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