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 #include "wx/palette.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 static const double INCHES_IN_METER = 39.3700787;
  67
  68 // ----------------------------------------------------------------------------
  69 // local functions
  70 // ----------------------------------------------------------------------------
  71
  72 // return the kind of transparency needed for this image assuming that it does
  73 // have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
  74 static Transparency
  75 CheckTransparency(unsigned char **lines,
  76                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
  77                   size_t numColBytes);
  78
  79 // init the alpha channel for the image and fill it with 1s up to (x, y)
  80 static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);
  81
  82 // find a free colour for the mask in the PNG data array
  83 static void
  84 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
  85                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);
  86
  87 // is the pixel with this value of alpha a fully opaque one?
  88 static inline
  89 bool IsOpaque(unsigned char a)
  90 {
  91     return a == 0xff;
  92 }
  93
  94 // is the pixel with this value of alpha a fully transparent one?
  95 static inline
  96 bool IsTransparent(unsigned char a)
  97 {
  98     return !a;
  99 }
 100
 101 // ============================================================================
 102 // wxPNGHandler implementation
 103 // ============================================================================
 104
 105 IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
 106
 107 #if wxUSE_STREAMS
 108
 109 #ifndef PNGLINKAGEMODE
 110     #ifdef __WATCOMC__
 111         // we need an explicit cdecl for Watcom, at least according to
 112         //
 113         // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
 114         //
 115         // more testing is needed for this however, please remove this comment
 116         // if you can confirm that my fix works with Watcom 11
 117         #define PNGLINKAGEMODE cdecl
 118     #else
 119         #define PNGLINKAGEMODE LINKAGEMODE
 120     #endif
 121 #endif
 122
 123
 124 // VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
 125 //     First, let me describe what's the problem: libpng uses jmp_buf in
 126 //     its png_struct structure. Unfortunately, this structure is
 127 //     compiler-specific and may vary in size, so if you use libpng compiled
 128 //     as DLL with another compiler than the main executable, it may not work
 129 //     (this is for example the case with wxMGL port and SciTech MGL library
 130 //     that provides custom runtime-loadable libpng implementation with jmpbuf
 131 //     disabled altogether). Luckily, it is still possible to use setjmp() &
 132 //     longjmp() as long as the structure is not part of png_struct.
 133 //
 134 //     Sadly, there's no clean way to attach user-defined data to png_struct.
 135 //     There is only one customizable place, png_struct.io_ptr, which is meant
 136 //     only for I/O routines and is set with png_set_read_fn or
 137 //     png_set_write_fn. The hacky part is that we use io_ptr to store
 138 //     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.
 139
 140 struct wxPNGInfoStruct
 141 {
 142     jmp_buf jmpbuf;
 143     bool verbose;
 144
 145     union
 146     {
 147         wxInputStream  *in;
 148         wxOutputStream *out;
 149     } stream;
 150 };
 151
 152 #define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))
 153
 154 // ----------------------------------------------------------------------------
 155 // helper functions
 156 // ----------------------------------------------------------------------------
 157
 158 extern "C"
 159 {
 160
 161 void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
 162                                           png_size_t length )
 163 {
 164     WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 165 }
 166
 167 void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
 168                                           png_size_t length )
 169 {
 170     WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 171 }
 172
 173 void
 174 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 175 {
 176     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 177     if ( !info || info->verbose )
 178         wxLogWarning( wxString::FromAscii(message) );
 179 }
 180
 181 // from pngerror.c
 182 // so that the libpng doesn't send anything on stderr
 183 void
 184 PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 185 {
 186     wx_png_warning(NULL, message);
 187
 188     // we're not using libpng built-in jump buffer (see comment before
 189     // wxPNGInfoStruct above) so we have to return ourselves, otherwise libpng
 190     // would just abort
 191     longjmp(WX_PNG_INFO(png_ptr)->jmpbuf, 1);
 192 }
 193
