void update_field(short player_x, short player_y, short player_angle) {
	short angle=player_angle-30;
	short ray=0;
	short drawn=0;
	raytrace horiz;
	raytrace vert;
		
		
	if(angle>0 && angle<180)
			horiz.step_y=-WALL_SIDE;
	if(angle>180 && angle<360)
			horiz.step_y=WALL_SIDE;
	
				
	if(angle<90 && angle>270)
			vert.step_x=-WALL_SIDE;
	if(angle>90 && angle<270)
			vert.step_x=WALL_SIDE;
	
	
	for(;ray<PLANE_WIDTH;ray++,angle+=ANGLE_INCREMENT) {
		/////////////////////////////////////////////
		//_____cast ray, and look for collision____//
		/////////////////////////////////////////////
		if(angle != 0 && angle != 180)
			horiz.step_x=WALL_SIDE/tan(angle);
		vert.step_y=WALL_SIDE*tan(angle);
		
		drawn=0;
		
		//set initial horizontal collision point
		if(angle>0 && angle<180)
				horiz.point_y=((player_y/WALL_SIDE)*WALL_SIDE)-1;
		if(angle>180 && angle<360)
				horiz.point_y=((player_y/WALL_SIDE)*WALL_SIDE)+WALL_SIDE;
				
		horiz.grid_y=horiz.point_y/WALL_SIDE; //the y grid coordinate of the questioned wall
		if(angle!=0 && angle!=180) //watch out for divide by zero	
				horiz.point_x=player_x+(player_y-horiz.point_y)/tan(angle);
		horiz.grid_x=horiz.point_x/WALL_SIDE; //the y grid coordinate of the questioned wall
		//______________________________________
		
		//set initial vertical collision point	
		if(angle<90 && angle>270)
				vert.point_x=(vert.point_x/WALL_SIDE)*WALL_SIDE+WALL_SIDE;
		if(angle>90 && angle<270)
				vert.point_x=(vert.point_x/WALL_SIDE)*WALL_SIDE-1;
		vert.grid_x=vert.point_y/WALL_SIDE;		
		vert.point_y=player_y+(player_x-vert.point_x)*tan(angle);
		vert.grid_y=vert.point_y/WALL_SIDE;
		//______________________________________
		
		//we now have the initial grid coords for vert and horiz checking
		
		//check for collision
		while(horiz.grid_y>=0 && horiz.grid_y<MAP_HEIGHT && horiz.grid_x>=0 && horiz.grid_x<MAP_WIDTH
		&& vert.grid_y>=0 && vert.grid_y<MAP_HEIGHT && vert.grid_x>=0 && vert.grid_x<MAP_WIDTH) {
				//___check for horizontal collision___//		
				
				if(map[horiz.grid_y][horiz.grid_x] && angle !=0 && angle != 180) {
					//draw the strip
					drawn=1;
					break;
				}
				if(map[vert.grid_y][vert.grid_x]) {
					//draw the strip
					drawn=1;
					break;
				}				

				
				//move to the next possible wall position
				horiz.grid_y=(horiz.point_y+=horiz.step_y)/WALL_SIDE;
				horiz.grid_x=(horiz.point_x+=horiz.step_x)/WALL_SIDE;
				vert.grid_y=(vert.point_y+=vert.step_y)/WALL_SIDE;
				vert.grid_x=(vert.point_x+=vert.step_x)/WALL_SIDE;
			
		}	
			
	}	
	
	
	
	
}

@HEADER:

#define MAP_HEIGHT 8
#define MAP_WIDTH 8

#define FOV 60
#define PLAYER_HEIGHT 16
#define WALL_SIDE 64
#define PLANE_HEIGHT 100
#define PLANE_WIDTH 160
#define ANGLE_INCREMENT FOV/PLANE_WIDTH

extern char map[MAP_HEIGHT][MAP_WIDTH];

typedef struct {
	short point_x;
	short point_y;
	short grid_x;
	short grid_y;
	short step_y;
	short step_x;
} raytrace;