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POGetDIBits failing when trying to save screenshot with ctypes?
 

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  1. POGetDIBits failing when trying to save screenshot with ctypes?
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    <p>I'm attempting to take and save a screenshot using just <code>ctypes</code>. I'm not terrifically familiar with the Windows API, so I've been leaning pretty heavily on the various example in the Microsoft Developer Network. </p> <p>I've been using the following code from the <code>MSDN</code> as a template to try to recreate with ctypes. </p> <pre><code>void SaveBitmap(char *szFilename,HBITMAP hBitmap) { HDC hdc=NULL; FILE* fp=NULL; LPVOID pBuf=NULL; BITMAPINFO bmpInfo; BITMAPFILEHEADER bmpFileHeader; do{ hdc=GetDC(NULL); ZeroMemory(&amp;bmpInfo,sizeof(BITMAPINFO)); bmpInfo.bmiHeader.biSize=sizeof(BITMAPINFOHEADER); GetDIBits(hdc,hBitmap,0,0,NULL,&amp;bmpInfo,DIB_RGB_COLORS); if(bmpInfo.bmiHeader.biSizeImage&lt;=0) bmpInfo.bmiHeader.biSizeImage=bmpInfo.bmiHeader.biWidth*abs(bmpInfo.bmiHeader.biHeight)*(bmpInfo.bmiHeader.biBitCount+7)/8; if((pBuf = malloc(bmpInfo.bmiHeader.biSizeImage))==NULL) { //MessageBox( NULL, "Unable to Allocate Bitmap Memory", break; } bmpInfo.bmiHeader.biCompression=BI_RGB; GetDIBits(hdc,hBitmap,0,bmpInfo.bmiHeader.biHeight,pBuf, &amp;bmpInfo, DIB_RGB_COLORS); if((fp = fopen(szFilename,"wb"))==NULL) { //MessageBox( NULL, "Unable to Create Bitmap File", "Error", MB_OK|MB_ICONERROR); break; } bmpFileHeader.bfReserved1=0; bmpFileHeader.bfReserved2=0; bmpFileHeader.bfSize=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+bmpInfo.bmiHeader.biSizeImage; bmpFileHeader.bfType='MB'; bmpFileHeader.bfOffBits=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER); fwrite(&amp;bmpFileHeader,sizeof(BITMAPFILEHEADER),1,fp); fwrite(&amp;bmpInfo.bmiHeader,sizeof(BITMAPINFOHEADER),1,fp); fwrite(pBuf,bmpInfo.bmiHeader.biSizeImage,1,fp); }while(false); if(hdc) ReleaseDC(NULL,hdc); if(pBuf) free(pBuf); if(fp) fclose(fp); </code></pre> <p>However, I'm having terrible luck getting the <code>GetDIBits</code> function to succeed. I'm moderately confident that I've got the actual screengrab code correct, but the save code is giving me a lot of trouble. And frustratingly, I'm not sure <em>why</em> these functions are failing. </p> <p>My Python code: </p> <pre><code>libc = ctypes.cdll.msvcrt # handle to the entire desktop Window hdc = windll.user32.GetDC(None) # DC for the entire window h_dest = windll.gdi32.CreateCompatibleDC(hdc) width = windll.user32.GetSystemMetrics(SM_CXSCREEN) height = windll.user32.GetSystemMetrics(SM_CYSCREEN) hb_desktop = windll.gdi32.CreateCompatibleBitmap(hdc, width, height) windll.gdi32.SelectObject(h_dest, hb_desktop) print windll.gdi32.BitBlt(h_dest, 0,0, width, height, hdc, 0, 0, 'SRCCOPY') # Save Section # ============== bmp_info = BITMAPINFO() bmp_header = BITMAPFILEHEADER() hdc = windll.user32.GetDC(None) bmp_info.bmiHeader.biSize = sizeof(BITMAPINFOHEADER) DIB_RGB_COLORS = 0 print windll.gdi32.GetDIBits(hdc, hCaptureBitmap, 0,0, None, byref(bmp_info), DIB_RGB_COLORS) bmp_info.bmiHeader.biSizeImage = bmp_info.bmiHeader.biWidth *abs(bmp_info.bmiHeader.biHeight) * (bmp_info.bmiHeader.biBitCount+7)/8; pBuf = (c_char * bmp_info.bmiHeader.biSizeImage)() BI_RGB = 0 bmp_info.bmiHeader.biCompression = BI_RGB print windll.gdi32.GetDIBits(hdc, hCaptureBitmap, 0, bmp_info.bmiHeader.biHeight, pBuf, byref(bmp_info), 0x00) bmp_header.bfReserved1 = 0 bmp_header.bfReserved2 = 0 bmp_header.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + bmp_info.bmiHeader.biSizeImage bmp_header.bfType = 0x4D42 bmp_header.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) fp = libc.fopen('test.bmp',"wb") libc.fwrite(byref(bmp_header), sizeof(BITMAPFILEHEADER), 1, fp) libc.fwrite(byref(bmp_info.bmiHeader), sizeof(BITMAPFILEHEADER), 1, fp) libc.fwrite(pBuf, bmp_info.bmiHeader.biSizeImage, 1, fp) </code></pre> <p>I've added <code>print</code> statements to each <code>GetDIBits</code> call, and sure enough, they're all returning a failed code. I'm completely stumped here. </p>
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    1. PTQuestion
    1. USZack Yoshyaro
    1. USZack Yoshyaro
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    1. COUse `sizeof(BITMAPINFOHEADER)` and make similar fixes throughout your code. If `len(bytes(BITMAPINFOHEADER))` isn't rasing a `TypeError` then you're using 2.x and it's really `str(BITMAPINFOHEADER)`, i.e. something like `len("<class 'BITMAPINFOHEADER'>")`.
      singulars
      1. POGetDIBits failing when trying to save screenshot with ctypes?
      1. USeryksun
    2. COLet ctypes manage the allocation: `pBuf = (c_char * bmp_info.bmiHeader.biSizeImage)()`.
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      1. POGetDIBits failing when trying to save screenshot with ctypes?
      1. USeryksun
    3. COYou don't need `fopen`; ctypes data types implement Python's buffer protocol; use a Python file.
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      1. POGetDIBits failing when trying to save screenshot with ctypes?
      1. USeryksun
 

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