 194 } // extern "C"
 195
 196 // ----------------------------------------------------------------------------
 197 // LoadFile() helpers
 198 // ----------------------------------------------------------------------------
 199
 200 // determine the kind of transparency we need for this image: if the only alpha
 201 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 202 // create a mask for it, we should be ok with a simple mask but otherwise we
 203 // need a full blown alpha channel in wxImage
 204 //
 205 // parameters:
 206 //      lines           raw PNG data
 207 //      x, y            starting position
 208 //      w, h            size of the image
 209 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 210 //                      (NB: alpha always follows the colour bytes)
 211 Transparency
 212 CheckTransparency(unsigned char **lines,
 213                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 214                   size_t numColBytes)
 215 {
 216     // suppose that a mask will suffice and check all the remaining alpha
 217     // values to see if it does
 218     for ( ; y < h; y++ )
 219     {
 220         // each pixel is numColBytes+1 bytes, offset into the current line by
 221         // the current x position
 222         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 223
 224         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 225         {
 226             // skip the grey or colour byte(s)
 227             ptr += numColBytes;
 228
 229             unsigned char a2 = *ptr++;
 230
 231             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 232             {
 233                 // not fully opaque nor fully transparent, hence need alpha
 234                 return Transparency_Alpha;
 235             }
 236         }
 237
 238         // during the next loop iteration check all the pixels in the row
 239         x = 0;
 240     }
 241
 242     // mask will be enough
 243     return Transparency_Mask;
 244 }
 245
 246 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 247 {
 248     // create alpha channel
 249     image->SetAlpha();
 250
 251     unsigned char *alpha = image->GetAlpha();
 252
 253     // set alpha for the pixels we had so far
 254     png_uint_32 end = y * image->GetWidth() + x;
 255     for ( png_uint_32 i = 0; i < end; i++ )
 256     {
 257         // all the previous pixels were opaque
 258         *alpha++ = 0xff;
 259     }
 260
 261     return alpha;
 262 }
 263
 264 void
 265 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 266                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 267 {
 268     // choosing the colour for the mask is more
 269     // difficult: we need to iterate over the entire
 270     // image for this in order to choose an unused
 271     // colour (this is not very efficient but what else
 272     // can we do?)
 273     wxImageHistogram h;
 274     unsigned nentries = 0;
 275     unsigned char r2, g2, b2;
 276     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 277     {
 278         const unsigned char *p = lines[y2];
 279         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 280         {
 281             r2 = *p++;
 282             g2 = *p++;
 283             b2 = *p++;
 284             ++p; // jump over alpha
 285
 286             wxImageHistogramEntry&
 287                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 288
 289             if ( entry.value++ == 0 )
 290                 entry.index = nentries++;
 291         }
 292     }
 293
 294     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 295     {
 296         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 297
 298         // use a fixed mask colour and we'll fudge
 299         // the real pixels with this colour (see
 300         // below)
 301         rMask = 0xfe;
 302         gMask = 0;
 303         bMask = 0xff;
 304     }
 305 }
 306
 307 // ----------------------------------------------------------------------------
 308 // reading PNGs
 309 // ----------------------------------------------------------------------------
 310
 311 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 312 {
 313     unsigned char hdr[4];
 314
 315     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 316         return false;
 317
 318     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 319 }
 320
 321 // convert data from RGB to wxImage format
 322 static
 323 void CopyDataFromPNG(wxImage *image,
 324                      unsigned char **lines,
 325                      png_uint_32 width,
 326                      png_uint_32 height,
 327                      int color_type)
 328 {
 329     Transparency transparency = Transparency_None;
 330
 331     // only non NULL if transparency == Transparency_Alpha
 332     unsigned char *alpha = NULL;
 333
 334     // RGB of the mask colour if transparency == Transparency_Mask
 335     // (but init them anyhow to avoid compiler warnings)
