L_LoadMemory

Summary

Loads any supported file from memory using a callback function.

Syntax

L_LTFIL_API L_INT L_LoadMemory(pBuffer, pBitmap, uStructSize, nBitsPerPixel, nOrder, uFlags, pfnCallback, pUserData, nBufferSize, pLoadOptions, pFileInfo)

Parameters

L_UCHAR* pBuffer

Pointer to the file in memory to be loaded.

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle referencing the bitmap to be filled with image data.

L_UINT uStructSize

Size in bytes, of the structure pointed to by pBitmap, for versioning. Use sizeof(BITMAPHANDLE).

L_INT nBitsPerPixel

Resulting bitmap pixel depth. The following are valid values:

L_INT nOrder

The desired color order. Possible values are:

L_UINT uFlags

Binary flags that determine the behavior of L_LoadMemory. You can specify one or more of the following values:

FILEREADCALLBACK pfnCallback

Optional callback function for additional processing.

If you do not provide a callback function, use NULL as the value of this parameter.

If you do provide a callback function, use the function pointer as the value of this parameter.

The callback function must adhere to the function prototype described in FILEREADCALLBACK Function.

L_VOID* pUserData

Void pointer that you can use to pass one or more additional parameters that the callback function needs.

To use this feature, assign a value to a variable or create a structure that contains as many fields as you need. Then, in this parameter, pass the address of the variable or structure, casting it to L_VOID *. The callback function, which receives the address in its own pUserData parameter, can cast it to a pointer of the appropriate data type to access your variable or structure.

If the additional parameters are not needed, you can pass NULL in this parameter.

L_SSIZE_T nBufferSize

Size of the file in memory (in bytes).

pLOADFILEOPTION pLoadOptions

Pointer to optional extended load options. Pass NULL to use the default load options.

pFILEINFO pFileInfo

Pointer to a FILEINFO structure. This structure may contain file information used in loading an image, or it may be updated with information about the file being loaded.

If nothing is known about the file, pass NULL for this parameter, or declare a variable of type FILEINFO and set the FILEINFO.Flags to 0, then pass the address of the FILEINFO structure in this parameter. In this case, if the address of a FILEINFO structure is passed, the FILEINFO structure will be updated with the results of L_FileInfo.

If only the file type is known, set pFileInfo.Format to the file type and set pFileInfo.Flags to FILEINFO_FORMATVALID. This can also be done if L_FileInfo has been called previously, but values that affect the size of the image loaded have been changed (for example, by calling L_SetPCDResolution or L_SetWMFResolution). In this case the FILEINFO structure pointed to by pFileInfo will be updated with the results of L_FileInfo.

Some file formats do not contain a well-defined file signature. This is especially true for document file formats (TXT, PST, etc). LEADTOOLS can still detect the file format using the filename extension (ex. ".PST"). However, when loading files from memory the filename extension is not available. To provide this function with a filename extension, set pFileInfo.Name to the image file's name with extension and pFileInfo.Flags to FILEINFO_NAMEVALID when loading from memory.

If L_FileInfo has been called prior to calling this function, and no changes have been made to the contents of the structure filled by L_FileInfo, then the address of the filled FILEINFO structure can be passed for this parameter. In this case, the FILEINFO.Flags member should be set to FILEINFO_INFOVALID. The L_FileInfo function will set the FILEINFO.Flags to FILEINFO_INFOVALID. In this case the load will be faster since this function does not have to query the file filters for the file type.

Note: Local variables are not initialized (since they are placed on the stack). So if you have a FILEINFO structure as a local variable, the value of its Flags parameter is undefined, possibly having FILEINFO_INFOVALID or FILEINFO_FORMATVALID set. That is why it is important to initialize FILEINFO.Flags before passing the address of the FILEINFO structure to the function.

Returns

Comments

Support for 12- and 16-bit grayscale images is only available in Document and Medical Imaging toolkits.

The callback function can display the image to the screen, write to a file, or do other useful things.

This function will create a buffer and fill it with the actual image data. Once the buffer is full, the callback function is called.

Before calling this function, you may need to get or set file information, such as the page number of a multipage file. Refer to Getting and Setting File Information.

This function cannot be used in combination with L_RedirectIO.

Notes:

• Redirected IO is not supported for some file formats. For more information, refer to File Formats for Which Redirected IO is Not Supported.

• More options are available in the LOADFILEOPTION structure.

• You should never pass an uninitialized FILEINFO structure to this function.

Required DLLs and Libraries

• LTFIL
• File format DLLs
• For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Platforms

Win32, x64, Linux.

See Also

Functions

• L_LoadBitmapMemory
• L_LoadBitmapMemory
• L_LoadMemory
• L_SetWMFResolution
• L_SetLoadInfoCallback
• L_DlgOpen
• L_CreatePanWindow
• L_SetLoadResolution
• L_SetPCDResolution
• For Vector files:
• L_2DGetViewMode
• L_2DGetViewPort
• L_2DSetViewMode
• L_2DSetViewPort

Topics

• Raster Image Functions: Loading Files
• Raster Image Functions: Redirecting Input and Output
• Raster Image Functions: Input and Output
• Loading and Saving Images
• Using a PanWindow
• For a list of functions that utilize the LOADFILEOPTION or SAVEFILEOPTION structures, refer to the Usage section of their documentation.

