xPNG.c

#include <assert.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>

#include <png.h>
#include <SDL2/SDL.h>

#include "xPNG.h"

static const char *e_msg = "";

static int
png_colortype_from_surface(SDL_Surface *surface) {
  int colortype = PNG_COLOR_MASK_COLOR; /* grayscale not supported */

  if (surface->format->palette) {
    colortype |= PNG_COLOR_MASK_PALETTE;
  }
  else if (surface->format->Amask) {
    colortype |= PNG_COLOR_TYPE_RGB_ALPHA;
  }

  return colortype;
}

static void
xpng_user_warn(png_structp ctx, png_const_charp str) {
  (void) ctx;
  e_msg = str;
}

static void
xpng_user_error(png_structp ctx, png_const_charp str) {
  (void) ctx;
  e_msg = str;
}

int
xpng_save_surface(const char *filename, SDL_Surface *surf) {
  assert(surf);
  assert(filename);
  assert(*filename);

  FILE *fp;
  png_structp png_ptr;
  png_infop info_ptr;
  int i, colortype;
  png_bytep *row_pointers;

  /* Opening output file */
  fp = fopen(filename, "wb");
  if (fp == NULL) {
    return X_PNG_FAIL_LIBC;
  }

  /* Initializing png structures and callbacks */
  png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL,
    xpng_user_error, xpng_user_warn);
  if (png_ptr == NULL) {
    return X_PNG_FAIL;
  }

  info_ptr = png_create_info_struct(png_ptr);
  if (info_ptr == NULL) {
    png_destroy_write_struct(&png_ptr, (png_infopp) NULL);
    return X_PNG_FAIL;
  }

  if (setjmp(png_jmpbuf(png_ptr))) {
    png_destroy_write_struct(&png_ptr, &info_ptr);
    fclose(fp);
    return X_PNG_FAIL;
  }

  png_init_io(png_ptr, fp);

  colortype = png_colortype_from_surface(surf);
  png_set_IHDR(png_ptr, info_ptr, (png_uint_32) surf->w, (png_uint_32)surf->h,
    8, colortype, PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
    PNG_FILTER_TYPE_DEFAULT);

  /* Writing the image */
  png_write_info(png_ptr, info_ptr);
  png_set_packing(png_ptr);

  row_pointers = (png_bytep*) malloc(sizeof(png_bytep) * (size_t) surf->h);
  for (i = 0; i < surf->h; i++) {
    row_pointers[i] = (png_bytep)(Uint8 *)surf->pixels + i*surf->pitch;
  }
  png_write_image(png_ptr, row_pointers);
  png_write_end(png_ptr, info_ptr);

  /* Cleaning out... */
  free(row_pointers);
  png_destroy_write_struct(&png_ptr, &info_ptr);
  fclose(fp);

  return X_PNG_OK;
}

const char *
xpng_strerror(int code) {
  switch (code) {
    case X_PNG_FAIL:
      assert(e_msg);
      return e_msg;
    case X_PNG_FAIL_LIBC:
      return strerror(errno);
  }
  return 0;
}