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__)
 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 // from pngerror.c
 172 // so that the libpng doesn't send anything on stderr
 173 void
 174 PNGLINKAGEMODE wx_png_error(png_structp WXUNUSED(png_ptr), png_const_charp message)
 175 {
 176     wxLogFatalError( wxString::FromAscii(message) );
 177 }
 178
 179 void
 180 PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 181 {
 182     wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
 183     if ( !info || info->verbose )
 184         wxLogWarning( wxString::FromAscii(message) );
 185 }
 186
 187 } // extern "C"
 188
 189 // ----------------------------------------------------------------------------
 190 // LoadFile() helpers
 191 // ----------------------------------------------------------------------------
 192
 193 // determine the kind of transparency we need for this image: if the only alpha
 194 // values it has are 0 (transparent) and 0xff (opaque) then we can simply
 195 // create a mask for it, we should be ok with a simple mask but otherwise we
 196 // need a full blown alpha channel in wxImage
 197 //
 198 // parameters:
 199 //      lines           raw PNG data
 200 //      x, y            starting position
 201 //      w, h            size of the image
 202 //      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
 203 //                      (NB: alpha always follows the colour bytes)
 204 Transparency
 205 CheckTransparency(unsigned char **lines,
 206                   png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
 207                   size_t numColBytes)
 208 {
 209     // suppose that a mask will suffice and check all the remaining alpha
 210     // values to see if it does
 211     for ( ; y < h; y++ )
 212     {
 213         // each pixel is numColBytes+1 bytes, offset into the current line by
 214         // the current x position
 215         unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));
 216
 217         for ( png_uint_32 x2 = x; x2 < w; x2++ )
 218         {
 219             // skip the grey or colour byte(s)
 220             ptr += numColBytes;
 221
 222             unsigned char a2 = *ptr++;
 223
 224             if ( !IsTransparent(a2) && !IsOpaque(a2) )
 225             {
 226                 // not fully opaque nor fully transparent, hence need alpha
 227                 return Transparency_Alpha;
 228             }
 229         }
 230
 231         // during the next loop iteration check all the pixels in the row
 232         x = 0;
 233     }
 234
 235     // mask will be enough
 236     return Transparency_Mask;
 237 }
 238
 239 unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
 240 {
 241     // create alpha channel
 242     image->SetAlpha();
 243
 244     unsigned char *alpha = image->GetAlpha();
 245
 246     // set alpha for the pixels we had so far
 247     png_uint_32 end = y * image->GetWidth() + x;
 248     for ( png_uint_32 i = 0; i < end; i++ )
 249     {
 250         // all the previous pixels were opaque
 251         *alpha++ = 0xff;
 252     }
 253
 254     return alpha;
 255 }
 256
 257 void
 258 FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
 259                unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
 260 {
 261     // choosing the colour for the mask is more
 262     // difficult: we need to iterate over the entire
 263     // image for this in order to choose an unused
 264     // colour (this is not very efficient but what else
 265     // can we do?)
 266     wxImageHistogram h;
 267     unsigned nentries = 0;
 268     unsigned char r2, g2, b2;
 269     for ( png_uint_32 y2 = 0; y2 < height; y2++ )
 270     {
 271         const unsigned char *p = lines[y2];
 272         for ( png_uint_32 x2 = 0; x2 < width; x2++ )
 273         {
 274             r2 = *p++;
 275             g2 = *p++;
 276             b2 = *p++;
 277
 278             wxImageHistogramEntry&
 279                 entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];
 280
 281             if ( entry.value++ == 0 )
 282                 entry.index = nentries++;
 283         }
 284     }
 285
 286     if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
 287     {
 288         wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));
 289
 290         // use a fixed mask colour and we'll fudge
 291         // the real pixels with this colour (see
 292         // below)
 293         rMask = 0xfe;
 294         gMask = 0;
 295         bMask = 0xff;
 296     }
 297 }
 298
