shader.c

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

#include <GL/glew.h>

#include "shader.h"

// http://en.wikipedia.org/wiki/Vertex_Buffer_Object#Example_usage_in_C_Using_OpenGL_3.x_and_OpenGL_4.x

char* file2buf(char *file) {
  FILE *fptr;
  long length;
  char *buf;

  fptr = fopen(file, "r");
  if (!fptr) { return NULL; }
  fseek(fptr, 0, SEEK_END);
  length = ftell(fptr);
  buf = malloc(length+1);
  fseek(fptr, 0, SEEK_SET);
  fread(buf, length, 1, fptr);
  fclose(fptr);
  buf[length] = 0;

  return buf;
}

void dump_shader_info_log(GLuint shader) {
  int info_log_len;
  glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &info_log_len);
  if (info_log_len > 0) {
    // GetShaderInfoLog always reads from the beginning
    // need to allocate a buffer large enough for the whole message
    char *buffer = malloc(info_log_len);
    if (buffer) {
      glGetShaderInfoLog(shader, info_log_len, NULL, (GLchar *)buffer);
      fprintf(stderr, "%s", buffer);
      free(buffer);
    }
  }
}

void dump_program_info_log(GLuint program) {
  int info_log_len;
  glGetProgramiv(program, GL_INFO_LOG_LENGTH, &info_log_len);
  if (info_log_len > 0) {
    // assuming that GetProgramInfoLog also always reads from the beginning
    // allocating a buffer large enough for the whole message
    char *buffer = malloc(info_log_len);
    if (buffer) {
      glGetProgramInfoLog(program, info_log_len, NULL, (GLchar *)buffer);
      fprintf(stderr, "%s", buffer);
      free(buffer);
    }
  }
}

GLuint load_shader(GLuint program, GLenum type, char *file) {
  GLuint shader = glCreateShader(type);
  char *src = file2buf(file);

  int success = 0;

  fprintf(stderr, "loading shader from \"%s\"...\n", file);
  if ( (shader != 0) & (src != NULL) ) {
    glShaderSource(shader, 1, (const GLchar **)&src, NULL);
    glCompileShader(shader);
    int compiled;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
    if (compiled) {
      glAttachShader(program, shader);
      success = -1;
    }
    dump_shader_info_log(shader);
  }

  free(src);
  glDeleteShader(shader);

  if (success) { return shader; }
  else { return 0; }
}

int link_program(GLuint program) {
  int success = 0;

  glLinkProgram(program);
  int is_linked;
  glGetProgramiv(program, GL_LINK_STATUS, &is_linked);
  if (is_linked) { success = -1; }
  dump_program_info_log(program);

  if (success) { return 0; }
  else { return -1; }
}

shader.h

GLuint load_shader(GLuint program, GLenum type, char *file);
int link_program(GLuint program);