Alpha-Blended-BMP => the easy way

[Antonio Linares]

Got it !!!

Please add this function in FWH\source\winapi\dibbmp.c

Code: Select all  Expand view

CLIPPER HASALPHA( PARAMS ) // hBitmap --> lYesNo
{
   HANDLE hDib = DibFromBitmap( ( HBITMAP ) _parnl( 1 ), 0, 0,
                                ( HPALETTE ) _parnl( 2 ) );
   BOOL bAlphaChannel = FALSE;
           
   if( hDib )
   {
      LPBITMAPINFO lpbmi = ( LPBITMAPINFO ) GlobalLock( hDib );
      unsigned char * uc = ( LPBYTE ) lpbmi + ( WORD ) lpbmi->bmiHeader.biSize + PaletteSize( lpbmi );
      unsigned long ul;

      for( ul = 0; ul < lpbmi->bmiHeader.biSizeImage; ul += 4 )
         if( uc[ ul + 3 ] != 0 )
            bAlphaChannel = TRUE;    

      GlobalUnlock( hDib );
   }
   
   _retl( bAlphaChannel );
}        
 

[Antonio Linares]

Here you have a self contained working example. I appreciate your feedback testing different bitmaps with/without alpha channel, thanks!

test.prg

Code: Select all  Expand view

#include "FiveWin.ch"

function Main()

   local oBmp

   // DEFINE BITMAP oBmp FILENAME "c:\fwh\bitmaps\arrow.bmp" // No alpha

   DEFINE BITMAP oBmp FILENAME "c:\fwh\bitmaps\AlphaBmp\world.bmp" // with alpha

   MsgInfo( HasAlpha( oBmp:hBitmap ) )

   oBmp:End()

return nil

#pragma BEGINDUMP

#include <windows.h>
#include <hbapi.h>

WORD DibNumColors( void * pv );
HANDLE DibFromBitmap( HBITMAP, DWORD, WORD, HPALETTE );

static WORD PaletteSize( void * pv )
{
    LPBITMAPINFOHEADER lpbi = ( LPBITMAPINFOHEADER ) pv;
    WORD NumColors = DibNumColors( lpbi );

    if( lpbi->biSize == sizeof( BITMAPCOREHEADER ) )
       return ( WORD )( NumColors * sizeof( RGBTRIPLE ) );
    else
       return ( WORD )( NumColors * sizeof( RGBQUAD ) );
}

HB_FUNC( HASALPHA ) // hBitmap --> lYesNo
{
   HANDLE hDib = DibFromBitmap( ( HBITMAP ) hb_parnl( 1 ), 0, 0,
                                ( HPALETTE ) hb_parnl( 2 ) );
   BOOL bAlphaChannel = FALSE;
           
   if( hDib )
   {
      LPBITMAPINFO lpbmi = ( LPBITMAPINFO ) GlobalLock( hDib );
      unsigned char * uc = ( LPBYTE ) lpbmi + ( WORD ) lpbmi->bmiHeader.biSize + PaletteSize( lpbmi );
      unsigned long ul;

      for( ul = 0; ul < lpbmi->bmiHeader.biSizeImage; ul += 4 )
         if( uc[ ul + 3 ] != 0 )
            bAlphaChannel = TRUE;    

      GlobalUnlock( hDib );
   }
   
   hb_retl( bAlphaChannel );
}        

#pragma ENDDUMP
 

[nageswaragunupudi]

Congratulations that you finally got it.
Here is a small program using the above code to check all bitmap files in any selected folder and show which bitmaps have alpha channel and which do not.

Code: Select all  Expand view

#include "FiveWin.ch"

function Main()

   local cDir  := cGetDir( "Bitmap Directory", "c:\fwh\bitmaps" )
   local aDir, aAlpha   := {}
   local n, oBmp

   aDir     := Directory( cDir + "\*.bmp" )
   aEval( aDir, { |a| AAdd( aAlpha,  { cDir + "\" + a[ 1 ], "no alpha" } ) } )

   for n := 1 to Len( aAlpha )
      DEFINE BITMAP oBmp FILENAME aAlpha[ n ][ 1 ]
      if HasAlpha( oBmp:hBitmap )
         aAlpha[ n ][ 2 ]  := "HAS ALPHA"
      endif
      oBmp:End()
   next n
   xbrowse( aAlpha, cDir )


return nil


#pragma BEGINDUMP

#include <windows.h>
#include <hbapi.h>

WORD DibNumColors( void * pv );
HANDLE DibFromBitmap( HBITMAP, DWORD, WORD, HPALETTE );

static WORD PaletteSize( void * pv )
{
    LPBITMAPINFOHEADER lpbi = ( LPBITMAPINFOHEADER ) pv;
    WORD NumColors = DibNumColors( lpbi );

    if( lpbi->biSize == sizeof( BITMAPCOREHEADER ) )
       return ( WORD )( NumColors * sizeof( RGBTRIPLE ) );
    else
       return ( WORD )( NumColors * sizeof( RGBQUAD ) );
}

HB_FUNC( HASALPHA ) // hBitmap --> lYesNo
{
   HANDLE hDib = DibFromBitmap( ( HBITMAP ) hb_parnl( 1 ), 0, 0,
                                ( HPALETTE ) hb_parnl( 2 ) );
   BOOL bAlphaChannel = FALSE;

   if( hDib )
   {
      LPBITMAPINFO lpbmi = ( LPBITMAPINFO ) GlobalLock( hDib );
      unsigned char * uc = ( LPBYTE ) lpbmi + ( WORD ) lpbmi->bmiHeader.biSize + PaletteSize( lpbmi );
      unsigned long ul;

      for( ul = 0; ul < lpbmi->bmiHeader.biSizeImage; ul += 4 )
         if( uc[ ul + 3 ] != 0 )
            bAlphaChannel = TRUE;

      GlobalUnlock( hDib );
   }

   hb_retl( bAlphaChannel );
}


#pragma ENDDUMP

Compile run and see the results in xbrowse for all bitmaps

[Antonio Linares]

We can optimize HasAlpha() this way:

for( ul = 0; ul < lpbmi->bmiHeader.biSizeImage && ! bAlphaChannel; ul += 4 )

so there is no need to step through the whole array of bytes, once we find one that matches what we are looking for

[anserkk]

Dear Mr.Antonio & Mr.Nageshwara Rao,

I have tested my Application's Images folder wich contains BMP's with and without AlphaChannels and the new function HasAlpha is working perfectly.

I tried to upload a screen snapshot using Imageshack but right now here unable to upload using ImageShack. Don't know the reason. After browsing the pic and click upload, ImageShack say's "no files uploaded"

Anyway HasAlpha is working perfectly

Regards

Anser