/// <summary>
/// Advance the current position some distance on the flight path.
/// </summary>
/// <param name="distance"></param>
/// <param name="destination">position after the advance</param>
/// <param name="cCfinalDirection">direction of the segment that the position is on after the advance</param>
internal void Advance(CCPoint currentPosition, float distance, out CCPoint destination, out float CCfinalDirection)
{
int currentIndex = (int)AdvancementAsQuasiIndex;
float relativeAdvancementToNextPoint = AdvancementAsQuasiIndex % 1;
if (currentIndex == Path.Length - 1) // if you've already reached the end you're done
{
destination = EndPoint;
CCfinalDirection = DirectionAt(currentIndex);
return;
}
float absoluteAdvancementToNextPoint = relativeAdvancementToNextPoint * CCPoint.Distance(Path[currentIndex], Path[currentIndex + 1]);
float directionToNextPointInRadians = Constants.CCDegreesToMathRadians(DirectionAt(currentIndex));
float absoluteXAdvancement = absoluteAdvancementToNextPoint * (float)Math.Cos(directionToNextPointInRadians);
float absoluteYAdvancement = absoluteAdvancementToNextPoint * (float)Math.Sin(directionToNextPointInRadians);
//CCPoint currentPosition = new CCPoint(Path[currentIndex].X + absoluteXAdvancement, Path[currentIndex].Y + absoluteYAdvancement);
// try to advance from the current position to the next point on the Path
float distanceToNextPoint = CCPoint.Distance(currentPosition, Path[currentIndex + 1]);
while (distanceToNextPoint < distance)
{
currentIndex = currentIndex + 1;
currentPosition = Path[currentIndex];
distance -= distanceToNextPoint;
AdvancementAsQuasiIndex = currentIndex;
if (currentIndex == Path.Length - 1)
{
break;
}
distanceToNextPoint = CCPoint.Distance(currentPosition, Path[currentIndex + 1]);
}
// if you can't go far enough just move towards the point
if (distance > 0 && currentIndex != Path.Length - 1)
{
// update the direction
directionToNextPointInRadians = Constants.CCDegreesToMathRadians(DirectionAt(currentIndex));
// calculate how far you can go
// relative between the points
float relativeAdvanche = distance / distanceToNextPoint;
// in x direction
float newX = currentPosition.X + distance * (float)Math.Cos(directionToNextPointInRadians);
// in y direction
float newY = currentPosition.Y + distance * (float)Math.Sin(directionToNextPointInRadians);
AdvancementAsQuasiIndex = (float)currentIndex + relativeAdvanche;
destination = new CCPoint(newX, newY);
CCfinalDirection = Constants.RadiansToCCDegrees(directionToNextPointInRadians);
}
else
{
destination = Path[currentIndex];
CCfinalDirection = DirectionAt(currentIndex);
}
//
}
/// <summary>
/// Returns the (relative) rotation angle (for MyRotation) indicating how far into which direction the weapon
/// should be turned to be able to hit the target perfectly.
/// </summary>
/// <returns></returns>
internal float AngleToAimFor()
{
// as there is no exact solution the solution is here approched by iteration
CCPoint TargetToMyPart = MyPart.PositionWorldspace - TargetPart.PositionWorldspace;
// rotate the vector, so that the movement direction of the target is identical to the x axis
float transformationRotation = -Constants.DxDyToRadians(TargetAircraft.VelocityVector.X, TargetAircraft.VelocityVector.Y);
TargetToMyPart = CCPoint.RotateByAngle(TargetToMyPart, CCPoint.Zero, transformationRotation);
// now the cordinate system is simpler and we can compute the difference between
// a) the intersection of the flight path and the bullet path
// and b) the point where the target actually is going to be by then
// of course we want to minimize this error, for this we will iterate
// ITERATION USING THE BISECTION METHOD
double epsilon = 1;
double angle = 0;
// define the interval
double startAngle = Constants.DxDyToRadians(-TargetToMyPart.X, -TargetToMyPart.Y);
double endAngle = 0;
float totalBulletVelocity = ProjectileBlueprint.Velocity + AircraftVelocityBoost();
double deltaStart = TargetToMyPart.X - TargetToMyPart.Y / Math.Tan(startAngle) + (TargetToMyPart.Y * TargetAircraft.VelocityVector.Length) / (Math.Sin(startAngle) * totalBulletVelocity);
for (int i = 0; i < 6; i++) // iterate 6 times at max
{
angle = (startAngle + endAngle) / 2;
double delta = TargetToMyPart.X - TargetToMyPart.Y / Math.Tan(angle) + (TargetToMyPart.Y * TargetAircraft.VelocityVector.Length) / (Math.Sin(angle) * totalBulletVelocity);
if (Math.Abs(delta) < epsilon) // you're close enough so break already
break;
// delta is negative when the bullet hits behind the part -> angle needs to be closer to 0
if (Math.Sign(deltaStart) == Math.Sign(delta))
{
startAngle = angle;
deltaStart = delta;
}
else
{
endAngle = angle;
}
}
// subtract the transformation rotation to get the total angle
float totalAngle = Constants.RadiansToCCDegrees((float)angle - transformationRotation);
// for the final angle transform the total angle to a relative angle
return Constants.AngleFromToDeg(((IGameObject)MyPart.Parent).TotalRotation, totalAngle);
}
