src/common/imagpng.cpp

   1 /////////////////////////////////////////////////////////////////////////////
   2 // Name:        src/common/imagepng.cpp
   3 // Purpose:     wxImage PNG handler
   4 // Author:      Robert Roebling
   5 // RCS-ID:      $Id$
   6 // Copyright:   (c) Robert Roebling
   7 // Licence:     wxWindows licence
   8 /////////////////////////////////////////////////////////////////////////////
   9
  10 // ============================================================================
  11 // declarations
  12 // ============================================================================
  13
  14 // ----------------------------------------------------------------------------
  15 // headers
  16 // ----------------------------------------------------------------------------
  17
  18 // For compilers that support precompilation, includes "wx.h".
  19 #include "wx/wxprec.h"
  20
  21 #ifdef __BORLANDC__
  22     #pragma hdrstop
  23 #endif
  24
  25 #if wxUSE_IMAGE && wxUSE_LIBPNG
  26
  27 #include "wx/imagpng.h"
  28
  29 #ifndef WX_PRECOMP
  30     #include "wx/log.h"
  31     #include "wx/app.h"
  32     #include "wx/bitmap.h"
  33     #include "wx/module.h"
  34 #endif
  35
  36 #include "png.h"
  37 #include "wx/filefn.h"
  38 #include "wx/wfstream.h"
  39 #include "wx/intl.h"
  40
  41 // For memcpy
  42 #include <string.h>
  43
  44 #ifdef __SALFORDC__
  45 #ifdef FAR
  46 #undef FAR
  47 #endif
  48 #endif
  49
  50 // ----------------------------------------------------------------------------
  51 // constants
  52 // ----------------------------------------------------------------------------
  53
  54 // image can not have any transparent pixels at all, have only 100% opaque
  55 // and/or 100% transparent pixels in which case a simple mask is enough to
  56 // store this information in wxImage or have a real alpha channel in which case
  57 // we need to have it in wxImage as well
  58 enum Transparency
  59 {
  60     Transparency_None,
  61     Transparency_Mask,
  62     Transparency_Alpha
  63 };
  64
  65 // ----------------------------------------------------------------------------
  66 // local functions
  67 // ----------------------------------------------------------------------------
  68
  69 // return the kind of transparency needed for this image assuming that it does
  70 // have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
  71 static Transparency
  72 CheckTransparency(unsigned char **lines,
  73                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
  74                   size_t numColBytes);
  75
  76 // init the alpha channel for the image and fill it with 1s up to (x, y)
  77 static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);
  78
  79 // find a free colour for the mask in the PNG data array
  80 static void
  81 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
  82                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);
  83
  84 // is the pixel with this value of alpha a fully opaque one?
  85 static inline
  86 bool IsOpaque(unsigned char a)
  87 {
  88     return a == 0xff;
  89 }
  90
  91 // is the pixel with this value of alpha a fully transparent one?
  92 static inline
  93 bool IsTransparent(unsigned char a)
  94 {
  95     return !a;
  96 }
  97
  98 // ============================================================================
  99 // wxPNGHandler implementation
 100 // ============================================================================
 101
 102 IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
 103
 104 #if wxUSE_STREAMS
 105
 106 #ifndef PNGLINKAGEMODE
 107     #if defined(__WATCOMC__) && ( defined(__WXMSW__) || defined(__WXMGL__) )
 108         // we need an explicit cdecl for Watcom, at least according to
 109         //
 110         // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
 111         //
 112         // more testing is needed for this however, please remove this comment
 113         // if you can confirm that my fix works with Watcom 11
 114         #define PNGLINKAGEMODE cdecl
 115     #else
 116         #define PNGLINKAGEMODE LINKAGEMODE
 117     #endif
 118 #endif
 119
 120
 121 // VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
 122 //     First, let me describe what's the problem: libpng uses jmp_buf in
 123 //     its png_struct structure. Unfortunately, this structure is
 124 //     compiler-specific and may vary in size, so if you use libpng compiled
 125 //     as DLL with another compiler than the main executable, it may not work
 126 //     (this is for example the case with wxMGL port and SciTech MGL library
 127 //     that provides custom runtime-loadable libpng implementation with jmpbuf
 128 //     disabled altogether). Luckily, it is still possible to use setjmp() &
 129 //     longjmp() as long as the structure is not part of png_struct.
