src/msw/dib.cpp

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // Name:        src/msw/dib.cpp
   3 // Purpose:     implements wxDIB class
   4 // Author:      Vadim Zeitlin
   5 // Modified by:
   6 // Created:     03.03.03 (replaces the old file with the same name)
   7 // RCS-ID:      $Id$
   8 // Copyright:   (c) 2003 Vadim Zeitlin <vadim@wxwindows.org>
   9 // License:     wxWindows licence
  10 ///////////////////////////////////////////////////////////////////////////////
  11
  12 /*
  13     TODO: support for palettes is very incomplete, several functions simply
  14           ignore them (we should select and realize the palette, if any, before
  15           caling GetDIBits() in the DC we use with it.
  16  */
  17
  18 // ============================================================================
  19 // declarations
  20 // ============================================================================
  21
  22 // ----------------------------------------------------------------------------
  23 // headers
  24 // ----------------------------------------------------------------------------
  25
  26 // For compilers that support precompilation, includes "wx.h".
  27 #include "wx/wxprec.h"
  28
  29 #ifdef __BORLANDC__
  30     #pragma hdrstop
  31 #endif
  32
  33 #ifndef WX_PRECOMP
  34     #include "wx/string.h"
  35     #include "wx/log.h"
  36 #endif //WX_PRECOMP
  37
  38 #if wxUSE_WXDIB
  39
  40 #include "wx/bitmap.h"
  41 #include "wx/intl.h"
  42 #include "wx/file.h"
  43
  44 #include <stdio.h>
  45 #include <stdlib.h>
  46
  47 #if !defined(__MWERKS__) && !defined(__SALFORDC__)
  48     #include <memory.h>
  49 #endif
  50
  51 #ifdef __GNUWIN32_OLD__
  52     #include "wx/msw/gnuwin32/extra.h"
  53 #endif
  54
  55 #include "wx/image.h"
  56 #include "wx/msw/dib.h"
  57
  58 #ifdef __WXWINCE__
  59     #include <shellapi.h>       // for SHLoadDIBitmap()
  60 #endif
  61
  62 // ----------------------------------------------------------------------------
  63 // private functions
  64 // ----------------------------------------------------------------------------
  65
  66 // calculate the number of palette entries needed for the bitmap with this
  67 // number of bits per pixel
  68 static inline WORD GetNumberOfColours(WORD bitsPerPixel)
  69 {
  70     // only 1, 4 and 8bpp bitmaps use palettes (well, they could be used with
  71     // 24bpp ones too but we don't support this as I think it's quite uncommon)
  72     return (WORD)(bitsPerPixel <= 8 ? 1 << bitsPerPixel : 0);
  73 }
  74
  75 // wrapper around ::GetObject() for DIB sections
  76 static inline bool GetDIBSection(HBITMAP hbmp, DIBSECTION *ds)
  77 {
  78     // note that at least under Win9x (this doesn't seem to happen under Win2K
  79     // but this doesn't mean anything, of course), GetObject() may return
  80     // sizeof(DIBSECTION) for a bitmap which is *not* a DIB section and the way
  81     // to check for it is by looking at the bits pointer
  82     return ::GetObject(hbmp, sizeof(DIBSECTION), ds) == sizeof(DIBSECTION) &&
  83                 ds->dsBm.bmBits;
  84 }
  85
  86 // ============================================================================
  87 // implementation
  88 // ============================================================================
  89
  90 // ----------------------------------------------------------------------------
  91 // wxDIB creation
  92 // ----------------------------------------------------------------------------
  93
  94 bool wxDIB::Create(int width, int height, int depth)
  95 {
  96     // we don't support formats using palettes right now so we only create
  97     // either 24bpp (RGB) or 32bpp (RGBA) bitmaps
  98     wxASSERT_MSG( depth, _T("invalid image depth in wxDIB::Create()") );
  99     if ( depth < 24 )
 100         depth = 24;
 101
 102     // allocate memory for bitmap structures
 103     static const int sizeHeader = sizeof(BITMAPINFOHEADER);
 104
 105     BITMAPINFO *info = (BITMAPINFO *)malloc(sizeHeader);
 106     wxCHECK_MSG( info, false, _T("malloc(BITMAPINFO) failed") );
 107
 108     memset(info, 0, sizeHeader);
 109
 110     info->bmiHeader.biSize = sizeHeader;
 111     info->bmiHeader.biWidth = width;
 112
 113     // we use positive height here which corresponds to a DIB with normal, i.e.