 299 // ----------------------------------------------------------------------------
 300 // reading PNGs
 301 // ----------------------------------------------------------------------------
 302
 303 bool wxPNGHandler::DoCanRead( wxInputStream& stream )
 304 {
 305     unsigned char hdr[4];
 306
 307     if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
 308         return false;
 309
 310     return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
 311 }
 312
 313 // convert data from RGB to wxImage format
 314 static
 315 void CopyDataFromPNG(wxImage *image,
 316                      unsigned char **lines,
 317                      png_uint_32 width,
 318                      png_uint_32 height,
 319                      int color_type)
 320 {
 321     Transparency transparency = Transparency_None;
 322
 323     // only non NULL if transparency == Transparency_Alpha
 324     unsigned char *alpha = NULL;
 325
 326     // RGB of the mask colour if transparency == Transparency_Mask
 327     // (but init them anyhow to avoid compiler warnings)
 328     unsigned char rMask = 0,
 329                   gMask = 0,
 330                   bMask = 0;
 331
 332     unsigned char *ptrDst = image->GetData();
 333     if ( !(color_type & PNG_COLOR_MASK_COLOR) )
 334     {
 335         // grey image: GAGAGA... where G == grey component and A == alpha
 336         for ( png_uint_32 y = 0; y < height; y++ )
 337         {
 338             const unsigned char *ptrSrc = lines[y];
 339             for ( png_uint_32 x = 0; x < width; x++ )
 340             {
 341                 unsigned char g = *ptrSrc++;
 342                 unsigned char a = *ptrSrc++;
 343
 344                 // the first time we encounter a transparent pixel we must
 345                 // decide about what to do about them
 346                 if ( !IsOpaque(a) && transparency == Transparency_None )
 347                 {
 348                     // we'll need at least the mask for this image and
 349                     // maybe even full alpha channel info: the former is
 350                     // only enough if we have alpha values of 0 and 0xff
 351                     // only, otherwisewe need the latter
 352                     transparency = CheckTransparency
 353                                    (
 354                                         lines,
 355                                         x, y,
 356                                         width, height,
 357                                         1
 358                                    );
 359
 360                     if ( transparency == Transparency_Mask )
 361                     {
 362                         // let's choose this colour for the mask: this is
 363                         // not a problem here as all the other pixels are
 364                         // grey, i.e. R == G == B which is not the case for
 365                         // this one so no confusion is possible
 366                         rMask = 0xff;
 367                         gMask = 0;
 368                         bMask = 0xff;
 369                     }
 370                     else // transparency == Transparency_Alpha
 371                     {
 372                         alpha = InitAlpha(image, x, y);
 373                     }
 374                 }
 375
 376                 switch ( transparency )
 377                 {
 378                     case Transparency_Mask:
 379                         if ( IsTransparent(a) )
 380                         {
 381                             *ptrDst++ = rMask;
 382                             *ptrDst++ = bMask;
 383                             *ptrDst++ = gMask;
 384                             break;
 385                         }
 386                         // else: !transparent
 387
 388                         // must be opaque then as otherwise we shouldn't be
 389                         // using the mask at all
 390                         wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 391
 392                         // fall through
 393
 394                     case Transparency_Alpha:
 395                         if ( alpha )
 396                             *alpha++ = a;
 397                         // fall through
 398
 399                     case Transparency_None:
 400                         *ptrDst++ = g;
 401                         *ptrDst++ = g;
 402                         *ptrDst++ = g;
 403                         break;
 404                 }
 405             }
 406         }
 407     }
 408     else // colour image: RGBRGB...