 130 //
 131 //     Sadly, there's no clean way to attach user-defined data to png_struct.
 132 //     There is only one customizable place, png_struct.io_ptr, which is meant
 133 //     only for I/O routines and is set with png_set_read_fn or
 134 //     png_set_write_fn. The hacky part is that we use io_ptr to store
 135 //     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.
 136
 137 struct wxPNGInfoStruct
 138 {
 139     jmp_buf jmpbuf;
 140     bool verbose;
 141
 142     union
 143     {
 144         wxInputStream  *in;
 145         wxOutputStream *out;
 146     } stream;
 147 };
 148
 149 #define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))
 150
 151 // ----------------------------------------------------------------------------
 152 // helper functions
 153 // ----------------------------------------------------------------------------
 154
 155 extern "C"
 156 {
 157
 158 void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
 159                                           png_size_t length )
 160 {
 161     WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 162 }
 163
 164 void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
 165                                           png_size_t length )
 166 {
 167     WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 168 }
 169
 170 void
 171 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 172 {
 173     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 174     if ( !info || info->verbose )
 175         wxLogWarning( wxString::FromAscii(message) );
 176 }
 177
 178 // from pngerror.c
 179 // so that the libpng doesn't send anything on stderr
 180 void
 181 PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 182 {
 183     wx_png_warning(NULL, message);
 184
 185     // we're not using libpng built-in jump buffer (see comment before
 186     // wxPNGInfoStruct above) so we have to return ourselves, otherwise libpng
 187     // would just abort
 188     longjmp(WX_PNG_INFO(png_ptr)->jmpbuf, 1);
 189 }
 190
 191 } // extern "C"
 192
 193 // ----------------------------------------------------------------------------
 194 // LoadFile() helpers
 195 // ----------------------------------------------------------------------------
 196
 197 // determine the kind of transparency we need for this image: if the only alpha
 198 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 199 // create a mask for it, we should be ok with a simple mask but otherwise we
 200 // need a full blown alpha channel in wxImage
 201 //
 202 // parameters:
 203 //      lines           raw PNG data
 204 //      x, y            starting position
 205 //      w, h            size of the image
 206 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 207 //                      (NB: alpha always follows the colour bytes)
 208 Transparency
 209 CheckTransparency(unsigned char **lines,
 210                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 211                   size_t numColBytes)
 212 {
 213     // suppose that a mask will suffice and check all the remaining alpha
 214     // values to see if it does
 215     for ( ; y < h; y++ )
 216     {
 217         // each pixel is numColBytes+1 bytes, offset into the current line by
 218         // the current x position
 219         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 220
 221         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 222         {
 223             // skip the grey or colour byte(s)
 224             ptr += numColBytes;
 225
 226             unsigned char a2 = *ptr++;
 227
 228             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 229             {
 230                 // not fully opaque nor fully transparent, hence need alpha
 231                 return Transparency_Alpha;
 232             }
 233         }
 234
 235         // during the next loop iteration check all the pixels in the row
 236         x = 0;
 237     }
 238
 239     // mask will be enough
 240     return Transparency_Mask;
 241 }
 242
 243 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 244 {
 245     // create alpha channel
 246     image->SetAlpha();
 247
 248     unsigned char *alpha = image->GetAlpha();
 249
 250     // set alpha for the pixels we had so far
 251     png_uint_32 end = y * image->GetWidth() + x;
 252     for ( png_uint_32 i = 0; i < end; i++ )
 253     {
 254         // all the previous pixels were opaque
 255         *alpha++ = 0xff;
 256     }
 257
 258     return alpha;
 259 }
 260
 261 void
 262 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 263                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 264 {
 265     // choosing the colour for the mask is more
 266     // difficult: we need to iterate over the entire
 267     // image for this in order to choose an unused
 268     // colour (this is not very efficient but what else
 269     // can we do?)