 114     // bottom to top, order -- normally using negative height (which means
 115     // reversed for MS and hence natural for all the normal people top to
 116     // bottom line scan order) could be used to avoid the need for the image
 117     // reversal in Create(image) but this doesn't work under NT, only Win9x!
 118     info->bmiHeader.biHeight = height;
 119
 120     info->bmiHeader.biPlanes = 1;
 121     info->bmiHeader.biBitCount = (WORD)depth;
 122     info->bmiHeader.biSizeImage = GetLineSize(width, depth)*height;
 123
 124     m_handle = ::CreateDIBSection
 125                  (
 126                     0,              // hdc (unused with DIB_RGB_COLORS)
 127                     info,           // bitmap description
 128                     DIB_RGB_COLORS, // use RGB, not palette
 129                     &m_data,        // [out] DIB bits
 130                     NULL,           // don't use file mapping
 131                     0               // file mapping offset (not used here)
 132                  );
 133
 134     free(info);
 135
 136     if ( !m_handle )
 137     {
 138         wxLogLastError(wxT("CreateDIBSection"));
 139
 140         return false;
 141     }
 142
 143     m_width = width;
 144     m_height = height;
 145     m_depth = depth;
 146
 147     return true;
 148 }
 149
 150 bool wxDIB::Create(const wxBitmap& bmp)
 151 {
 152     wxCHECK_MSG( bmp.Ok(), false, _T("wxDIB::Create(): invalid bitmap") );
 153
 154     if ( !Create(GetHbitmapOf(bmp)) )
 155         return false;
 156
 157     m_hasAlpha = bmp.HasAlpha();
 158
 159     return true;
 160 }
 161
 162 bool wxDIB::Create(HBITMAP hbmp)
 163 {
 164     // this bitmap could already be a DIB section in which case we don't need
 165     // to convert it to DIB
 166     DIBSECTION ds;
 167     if ( GetDIBSection(hbmp, &ds) )
 168     {
 169         m_handle = hbmp;
 170
 171         // wxBitmap will free it, not we
 172         m_ownsHandle = false;
 173
 174         // copy all the bitmap parameters too as we have them now anyhow
 175         m_width = ds.dsBm.bmWidth;
 176         m_height = ds.dsBm.bmHeight;
 177         m_depth = ds.dsBm.bmBitsPixel;
 178
 179         m_data = ds.dsBm.bmBits;
 180     }
 181     else // no, it's a DDB -- convert it to DIB
 182     {
 183         // prepare all the info we need
 184         BITMAP bm;
 185         if ( !::GetObject(hbmp, sizeof(bm), &bm) )
 186         {
 187             wxLogLastError(wxT("GetObject(bitmap)"));
 188
 189             return false;
 190         }
 191
 192         int d = bm.bmBitsPixel;
 193         if ( d <= 0 )
 194             d = wxDisplayDepth();
 195
 196         if ( !Create(bm.bmWidth, bm.bmHeight, d) || !CopyFromDDB(hbmp) )
 197             return false;
 198     }
 199
 200     return true;
 201 }
 202
 203 // Windows CE doesn't have GetDIBits() so use an alternative implementation
 204 // for it
 205 //
 206 // in fact I'm not sure if GetDIBits() is really much better than using
 207 // BitBlt() like this -- it should be faster but I didn't do any tests, if
 208 // anybody has time to do them and by chance finds that GetDIBits() is not
 209 // much faster than BitBlt(), we could always use the Win CE version here
 210 #ifdef __WXWINCE__
 211
 212 bool wxDIB::CopyFromDDB(HBITMAP hbmp)
 213 {
 214     MemoryHDC hdcSrc;
 215     if ( !hdcSrc )
 216         return false;
 217
 218     SelectInHDC selectSrc(hdcSrc, hbmp);
 219     if ( !selectSrc )
 220         return false;
 221
 222     MemoryHDC hdcDst;
 223     if ( !hdcDst )
 224         return false;
 225
 226     SelectInHDC selectDst(hdcDst, m_handle);
 227     if ( !selectDst )
 228         return false;
 229
 230
 231     if ( !::BitBlt(
 232                     hdcDst,
