After searching different libraries that can load .png images, i’v settled with libPNG. I’v googled for days through other peoples posts and tutorials but to no avail.
So i started by taking the sample loading function for libpng directly from opengl’s wiki page.
The function it took from opengl’s wiki looks this, with my global includes and such:
#include <iostream>
#include <stdlib.h>
#include <gl/glut.h>
#include <png.h>
#include <string>
#define TEXTURE_LOAD_ERROR 0;
using namespace std;
GLuint loadTexture(const string filename, int &width, int &height)
{
//header for testing if it is a png
png_byte header[8];
//open file as binary
FILE *fp = fopen(filename.c_str(), "vtr.png");
if (!fp) {
return TEXTURE_LOAD_ERROR;
}
//read the header
fread(header, 1, 8, fp);
//test if png
int is_png = !png_sig_cmp(header, 0, 8);
if (!is_png) {
fclose(fp);
return TEXTURE_LOAD_ERROR;
}
//create png struct
png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
NULL, NULL);
if (!png_ptr) {
fclose(fp);
return TEXTURE_LOAD_ERROR;
}
//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 TEXTURE_LOAD_ERROR;
}
//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 TEXTURE_LOAD_ERROR;
}
//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 TEXTURE_LOAD_ERROR;
}
//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 width and height based on png info
width = twidth;
height = theight;
// Update the png info struct.
png_read_update_info(png_ptr, info_ptr);
// Row size in bytes.
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 * height];
if (!image_data) {
//clean up memory and close stuff
png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
fclose(fp);
return TEXTURE_LOAD_ERROR;
}
//row_pointers is for pointing to image_data for reading the png with libpng
png_bytep *row_pointers = new png_bytep[height];
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 TEXTURE_LOAD_ERROR;
}
// set the individual row_pointers to point at the correct offsets of image_data
for (int i = 0; i < height; ++i)
row_pointers[height - 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, width, height, 0,
GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid*) image_data);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_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;
}
I don’t have any red lines, so i figure i have included all the files correctly, but i get errors immeadiatly after i try to compile my program with this function. And note i havent even tried to use the function elsewhere in my program yet, and i get 10 linking errors ->
1>------ Build started: Project: Light, Configuration: Debug Win32 ------
1> main.cpp
1>c:\users\shawn\documents
ew folder\first project - visual\light\light\main.cpp(25): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
1> c:\program files (x86)\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen'
1>main.obj : error LNK2019: unresolved external symbol _png_read_image referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_get_rowbytes referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_read_update_info referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_get_IHDR referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_read_info referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_set_sig_bytes referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_init_io referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_set_longjmp_fn referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_destroy_read_struct referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_create_info_struct referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_create_read_struct referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>main.obj : error LNK2019: unresolved external symbol _png_sig_cmp referenced in function "unsigned int __cdecl loadTexture(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int &,int &)" (?loadTexture@@YAIV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AAH1@Z)
1>C:\Users\Shawn\Documents\New folder\First Project - visual\Light\Debug\Light.exe : fatal error LNK1120: 12 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========