imagpng.cpp

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/////////////////////////////////////////////////////////////////////////////
// Name:        src/common/imagepng.cpp
// Purpose:     wxImage PNG handler
// Author:      Robert Roebling
// RCS-ID:      $Id: imagpng.cpp,v 1.56.2.4 2006/03/22 17:03:56 VZ Exp $
// Copyright:   (c) Robert Roebling
// Licence:     wxWindows licence
/////////////////////////////////////////////////////////////////////////////

// ============================================================================
// declarations
// ============================================================================

#if defined(__GNUG__) && !defined(NO_GCC_PRAGMA)
#pragma implementation "imagpng.h"
#endif

// ----------------------------------------------------------------------------
// headers
// ----------------------------------------------------------------------------

// For compilers that support precompilation, includes "wx.h".
#include "wx/wxprec.h"

#ifdef __BORLANDC__
  #pragma hdrstop
#endif

#ifndef WX_PRECOMP
  #include "wx/defs.h"
#endif

#if wxUSE_IMAGE && wxUSE_LIBPNG

#include "wx/imagpng.h"
#include "wx/bitmap.h"
#include "wx/debug.h"
#include "wx/log.h"
#include "wx/app.h"
#include "png.h"
#include "wx/filefn.h"
#include "wx/wfstream.h"
#include "wx/intl.h"
#include "wx/module.h"

// For memcpy
#include <string.h>

#ifdef __SALFORDC__
#ifdef FAR
#undef FAR
#endif
#endif

// ----------------------------------------------------------------------------
// constants
// ----------------------------------------------------------------------------

// image can not have any transparent pixels at all, have only 100% opaque
// and/or 100% transparent pixels in which case a simple mask is enough to
// store this information in wxImage or have a real alpha channel in which case
// we need to have it in wxImage as well
enum Transparency
{
    Transparency_None,
    Transparency_Mask,
    Transparency_Alpha
};

// ----------------------------------------------------------------------------
// local functions
// ----------------------------------------------------------------------------

// return the kind of transparency needed for this image assuming that it does
// have transparent pixels, i.e. either Transparency_Alpha or Transparency_Mask
static Transparency
CheckTransparency(unsigned char **lines,
                  png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
                  size_t numColBytes);

// init the alpha channel for the image and fill it with 1s up to (x, y)
static unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y);

// find a free colour for the mask in the PNG data array
static void
FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
               unsigned char& rMask, unsigned char& gMask, unsigned char& bMask);

// is the pixel with this value of alpha a fully opaque one?
static inline
bool IsOpaque(unsigned char a)
{
    return a == 0xff;
}

// is the pixel with this value of alpha a fully transparent one?
static inline
bool IsTransparent(unsigned char a)
{
    return !a;
}

// ============================================================================
// wxPNGHandler implementation
// ============================================================================

IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)

#if wxUSE_STREAMS

#ifndef PNGLINKAGEMODE
    #if defined(__WATCOMC__) && ( defined(__WXMSW__) || __WATCOMC__ > 1230 )
        // we need an explicit cdecl for Watcom, at least according to
        //
        // http://sf.net/tracker/index.php?func=detail&aid=651492&group_id=9863&atid=109863
        //
        // more testing is needed for this however, please remove this comment
        // if you can confirm that my fix works with Watcom 11
        #define PNGLINKAGEMODE cdecl
    #else
        #define PNGLINKAGEMODE LINKAGEMODE
    #endif
#endif


// VS: wxPNGInfoStruct declared below is a hack that needs some explanation.
//     First, let me describe what's the problem: libpng uses jmp_buf in
//     its png_struct structure. Unfortunately, this structure is
//     compiler-specific and may vary in size, so if you use libpng compiled
//     as DLL with another compiler than the main executable, it may not work
//     (this is for example the case with wxMGL port and SciTech MGL library
//     that provides custom runtime-loadable libpng implementation with jmpbuf
//     disabled altogether). Luckily, it is still possible to use setjmp() &
//     longjmp() as long as the structure is not part of png_struct.
//
//     Sadly, there's no clean way to attach user-defined data to png_struct.
//     There is only one customizable place, png_struct.io_ptr, which is meant
//     only for I/O routines and is set with png_set_read_fn or
//     png_set_write_fn. The hacky part is that we use io_ptr to store
//     a pointer to wxPNGInfoStruct that holds I/O structures _and_ jmp_buf.