 270     wxImageHistogram h;
 271     unsigned nentries = 0;
 272     unsigned char r2, g2, b2;
 273     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 274     {
 275         const unsigned char *p = lines[y2];
 276         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 277         {
 278             r2 = *p++;
 279             g2 = *p++;
 280             b2 = *p++;
 281
 282             wxImageHistogramEntry&
 283                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 284
 285             if ( entry.value++ == 0 )
 286                 entry.index = nentries++;
 287         }
 288     }
 289
 290     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 291     {
 292         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 293
 294         // use a fixed mask colour and we'll fudge
 295         // the real pixels with this colour (see
 296         // below)
 297         rMask = 0xfe;
 298         gMask = 0;
 299         bMask = 0xff;
 300     }
 301 }
 302
 303 // ----------------------------------------------------------------------------
 304 // reading PNGs
 305 // ----------------------------------------------------------------------------
 306
 307 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 308 {
 309     unsigned char hdr[4];
 310
 311     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 312         return false;
 313
 314     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 315 }
 316
 317 // convert data from RGB to wxImage format
 318 static
 319 void CopyDataFromPNG(wxImage *image,
 320                      unsigned char **lines,
 321                      png_uint_32 width,
 322                      png_uint_32 height,
 323                      int color_type)
 324 {
 325     Transparency transparency = Transparency_None;
 326
 327     // only non NULL if transparency == Transparency_Alpha
 328     unsigned char *alpha = NULL;
 329
 330     // RGB of the mask colour if transparency == Transparency_Mask
 331     // (but init them anyhow to avoid compiler warnings)
 332     unsigned char rMask = 0,
 333                   gMask = 0,
 334                   bMask = 0;
 335
 336     unsigned char *ptrDst = image->GetData();
 337     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 338     {
 339         // grey image: GAGAGA... where G == grey component and A == alpha
 340         for ( png_uint_32 y = 0; y < height; y++ )
 341         {
 342             const unsigned char *ptrSrc = lines[y];
 343             for ( png_uint_32 x = 0; x < width; x++ )
 344             {
 345                 unsigned char g = *ptrSrc++;
 346                 unsigned char a = *ptrSrc++;
 347
 348                 // the first time we encounter a transparent pixel we must
 349                 // decide about what to do about them
 350                 if ( !IsOpaque(a) && transparency == Transparency_None )
 351                 {
 352                     // we'll need at least the mask for this image and
 353                     // maybe even full alpha channel info: the former is
 354                     // only enough if we have alpha values of 0 and 0xff
 355                     // only, otherwisewe need the latter
 356                     transparency = CheckTransparency
 357                                    (
 358                                         lines,
 359                                         x, y,
 360                                         width, height,
 361                                         1
 362                                    );
 363
 364                     if ( transparency == Transparency_Mask )
 365                     {
 366                         // let's choose this colour for the mask: this is
 367                         // not a problem here as all the other pixels are
 368                         // grey, i.e. R == G == B which is not the case for
 369                         // this one so no confusion is possible
 370                         rMask = 0xff;
 371                         gMask = 0;
 372                         bMask = 0xff;
 373                     }
 374                     else // transparency == Transparency_Alpha
 375                     {
 376                         alpha = InitAlpha(image, x, y);
 377                     }
 378                 }
 379
 380                 switch ( transparency )
 381                 {
 382                     case Transparency_Mask:
 383                         if ( IsTransparent(a) )
 384                         {
 385                             *ptrDst++ = rMask;
 386                             *ptrDst++ = bMask;
 387                             *ptrDst++ = gMask;
 388                             break;
 389                         }
 390                         // else: !transparent
 391
 392                         // must be opaque then as otherwise we shouldn't be
 393                         // using the mask at all
 394                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 395
 396                         // fall through
 397
 398                     case Transparency_Alpha:
 399                         if ( alpha )
 400                             *alpha++ = a;
 401                         // fall through
 402
 403                     case Transparency_None:
 404                         *ptrDst++ = g;
 405                         *ptrDst++ = g;
 406                         *ptrDst++ = g;
 407                         break;
 408                 }
 409             }
 410         }
 411     }
 412     else // colour image: RGBRGB...