 336     unsigned char rMask = 0,
 337                   gMask = 0,
 338                   bMask = 0;
 339
 340     unsigned char *ptrDst = image->GetData();
 341     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 342     {
 343         // grey image: GAGAGA... where G == grey component and A == alpha
 344         for ( png_uint_32 y = 0; y < height; y++ )
 345         {
 346             const unsigned char *ptrSrc = lines[y];
 347             for ( png_uint_32 x = 0; x < width; x++ )
 348             {
 349                 unsigned char g = *ptrSrc++;
 350                 unsigned char a = *ptrSrc++;
 351
 352                 // the first time we encounter a transparent pixel we must
 353                 // decide about what to do about them
 354                 if ( !IsOpaque(a) && transparency == Transparency_None )
 355                 {
 356                     // we'll need at least the mask for this image and
 357                     // maybe even full alpha channel info: the former is
 358                     // only enough if we have alpha values of 0 and 0xff
 359                     // only, otherwisewe need the latter
 360                     transparency = CheckTransparency
 361                                    (
 362                                         lines,
 363                                         x, y,
 364                                         width, height,
 365                                         1
 366                                    );
 367
 368                     if ( transparency == Transparency_Mask )
 369                     {
 370                         // let's choose this colour for the mask: this is
 371                         // not a problem here as all the other pixels are
 372                         // grey, i.e. R == G == B which is not the case for
 373                         // this one so no confusion is possible
 374                         rMask = 0xff;
 375                         gMask = 0;
 376                         bMask = 0xff;
 377                     }
 378                     else // transparency == Transparency_Alpha
 379                     {
 380                         alpha = InitAlpha(image, x, y);
 381                     }
 382                 }
 383
 384                 switch ( transparency )
 385                 {
 386                     case Transparency_Mask:
 387                         if ( IsTransparent(a) )
 388                         {
 389                             *ptrDst++ = rMask;
 390                             *ptrDst++ = gMask;
 391                             *ptrDst++ = bMask;
 392                             break;
 393                         }
 394                         // else: !transparent
 395
 396                         // must be opaque then as otherwise we shouldn't be
 397                         // using the mask at all
 398                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 399
 400                         // fall through
 401
 402                     case Transparency_Alpha:
 403                         if ( alpha )
 404                             *alpha++ = a;
 405                         // fall through
 406
 407                     case Transparency_None:
 408                         *ptrDst++ = g;
 409                         *ptrDst++ = g;
 410                         *ptrDst++ = g;
 411                         break;
 412                 }
 413             }
 414         }
 415     }
 416     else // colour image: RGBRGB...
 417     {
 418         for ( png_uint_32 y = 0; y < height; y++ )
 419         {
 420             const unsigned char *ptrSrc = lines[y];
 421             for ( png_uint_32 x = 0; x < width; x++ )
 422             {
 423                 unsigned char r = *ptrSrc++;
 424                 unsigned char g = *ptrSrc++;
 425                 unsigned char b = *ptrSrc++;
 426                 unsigned char a = *ptrSrc++;
 427
 428                 // the logic here is the same as for the grey case except
 429                 // where noted
 430                 if ( !IsOpaque(a) && transparency == Transparency_None )
 431                 {
 432                     transparency = CheckTransparency
 433                                    (
 434                                         lines,
 435                                         x, y,
 436                                         width, height,
 437                                         3
 438                                    );
 439
 440                     if ( transparency == Transparency_Mask )
 441                     {
 442                         FindMaskColour(lines, width, height,
 443                                        rMask, gMask, bMask);
 444                     }
 445                     else // transparency == Transparency_Alpha
 446                     {
 447                         alpha = InitAlpha(image, x, y);
 448                     }
 449
 450                 }
 451
