modified wxPNGHandler to not use png_struct.jmpbuf

(its size is compiler-dependant, so it wasn't possible to use libpng as a DLL,
and that's a problem since MGL exports it's own libpng)


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@13815 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/imagpng.cpp

@@ -60,38 +60,77 @@ IMPLEMENT_DYNAMIC_CLASS(wxPNGHandler,wxImageHandler)
   #define PNGLINKAGEMODE LINKAGEMODE
 #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))
+
+
 extern "C"
 {
 
 void PNGLINKAGEMODE _PNG_stream_reader( png_structp png_ptr, png_bytep data, png_size_t length )
 {
-    ((wxInputStream*) png_get_io_ptr( png_ptr )) -> Read(data, length);
+    WX_PNG_INFO(png_ptr)->stream.in->Read(data, length);
 }
 
 void PNGLINKAGEMODE _PNG_stream_writer( png_structp png_ptr, png_bytep data, png_size_t length )
 {
-    ((wxOutputStream*) png_get_io_ptr( png_ptr )) -> Write(data, length);
+    WX_PNG_INFO(png_ptr)->stream.out->Write(data, length);
 }
 
 // from pngerror.c
 // so that the libpng doesn't send anything on stderr
 void
-PNGLINKAGEMODE png_silent_error(png_structp png_ptr, png_const_charp WXUNUSED(message))
+PNGLINKAGEMODE wx_png_error(png_structp png_ptr, png_const_charp message)
 {
+    wxPNGInfoStruct *info = WX_PNG_INFO(png_ptr);
+    if ( info->verbose )
+        wxLogError(wxString(message));
+
 #ifdef USE_FAR_KEYWORD
     {
        jmp_buf jmpbuf;
-      png_memcpy(jmpbuf,png_ptr->jmpbuf,sizeof(jmp_buf));
+       png_memcpy(jmpbuf,info->jmpbuf,sizeof(jmp_buf));
        longjmp(jmpbuf, 1);
     }
 #else
-   longjmp(png_ptr->jmpbuf, 1);
+    longjmp(info->jmpbuf, 1);
 #endif
 }
 
 void
-PNGLINKAGEMODE png_silent_warning(png_structp WXUNUSED(png_ptr), png_const_charp WXUNUSED(message))
+PNGLINKAGEMODE wx_png_warning(png_structp png_ptr, png_const_charp message)
 {
+    wxPNGInfoStruct *info = WX_PNG_INFO(png_ptr);
+    if ( info->verbose )
+        wxLogWarning(wxString(message));
 }
 
 } // extern "C"
@@ -110,6 +149,10 @@ bool wxPNGHandler::LoadFile( wxImage *image, wxInputStream& stream, bool verbose
     unsigned char **lines;
     unsigned int i;
     png_infop info_ptr = (png_infop) NULL;   
+    wxPNGInfoStruct wxinfo;
+
+    wxinfo.verbose = verbose;
+    wxinfo.stream.in = &stream;
 
     image->Destroy();
 
@@ -120,21 +163,22 @@ bool wxPNGHandler::LoadFile( wxImage *image, wxInputStream& stream, bool verbose
     if (!png_ptr)
         goto error_nolines;
 
-    // the file example.c explain how to guess if the stream is a png image
+    png_set_error_fn(png_ptr, (png_voidp)NULL, wx_png_error, wx_png_warning);
-    if (!verbose) png_set_error_fn(png_ptr, (png_voidp)NULL, png_silent_error, png_silent_warning);
+
+    // NB: please see the comment near wxPNGInfoStruct declaration for
+    //     explanation why this line is mandatory
+    png_set_read_fn( png_ptr, &wxinfo, _PNG_stream_reader);
 
     info_ptr = png_create_info_struct( png_ptr );
     if (!info_ptr)
         goto error_nolines;
 
-    if (setjmp(png_ptr->jmpbuf))
+    if (setjmp(wxinfo.jmpbuf))
         goto error_nolines;
 
     if (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
         goto error_nolines;
 
-    png_set_read_fn( png_ptr, &stream, _PNG_stream_reader);
-
     png_uint_32 width,height;
     int bit_depth,color_type,interlace_type;
 
@@ -278,29 +322,41 @@ bool wxPNGHandler::LoadFile( wxImage *image, wxInputStream& stream, bool verbose
 
 bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbose )
 {
-    {
+    wxPNGInfoStruct wxinfo;
+
+    wxinfo.verbose = verbose;
+    wxinfo.stream.out = &stream;
+
     png_structp png_ptr = png_create_write_struct( PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
     if (!png_ptr)
     {
+        if (verbose)
+           wxLogError(_("Couldn't save PNG image."));
         return FALSE;
     }
 
-        if (!verbose) png_set_error_fn(png_ptr, (png_voidp)NULL, png_silent_error, png_silent_warning);
+    png_set_error_fn(png_ptr, (png_voidp)NULL, wx_png_error, wx_png_warning);
 
     png_infop info_ptr = png_create_info_struct(png_ptr);
     if (info_ptr == NULL)
     {
         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
+        if (verbose)
+           wxLogError(_("Couldn't save PNG image."));
         return FALSE;
     }
 
-        if (setjmp(png_ptr->jmpbuf))
+    if (setjmp(wxinfo.jmpbuf))
     {
         png_destroy_write_struct( &png_ptr, (png_infopp)NULL );
+        if (verbose)
+           wxLogError(_("Couldn't save PNG image."));
         return FALSE;
     }
 
-        png_set_write_fn( png_ptr, &stream, _PNG_stream_writer, NULL);
+    // NB: please see the comment near wxPNGInfoStruct declaration for
+    //     explanation why this line is mandatory
+    png_set_write_fn( png_ptr, &wxinfo, _PNG_stream_writer, NULL);
 
     png_set_IHDR( png_ptr, info_ptr, image->GetWidth(), image->GetHeight(), 8,
         PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
@@ -350,7 +406,7 @@ bool wxPNGHandler::SaveFile( wxImage *image, wxOutputStream& stream, bool verbos
     free(data);
     png_write_end( png_ptr, info_ptr );
     png_destroy_write_struct( &png_ptr, (png_infopp)&info_ptr );
-    }
+
     return TRUE;
 }