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