L_GetPNGTRNS

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#include "l_bitmap.h"

L_LTFIL_API L_UINT L_GetPNGTRNS (pData)

/* pointer to a buffer */

Gets the transparency data used by LEADTOOLS when loading PNG files.

Parameter	Description
pData	Pointer to a buffer to be updated with the transparency data used when loading PNG files.

Returns

0 or > 1	The length of the data buffer.
< 1	An error occurred. Refer to Return Codes.

Comments

This function supports1-bit to 8-bit PNG images.

To set the transparency data used when saving PNG files, use L_SetPNGTRNS function.

The transparency data obtained by this function is valid for the current thread.

Required DLLs and Libraries

LTFIL

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_SetPNGTRNS, L_SetBitmapAlpha, L_CreateMaskFromBitmapRgn, L_SetBitmapRgnFromMask
Topics:	Raster Image Functions: Loading Files
	Loading and Saving Images
	PNG Files and Transparency

Example

//This example gets PNG transparency data

#define MAKE_IMAGE_PATH(pFileName) TEXT("C:\\Users\\Public\\Documents\\LEADTOOLS Images\\")pFileName


L_INT GetPNGTRNSExample(L_VOID)
{
   L_INT nRet;
   BITMAPHANDLE Bitmap;

   // Load an image with or without transparency
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("LittleGFlyingAlpha.png")), &Bitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGRORGRAY, NULL, NULL);
   if( nRet != SUCCESS)
      return nRet;

   Bitmap.Flags.Transparency = TRUE;

   //Get the PNG transparency data
   L_UCHAR* pData = NULL;

   //Allocate memory for the transparency data buffer
   pData = (L_UCHAR *)malloc(256 * sizeof(L_UCHAR));
   memset(pData, 0, 256 * sizeof(L_UCHAR));

   // This will likely return 0 if we loaded an image without transparency
   nRet = L_GetPNGTRNS(pData);
   if(nRet == 0)
   {
      OutputDebugString(L_TEXT("No transparencey found!\n"));
   }

   //print out the transparency loaded from PNG
   L_TCHAR msg[200] = L_TEXT("");
   for (int i = 0; i < 256; i++)
   {
      wsprintf(msg, L_TEXT("pData[%d]: %d\t"), i, pData[i]);
      OutputDebugString(msg);
      if (((i+1)%4) == 0)
         OutputDebugString(L_TEXT("\n"));
   }

   //print out the palette
   for (int i = 0; i < 256; i++)
   {
      wsprintf(msg, L_TEXT("pPalette[%d]: %d\t"), i, Bitmap.pPalette[i]);
      OutputDebugString(msg);
      if (((i+1)%4) == 0)
         OutputDebugString(L_TEXT("\n"));
   }

   //change the alpha values and print out
   for (int i = 0; i < 256; i+=4)
   {
      // every four colors are 100%, 75%, 50%, and 0% transparent
      pData[i] = 0;
      pData[i + 1] = 64;
      pData[i + 2] = 128;
      pData[i + 3] = 255;
      wsprintf(msg, L_TEXT("pData[%d]: %d\tpData[%d]: %d\tpData[%d]: %d\tpData[%d]: %d\t\n"), i, pData[i], i + 1, pData[i + 1], i + 2, pData[i + 2], i + 3, pData[i + 3]);
      OutputDebugString(msg);
      if (((i+1)%4) == 0)
         OutputDebugString(L_TEXT("\n"));
   }

   // Set the transparency data and save the file
   nRet = L_SetPNGTRNS(pData, 256);
   free(pData);

   if(nRet != SUCCESS)
   {
      L_FreeBitmap(&Bitmap);
      return nRet;
   }

   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("output.png")), &Bitmap, FILE_PNG, 8, 0, NULL);
   L_FreeBitmap(&Bitmap);

   return nRet;
}