struct wxPNGInfoStruct
{
    jmp_buf jmpbuf;
    bool verbose;

    union
    {
        wxInputStream  *in;
        wxOutputStream *out;
    } stream;
};

#define WX_PNG_INFO(png_ptr) ((wxPNGInfoStruct*)png_get_io_ptr(png_ptr))

// ----------------------------------------------------------------------------
// helper functions
// ----------------------------------------------------------------------------

extern "C"
{

void PNGLINKAGEMODE wx_PNG_stream_reader( png_structp png_ptr, png_bytep data,
                                          png_size_t length )
{
    WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
}

void PNGLINKAGEMODE wx_PNG_stream_writer( png_structp png_ptr, png_bytep data,
                                          png_size_t length )
{
    WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
}

void
PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
{
    wxPNGInfoStruct *info = png_ptr ? WX_PNG_INFO(png_ptr) : NULL;
    if ( !info || info->verbose )
        wxLogWarning( wxString::FromAscii(message) );
}

// from pngerror.c
// so that the libpng doesn't send anything on stderr
void
PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
{
    wx_png_warning(NULL, message);

    // we're not using libpng built-in jump buffer (see comment before
    // wxPNGInfoStruct above) so we have to return ourselves, otherwise libpng
    // would just abort
    longjmp(WX_PNG_INFO(png_ptr)->jmpbuf, 1);
}

} // extern "C"

// ----------------------------------------------------------------------------
// LoadFile() helpers
// ----------------------------------------------------------------------------

// determine the kind of transparency we need for this image: if the only alpha
// values it has are 0 (transparent) and 0xff (opaque) then we can simply
// create a mask for it, we should be ok with a simple mask but otherwise we
// need a full blown alpha channel in wxImage
//
// parameters:
//      lines           raw PNG data
//      x, y            starting position
//      w, h            size of the image
//      numColBytes     number of colour bytes (1 for grey scale, 3 for RGB)
//                      (NB: alpha always follows the colour bytes)
Transparency
CheckTransparency(unsigned char **lines,
                  png_uint_32 x, png_uint_32 y, png_uint_32 w, png_uint_32 h,
                  size_t numColBytes)
{
    // suppose that a mask will suffice and check all the remaining alpha
    // values to see if it does
    for ( ; y < h; y++ )
    {
        // each pixel is numColBytes+1 bytes, offset into the current line by
        // the current x position
        unsigned const char *ptr = lines[y] + (x * (numColBytes + 1));

        for ( png_uint_32 x2 = x; x2 < w; x2++ )
        {
            // skip the grey or colour byte(s)
            ptr += numColBytes;

            unsigned char a2 = *ptr++;

            if ( !IsTransparent(a2) && !IsOpaque(a2) )
            {
                // not fully opaque nor fully transparent, hence need alpha
                return Transparency_Alpha;
            }
        }

        // during the next loop iteration check all the pixels in the row
        x = 0;
    }

    // mask will be enough
    return Transparency_Mask;
}

unsigned char *InitAlpha(wxImage *image, png_uint_32 x, png_uint_32 y)
{
    // create alpha channel
    image->SetAlpha();

    unsigned char *alpha = image->GetAlpha();

    // set alpha for the pixels we had so far
    png_uint_32 end = y * image->GetWidth() + x;
    for ( png_uint_32 i = 0; i < end; i++ )
    {
        // all the previous pixels were opaque
        *alpha++ = 0xff;
    }

    return alpha;
}

void
FindMaskColour(unsigned char **lines, png_uint_32 width, png_uint_32 height,
               unsigned char& rMask, unsigned char& gMask, unsigned char& bMask)
{
    // choosing the colour for the mask is more
    // difficult: we need to iterate over the entire
    // image for this in order to choose an unused
    // colour (this is not very efficient but what else
    // can we do?)
    wxImageHistogram h;
    unsigned nentries = 0;
    unsigned char r2, g2, b2;
    for ( png_uint_32 y2 = 0; y2 < height; y2++ )
    {
        const unsigned char *p = lines[y2];
        for ( png_uint_32 x2 = 0; x2 < width; x2++ )
        {
            r2 = *p++;
            g2 = *p++;
            b2 = *p++;

            wxImageHistogramEntry&
                entry = h[wxImageHistogram:: MakeKey(r2, g2, b2)];

            if ( entry.value++ == 0 )
                entry.index = nentries++;
        }
    }

    if ( !h.FindFirstUnusedColour(&rMask, &gMask, &bMask) )
    {
        wxLogWarning(_("Too many colours in PNG, the image may be slightly blurred."));