 413     {
 414         for ( png_uint_32 y = 0; y < height; y++ )
 415         {
 416             const unsigned char *ptrSrc = lines[y];
 417             for ( png_uint_32 x = 0; x < width; x++ )
 418             {
 419                 unsigned char r = *ptrSrc++;
 420                 unsigned char g = *ptrSrc++;
 421                 unsigned char b = *ptrSrc++;
 422                 unsigned char a = *ptrSrc++;
 423
 424                 // the logic here is the same as for the grey case except
 425                 // where noted
 426                 if ( !IsOpaque(a) && transparency == Transparency_None )
 427                 {
 428                     transparency = CheckTransparency
 429                                    (
 430                                         lines,
 431                                         x, y,
 432                                         width, height,
 433                                         3
 434                                    );
 435
 436                     if ( transparency == Transparency_Mask )
 437                     {
 438                         FindMaskColour(lines, width, height,
 439                                        rMask, gMask, bMask);
 440                     }
 441                     else // transparency == Transparency_Alpha
 442                     {
 443                         alpha = InitAlpha(image, x, y);
 444                     }
 445
 446                 }
 447
 448                 switch ( transparency )
 449                 {
 450                     case Transparency_Mask:
 451                         if ( IsTransparent(a) )
 452                         {
 453                             *ptrDst++ = rMask;
 454                             *ptrDst++ = bMask;
 455                             *ptrDst++ = gMask;
 456                             break;
 457                         }
 458                         else // !transparent
 459                         {
 460                             // must be opaque then as otherwise we shouldn't be
 461                             // using the mask at all
 462                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 463
 464                             // if we couldn't find a unique colour for the
 465                             // mask, we can have real pixels with the same
 466                             // value as the mask and it's better to slightly
 467                             // change their colour than to make them
 468                             // transparent
 469                             if ( r == rMask && g == gMask && b == bMask )
 470                             {
 471                                 r++;
 472                             }
 473                         }
 474
 475                         // fall through
 476
 477                     case Transparency_Alpha:
 478                         if ( alpha )
 479                             *alpha++ = a;
 480                         // fall through
 481
 482                     case Transparency_None:
 483                         *ptrDst++ = r;
 484                         *ptrDst++ = g;
 485                         *ptrDst++ = b;
 486                         break;
 487                 }
 488             }
 489         }
 490     }
 491
 492     if ( transparency == Transparency_Mask )
 493     {
 494         image->SetMaskColour(rMask, gMask, bMask);
 495     }
 496 }
 497
 498 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 499 // C++ object destruction is non-portable) - I don't see any dtors here
 500 #ifdef __VISUALC__
 501     #pragma warning(disable:4611)
 502 #endif /* VC++ */
 503
 504 bool
 505 wxPNGHandler::LoadFile(wxImage *image,
 506                        wxInputStream& stream,
 507                        bool verbose,
 508                        int WXUNUSED(index))
 509 {
 510     // VZ: as this function uses setjmp() the only fool-proof error handling
 511     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 512
 513     unsigned char **lines = NULL;
 514     png_infop info_ptr = (png_infop) NULL;
 515     wxPNGInfoStruct wxinfo;
 516
 517     png_uint_32 i, width, height = 0;
 518     int bit_depth, color_type, interlace_type;
 519
 520     wxinfo.verbose = verbose;
 521     wxinfo.stream.in = &stream;
 522
 523     image->Destroy();
 524
 525     png_structp png_ptr = png_create_read_struct
 526                           (
 527                             PNG_LIBPNG_VER_STRING,
 528                             (voidp) NULL,
 529                             wx_png_error,
 530                             wx_png_warning
 531                           );
 532     if (!png_ptr)
 533         goto error;
 534
 535     // NB: please see the comment near wxPNGInfoStruct declaration for
 536     //     explanation why this line is mandatory
 537     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 538
 539     info_ptr = png_create_info_struct( png_ptr );