 452                 switch ( transparency )
 453                 {
 454                     case Transparency_Mask:
 455                         if ( IsTransparent(a) )
 456                         {
 457                             *ptrDst++ = rMask;
 458                             *ptrDst++ = gMask;
 459                             *ptrDst++ = bMask;
 460                             break;
 461                         }
 462                         else // !transparent
 463                         {
 464                             // must be opaque then as otherwise we shouldn't be
 465                             // using the mask at all
 466                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 467
 468                             // if we couldn't find a unique colour for the
 469                             // mask, we can have real pixels with the same
 470                             // value as the mask and it's better to slightly
 471                             // change their colour than to make them
 472                             // transparent
 473                             if ( r == rMask && g == gMask && b == bMask )
 474                             {
 475                                 r++;
 476                             }
 477                         }
 478
 479                         // fall through
 480
 481                     case Transparency_Alpha:
 482                         if ( alpha )
 483                             *alpha++ = a;
 484                         // fall through
 485
 486                     case Transparency_None:
 487                         *ptrDst++ = r;
 488                         *ptrDst++ = g;
 489                         *ptrDst++ = b;
 490                         break;
 491                 }
 492             }
 493         }
 494     }
 495
 496     if ( transparency == Transparency_Mask )
 497     {
 498         image->SetMaskColour(rMask, gMask, bMask);
 499     }
 500 }
 501
 502 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 503 // C++ object destruction is non-portable) - I don't see any dtors here
 504 #ifdef __VISUALC__
 505     #pragma warning(disable:4611)
 506 #endif /* VC++ */
 507
 508 bool
 509 wxPNGHandler::LoadFile(wxImage *image,
 510                        wxInputStream& stream,
 511                        bool verbose,
 512                        int WXUNUSED(index))
 513 {
 514     // VZ: as this function uses setjmp() the only fool-proof error handling
 515     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 516
 517     unsigned char **lines = NULL;
 518     png_infop info_ptr = (png_infop) NULL;
 519     wxPNGInfoStruct wxinfo;
 520
 521     png_uint_32 i, width, height = 0;
 522     int bit_depth, color_type, interlace_type;
 523
 524     wxinfo.verbose = verbose;
 525     wxinfo.stream.in = &stream;
 526
 527     image->Destroy();
 528
 529     png_structp png_ptr = png_create_read_struct
 530                           (
 531                             PNG_LIBPNG_VER_STRING,
 532                             (voidp) NULL,
 533                             wx_png_error,
 534                             wx_png_warning
 535                           );
 536     if (!png_ptr)
 537         goto error;
 538
 539     // NB: please see the comment near wxPNGInfoStruct declaration for
 540     //     explanation why this line is mandatory
 541     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 542
 543     info_ptr = png_create_info_struct( png_ptr );
 544     if (!info_ptr)
 545         goto error;
 546
 547     if (setjmp(wxinfo.jmpbuf))
 548         goto error;
 549
 550     png_read_info( png_ptr, info_ptr );
 551     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 552
 553     if (color_type == PNG_COLOR_TYPE_PALETTE)
 554         png_set_expand( png_ptr );
 555
 556     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 557     if (bit_depth < 8)
 558         png_set_expand( png_ptr );
 559
 560     png_set_strip_16( png_ptr );
 561     png_set_packing( png_ptr );
 562     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 563         png_set_expand( png_ptr );
 564     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 565
 566     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 567
 568     if (!image->Ok())
 569         goto error;
 570
 571     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 572     if ( !lines )
 573         goto error;
 574
 575     for (i = 0; i < height; i++)
 576     {
 577         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 578         {
 579             for ( unsigned int n = 0; n < i; n++ )
 580                 free( lines[n] );
 581             goto error;
 582         }
 583     }
 584
 585     png_read_image( png_ptr, lines );
 586     png_read_end( png_ptr, info_ptr );
 587
 588 #if wxUSE_PALETTE
 589     if (color_type == PNG_COLOR_TYPE_PALETTE)
 590     {
 591         const size_t ncolors = info_ptr->num_palette;