 233                     0, 0, m_width, m_height,
 234                     hdcSrc,
 235                     0, 0,
 236                     SRCCOPY
 237                   ) )
 238     {
 239         wxLogLastError(_T("BitBlt(DDB -> DIB)"));
 240
 241         return false;
 242     }
 243
 244     return true;
 245 }
 246
 247 #else // !__WXWINCE__
 248
 249 bool wxDIB::CopyFromDDB(HBITMAP hbmp)
 250 {
 251     DIBSECTION ds;
 252     if ( !GetDIBSection(m_handle, &ds) )
 253     {
 254         // we're sure that our handle is a DIB section, so this should work
 255         wxFAIL_MSG( _T("GetObject(DIBSECTION) unexpectedly failed") );
 256
 257         return false;
 258     }
 259
 260     if ( !::GetDIBits
 261             (
 262                 ScreenHDC(),                // the DC to use
 263                 hbmp,                       // the source DDB
 264                 0,                          // first scan line
 265                 m_height,                   // number of lines to copy
 266                 ds.dsBm.bmBits,             // pointer to the buffer
 267                 (BITMAPINFO *)&ds.dsBmih,   // bitmap header
 268                 DIB_RGB_COLORS              // and not DIB_PAL_COLORS
 269             ) )
 270     {
 271         wxLogLastError(wxT("GetDIBits()"));
 272
 273         return false;
 274     }
 275
 276     return true;
 277 }
 278
 279 #endif // __WXWINCE__/!__WXWINCE__
 280
 281 // ----------------------------------------------------------------------------
 282 // Loading/saving the DIBs
 283 // ----------------------------------------------------------------------------
 284
 285 bool wxDIB::Load(const wxString& filename)
 286 {
 287 #ifdef __WXWINCE__
 288     m_handle = SHLoadDIBitmap(filename);
 289 #else // !__WXWINCE__
 290     m_handle = (HBITMAP)::LoadImage
 291                          (
 292                             wxGetInstance(),
 293                             filename,
 294                             IMAGE_BITMAP,
 295                             0, 0, // don't specify the size
 296                             LR_CREATEDIBSECTION | LR_LOADFROMFILE
 297                          );
 298 #endif // __WXWINCE__
 299
 300     if ( !m_handle )
 301     {
 302         wxLogLastError(_T("Loading DIB from file"));
 303
 304         return false;
 305     }
 306
 307     return true;
 308 }
 309
 310 bool wxDIB::Save(const wxString& filename)
 311 {
 312     wxCHECK_MSG( m_handle, false, _T("wxDIB::Save(): invalid object") );
 313
 314     wxFile file(filename, wxFile::write);
 315     bool ok = file.IsOpened();
 316     if ( ok )
 317     {
 318         DIBSECTION ds;
 319         if ( !GetDIBSection(m_handle, &ds) )
 320         {
 321             wxLogLastError(_T("GetObject(hDIB)"));
 322         }
 323         else
 324         {
 325             BITMAPFILEHEADER bmpHdr;
 326             wxZeroMemory(bmpHdr);
 327
 328             const size_t sizeHdr = ds.dsBmih.biSize;
 329             const size_t sizeImage = ds.dsBmih.biSizeImage;
 330
 331             bmpHdr.bfType = 0x4d42;    // 'BM' in little endian
 332             bmpHdr.bfOffBits = sizeof(BITMAPFILEHEADER) + ds.dsBmih.biSize;
 333             bmpHdr.bfSize = bmpHdr.bfOffBits + sizeImage;
 334
 335             // first write the file header, then the bitmap header and finally the
 336             // bitmap data itself
 337             ok = file.Write(&bmpHdr, sizeof(bmpHdr)) == sizeof(bmpHdr) &&
 338                     file.Write(&ds.dsBmih, sizeHdr) == sizeHdr &&
 339                         file.Write(ds.dsBm.bmBits, sizeImage) == sizeImage;
 340         }
 341     }
 342
 343     if ( !ok )
 344     {
 345         wxLogError(_("Failed to save the bitmap image to file \"%s\"."),
 346                    filename.c_str());
