libjpeg死亡而沒有消息

Question

我正在嘗試使用libjpeg從opengl緩沖區保存屏幕截圖。

我使用的功能是這個

void OnKeyPress(unsigned char key, int x, int y) {
  if (key != static_cast<unsigned char>('p'))
    return;

  int width = g_current_width;
  int height = g_current_height;
  boost::scoped_array<boost::uint8_t> buffer(new boost::uint8_t[3 * width * height]);

  glReadBuffer(GL_FRONT);
  glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE,
              reinterpret_cast<GLvoid *>(buffer.get()));
  glReadBuffer(GL_BACK);

  FlipImage(buffer.get(), width, height);

  // Generate a BMP files for testing purposes
  SaveRGB("screenshot.bmp", buffer.get(), width, height);

  boost::shared_ptr<FILE> outfile(fopen("screenshot.jpeg", "wb"), fclose);
  if (!outfile)
    return;

  jpeg_compress_struct cinfo;
  jpeg_error_mgr jerr;
  cinfo.err = jpeg_std_error(&jerr);
  jerr.trace_level = 10;
  jpeg_create_compress(&cinfo);
  jpeg_stdio_dest(&cinfo, outfile.get());

  cinfo.image_width = width;
  cinfo.image_height = height;
  cinfo.input_components = 3;
  cinfo.in_color_space = JCS_RGB;
  jpeg_set_defaults(&cinfo);

  jpeg_set_quality(&cinfo, 100, true);
  jpeg_start_compress(&cinfo, true);
  int row_stride = width * 3;
  JSAMPROW row_pointer[1];
  int counter = 0;
  std::cout << boost::format("height: %d\n") % height;
  boost::uint8_t *r_buffer = buffer.get();
  while (cinfo.next_scanline < cinfo.image_height) {
    row_pointer[0] = &r_buffer[cinfo.next_scanline * row_stride];
    jpeg_write_scanlines(&cinfo, row_pointer, 1);
    std::cout << boost::format("current line: %d\n") % (counter++);
  }
  jpeg_finish_compress(&cinfo); // never reaches this point
  outfile.reset();
  jpeg_destroy_compress(&cinfo);
}

該函數啟動，但是經過一些迭代（大約100 – 150）后，該函數返回，而沒有在文件中寫入任何內容，也沒有生成警告或錯誤。

如果我使用內存編碼（實際上是我所需要的），該函數將完成，但結果沒有意義。 此外，任何釋放緩沖區的嘗試都將導致錯誤。 這是內存目標版本

void OnKeyPress(unsigned char key, int x, int y) {
  if (key != static_cast<unsigned char>('p'))
    return;

  int width = g_current_width;
  int height = g_current_height;
  boost::scoped_array<boost::uint8_t> buffer(new boost::uint8_t[3 * width * height]);

  glReadBuffer(GL_FRONT);
  glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE,
              reinterpret_cast<GLvoid *>(buffer.get()));
  glReadBuffer(GL_BACK);

  FlipImage(buffer.get(), width, height);

  // Generate a BMP files for testing purposes
  SaveRGB("screenshot.bmp", buffer.get(), width, height);

  jpeg_compress_struct cinfo;
  jpeg_error_mgr jerr;
  cinfo.err = jpeg_std_error(&jerr);
  jerr.trace_level = 10;
  jpeg_create_compress(&cinfo);
  boost::uint8_t *jpeg_buffer_raw = NULL;
  unsigned long outbuffer_size = 0;
  jpeg_mem_dest(&cinfo, &jpeg_buffer_raw, &outbuffer_size);

  cinfo.image_width = width;
  cinfo.image_height = height;
  cinfo.input_components = 3;
  cinfo.in_color_space = JCS_RGB;
  jpeg_set_defaults(&cinfo);

  jpeg_set_quality(&cinfo, 100, true);
  jpeg_start_compress(&cinfo, true);
  int row_stride = width * 3;
  JSAMPROW row_pointer[1];
  int counter = 0;
  std::cout << boost::format("height: %d\n") % height;
  boost::uint8_t *r_buffer = buffer.get();
  while (cinfo.next_scanline < cinfo.image_height) {
    row_pointer[0] = &r_buffer[cinfo.next_scanline * row_stride];
    jpeg_write_scanlines(&cinfo, row_pointer, 1);
    std::cout << boost::format("current line: %d\n") % (counter++);
  }
  jpeg_finish_compress(&cinfo);
  jpeg_destroy_compress(&cinfo);
  std::ofstream jpegfile("screenshot.jpg");
  jpegfile.write(reinterpret_cast<const char*>(jpeg_buffer_raw), outbuffer_size);
  jpegfile.flush();
  // calling free(jpeg_buffer_raw); or delete[] jpeg_buffer_raw; generates an error
}

此函數生成以下jpeg圖像：

相比之下，保存位圖文件的行將生成以下內容：

Answer 1

我發現的問題是FILE *處理程序不能跨DLL移植。 使用靜態版本的庫可以解決此問題。

可以通過如下打開文件來解決內存中版本：

std::ofstream jpegfile("screenshot.jpg", std::ios_base::out | std::ios_base::binary);