 540     if (!info_ptr)
 541         goto error;
 542
 543     if (setjmp(wxinfo.jmpbuf))
 544         goto error;
 545
 546     png_read_info( png_ptr, info_ptr );
 547     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 548
 549     if (color_type == PNG_COLOR_TYPE_PALETTE)
 550         png_set_expand( png_ptr );
 551
 552     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 553     if (bit_depth < 8)
 554         png_set_expand( png_ptr );
 555
 556     png_set_strip_16( png_ptr );
 557     png_set_packing( png_ptr );
 558     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 559         png_set_expand( png_ptr );
 560     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 561
 562     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 563
 564     if (!image->Ok())
 565         goto error;
 566
 567     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 568     if ( !lines )
 569         goto error;
 570
 571     for (i = 0; i < height; i++)
 572     {
 573         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 574         {
 575             for ( unsigned int n = 0; n < i; n++ )
 576                 free( lines[n] );
 577             goto error;
 578         }
 579     }
 580
 581     png_read_image( png_ptr, lines );
 582     png_read_end( png_ptr, info_ptr );
 583     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 584
 585     // loaded successfully, now init wxImage with this data
 586     CopyDataFromPNG(image, lines, width, height, color_type);
 587
 588     for ( i = 0; i < height; i++ )
 589         free( lines[i] );
 590     free( lines );
 591
 592     return true;
 593
 594 error:
 595     if (verbose)
 596        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 597
 598     if ( image->Ok() )
 599     {
 600         image->Destroy();
 601     }
 602
 603     if ( lines )
 604     {
 605         for ( unsigned int n = 0; n < height; n++ )
 606             free( lines[n] );
 607
 608         free( lines );
 609     }
 610
 611     if ( png_ptr )
 612     {
 613         if ( info_ptr )
 614         {
 615             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 616             free(info_ptr);
 617         }
 618         else
 619             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 620     }
 621     return false;
 622 }
 623
 624 // ----------------------------------------------------------------------------
 625 // writing PNGs
 626 // ----------------------------------------------------------------------------
 627
 628 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 629 {
 630     wxPNGInfoStruct wxinfo;
 631
 632     wxinfo.verbose = verbose;
 633     wxinfo.stream.out = &stream;
 634
 635     png_structp png_ptr = png_create_write_struct
 636                           (
 637                             PNG_LIBPNG_VER_STRING,
 638                             NULL,
 639                             wx_png_error,
 640                             wx_png_warning
 641                           );
 642     if (!png_ptr)
 643     {
 644         if (verbose)
 645            wxLogError(_("Couldn't save PNG image."));
 646         return false;
 647     }
 648
 649     png_infop info_ptr = png_create_info_struct(png_ptr);
 650     if (info_ptr == NULL)
 651     {
 652         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 653         if (verbose)
 654            wxLogError(_("Couldn't save PNG image."));
 655         return false;
 656     }
 657
 658     if (setjmp(wxinfo.jmpbuf))
 659     {
 660         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 661         if (verbose)
 662            wxLogError(_("Couldn't save PNG image."));
 663         return false;
 664     }
 665
 666     // NB: please see the comment near wxPNGInfoStruct declaration for
 667     //     explanation why this line is mandatory
 668     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 669
 670     const int iColorType = image->HasOption(wxIMAGE_OPTION_PNG_FORMAT)
 671                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_FORMAT)
 672                             : wxPNG_TYPE_COLOUR;
 673     const int iBitDepth = image->HasOption(wxIMAGE_OPTION_PNG_BITDEPTH)
 674                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_BITDEPTH)
 675                             : 8;
 676
 677     wxASSERT_MSG( iBitDepth == 8 || iBitDepth == 16,
 678                     _T("PNG bit depth must be 8 or 16") );
 679
 680     bool bHasAlpha = image->HasAlpha();
 681     bool bHasMask = image->HasMask();
 682     bool bUseAlpha = bHasAlpha || bHasMask;
 683
 684     int iPngColorType;
 685     if ( iColorType==wxPNG_TYPE_COLOUR )
 686     {
 687         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_RGB_ALPHA
 688                                   : PNG_COLOR_TYPE_RGB;
 689     }
 690     else
 691     {
 692         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_GRAY_ALPHA
 693                                   : PNG_COLOR_TYPE_GRAY;
