/****************************************************************************
 * Func: rotate_90                                                          *
 *                                                                          *
 * Desc: rotates an image clockwise by simply transposing rows.             *
 *       No interpolation                                                   *
 *                                                                          *
 * Params: buffer - pointer to image in memory                              *
 *         fileout - output file name                                       *
 *         rows - number of rows in source image                            *
 *         cols - number of cols in source image                            *
 *         type - file type (5 = PGM     6 = PPM)                           *
 ****************************************************************************/

void rotate_90(image_ptr buffer, char *fileout, int rows, int cols, int type)
    {
    unsigned long x,y;           /* x and y indices to source image */
    unsigned long index;         /* index to output line buffer */
    unsigned long source_index;  /* index into source image */
    unsigned char *line_buff;    /* line buffer */
    unsigned line;               /* size of line in pixels */
    FILE *fp;                    /* output file pointer */
    int temp;                    /* temp variable */
    pixel_ptr color_buff;        /* pointer to a color image */

    /* open new output file */
    if((fp=fopen(fileout, "wb")) == NULL)
	{
	printf("Unable to open %s for output\n",fileout);
	exit(1);
	}

    /* swap rows and cols */
    temp = rows;
    rows = cols;
    cols = temp;

    /* print out the portable bitmap header */
    fprintf(fp, "P%d\n%d %d\n255\n", type, cols, rows);

    if(type == 5)        /* PGM file */
	line = cols;
    else                 /* PPM file */
	{
	line = cols * 3;
	color_buff = (pixel_ptr) buffer;
	}

    line_buff = (unsigned char *) malloc(line);

    for(y=0; y<rows; y++)
	{
	index = 0;
	for(x=0; x<cols; x++)
	    {
	    source_index = (cols - x) * rows + y;
	    if(type == 5)
		line_buff[index++] = buffer[source_index];
	    else
		{
		line_buff[index++] = color_buff[source_index].r;
		line_buff[index++] = color_buff[source_index].g;
		line_buff[index++] = color_buff[source_index].b;
		}
	    }
	fwrite(line_buff, 1, line, fp);
	}
    fclose(fp);
    }