 409     {
 410         for ( png_uint_32 y = 0; y < height; y++ )
 411         {
 412             const unsigned char *ptrSrc = lines[y];
 413             for ( png_uint_32 x = 0; x < width; x++ )
 414             {
 415                 unsigned char r = *ptrSrc++;
 416                 unsigned char g = *ptrSrc++;
 417                 unsigned char b = *ptrSrc++;
 418                 unsigned char a = *ptrSrc++;
 419
 420                 // the logic here is the same as for the grey case except
 421                 // where noted
 422                 if ( !IsOpaque(a) && transparency == Transparency_None )
 423                 {
 424                     transparency = CheckTransparency
 425                                    (
 426                                         lines,
 427                                         x, y,
 428                                         width, height,
 429                                         3
 430                                    );
 431
 432                     if ( transparency == Transparency_Mask )
 433                     {
 434                         FindMaskColour(lines, width, height,
 435                                        rMask, gMask, bMask);
 436                     }
 437                     else // transparency == Transparency_Alpha
 438                     {
 439                         alpha = InitAlpha(image, x, y);
 440                     }
 441
 442                 }
 443
 444                 switch ( transparency )
 445                 {
 446                     case Transparency_Mask:
 447                         if ( IsTransparent(a) )
 448                         {
 449                             *ptrDst++ = rMask;
 450                             *ptrDst++ = bMask;
 451                             *ptrDst++ = gMask;
 452                             break;
 453                         }
 454                         else // !transparent
 455                         {
 456                             // must be opaque then as otherwise we shouldn't be
 457                             // using the mask at all
 458                             wxASSERT_MSG( IsOpaque(a), _T("logic error") );
 459
 460                             // if we couldn't find a unique colour for the
 461                             // mask, we can have real pixels with the same
 462                             // value as the mask and it's better to slightly
 463                             // change their colour than to make them
 464                             // transparent
 465                             if ( r == rMask && g == gMask && b == bMask )
 466                             {
 467                                 r++;
 468                             }
 469                         }
 470
 471                         // fall through
 472
 473                     case Transparency_Alpha:
 474                         if ( alpha )
 475                             *alpha++ = a;
 476                         // fall through
 477
 478                     case Transparency_None:
 479                         *ptrDst++ = r;
 480                         *ptrDst++ = g;
 481                         *ptrDst++ = b;
 482                         break;
 483                 }
 484             }
 485         }
 486     }
 487
 488     if ( transparency == Transparency_Mask )
 489     {
 490         image->SetMaskColour(rMask, gMask, bMask);
 491     }
 492 }
 493
 494 // temporarily disable the warning C4611 (interaction between '_setjmp' and
 495 // C++ object destruction is non-portable) - I don't see any dtors here
 496 #ifdef __VISUALC__
 497     #pragma warning(disable:4611)
 498 #endif /* VC++ */
 499
 500 bool
 501 wxPNGHandler::LoadFile(wxImage *image,
 502                        wxInputStream& stream,
 503                        bool verbose,
 504                        int WXUNUSED(index))
 505 {
 506     // VZ: as this function uses setjmp() the only fool proof error handling
 507     //     method is to use goto (setjmp is not really C++ dtors friendly...)
 508
 509     unsigned char **lines = NULL;
 510     png_infop info_ptr = (png_infop) NULL;
 511     wxPNGInfoStruct wxinfo;
 512
 513     wxinfo.verbose = verbose;
 514     wxinfo.stream.in = &stream;
 515
 516     image->Destroy();
 517
 518     png_structp png_ptr = png_create_read_struct
 519                           (
 520                             PNG_LIBPNG_VER_STRING,
 521                             (voidp) NULL,
 522                             wx_png_error,
 523                             wx_png_warning
 524                           );
 525     if (!png_ptr)
 526         goto error;
 527
 528     // NB: please see the comment near wxPNGInfoStruct declaration for
 529     //     explanation why this line is mandatory
 530     png_set_read_fn( png_ptr, &wxinfo, wx_PNG_stream_reader);
 531
 532     info_ptr = png_create_info_struct( png_ptr );
 533     if (!info_ptr)
 534         goto error;
 535
