bitmap.cpp

#include <GL/gl3w.h>
#include <stdio.h>


GLuint loadBMP_custom(const char * imagepath){

  printf("Reading image %s\n", imagepath);

  // Data read from the header of the BMP file
  unsigned char header[54];
  unsigned int dataPos;
  unsigned int imageSize;
  unsigned int width, height;
  // Actual RGB data
  unsigned char * data;

  // Open the file
  FILE * file = fopen(imagepath,"rb");
  if (!file){
    printf("%s could not be opened. Are you in the right directory ? Don't forget to read the FAQ !\n", imagepath);
    getchar();
    return 0;
  }

  // Read the header, i.e. the 54 first bytes

  // If less than 54 bytes are read, problem
  if ( fread(header, 1, 54, file)!=54 ){
    printf("Not a correct BMP file\n");
    fclose(file);
    return 0;
  }
  // A BMP files always begins with "BM"
  if ( header[0]!='B' || header[1]!='M' ){
    printf("Not a correct BMP file\n");
    fclose(file);
    return 0;
  }
  // Make sure this is a 24bpp file
  if ( *(int*)&(header[0x1E])!=0  )         {printf("Not a correct BMP file\n");    fclose(file); return 0;}
  if ( *(int*)&(header[0x1C])!=24 )         {printf("Not a correct BMP file\n");    fclose(file); return 0;}

  // Read the information about the image
  dataPos    = *(int*)&(header[0x0A]);
  imageSize  = *(int*)&(header[0x22]);
  width      = *(int*)&(header[0x12]);
  height     = *(int*)&(header[0x16]);

  // Some BMP files are misformatted, guess missing information
  if (imageSize==0)    imageSize=width*height*3; // 3 : one byte for each Red, Green and Blue component
  if (dataPos==0)      dataPos=54; // The BMP header is done that way

  // Create a buffer
  data = new unsigned char [imageSize];

  // Read the actual data from the file into the buffer
  fread(data,1,imageSize,file);

  // Everything is in memory now, the file can be closed.
  fclose (file);

  // Create one OpenGL texture
  GLuint textureID;
  glGenTextures(1, &textureID);

  // "Bind" the newly created texture : all future texture functions will modify this texture
  glBindTexture(GL_TEXTURE_2D, textureID);

  // Give the image to OpenGL
  glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);

  // OpenGL has now copied the data. Free our own version
  delete [] data;

  // Poor filtering, or ...
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

  // ... nice trilinear filtering ...
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
  // ... which requires mipmaps. Generate them automatically.
  glGenerateMipmap(GL_TEXTURE_2D);

  // Return the ID of the texture we just created
  return textureID;
}