// Program makes shooters aim at a target.

// Tries to predict where the target is located
// when the 'bullet' reaches it (deflection shooting).

// Also, it compensates for the pitch the vehicle has.
// After all, aim() adjusts relative to the vehicle!

// The gun is approximately 1.5 m. above 'position.z'.
// This is compensated for as well.

// There is a function that calculates if there is Line
// of Sight (LOS).

extern void object::Aim()
{
	object item;
	float
	  dist,
	  dir,
	  angle,
	  oldangle,
	  aimangle,
	  bearing,
	  oldbearing,
	  xdefl,
	  ydefl,
	  deflconst = 0.15;
	
	item = radar(Me);  // Whatever you are aiming for.
	
	// Initialization of variables 'oldbearing' and 'oldangle'.
	dist = distance2d(position, item.position);
	dir = direction(item.position);
	oldbearing = dir + orientation;
	oldangle = atan((item.position.z - position.z - 1.5) / dist);
	
	while (true)
	{
		// Calculate distance, direction, bearing and angle.
		// Bearing: (east = 0, north = 90, ...)
		dist = distance2d(position, item.position);
		dir = direction(item.position);
		bearing = dir + orientation;
		// Gun is 1.5 meters above 'position.z'
		angle = atan((item.position.z - (position.z + 1.5)) / dist);
		
		// Deflection angles.
		xdefl = bearing - oldbearing;
		// Some arithmetic when target has crossed east-line.
		if (xdefl < -180) xdefl += 360;
		if (xdefl > 180) xdefl -= 360;
		// If the target is further away, more deflection is neccesary,
		// because the 'bullet' takes longer to reach the target.
		// Hence '* dist'.
		// Experiment with deflection constant, 0.15 works for me.
		xdefl *= (dist * deflconst);
		ydefl = (angle - oldangle) * dist * deflconst;
		
		// Prepare variables for next pass.
		oldbearing = bearing;
		oldangle = angle;
		
		// Compensate for deflection and pitch of craft.
		turn(dir + xdefl);
		aimangle = angle - pitch + ydefl;
		aim(aimangle);
		
		// If all is well, fire.
		if (dist < 40 && aimangle > -25 && aimangle < 15 && CheckLOS(item) == 1)
		{
			fire(0.05);
		}
	}
}

int object::CheckLOS(object target)
{
	point midway;
	
	// Calculate the point halfway to the target.
	midway.x = (position.x + target.position.x) / 2;
	midway.y = (position.y + target.position.y) / 2;
	midway.z = (position.z + 1.5 + target.position.z) / 2;
	
	// See if there is 'ground' there.
	if (topo(midway) < midway.z)
	  return 1;  // There is LOS
	else
	  return 0;  // Ther is no LOS
}