 592         unsigned char* r = new unsigned char[ncolors];
 593         unsigned char* g = new unsigned char[ncolors];
 594         unsigned char* b = new unsigned char[ncolors];
 595
 596         for (size_t j = 0; j < ncolors; j++)
 597         {
 598             r[j] = info_ptr->palette[j].red;
 599             g[j] = info_ptr->palette[j].green;
 600             b[j] = info_ptr->palette[j].blue;
 601         }
 602
 603         image->SetPalette(wxPalette(ncolors, r, g, b));
 604         delete[] r;
 605         delete[] g;
 606         delete[] b;
 607     }
 608 #endif // wxUSE_PALETTE
 609
 610     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 611
 612     // loaded successfully, now init wxImage with this data
 613     CopyDataFromPNG(image, lines, width, height, color_type);
 614
 615     for ( i = 0; i < height; i++ )
 616         free( lines[i] );
 617     free( lines );
 618
 619     return true;
 620
 621 error:
 622     if (verbose)
 623        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 624
 625     if ( image->Ok() )
 626     {
 627         image->Destroy();
 628     }
 629
 630     if ( lines )
 631     {
 632         for ( unsigned int n = 0; n < height; n++ )
 633             free( lines[n] );
 634
 635         free( lines );
 636     }
 637
 638     if ( png_ptr )
 639     {
 640         if ( info_ptr )
 641         {
 642             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 643             free(info_ptr);
 644         }
 645         else
 646             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 647     }
 648     return false;
 649 }
 650
 651 // ----------------------------------------------------------------------------
 652 // writing PNGs
 653 // ----------------------------------------------------------------------------
 654
 655 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 656 {
 657     wxPNGInfoStruct wxinfo;
 658
 659     wxinfo.verbose = verbose;
 660     wxinfo.stream.out = &stream;
 661
 662     png_structp png_ptr = png_create_write_struct
 663                           (
 664                             PNG_LIBPNG_VER_STRING,
 665                             NULL,
 666                             wx_png_error,
 667                             wx_png_warning
 668                           );
 669     if (!png_ptr)
 670     {
 671         if (verbose)
 672            wxLogError(_("Couldn't save PNG image."));
 673         return false;
 674     }
 675
 676     png_infop info_ptr = png_create_info_struct(png_ptr);
 677     if (info_ptr == NULL)
 678     {
 679         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 680         if (verbose)
 681            wxLogError(_("Couldn't save PNG image."));
 682         return false;
 683     }
 684
 685     if (setjmp(wxinfo.jmpbuf))
 686     {
 687         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 688         if (verbose)
 689            wxLogError(_("Couldn't save PNG image."));
 690         return false;
 691     }
 692
 693     // NB: please see the comment near wxPNGInfoStruct declaration for
 694     //     explanation why this line is mandatory
 695     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 696
 697     const int iColorType = image->HasOption(wxIMAGE_OPTION_PNG_FORMAT)
 698                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_FORMAT)
 699                             : wxPNG_TYPE_COLOUR;
 700     const int iBitDepth = image->HasOption(wxIMAGE_OPTION_PNG_BITDEPTH)
 701                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_BITDEPTH)
 702                             : 8;
 703
 704     wxASSERT_MSG( iBitDepth == 8 || iBitDepth == 16,
 705                     _T("PNG bit depth must be 8 or 16") );
 706
 707     bool bHasAlpha = image->HasAlpha();
 708     bool bHasMask = image->HasMask();
 709     bool bUseAlpha = bHasAlpha || bHasMask;
 710
 711     int iPngColorType;
 712     if ( iColorType==wxPNG_TYPE_COLOUR )
 713     {
 714         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_RGB_ALPHA
 715                                   : PNG_COLOR_TYPE_RGB;
 716     }
 717     else
 718     {
 719         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_GRAY_ALPHA
 720                                   : PNG_COLOR_TYPE_GRAY;
 721     }
 722
 723     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(),
 724                   iBitDepth, iPngColorType,
 725                   PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 726                   PNG_FILTER_TYPE_BASE);
 727
 728     int iElements;
 729     png_color_8 sig_bit;
 730
 731     if ( iPngColorType & PNG_COLOR_MASK_COLOR )
 732     {
 733         sig_bit.red =
 734         sig_bit.green =
 735         sig_bit.blue = (png_byte)iBitDepth;
 736         iElements = 3;
 737     }
 738     else // grey
 739     {
 740         sig_bit.gray = (png_byte)iBitDepth;
 741         iElements = 1;
 742     }
 743
 744     if ( iPngColorType & PNG_COLOR_MASK_ALPHA )
