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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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#include "FGPNGTextureLoader.hxx"
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#include <GLUT/glut.h>
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GLuint FGPNGTextureLoader::loadTexture( const string & filename )
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//header for testing if it is a png
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FILE *fp = fopen(filename.c_str(), "rb");
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fread(header, 1, 8, fp);
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int is_png = !png_sig_cmp(header, 0, 8);
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png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
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//create png info struct
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png_infop info_ptr = png_create_info_struct(png_ptr);
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png_destroy_read_struct(&png_ptr, (png_infopp) NULL, (png_infopp) NULL);
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//create png info struct
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png_infop end_info = png_create_info_struct(png_ptr);
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png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp) NULL);
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//png error stuff, not sure libpng man suggests this.
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if (setjmp(png_jmpbuf(png_ptr))) {
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png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
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png_init_io(png_ptr, fp);
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//let libpng know you already read the first 8 bytes
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png_set_sig_bytes(png_ptr, 8);
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// read all the info up to the image data
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png_read_info(png_ptr, info_ptr);
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//variables to pass to get info
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int bit_depth, color_type;
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png_uint_32 twidth, theight;
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// get info about png
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png_get_IHDR(png_ptr, info_ptr, &twidth, &theight, &bit_depth, &color_type,
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// Update the png info struct.
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png_read_update_info(png_ptr, info_ptr);
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// Row size in bytes.
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int rowbytes = png_get_rowbytes(png_ptr, info_ptr);
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// Allocate the image_data as a big block, to be given to opengl
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png_byte *image_data = new png_byte[rowbytes * theight];
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//clean up memory and close stuff
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png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
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//row_pointers is for pointing to image_data for reading the png with libpng
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png_bytep *row_pointers = new png_bytep[theight];
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//clean up memory and close stuff
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png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
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// set the individual row_pointers to point at the correct offsets of image_data
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for (png_uint_32 i = 0; i < theight; ++i)
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row_pointers[theight - 1 - i] = image_data + i * rowbytes;
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//read the png into image_data through row_pointers
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png_read_image(png_ptr, row_pointers);
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//Now generate the OpenGL texture object
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glGenTextures(1, &texture);
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glBindTexture(GL_TEXTURE_2D, texture);
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gluBuild2DMipmaps( GL_TEXTURE_2D, 4, twidth, theight, GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*)image_data );
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glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
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glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR_MIPMAP_LINEAR );
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// glTexImage2D(GL_TEXTURE_2D,0, GL_RGBA, twidth, theight, 0,
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// GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*) image_data);
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// glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
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//clean up memory and close stuff
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png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
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delete[] row_pointers;