 347     }
 348
 349     return ok;
 350 }
 351
 352 // ----------------------------------------------------------------------------
 353 // wxDIB accessors
 354 // ----------------------------------------------------------------------------
 355
 356 void wxDIB::DoGetObject() const
 357 {
 358     // only do something if we have a valid DIB but we don't [yet] have valid
 359     // data
 360     if ( m_handle && !m_data )
 361     {
 362         // although all the info we need is in BITMAP and so we don't really
 363         // need DIBSECTION we still ask for it as modifying the bit values only
 364         // works for the real DIBs and not for the bitmaps and it's better to
 365         // check for this now rather than trying to find out why it doesn't
 366         // work later
 367         DIBSECTION ds;
 368         if ( !GetDIBSection(m_handle, &ds) )
 369         {
 370             wxLogLastError(_T("GetObject(hDIB)"));
 371             return;
 372         }
 373
 374         wxDIB *self = wxConstCast(this, wxDIB);
 375
 376         self->m_width = ds.dsBm.bmWidth;
 377         self->m_height = ds.dsBm.bmHeight;
 378         self->m_depth = ds.dsBm.bmBitsPixel;
 379         self->m_data = ds.dsBm.bmBits;
 380     }
 381 }
 382
 383 // ----------------------------------------------------------------------------
 384 // DDB <-> DIB conversions
 385 // ----------------------------------------------------------------------------
 386
 387 #ifndef __WXWINCE__
 388
 389 HBITMAP wxDIB::CreateDDB(HDC hdc) const
 390 {
 391     wxCHECK_MSG( m_handle, 0, _T("wxDIB::CreateDDB(): invalid object") );
 392
 393     DIBSECTION ds;
 394     if ( !GetDIBSection(m_handle, &ds) )
 395     {
 396         wxLogLastError(_T("GetObject(hDIB)"));
 397
 398         return 0;
 399     }
 400
 401     return ConvertToBitmap((BITMAPINFO *)&ds.dsBmih, hdc, ds.dsBm.bmBits);
 402 }
 403
 404 /* static */
 405 HBITMAP wxDIB::ConvertToBitmap(const BITMAPINFO *pbmi, HDC hdc, void *bits)
 406 {
 407     wxCHECK_MSG( pbmi, 0, _T("invalid DIB in ConvertToBitmap") );
 408
 409     // here we get BITMAPINFO struct followed by the actual bitmap bits and
 410     // BITMAPINFO starts with BITMAPINFOHEADER followed by colour info
 411     const BITMAPINFOHEADER *pbmih = &pbmi->bmiHeader;
 412
 413     // get the pointer to the start of the real image data if we have a plain
 414     // DIB and not a DIB section (in the latter case the pointer must be passed
 415     // to us by the caller)
 416     if ( !bits )
 417     {
 418         // we must skip over the colour table to get to the image data
 419         //
 420         // colour table either has the real colour data in which case its
 421         // number of entries is given by biClrUsed or is used for masks to be
 422         // used for extracting colour information from true colour bitmaps in
 423         // which case it always have exactly 3 DWORDs
 424         int numColors;
 425         switch ( pbmih->biCompression )
 426         {
 427             case BI_BITFIELDS:
 428                 numColors = 3;
 429                 break;
 430
 431             case BI_RGB:
 432                 // biClrUsed has the number of colors but it may be not initialized at
 433                 // all
 434                 numColors = pbmih->biClrUsed;
 435                 if ( !numColors )
 436                 {
 437                     numColors = GetNumberOfColours(pbmih->biBitCount);
 438                 }
 439                 break;
 440
 441             default:
 442                 // no idea how it should be calculated for the other cases
 443                 numColors = 0;
 444         }
 445
 446         bits = (char *)pbmih + sizeof(*pbmih) + numColors*sizeof(RGBQUAD);