 694     }
 695
 696     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(),
 697                   iBitDepth, iPngColorType,
 698                   PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 699                   PNG_FILTER_TYPE_BASE);
 700
 701     int iElements;
 702     png_color_8 sig_bit;
 703
 704     if ( iPngColorType & PNG_COLOR_MASK_COLOR )
 705     {
 706         sig_bit.red =
 707         sig_bit.green =
 708         sig_bit.blue = (png_byte)iBitDepth;
 709         iElements = 3;
 710     }
 711     else // grey
 712     {
 713         sig_bit.gray = (png_byte)iBitDepth;
 714         iElements = 1;
 715     }
 716
 717     if ( iPngColorType & PNG_COLOR_MASK_ALPHA )
 718     {
 719         sig_bit.alpha = (png_byte)iBitDepth;
 720         iElements++;
 721     }
 722
 723     if ( iBitDepth == 16 )
 724         iElements *= 2;
 725
 726     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 727     png_write_info( png_ptr, info_ptr );
 728     png_set_shift( png_ptr, &sig_bit );
 729     png_set_packing( png_ptr );
 730
 731     unsigned char *
 732         data = (unsigned char *)malloc( image->GetWidth() * iElements );
 733     if ( !data )
 734     {
 735         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 736         return false;
 737     }
 738
 739     unsigned char *
 740         pAlpha = (unsigned char *)(bHasAlpha ? image->GetAlpha() : NULL);
 741     int iHeight = image->GetHeight();
 742     int iWidth = image->GetWidth();
 743
 744     unsigned char uchMaskRed = 0, uchMaskGreen = 0, uchMaskBlue = 0;
 745
 746     if ( bHasMask )
 747     {
 748         uchMaskRed = image->GetMaskRed();
 749         uchMaskGreen = image->GetMaskGreen();
 750         uchMaskBlue = image->GetMaskBlue();
 751     }
 752
 753     unsigned char *pColors = image->GetData();
 754
 755     for (int y = 0; y != iHeight; ++y)
 756     {
 757         unsigned char *pData = data;
 758         for (int x = 0; x != iWidth; x++)
 759         {
 760             unsigned char uchRed = *pColors++;
 761             unsigned char uchGreen = *pColors++;
 762             unsigned char uchBlue = *pColors++;
 763
 764             switch ( iColorType )
 765             {
 766                 default:
 767                     wxFAIL_MSG( _T("unknown wxPNG_TYPE_XXX") );
 768                     // fall through
 769
 770                 case wxPNG_TYPE_COLOUR:
 771                     *pData++ = uchRed;
 772                     if ( iBitDepth == 16 )
 773                         *pData++ = 0;
 774                     *pData++ = uchGreen;
 775                     if ( iBitDepth == 16 )
 776                         *pData++ = 0;
 777                     *pData++ = uchBlue;
 778                     if ( iBitDepth == 16 )
 779                         *pData++ = 0;
 780                     break;
 781
 782                 case wxPNG_TYPE_GREY:
 783                     {
 784                         // where do these coefficients come from? maybe we
 785                         // should have image options for them as well?
 786                         unsigned uiColor =
 787                             (unsigned) (76.544*(unsigned)uchRed +
 788                                         150.272*(unsigned)uchGreen +
 789                                         36.864*(unsigned)uchBlue);
 790
 791                         *pData++ = (unsigned char)((uiColor >> 8) & 0xFF);
 792                         if ( iBitDepth == 16 )
 793                             *pData++ = (unsigned char)(uiColor & 0xFF);
 794                     }
 795                     break;
 796
 797                 case wxPNG_TYPE_GREY_RED:
 798                     *pData++ = uchRed;
 799                     if ( iBitDepth == 16 )
 800                         *pData++ = 0;
 801                     break;
 802             }
 803
 804             if ( bUseAlpha )
 805             {
 806                 unsigned char uchAlpha = 255;
 807                 if ( bHasAlpha )
 808                     uchAlpha = *pAlpha++;
 809
 810                 if ( bHasMask )
 811                 {
 812                     if ( (uchRed == uchMaskRed)
 813                             && (uchGreen == uchMaskGreen)
 814                                 && (uchBlue == uchMaskBlue) )
 815                         uchAlpha = 0;
 816                 }
 817
 818                 *pData++ = uchAlpha;
 819                 if ( iBitDepth == 16 )
 820                     *pData++ = 0;
 821             }
 822         }
 823
 824         png_bytep row_ptr = data;
 825         png_write_rows( png_ptr, &row_ptr, 1 );
 826     }
 827
 828     free(data);
 829     png_write_end( png_ptr, info_ptr );
 830     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 831
 832     return true;
 833 }
 834
 835 #ifdef __VISUALC__
 836     #pragma warning(default:4611)
 837 #endif /* VC++ */
 838
 839 #endif  // wxUSE_STREAMS
 840
 841 #endif  // wxUSE_LIBPNG