libwebp/examples/pngdec.c

// Copyright 2012 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
//  Software License Agreement:  http://www.webmproject.org/license/software/
//  Additional IP Rights Grant:  http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// PNG decode.

#include "./pngdec.h"

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>

#ifdef WEBP_HAVE_PNG
#include <png.h>
#include <setjmp.h>   // note: this must be included *after* png.h
#include <stdlib.h>

#include "webp/encode.h"

static void PNGAPI error_function(png_structp png, png_const_charp dummy) {
  (void)dummy;  // remove variable-unused warning
  longjmp(png_jmpbuf(png), 1);
}

int ReadPNG(FILE* in_file, WebPPicture* const pic, int keep_alpha) {
  png_structp png;
  png_infop info;
  int color_type, bit_depth, interlaced;
  int has_alpha;
  int num_passes;
  int p;
  int ok = 0;
  png_uint_32 width, height, y;
  int stride;
  uint8_t* rgb = NULL;

  png = png_create_read_struct(PNG_LIBPNG_VER_STRING, 0, 0, 0);
  if (png == NULL) {
    goto End;
  }

  png_set_error_fn(png, 0, error_function, NULL);
  if (setjmp(png_jmpbuf(png))) {
 Error:
    png_destroy_read_struct(&png, NULL, NULL);
    free(rgb);
    goto End;
  }

  info = png_create_info_struct(png);
  if (info == NULL) goto Error;

  png_init_io(png, in_file);
  png_read_info(png, info);
  if (!png_get_IHDR(png, info,
                    &width, &height, &bit_depth, &color_type, &interlaced,
                    NULL, NULL)) goto Error;

  png_set_strip_16(png);
  png_set_packing(png);
  if (color_type == PNG_COLOR_TYPE_PALETTE) png_set_palette_to_rgb(png);
  if (color_type == PNG_COLOR_TYPE_GRAY ||
      color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
    if (bit_depth < 8) {
      png_set_expand_gray_1_2_4_to_8(png);
    }
    png_set_gray_to_rgb(png);
  }
  if (png_get_valid(png, info, PNG_INFO_tRNS)) {
    png_set_tRNS_to_alpha(png);
    has_alpha = 1;
  } else {
    has_alpha = !!(color_type & PNG_COLOR_MASK_ALPHA);
  }

  if (!keep_alpha) {
    png_set_strip_alpha(png);
    has_alpha = 0;
  }

  num_passes = png_set_interlace_handling(png);
  png_read_update_info(png, info);
  stride = (has_alpha ? 4 : 3) * width * sizeof(*rgb);
  rgb = (uint8_t*)malloc(stride * height);
  if (rgb == NULL) goto Error;
  for (p = 0; p < num_passes; ++p) {
    for (y = 0; y < height; ++y) {
      png_bytep row = rgb + y * stride;
      png_read_rows(png, &row, NULL, 1);
    }
  }
  png_read_end(png, info);
  png_destroy_read_struct(&png, &info, NULL);

  pic->width = width;
  pic->height = height;
  ok = has_alpha ? WebPPictureImportRGBA(pic, rgb, stride)
                 : WebPPictureImportRGB(pic, rgb, stride);
  free(rgb);

  if (ok && has_alpha && keep_alpha == 2) {
    WebPCleanupTransparentArea(pic);
  }

 End:
  return ok;
}
#else  // !WEBP_HAVE_PNG
int ReadPNG(FILE* in_file, struct WebPPicture* const pic, int keep_alpha) {
  (void)in_file;
  (void)pic;
  (void)keep_alpha;
  fprintf(stderr, "PNG support not compiled. Please install the libpng "
          "development package before building.\n");
  return 0;
}
#endif  // WEBP_HAVE_PNG

// -----------------------------------------------------------------------------