 745     {
 746         sig_bit.alpha = (png_byte)iBitDepth;
 747         iElements++;
 748     }
 749
 750     if ( iBitDepth == 16 )
 751         iElements *= 2;
 752
 753     // save the image resolution if we have it
 754     int resX, resY;
 755     switch ( GetResolutionFromOptions(*image, &resX, &resY) )
 756     {
 757         case wxIMAGE_RESOLUTION_INCHES:
 758             resX *= INCHES_IN_METER;
 759             resY *= INCHES_IN_METER;
 760             break;
 761
 762         case wxIMAGE_RESOLUTION_CM:
 763             resX *= 100;
 764             resY *= 100;
 765             break;
 766
 767         case wxIMAGE_RESOLUTION_NONE:
 768             break;
 769
 770         default:
 771             wxFAIL_MSG( _T("unsupported image resolution units") );
 772     }
 773
 774     if ( resX && resY )
 775         png_set_pHYs( png_ptr, info_ptr, resX, resY, PNG_RESOLUTION_METER );
 776
 777     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 778     png_write_info( png_ptr, info_ptr );
 779     png_set_shift( png_ptr, &sig_bit );
 780     png_set_packing( png_ptr );
 781
 782     unsigned char *
 783         data = (unsigned char *)malloc( image->GetWidth() * iElements );
 784     if ( !data )
 785     {
 786         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 787         return false;
 788     }
 789
 790     unsigned char *
 791         pAlpha = (unsigned char *)(bHasAlpha ? image->GetAlpha() : NULL);
 792     int iHeight = image->GetHeight();
 793     int iWidth = image->GetWidth();
 794
 795     unsigned char uchMaskRed = 0, uchMaskGreen = 0, uchMaskBlue = 0;
 796
 797     if ( bHasMask )
 798     {
 799         uchMaskRed = image->GetMaskRed();
 800         uchMaskGreen = image->GetMaskGreen();
 801         uchMaskBlue = image->GetMaskBlue();
 802     }
 803
 804     unsigned char *pColors = image->GetData();
 805
 806     for (int y = 0; y != iHeight; ++y)
 807     {
 808         unsigned char *pData = data;
 809         for (int x = 0; x != iWidth; x++)
 810         {
 811             unsigned char uchRed = *pColors++;
 812             unsigned char uchGreen = *pColors++;
 813             unsigned char uchBlue = *pColors++;
 814
 815             switch ( iColorType )
 816             {
 817                 default:
 818                     wxFAIL_MSG( _T("unknown wxPNG_TYPE_XXX") );
 819                     // fall through
 820
 821                 case wxPNG_TYPE_COLOUR:
 822                     *pData++ = uchRed;
 823                     if ( iBitDepth == 16 )
 824                         *pData++ = 0;
 825                     *pData++ = uchGreen;
 826                     if ( iBitDepth == 16 )
 827                         *pData++ = 0;
 828                     *pData++ = uchBlue;
 829                     if ( iBitDepth == 16 )
 830                         *pData++ = 0;
 831                     break;
 832
 833                 case wxPNG_TYPE_GREY:
 834                     {
 835                         // where do these coefficients come from? maybe we
 836                         // should have image options for them as well?
 837                         unsigned uiColor =
 838                             (unsigned) (76.544*(unsigned)uchRed +
 839                                         150.272*(unsigned)uchGreen +
 840                                         36.864*(unsigned)uchBlue);
 841
 842                         *pData++ = (unsigned char)((uiColor >> 8) & 0xFF);
 843                         if ( iBitDepth == 16 )
 844                             *pData++ = (unsigned char)(uiColor & 0xFF);
 845                     }
 846                     break;
 847
 848                 case wxPNG_TYPE_GREY_RED:
 849                     *pData++ = uchRed;
 850                     if ( iBitDepth == 16 )
 851                         *pData++ = 0;
 852                     break;
 853             }
 854
 855             if ( bUseAlpha )
 856             {
 857                 unsigned char uchAlpha = 255;
 858                 if ( bHasAlpha )
 859                     uchAlpha = *pAlpha++;
 860
 861                 if ( bHasMask )
 862                 {
 863                     if ( (uchRed == uchMaskRed)
 864                             && (uchGreen == uchMaskGreen)
 865                                 && (uchBlue == uchMaskBlue) )
 866                         uchAlpha = 0;
 867                 }
 868
 869                 *pData++ = uchAlpha;
 870                 if ( iBitDepth == 16 )
 871                     *pData++ = 0;
 872             }
 873         }
 874
 875         png_bytep row_ptr = data;
 876         png_write_rows( png_ptr, &row_ptr, 1 );
 877     }
 878
 879     free(data);
 880     png_write_end( png_ptr, info_ptr );
 881     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 882
 883     return true;
 884 }
 885
 886 #ifdef __VISUALC__
 887     #pragma warning(default:4611)
 888 #endif /* VC++ */
 889
 890 #endif  // wxUSE_STREAMS
 891
 892 #endif  // wxUSE_LIBPNG