 447     }
 448
 449     HBITMAP hbmp = ::CreateDIBitmap
 450                      (
 451                         hdc ? hdc           // create bitmap compatible
 452                             : (HDC) ScreenHDC(),  //  with this DC
 453                         pbmih,              // used to get size &c
 454                         CBM_INIT,           // initialize bitmap bits too
 455                         bits,               // ... using this data
 456                         pbmi,               // this is used for palette only
 457                         DIB_RGB_COLORS      // direct or indexed palette?
 458                      );
 459
 460     if ( !hbmp )
 461     {
 462         wxLogLastError(wxT("CreateDIBitmap"));
 463     }
 464
 465     return hbmp;
 466 }
 467
 468 /* static */
 469 size_t wxDIB::ConvertFromBitmap(BITMAPINFO *pbi, HBITMAP hbmp)
 470 {
 471     wxASSERT_MSG( hbmp, wxT("invalid bmp can't be converted to DIB") );
 472
 473     // prepare all the info we need
 474     BITMAP bm;
 475     if ( !::GetObject(hbmp, sizeof(bm), &bm) )
 476     {
 477         wxLogLastError(wxT("GetObject(bitmap)"));
 478
 479         return 0;
 480     }
 481
 482     // we need a BITMAPINFO anyhow and if we're not given a pointer to it we
 483     // use this one
 484     BITMAPINFO bi2;
 485
 486     const bool wantSizeOnly = pbi == NULL;
 487     if ( wantSizeOnly )
 488         pbi = &bi2;
 489
 490     // just for convenience
 491     const int h = bm.bmHeight;
 492
 493     // init the header
 494     BITMAPINFOHEADER& bi = pbi->bmiHeader;
 495     wxZeroMemory(bi);
 496     bi.biSize = sizeof(BITMAPINFOHEADER);
 497     bi.biWidth = bm.bmWidth;
 498     bi.biHeight = h;
 499     bi.biPlanes = 1;
 500     bi.biBitCount = bm.bmBitsPixel;
 501
 502     // memory we need for BITMAPINFO only
 503     DWORD dwLen = bi.biSize + GetNumberOfColours(bm.bmBitsPixel) * sizeof(RGBQUAD);
 504
 505     // get either just the image size or the image bits
 506     if ( !::GetDIBits
 507             (
 508                 ScreenHDC(),                        // the DC to use
 509                 hbmp,                               // the source DDB
 510                 0,                                  // first scan line
 511                 h,                                  // number of lines to copy
 512                 wantSizeOnly ? NULL                 // pointer to the buffer or
 513                              : (char *)pbi + dwLen, // NULL if we don't have it
 514                 pbi,                                // bitmap header
 515                 DIB_RGB_COLORS                      // or DIB_PAL_COLORS
 516             ) )
 517     {
 518         wxLogLastError(wxT("GetDIBits()"));
 519
 520         return 0;
 521     }
 522
 523     // return the total size
 524     return dwLen + bi.biSizeImage;
 525 }
 526
 527 /* static */
 528 HGLOBAL wxDIB::ConvertFromBitmap(HBITMAP hbmp)
 529 {
 530     // first calculate the size needed
 531     const size_t size = ConvertFromBitmap(NULL, hbmp);
 532     if ( !size )
 533     {
 534         // conversion to DDB failed?
 535         return NULL;
 536     }
 537
 538     HGLOBAL hDIB = ::GlobalAlloc(GMEM_MOVEABLE, size);
 539     if ( !hDIB )
 540     {
 541         // this is an error which does risk to happen especially under Win9x
 542         // and which the user may understand so let him know about it
 543         wxLogError(_("Failed to allocated %luKb of memory for bitmap data."),
 544                    (unsigned long)(size / 1024));
 545
 546         return NULL;
 547     }
 548
 549     if ( !ConvertFromBitmap((BITMAPINFO *)(void *)GlobalPtr(hDIB), hbmp) )
 550     {
 551         // this really shouldn't happen... it worked the first time, why not
 552         // now?