Example

For complete sample code, refer to the MEMORYCB example.
This example loads a temporary bitmap, saves it as a file in memory, then loads the memory-resident file into the global bitmap handle.
It uses L_LoadMemory with a callback function to implement a paint-while-load feature. Refer to the FILEREADCALLBACK function to see how the callback function paints the image data.

/* Structure used for the callback function's user data */ 
typedef struct tagIMAGECBPARM 
{ 
   HWND hwnd;     /* Current window                        */ 
   HDC  hdc;      /* Device context for the current window */ 
} IMAGECBPARM; 
 
static L_INT EXT_CALLBACK LoadImageCB(pFILEINFO     pFileInfo, 
                                      pBITMAPHANDLE pBitmap, 
                                      L_UCHAR     * pBuffer, 
                                      L_UINT        uFlags, 
                                      L_INT         nRow, 
                                      L_INT         nLines, 
                                      L_VOID      * pUserData) 
{ 
   static RECT rLeadSource; 
   static RECT rLeadDest; 
   IMAGECBPARM *pData = (IMAGECBPARM*)pUserData; 
 
   /* If this is the first call (row 0), select and realize the palette */ 
   if((uFlags & FILEREAD_FIRSTPASS) && (uFlags & FILEREAD_FIRSTROW) ) 
   { 
      /* Set the source rectangle to use the whole bitmap */ 
      SetRect(&rLeadSource, 0, 0, pFileInfo->Width, pFileInfo->Height); 
      /* Set the dest rectangle to use the whole client area */ 
      GetClientRect(pData->hwnd, &rLeadDest); 
   } 
 
   /* Paint the buffer to the specified device context */ 
   L_PaintDCBuffer( pData->hdc, /* Device context - from function parameter */ 
                    pBitmap, /* Bitmap handle - from function parameter */ 
                    &rLeadSource, /* Source rect - set globally in WM_CREATE */ 
                    &rLeadSource, /* Source clip rect - same as source rect */ 
                    &rLeadDest, /* Destination rect - set globally in WM_CREATE */ 
                    &rLeadDest, /* Destination clip rect - same as destination rect */ 
                    SRCCOPY, /* ROP code for normal painting */  
                    pBuffer, /* Input buffer - from function parameter */  
                    nRow, /* First row in the buffer - from function parameter */  
                   (uFlags & FILEREAD_COMPRESSED) ? -nLines : nLines ); 
   return( SUCCESS ); 
} 
 
L_INT LoadMemoryExample(HWND hWnd) 
{ 
   L_INT nRet;  
   BITMAPHANDLE TmpBitmap;       /* Bitmap handle for the initial image */ 
   HGLOBAL hFileInMemory=NULL;   /* Memory handle                       */ 
   L_SIZE_T uMemSize;            /* Size of the data in memory          */ 
   L_UCHAR *pData;               /* Pointer to the data in memory       */ 
   static IMAGECBPARM UserData;  /* Structure used for the callback function's user data */ 
   FILEREADCALLBACK lpfnCallBack; 
 
   /* Load a bitmap at its own bits per pixel  */ 
   nRet = L_LoadBitmap (MAKE_IMAGE_PATH(TEXT("ImageProcessingDemo\\Image3.cmp")), &TmpBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Save the image as a CMP file in memory */ 
   nRet = L_SaveBitmapMemory(&hFileInMemory, &TmpBitmap, FILE_CMP, 24, QS, &uMemSize, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Free the temporary bitmap */ 
   L_FreeBitmap(&TmpBitmap); 
 
   /* Get the pointer to the memory-resident file */ 
   pData = (L_UCHAR *) GlobalLock (hFileInMemory); 
 
   /* Set the user data used for the callback in the nRet = L_LoadFile function */ 
   UserData.hwnd = hWnd;         /* Current window */ 
   UserData.hdc = GetDC( hWnd ); /* Device context for the current window */ 
 
   /* Set the callback function for the L_LoadFile function.*/ 
   lpfnCallBack = (FILEREADCALLBACK)LoadImageCB; 
 
   /* Load the file, calling lpfnCallBack to paint the bitmap. */ 
   nRet = L_LoadMemory(pData, 
                      &TmpBitmap, sizeof(BITMAPHANDLE), 
                      0, 
                      ORDER_BGR, 
                      LOADFILE_ALLOCATE |  LOADFILE_STORE, 
                      lpfnCallBack, 
                      &UserData, 
                      uMemSize, 
                      NULL, NULL); 
   if(nRet != SUCCESS) 
      return nRet; 
 
   /* Clean up */ 
   GlobalUnlock (hFileInMemory); 
   GlobalFree (hFileInMemory); 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &TmpBitmap, FILE_BMP, 24, 0, NULL); 
   L_FreeBitmap(&TmpBitmap); 
 
   if(nRet != SUCCESS) 
      return nRet; 
   return SUCCESS; 
} 
 
/*******************************************************************************/