 536     if (setjmp(wxinfo.jmpbuf))
 537         goto error;
 538
 539     png_uint_32 i, width, height;
 540     int bit_depth, color_type, interlace_type;
 541
 542     png_read_info( png_ptr, info_ptr );
 543     png_get_IHDR( png_ptr, info_ptr, &width, &height, &bit_depth, &color_type, &interlace_type, (int*) NULL, (int*) NULL );
 544
 545     if (color_type == PNG_COLOR_TYPE_PALETTE)
 546         png_set_expand( png_ptr );
 547
 548     // Fix for Bug [ 439207 ] Monochrome PNG images come up black
 549     if (bit_depth < 8)
 550         png_set_expand( png_ptr );
 551
 552     png_set_strip_16( png_ptr );
 553     png_set_packing( png_ptr );
 554     if (png_get_valid( png_ptr, info_ptr, PNG_INFO_tRNS))
 555         png_set_expand( png_ptr );
 556     png_set_filler( png_ptr, 0xff, PNG_FILLER_AFTER );
 557
 558     image->Create((int)width, (int)height, (bool) false /* no need to init pixels */);
 559
 560     if (!image->Ok())
 561         goto error;
 562
 563     lines = (unsigned char **)malloc( (size_t)(height * sizeof(unsigned char *)) );
 564     if ( !lines )
 565         goto error;
 566
 567     for (i = 0; i < height; i++)
 568     {
 569         if ((lines[i] = (unsigned char *)malloc( (size_t)(width * (sizeof(unsigned char) * 4)))) == NULL)
 570         {
 571             for ( unsigned int n = 0; n < i; n++ )
 572                 free( lines[n] );
 573             goto error;
 574         }
 575     }
 576
 577     png_read_image( png_ptr, lines );
 578     png_read_end( png_ptr, info_ptr );
 579     png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 580
 581     // loaded successfully, now init wxImage with this data
 582     CopyDataFromPNG(image, lines, width, height, color_type);
 583
 584     for ( i = 0; i < height; i++ )
 585         free( lines[i] );
 586     free( lines );
 587
 588     return true;
 589
 590 error:
 591     if (verbose)
 592        wxLogError(_("Couldn't load a PNG image - file is corrupted or not enough memory."));
 593
 594     if ( image->Ok() )
 595     {
 596         image->Destroy();
 597     }
 598
 599     if ( lines )
 600     {
 601         free( lines );
 602     }
 603
 604     if ( png_ptr )
 605     {
 606         if ( info_ptr )
 607         {
 608             png_destroy_read_struct( &png_ptr, &info_ptr, (png_infopp) NULL );
 609             free(info_ptr);
 610         }
 611         else
 612             png_destroy_read_struct( &png_ptr, (png_infopp) NULL, (png_infopp) NULL );
 613     }
 614     return false;
 615 }
 616
 617 // ----------------------------------------------------------------------------
 618 // writing PNGs
 619 // ----------------------------------------------------------------------------
 620
 621 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 622 {
 623     wxPNGInfoStruct wxinfo;
 624
 625     wxinfo.verbose = verbose;
 626     wxinfo.stream.out = &stream;
 627
 628     png_structp png_ptr = png_create_write_struct
 629                           (
 630                             PNG_LIBPNG_VER_STRING,
 631                             NULL,
 632                             wx_png_error,
 633                             wx_png_warning
 634                           );
 635     if (!png_ptr)
 636     {
 637         if (verbose)
 638            wxLogError(_("Couldn't save PNG image."));
 639         return false;
 640     }
 641
 642     png_infop info_ptr = png_create_info_struct(png_ptr);
 643     if (info_ptr == NULL)
 644     {
 645         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 646         if (verbose)
 647            wxLogError(_("Couldn't save PNG image."));
 648         return false;
 649     }
 650
 651     if (setjmp(wxinfo.jmpbuf))
 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     // NB: please see the comment near wxPNGInfoStruct declaration for
 660     //     explanation why this line is mandatory
 661     png_set_write_fn( png_ptr, &wxinfo, wx_PNG_stream_writer, NULL);
 662
 663     const int iColorType = image->HasOption(wxIMAGE_OPTION_PNG_FORMAT)
 664                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_FORMAT)
 665                             : wxPNG_TYPE_COLOUR;
 666     const int iBitDepth = image->HasOption(wxIMAGE_OPTION_PNG_BITDEPTH)
 667                             ? image->GetOptionInt(wxIMAGE_OPTION_PNG_BITDEPTH)
 668                             : 8;
 669
 670     wxASSERT_MSG( iBitDepth == 8 || iBitDepth == 16,
 671                     _T("PNG bit depth must be 8 or 16") );
 672
 673     bool bHasAlpha = image->HasAlpha();
 674     bool bHasMask = image->HasMask();
 675     bool bUseAlpha = bHasAlpha || bHasMask;
 676
 677     int iPngColorType;
 678     if ( iColorType==wxPNG_TYPE_COLOUR )
 679     {
 680         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_RGB_ALPHA
 681                                   : PNG_COLOR_TYPE_RGB;
 682     }
 683     else
 684     {
 685         iPngColorType = bUseAlpha ? PNG_COLOR_TYPE_GRAY_ALPHA