 553         wxFAIL_MSG( _T("wxDIB::ConvertFromBitmap() unexpectedly failed") );
 554
 555         return NULL;
 556     }
 557
 558     return hDIB;
 559 }
 560
 561 #endif // __WXWINCE__
 562
 563 // ----------------------------------------------------------------------------
 564 // palette support
 565 // ----------------------------------------------------------------------------
 566
 567 #if wxUSE_PALETTE
 568
 569 wxPalette *wxDIB::CreatePalette() const
 570 {
 571     wxCHECK_MSG( m_handle, NULL, _T("wxDIB::CreatePalette(): invalid object") );
 572
 573     DIBSECTION ds;
 574     if ( !GetDIBSection(m_handle, &ds) )
 575     {
 576         wxLogLastError(_T("GetObject(hDIB)"));
 577
 578         return 0;
 579     }
 580
 581     // how many colours are we going to have in the palette?
 582     DWORD biClrUsed = ds.dsBmih.biClrUsed;
 583     if ( !biClrUsed )
 584     {
 585         // biClrUsed field might not be set
 586         biClrUsed = GetNumberOfColours(ds.dsBmih.biBitCount);
 587     }
 588
 589     if ( !biClrUsed )
 590     {
 591         // bitmaps of this depth don't have palettes at all
 592         //
 593         // NB: another possibility would be to return
 594         //     GetStockObject(DEFAULT_PALETTE) or even CreateHalftonePalette()?
 595         return NULL;
 596     }
 597
 598     // LOGPALETTE struct has only 1 element in palPalEntry array, we're
 599     // going to have biClrUsed of them so add necessary space
 600     LOGPALETTE *pPalette = (LOGPALETTE *)
 601         malloc(sizeof(LOGPALETTE) + (biClrUsed - 1)*sizeof(PALETTEENTRY));
 602     wxCHECK_MSG( pPalette, NULL, _T("out of memory") );
 603
 604     // initialize the palette header
 605     pPalette->palVersion = 0x300;  // magic number, not in docs but works
 606     pPalette->palNumEntries = (WORD)biClrUsed;
 607
 608     // and the colour table (it starts right after the end of the header)
 609     const RGBQUAD *pRGB = (RGBQUAD *)((char *)&ds.dsBmih + ds.dsBmih.biSize);
 610     for ( DWORD i = 0; i < biClrUsed; i++, pRGB++ )
 611     {
 612         pPalette->palPalEntry[i].peRed = pRGB->rgbRed;
 613         pPalette->palPalEntry[i].peGreen = pRGB->rgbGreen;
 614         pPalette->palPalEntry[i].peBlue = pRGB->rgbBlue;
 615         pPalette->palPalEntry[i].peFlags = 0;
 616     }
 617
 618     HPALETTE hPalette = ::CreatePalette(pPalette);
 619
 620     free(pPalette);
 621
 622     if ( !hPalette )
 623     {
 624         wxLogLastError(_T("CreatePalette"));
 625
 626         return NULL;
 627     }
 628
 629     wxPalette *palette = new wxPalette;
 630     palette->SetHPALETTE((WXHPALETTE)hPalette);
 631
 632     return palette;
 633 }
 634
 635 #endif // wxUSE_PALETTE
 636
 637 // ----------------------------------------------------------------------------
 638 // wxImage support
 639 // ----------------------------------------------------------------------------
 640
 641 #if wxUSE_IMAGE
 642
 643 bool wxDIB::Create(const wxImage& image)
 644 {
 645     wxCHECK_MSG( image.Ok(), false, _T("invalid wxImage in wxDIB ctor") );
 646
 647     const int h = image.GetHeight();
 648     const int w = image.GetWidth();
 649
 650     // if we have alpha channel, we need to create a 32bpp RGBA DIB, otherwise
 651     // a 24bpp RGB is sufficient
 652     m_hasAlpha = image.HasAlpha();
 653     const int bpp = m_hasAlpha ? 32 : 24;
 654
 655     if ( !Create(w, h, bpp) )
 656         return false;
 657
 658     // DIBs are stored in bottom to top order (see also the comment above in
 659     // Create()) so we need to copy bits line by line and starting from the end
 660     const int srcBytesPerLine = w * 3;
 661     const int dstBytesPerLine = GetLineSize(w, bpp);
 662     const unsigned char *src = image.GetData() + ((h - 1) * srcBytesPerLine);
 663     const unsigned char *alpha = m_hasAlpha ? image.GetAlpha() + (h - 1)*w
 664                                             : NULL;
 665     unsigned char *dstLineStart = (unsigned char *)m_data;
 666     for ( int y = 0; y < h; y++ )
 667     {
 668         // copy one DIB line
 669         unsigned char *dst = dstLineStart;
 670         if ( alpha )
 671         {
 672             for ( int x = 0; x < w; x++ )
 673             {
 674                 // RGB order is reversed, and we need to premultiply
 675                 // all channels by alpha value for use with ::AlphaBlend.
