How to get enemies to turn continuously using atan2()

Question

I am trying to build a game where you control a pirate ship and other computer pirate ships try to attack you. I'm currently working on code that gets the enemies to turn to face the player, and I am running into an issue when atan2() returns a value that jumps from 0 to 2PI (I am using the fmod function to change the range from -pi to pi).

The ships will be following and turning with the player until the player crosses over from the 1st quadrant to the 4th quadrant, and then the ship will turn in the exact opposite direction to face the player. Any ideas on how to fix it and make it a continuous smooth turn? Here is my code: rotation is the current angle that the enemy ship is facing

float angleReq = atan2(distToPlayer.y, distToPlayer.x);
angleReq = fmod(angleReq + (2 * M_PI), 2 * M_PI);

if(rotation - angleReq > 0.01) {
    rotation -= 0.01;
    rotation = fmod(rotation, 2 * M_PI);
} else if (rotation - angleReq < -0.01) {
    rotation += 0.01;
    rotation = fmod(rotation, 2 * M_PI);
}

What is the possible range of original values for `rotation`? — chux - Reinstate Monica, Jul 17 '22 at 04:40
I think you are focusing on the wrong problem. What happens if the shortest distance between two angles crosses 0↔2π ? — Dúthomhas, Jul 17 '22 at 04:57
@Alex Savic, "I am using the fmod function to change the range from -pi to pi" --> `fmod(angleReq + (2 * M_PI), 2 * M_PI)` reduces the range to [-2 * M_PI .. +2 * M_PI]. — chux - Reinstate Monica, Jul 17 '22 at 05:00

score 0 · Answer 1 · answered Jul 17 '22 at 05:14

I realized how to fix it. As someone stated I was thinking about the problem wrong, I needed to tell the enemy ship to go the "shorter route" in order to get to the required angle based on its current position. Here is the solution code that solved that problem:

float angleReq = atan2(distToPlayer.y, distToPlayer.x);
angleReq = fmod(angleReq + (2 * M_PI), 2 * M_PI);

/* Moves ship counter clockwise from 0 over to 2pi radians */
if ((2 * M_PI - angleReq) + rotation < angleReq - rotation) {
    rotation -= 0.01;
    rotation = fmod(rotation + (2 * M_PI), 2 * M_PI);
} /* Moves ship clockwise from 2pi over to 0 radians */
else if ((2 * M_PI - rotation) + angleReq < rotation - angleReq) {
    rotation += 0.01;
    rotation = fmod(rotation + (2 * M_PI), 2 * M_PI);
} /* Moves ship clockwise normally */
else if (angleReq - rotation > 0.01) {
    rotation += 0.01;
    rotation = fmod(rotation + (2 * M_PI), 2 * M_PI);
} /* Moves ship counterclockwise normally */
else if (angleReq - rotation < -0.01) {
    rotation -= 0.01;
    rotation = fmod(rotation + (2 * M_PI), 2 * M_PI);
}

How to get enemies to turn continuously using atan2()

1 Answers1