I read compressed image from libpng .. my EncoderWriteCallback write is ok and running
but the read (EncoderReadCallback) is not ok why?

is the same 1:1 QByteArray wo libpng has writteln ... why now it can not read?
the QByteArray is not from qpixmap or qimage.

on debug qbuffer is readable and having size ..


I start the callback so...
Qt Code: 
  1. png_ptr_read = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
  2.     if(png_ptr_read == NULL)  {
  3.         qWarning("unable to create read struct");
  4.         return;
  5.     }
  6.     info_ptr_read = png_create_info_struct(png_ptr_read);
  7.     if(info_ptr_read == NULL) {
  8.         qWarning("unable to create info struct");
  9.         return;
  10.     }
  11.     png_set_sig_bytes(png_ptr_read, 8);
  12.     APNGImageStream myqtchunk(0,frame.stream());   /* stream() = QByteArray */
  13.     png_set_read_fn(png_ptr_read,&myqtchunk,EncoderReadCallback);
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and this is reader and writer
Qt Code: 
  1. #define PNG_USER_MEM_SUPPORTED
  2. #define PNG_WRITE_bKGD_SUPPORTED
  3.  
  4.  
  5. ////base ref http://www.littlesvr.ca/apng/tutorial/x148.html
  6. /* png lib from firefox 3 is patch  to APNG format! */
  7. #include "../moz_png/png.h"
  8.  
  9. /* device to write or read image frames */
  10. class APNGImageStream {
  11.   public:
  12.   APNGImageStream( const int mode , QByteArray in = QByteArray() ) 
  13.   :dev(new QBuffer()),bytes(in) 
  14.   {
  15.    dev->setBuffer(&bytes);
  16.    if (mode == 1) {
  17.     dev->open(QIODevice::WriteOnly);
  18.    } else {
  19.     dev->open(QIODevice::ReadOnly);
  20.    }
  21.   }
  22.   ~APNGImageStream()
  23.   {
  24.    dev->close();
  25.   }
  26.   QBuffer *device() { return dev; }
  27.   bool isValid() { return img.loadFromData(dev->data()); }
  28.   QByteArray stream() { return dev->data(); }
  29.   QImage img;
  30.   QBuffer *dev;
  31.   QByteArray bytes;
  32. };
  33.  
  34. // Called by libpng to flush its internal buffer to ours.
  35. static void EncoderWriteCallback(png_structp png, png_bytep data,
  36.                                  png_size_t size) {
  37.   APNGImageStream *state = static_cast<APNGImageStream*>(png_get_io_ptr(png));
  38.   Q_ASSERT(state->device());
  39.   state->device()->write((char*)data,size);
  40. }
  41.  
  42. // Called by libpng to read original QByteArray that has self created .
  43. static void EncoderReadCallback(png_structp png, png_bytep data, 
  44.                                  png_size_t sizer)  {
  45.     APNGImageStream *state = static_cast<APNGImageStream*>(png_get_io_ptr(png));
  46.     Q_ASSERT(state->device());
  47.     qDebug() << "### size to read 1/0  " << state->stream().size() << "," << state->device()->isReadable();
  48.     state->device()->read((char*)data,sizer);
  49.     qDebug() << "### read callback length   " << sizer; 
  50. }
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