 676                 const unsigned char a = *alpha++;
 677                 *dst++ = (unsigned char)((src[2] * a + 127) / 255);
 678                 *dst++ = (unsigned char)((src[1] * a + 127) / 255);
 679                 *dst++ = (unsigned char)((src[0] * a + 127) / 255);
 680                 *dst++ = a;
 681                 src += 3;
 682             }
 683         }
 684         else // no alpha channel
 685         {
 686             for ( int x = 0; x < w; x++ )
 687             {
 688                 // RGB order is reversed.
 689                 *dst++ = src[2];
 690                 *dst++ = src[1];
 691                 *dst++ = src[0];
 692                 src += 3;
 693             }
 694         }
 695
 696         // pass to the previous line in the image
 697         src -= 2*srcBytesPerLine;
 698         if ( alpha )
 699             alpha -= 2*w;
 700
 701         // and to the next one in the DIB
 702         dstLineStart += dstBytesPerLine;
 703     }
 704
 705     return true;
 706 }
 707
 708 wxImage wxDIB::ConvertToImage() const
 709 {
 710     wxCHECK_MSG( IsOk(), wxNullImage,
 711                     wxT("can't convert invalid DIB to wxImage") );
 712
 713     // create the wxImage object
 714     const int w = GetWidth();
 715     const int h = GetHeight();
 716     wxImage image(w, h, false /* don't bother clearing memory */);
 717     if ( !image.Ok() )
 718     {
 719         wxFAIL_MSG( wxT("could not allocate data for image") );
 720         return wxNullImage;
 721     }
 722
 723     if ( m_hasAlpha )
 724     {
 725         image.SetAlpha();
 726     }
 727
 728     // this is the same loop as in Create() just above but with copy direction
 729     // reversed
 730     const int bpp = GetDepth();
 731     const int dstBytesPerLine = w * 3;
 732     const int srcBytesPerLine = GetLineSize(w, bpp);
 733     unsigned char *dst = image.GetData() + ((h - 1) * dstBytesPerLine);
 734     unsigned char *alpha = image.HasAlpha() ? image.GetAlpha() + (h - 1)*w
 735                                             : NULL;
 736     const bool is32bit = bpp == 32;
 737     const unsigned char *srcLineStart = (unsigned char *)GetData();
 738     for ( int y = 0; y < h; y++ )
 739     {
 740         // copy one DIB line
 741         const unsigned char *src = srcLineStart;
 742         for ( int x = 0; x < w; x++ )
 743         {
 744             dst[2] = *src++;
 745             dst[1] = *src++;
 746             dst[0] = *src++;
 747
 748             dst += 3;
 749
 750             if ( is32bit )
 751             {
 752                 if ( alpha )
 753                     *alpha++ = *src;
 754                 src++;
 755             }
 756         }
 757
 758         // pass to the previous line in the image
 759         dst -= 2*dstBytesPerLine;
 760         if ( alpha )
 761             alpha -= 2*w;
 762
 763         // and to the next one in the DIB
 764         srcLineStart += srcBytesPerLine;
 765     }
 766
 767     return image;
 768 }
 769
 770 #endif // wxUSE_IMAGE
 771
 772 #endif // wxUSE_WXDIB
 773