 686                                   : PNG_COLOR_TYPE_GRAY;
 687     }
 688
 689     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(),
 690                   iBitDepth, iPngColorType,
 691                   PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 692                   PNG_FILTER_TYPE_BASE);
 693
 694     int iElements;
 695     png_color_8 sig_bit;
 696
 697     if ( iPngColorType & PNG_COLOR_MASK_COLOR )
 698     {
 699         sig_bit.red =
 700         sig_bit.green =
 701         sig_bit.blue = (png_byte)iBitDepth;
 702         iElements = 3;
 703     }
 704     else // grey
 705     {
 706         sig_bit.gray = (png_byte)iBitDepth;
 707         iElements = 1;
 708     }
 709
 710     if ( iPngColorType & PNG_COLOR_MASK_ALPHA )
 711     {
 712         sig_bit.alpha = (png_byte)iBitDepth;
 713         iElements++;
 714     }
 715
 716     if ( iBitDepth == 16 )
 717         iElements *= 2;
 718
 719     png_set_sBIT( png_ptr, info_ptr, &sig_bit );
 720     png_write_info( png_ptr, info_ptr );
 721     png_set_shift( png_ptr, &sig_bit );
 722     png_set_packing( png_ptr );
 723
 724     unsigned char *
 725         data = (unsigned char *)malloc( image->GetWidth() * iElements );
 726     if ( !data )
 727     {
 728         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
 729         return false;
 730     }
 731
 732     unsigned char *
 733         pAlpha = (unsigned char *)(bHasAlpha ? image->GetAlpha() : NULL);
 734     int iHeight = image->GetHeight();
 735     int iWidth = image->GetWidth();
 736
 737     unsigned char uchMaskRed = 0, uchMaskGreen = 0, uchMaskBlue = 0;
 738
 739     if ( bHasMask )
 740     {
 741         uchMaskRed = image->GetMaskRed();
 742         uchMaskGreen = image->GetMaskGreen();
 743         uchMaskBlue = image->GetMaskBlue();
 744     }
 745
 746     unsigned char *pColors = image->GetData();
 747
 748     for (int y = 0; y != iHeight; ++y)
 749     {
 750         unsigned char *pData = data;
 751         for (int x = 0; x != iWidth; x++)
 752         {
 753             unsigned char uchRed = *pColors++;
 754             unsigned char uchGreen = *pColors++;
 755             unsigned char uchBlue = *pColors++;
 756
 757             switch ( iColorType )
 758             {
 759                 default:
 760                     wxFAIL_MSG( _T("unknown wxPNG_TYPE_XXX") );
 761                     // fall through
 762
 763                 case wxPNG_TYPE_COLOUR:
 764                     *pData++ = uchRed;
 765                     if ( iBitDepth == 16 )
 766                         *pData++ = 0;
 767                     *pData++ = uchGreen;
 768                     if ( iBitDepth == 16 )
 769                         *pData++ = 0;
 770                     *pData++ = uchBlue;
 771                     if ( iBitDepth == 16 )
 772                         *pData++ = 0;
 773                     break;
 774
 775                 case wxPNG_TYPE_GREY:
 776                     {
 777                         // where do these coefficients come from? maybe we
 778                         // should have image options for them as well?
 779                         unsigned uiColor =
 780                             (unsigned) (76.544*(unsigned)uchRed +
 781                                         150.272*(unsigned)uchGreen +
 782                                         36.864*(unsigned)uchBlue);
 783
 784                         *pData++ = (unsigned char)((uiColor >> 8) & 0xFF);
 785                         if ( iBitDepth == 16 )
 786                             *pData++ = (unsigned char)(uiColor & 0xFF);
 787                     }
 788                     break;
 789
 790                 case wxPNG_TYPE_GREY_RED:
 791                     *pData++ = uchRed;
 792                     if ( iBitDepth == 16 )
 793                         *pData++ = 0;
 794                     break;
 795             }
 796
 797             if ( bUseAlpha )
 798             {
 799                 unsigned char uchAlpha = 255;
 800                 if ( bHasAlpha )
 801                     uchAlpha = *pAlpha++;
 802
 803                 if ( bHasMask )
 804                 {
 805                     if ( (uchRed == uchMaskRed)
 806                             && (uchGreen == uchMaskGreen)
 807                                 && (uchBlue == uchMaskBlue) )
 808                         uchAlpha = 0;
 809                 }
 810
 811                 *pData++ = uchAlpha;
 812                 if ( iBitDepth == 16 )
 813                     *pData++ = 0;
 814             }
 815         }
 816
 817         png_bytep row_ptr = data;
 818         png_write_rows( png_ptr, &row_ptr, 1 );
 819     }
 820
 821     free(data);
 822     png_write_end( png_ptr, info_ptr );
 823     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
 824
 825     return true;
 826 }
 827
 828 #ifdef __VISUALC__
 829     #pragma warning(default:4611)
 830 #endif /* VC++ */
 831
 832 #endif  // wxUSE_STREAMS
 833
 834 #endif  // wxUSE_LIBPNG