flightgear/utils/fgpanel/FGPNGTextureLoader.cxx

//
//  This program is free software; you can redistribute it and/or
//  modify it under the terms of the GNU General Public License as
//  published by the Free Software Foundation; either version 2 of the
//  License, or (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful, but
//  WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
//  General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program; if not, write to the Free Software
//  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
//
#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#ifdef HAVE_WINDOWS_H
#include <windows.h>
#endif

#if defined (SG_MAC)
#include <OpenGL/gl.h>
#include <GLUT/glut.h>
#elif defined (_GLES2)
#include <GLES2/gl2.h>
#else
#include <GL/glew.h> // Must be included before <GL/gl.h>
#include <GL/gl.h>
#include <GL/glut.h>
#endif

#include <png.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>

#include "FGPNGTextureLoader.hxx"

using namespace std;

GLuint
FGPNGTextureLoader::loadTexture (const string &filename) {
  //header for testing if it is a png
  png_byte header[8];

  //open file as binary
  FILE * const fp (fopen (filename.c_str (), "rb"));
  if (!fp) {
    return NOTEXTURE;
  }

  //read the header
  fread (header, 1, 8, fp);

  //test if png
  const int is_png (!png_sig_cmp (header, 0, 8));
  if (!is_png) {
    fclose (fp);
    return NOTEXTURE;
  }

  //create png struct
  png_structp png_ptr (png_create_read_struct (PNG_LIBPNG_VER_STRING, NULL, NULL, NULL));
  if (!png_ptr) {
    fclose (fp);
    return NOTEXTURE;
  }

  //create png info struct
  png_infop info_ptr (png_create_info_struct (png_ptr));
  if (!info_ptr) {
    png_destroy_read_struct (&png_ptr, (png_infopp) NULL, (png_infopp) NULL);
    fclose (fp);
    return NOTEXTURE;
  }

  //create png info struct
  png_infop end_info (png_create_info_struct (png_ptr));
  if (!end_info) {
    png_destroy_read_struct (&png_ptr, &info_ptr, (png_infopp) NULL);
    fclose (fp);
    return NOTEXTURE;
  }

  //png error stuff, not sure libpng man suggests this.
  if (setjmp (png_jmpbuf (png_ptr))) {
    png_destroy_read_struct (&png_ptr, &info_ptr, &end_info);
    fclose (fp);
    return NOTEXTURE;
  }

  // init png reading
  png_init_io (png_ptr, fp);

  // let libpng know you already read the first 8 bytes
  png_set_sig_bytes (png_ptr, 8);

  // read all the info up to the image data
  png_read_info (png_ptr, info_ptr);

  // variables to pass to get info
  int bit_depth, color_type;
  png_uint_32 twidth, theight;

  // get info about png
  png_get_IHDR (png_ptr, info_ptr, &twidth, &theight, &bit_depth, &color_type, NULL, NULL, NULL);

  // Update the png info struct.
  png_read_update_info (png_ptr, info_ptr);

  // Row size in bytes.
  const int rowbytes (png_get_rowbytes (png_ptr, info_ptr));

  // Allocate the image_data as a big block, to be given to opengl
  png_byte *image_data (new png_byte[rowbytes * theight]);
  if (!image_data) {
    //clean up memory and close stuff
    png_destroy_read_struct (&png_ptr, &info_ptr, &end_info);
    fclose (fp);
    return NOTEXTURE;
  }

  // row_pointers is for pointing to image_data for reading the png with libpng
  png_bytep *row_pointers (new png_bytep[theight]);
  if (!row_pointers) {
    //clean up memory and close stuff
    png_destroy_read_struct (&png_ptr, &info_ptr, &end_info);
    delete []image_data;
    fclose (fp);
    return NOTEXTURE;
  }
  // set the individual row_pointers to point at the correct offsets of image_data
  for (png_uint_32 i = 0; i < theight; ++i) {
    row_pointers[theight - 1 - i] = image_data + i * rowbytes;
  }
  //read the png into image_data through row_pointers
  png_read_image (png_ptr, row_pointers);

  //Now generate the OpenGL texture object
  GLuint texture;
  glGenTextures (1, &texture);
  glBindTexture (GL_TEXTURE_2D, texture);
  glTexImage2D (GL_TEXTURE_2D, 0, GL_RGBA, twidth, theight, 0, GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*) image_data);
  glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
  glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

  //clean up memory and close stuff
  png_destroy_read_struct (&png_ptr, &info_ptr, &end_info);
  delete []image_data;
  delete []row_pointers;
  fclose (fp);
  return texture;
}