{
    HWND hWnd;
    HDC hDC;
    RECT rect;
    hWnd = FindWindow(NULL, L"Semi-Transparent Window");
    SetForegroundWindow(hWnd);
    ::GetWindowRect(hWnd, &rect);
    ScreenToClient(hWnd, (LPPOINT)&rect);
    ScreenToClient(hWnd, (LPPOINT)&rect.right);
    hDC = GetDC(hWnd);

    Capture(hDC, &rect, L"capture.bmp");
    return 0;
}

BOOL Capture(HDC hDC, LPRECT lpRect, LPCWSTR lpszFile)
{
    BITMAPINFO bmi = { 0 };

    LPBYTE pBits = NULL;
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = lpRect->right - lpRect->left;
    bmi.bmiHeader.biHeight = lpRect->bottom - lpRect->top;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 32;
    bmi.bmiHeader.biCompression = BI_RGB;
    HBITMAP hBitmap = CreateDIBSection(hDC, &bmi, 
        DIB_RGB_COLORS, (LPVOID*)&pBits, NULL, 0);

    HDC hMemDC = CreateCompatibleDC(hDC);
    HGDIOBJ hOld = SelectObject(hMemDC, hBitmap);
    BitBlt(hMemDC, 0, 0, 
        lpRect->right - lpRect->left,
        lpRect->bottom - lpRect->top,
        hDC, lpRect->left, lpRect->top, SRCCOPY);
    SelectObject(hMemDC, hOld);
    DeleteDC(hMemDC);

    DWORD nImageSize = ((((bmi.bmiHeader.biWidth * 
        bmi.bmiHeader.biBitCount) 
        + 31) & ~31) >> 3) 
        * bmi.bmiHeader.biHeight;

    BITMAPFILEHEADER header = { 0 };
    header.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + 
        (DWORD)sizeof(BITMAPINFOHEADER); 
    header.bfSize = nImageSize + sizeof(BITMAPFILEHEADER) + 
        sizeof(BITMAPINFOHEADER);
    header.bfType = 0x4D42;

    HANDLE hFile = CreateFile(lpszFile, GENERIC_WRITE,
        0, NULL, CREATE_ALWAYS, 
        FILE_ATTRIBUTE_NORMAL, NULL);   

    if (hFile != INVALID_HANDLE_VALUE) 
    {
        DWORD nWritten = 0;;
        WriteFile(hFile, (LPVOID)&header, 
            sizeof(BITMAPFILEHEADER), 
            &nWritten, NULL);
        WriteFile(hFile, (LPVOID)&bmi, 
            sizeof(BITMAPINFOHEADER), 
            &nWritten, NULL);
        WriteFile(hFile, (LPVOID)pBits, nImageSize, 
            &nWritten, NULL);
        CloseHandle(hFile);
    }

    return TRUE;
}

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0
 
LVL 33

Accepted Solution

by:
pgnatyuk earned 500 total points
ID: 33716853
It's Delphi:
http://users.telenet.be/ws36637/transparent2.html
People say to use CAPTUREBLT together with SRCCOPY in BitBlt. They also use CreateCompatibleBitmap instead of CreateDIBSection.
 
0
 

Author Closing Comment

by:Greg2FS
ID: 33716959
Yes just using SRCCOPY|CAPTUREBLT works !
0
 

Author Comment

by:Greg2FS
ID: 33716965
Thanks
0
 
LVL 33

Expert Comment

by:pgnatyuk
ID: 33716978
:)
I've already made a short example for you.
You are welcome.
 

#include <Windows.h>

BOOL Capture(HDC, LPRECT, LPCWSTR);

int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, 
                      LPWSTR lpCmdLine, int nCmdShow)
{

    HWND hWnd = GetDesktopWindow();
    HDC hDC = GetDC(hWnd);

    RECT rect = { 100, 100, 500, 500 };
    HDC hDCMem = ::CreateCompatibleDC(hDC);
    HBITMAP hBitmap = ::CreateCompatibleBitmap(hDC, 500, 500);
    HBITMAP hBmpOld = (HBITMAP)::SelectObject(hDCMem, hBitmap);

    BOOL bRet = ::BitBlt(hDCMem, 0, 0, 500, 500, hDC, 100, 100, SRCCOPY | CAPTUREBLT);

    Capture(hDCMem, &rect, L"capture.bmp");

    ::SelectObject(hDCMem, hBmpOld);
    ::DeleteObject(hBitmap);
    ::DeleteDC(hDCMem);
    return 0;
}

BOOL Capture(HDC hDC, LPRECT lpRect, LPCWSTR lpszFile)
{
    BITMAPINFO bmi = { 0 };

    LPBYTE pBits = NULL;
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = lpRect->right - lpRect->left;
    bmi.bmiHeader.biHeight = lpRect->bottom - lpRect->top;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 32;
    bmi.bmiHeader.biCompression = BI_RGB;
    HBITMAP hBitmap = CreateDIBSection(hDC, &bmi, 
        DIB_RGB_COLORS, (LPVOID*)&pBits, NULL, 0);

    HDC hMemDC = CreateCompatibleDC(hDC);
    HGDIOBJ hOld = SelectObject(hMemDC, hBitmap);
    BitBlt(hMemDC, 0, 0, 
        lpRect->right - lpRect->left,
        lpRect->bottom - lpRect->top,
        hDC, lpRect->left, lpRect->top, CAPTUREBLT | SRCCOPY);
    SelectObject(hMemDC, hOld);
    DeleteDC(hMemDC);

    DWORD nImageSize = ((((bmi.bmiHeader.biWidth * 
        bmi.bmiHeader.biBitCount) 
        + 31) & ~31) >> 3) 
        * bmi.bmiHeader.biHeight;

    BITMAPFILEHEADER header = { 0 };
    header.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + 
        (DWORD)sizeof(BITMAPINFOHEADER); 
    header.bfSize = nImageSize + sizeof(BITMAPFILEHEADER) + 
        sizeof(BITMAPINFOHEADER);
    header.bfType = 0x4D42;

    HANDLE hFile = CreateFile(lpszFile, GENERIC_WRITE,
        0, NULL, CREATE_ALWAYS, 
        FILE_ATTRIBUTE_NORMAL, NULL);   

    if (hFile != INVALID_HANDLE_VALUE) 
    {
        DWORD nWritten = 0;;
        WriteFile(hFile, (LPVOID)&header, 
            sizeof(BITMAPFILEHEADER), 
            &nWritten, NULL);
        WriteFile(hFile, (LPVOID)&bmi, 
            sizeof(BITMAPINFOHEADER), 
            &nWritten, NULL);
        WriteFile(hFile, (LPVOID)pBits, nImageSize, 
            &nWritten, NULL);
        CloseHandle(hFile);
    }

    return TRUE;
}

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capture.bmp
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