ImageUtils.cpp

#include <png.h>
#include <cstring>
#include "ImageUtils.h"

using namespace std;
using namespace dawn;

int ImageUtils::WriteImage(const string &path, int width, int height, uint8_t *pixels)
{
  FILE * fp;
  png_structp png_ptr = NULL;
  png_infop info_ptr = NULL;
  size_t x, y;
  png_byte ** row_pointers = NULL;
  /* "status" contains the return value of this function. At first
     it is set to a value which means 'failure'. When the routine
     has finished its work, it is set to a value which means
     'success'. */
  int status = -1;
  /* The following number is set by trial and error only. I cannot
     see where it it is documented in the libpng manual.
  */
  int pixel_size = 4;
  int depth = 8;
  
  fp = fopen (path.c_str(), "wb");
  if (! fp) {
      goto fopen_failed;
  }

  png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
  if (png_ptr == NULL) {
      goto png_create_write_struct_failed;
  }
  
  info_ptr = png_create_info_struct (png_ptr);
  if (info_ptr == NULL) {
      goto png_create_info_struct_failed;
  }
  
  /* Set up error handling. */

  if (setjmp (png_jmpbuf (png_ptr))) {
      goto png_failure;
  }
  
  /* Set image attributes. */

  png_set_IHDR (png_ptr,
                info_ptr,
                width,
                height,
                depth,
                PNG_COLOR_TYPE_RGBA,
                PNG_INTERLACE_NONE,
                PNG_COMPRESSION_TYPE_DEFAULT,
                PNG_FILTER_TYPE_DEFAULT);
  
  /* Initialize rows of PNG. */

  row_pointers = (png_byte **)png_malloc (png_ptr, height * sizeof(png_byte *));
  for (y = 0; y < height; ++y) {
      png_byte *row = (png_byte *)png_malloc (png_ptr, sizeof(uint8_t) * width * pixel_size);
      row_pointers[y] = row;

      memcpy(row, pixels + width * y * 4, width * 4);
  }
  
  /* Write the image data to "fp". */

  png_init_io (png_ptr, fp);
  png_set_rows (png_ptr, info_ptr, row_pointers);
  png_write_png (png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);

  /* The routine has successfully written the file, so we set
     "status" to a value which indicates success. */

  status = 0;
  
  for (y = 0; y < height; y++) {
      png_free (png_ptr, row_pointers[y]);
  }
  png_free (png_ptr, row_pointers);
  
png_failure:
png_create_info_struct_failed:
  png_destroy_write_struct (&png_ptr, &info_ptr);
png_create_write_struct_failed:
  fclose (fp);
fopen_failed:
  return status;
}