LoadTexture.c

/******************************************************************
*
* LoadTexture.c
*
* Description: Helper routine for loading texture.
* Adapted from texture loading code of the online OpenGL Tutorial:
*
* http://www.opengl-tutorial.org/	
*
* Computer Graphics Proseminar SS 2015
* 
* Interactive Graphics and Simulation Group
* Institute of Computer Science
* University of Innsbruck
*
*******************************************************************/

/* Standard includes */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Local includes */
#include "LoadTexture.h"


/*----------------------------------------------------------------*/


/******************************************************************
*
* LoadTexture
*
* This function loads a BMP texture from the file 'filename';
* it is used to read the image data into the texture.
* Note that the color data is provided for RGB and stored
* in the format BGR (3x8 bit per channel).
* Basic checking for correct file format is provided. 
*
*******************************************************************/

int LoadTexture(const char* filename, TextureDataPtr texture)
{
    printf("Reading image %s.\n", filename);

    /* Header data of BMP file */
    unsigned char header[54];
    unsigned int dataPos; 
    unsigned int imageSize;

    /* Open the file */
    FILE* file = fopen(filename,"rb");
    
    if (!file)							    
    {
        printf("%s could not be opened.\n", filename); 
        return 0;
    }

    /* Parse the header (i.e. try to read first 54 bytes) */
    if (fread(header, 1, 54, file) != 54)
    { 
        printf("Not a correct BMP file.\n");
        fclose (file);
        return 0;
    }

    /* BMP files begin with "BM" */
    if (header[0]!='B' || header[1]!='M')
    {
        printf("Not a correct BMP file.\n");
        fclose(file);
        return 0;
    }

    /* Make sure file is 24bpp */
    if (*(int*)&(header[0x1E]) !=0)  /* No compression */         
    { 
        printf("Not a correct BMP file\n");    
        return 0;
    }
	
    if (*(int*)&(header[0x1C]) != 24)  /* 24 bits per pixel */       
    {
        printf("Not a correct BMP file\n");    
        return 0;
    }

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

    /* Guess size if not provided, assuming one byte
     * each for RGB */
    if (imageSize == 0)    
        imageSize = texture->width * texture->height * 3; 
 
    /* Adjust for BMP header */	
    if (dataPos == 0)      
        dataPos = 54; 

    /* Allocate memory for RGB data */
    texture->data = malloc(sizeof(unsigned char) * (imageSize+1));

    /* Read data from file */
    fread(texture->data, 1, imageSize, file);

    fclose (file);
    return 1;
}