        // use a fixed mask colour and we'll fudge
        // the real pixels with this colour (see
        // below)
        rMask = 0xfe;
        gMask = 0;
        bMask = 0xff;
    }
}

// ----------------------------------------------------------------------------
// reading PNGs
// ----------------------------------------------------------------------------

bool wxPNGHandler::DoCanRead( wxInputStream& stream )
{
    unsigned char hdr[4];

    if ( !stream.Read(hdr, WXSIZEOF(hdr)) )
        return false;

    return memcmp(hdr, "\211PNG", WXSIZEOF(hdr)) == 0;
}

// convert data from RGB to wxImage format
static
void CopyDataFromPNG(wxImage *image,
                     unsigned char **lines,
                     png_uint_32 width,
                     png_uint_32 height,
                     int color_type)
{
    Transparency transparency = Transparency_None;

    // only non NULL if transparency == Transparency_Alpha
    unsigned char *alpha = NULL;

    // RGB of the mask colour if transparency == Transparency_Mask
    // (but init them anyhow to avoid compiler warnings)
    unsigned char rMask = 0,
                  gMask = 0,
                  bMask = 0;

    unsigned char *ptrDst = image->GetData();
    if ( !(color_type & PNG_COLOR_MASK_COLOR) )
    {
        // grey image: GAGAGA... where G == grey component and A == alpha
        for ( png_uint_32 y = 0; y < height; y++ )
        {
            const unsigned char *ptrSrc = lines[y];
            for ( png_uint_32 x = 0; x < width; x++ )
            {
                unsigned char g = *ptrSrc++;
                unsigned char a = *ptrSrc++;

                // the first time we encounter a transparent pixel we must
                // decide about what to do about them
                if ( !IsOpaque(a) && transparency == Transparency_None )
                {
                    // we'll need at least the mask for this image and
                    // maybe even full alpha channel info: the former is
                    // only enough if we have alpha values of 0 and 0xff
                    // only, otherwisewe need the latter
                    transparency = CheckTransparency
                                   (
                                        lines,
                                        x, y,
                                        width, height,
                                        1
                                   );

                    if ( transparency == Transparency_Mask )
                    {
                        // let's choose this colour for the mask: this is
                        // not a problem here as all the other pixels are
                        // grey, i.e. R == G == B which is not the case for
                        // this one so no confusion is possible
                        rMask = 0xff;
                        gMask = 0;
                        bMask = 0xff;
                    }
                    else // transparency == Transparency_Alpha
                    {
                        alpha = InitAlpha(image, x, y);
                    }
                }

                switch ( transparency )
                {
                    case Transparency_Mask:
                        if ( IsTransparent(a) )
                        {
                            *ptrDst++ = rMask;
                            *ptrDst++ = bMask;
                            *ptrDst++ = gMask;
                            break;
                        }
                        // else: !transparent

                        // must be opaque then as otherwise we shouldn't be
                        // using the mask at all
                        wxASSERT_MSG( IsOpaque(a), _T("logic error") );

                        // fall through

                    case Transparency_Alpha:
                        if ( alpha )
                            *alpha++ = a;
                        // fall through

                    case Transparency_None:
                        *ptrDst++ = g;
                        *ptrDst++ = g;
                        *ptrDst++ = g;
                        break;
                }
            }
        }
    }
    else // colour image: RGBRGB...
    {
        for ( png_uint_32 y = 0; y < height; y++ )
        {
            const unsigned char *ptrSrc = lines[y];
            for ( png_uint_32 x = 0; x < width; x++ )
            {
                unsigned char r = *ptrSrc++;