loadTexBMP.c

#include "project.h"

/*
 *  BEGIN LOADTEXBMP CONVENIENCE METHODS
 */

/*
 *  Reverse n bytes
 */
static void reverse(void* x,const int n)
{
   int k;
   char* ch = (char*)x;
   for (k=0;k<n/2;k++)
   {
      char tmp = ch[k];
      ch[k] = ch[n-1-k];
      ch[n-1-k] = tmp;
   }
}

/*
 *  Load texture from BMP file
 */
unsigned int loadTexBMP(char* file)
{
  unsigned int   texture;    /* Texture name */
  FILE*          f;          /* File pointer */
  unsigned short magic;      /* Image magic */
  unsigned int   dx,dy,size; /* Image dimensions */
  unsigned short nbp,bpp;    /* Planes and bits per pixel */
  unsigned char* image;      /* Image data */
  unsigned int   k;          /* Counter */

  /*  Open file */
  f = fopen(file,"rb");
  if (!f) fatal("Cannot open file %s\n",file);
  /*  Check image magic */
  if (fread(&magic,2,1,f)!=1) fatal("Cannot read magic from %s\n",file);
  if (magic!=0x4D42 && magic!=0x424D) fatal("Image magic not BMP in %s\n",file);
  /*  Seek to and read header */
  if (fseek(f,16,SEEK_CUR) || fread(&dx ,4,1,f)!=1 || fread(&dy ,4,1,f)!=1 ||
      fread(&nbp,2,1,f)!=1 || fread(&bpp,2,1,f)!=1 || fread(&k,4,1,f)!=1)
    fatal("Cannot read header from %s\n",file);
  /*  Reverse bytes on big endian hardware (detected by backwards magic) */
  if (magic==0x424D) {
    reverse(&dx,4);
    reverse(&dy,4);
    reverse(&nbp,2);
    reverse(&bpp,2);
    reverse(&k,4);
  }
  /*  Check image parameters */
  if (dx<1 || dx>65536) fatal("%s image width out of range: %d\n",file,dx);
  if (dy<1 || dy>65536) fatal("%s image height out of range: %d\n",file,dy);
  if (nbp!=1)  fatal("%s bit planes is not 1: %d\n",file,nbp);
  if (bpp!=24) fatal("%s bits per pixel is not 24: %d\n",file,bpp);
  if (k!=0)    fatal("%s compressed files not supported\n",file);
#ifndef GL_VERSION_2_0
  /*  OpenGL 2.0 lifts the restriction that texture size must be a power of two */
  for (k=1;k<dx;k*=2);
  if (k!=dx) fatal("%s image width not a power of two: %d\n",file,dx);
  for (k=1;k<dy;k*=2);
  if (k!=dy) fatal("%s image height not a power of two: %d\n",file,dy);
#endif

  /*  Allocate image memory */
  size = 3*dx*dy;
  image = (unsigned char*) malloc(size);
  if (!image) fatal("Cannot allocate %d bytes of memory for image %s\n",size,file);
  /*  Seek to and read image */
  if (fseek(f,20,SEEK_CUR) || fread(image,size,1,f)!=1) 
    fatal("Error reading data from image %s\n",file);
  fclose(f);
  /*  Reverse colors (BGR -> RGB) */
  for (k=0;k<size;k+=3) {
    unsigned char temp = image[k];
    image[k]   = image[k+2];
    image[k+2] = temp;
  }

  /*  Sanity check */
  errCheck("LoadTexBMP");
  /*  Generate 2D texture */
  glGenTextures(1,&texture);
  glBindTexture(GL_TEXTURE_2D,texture);
  /*  Copy image */
  glTexImage2D(GL_TEXTURE_2D,0,3,dx,dy,0,GL_RGB,GL_UNSIGNED_BYTE,image);
  if (glGetError()) fatal("Error in glTexImage2D %s %dx%d\n",file,dx,dy);
  /*  Scale linearly when image size doesn't match */
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

  /*  Free image memory */
  free(image);
  /*  Return texture name */
  return texture;
}