How to rotate an object so it faces another? - c++

Question

I am making a game in opengl, and i can't figure out how to make my enemy characters turn to face my player. I only need the enemy to rotate on the y axis towards the player. Then I want them to move towards him.I have tried a bunch of different methods but haven't been able to get anything to work.

Answer 1

There are a few things you need to decide on yourself at the beginning of the project to be used throughout the project, like the representation of positions and the orientation (as well as the setup of the screen/clip planes etc.) However, you haven't mentioned any of this. So you may have to adapt the code below to suit your game, but it should be easily adaptable and applicable.
For the following example, I'll assume that -y axis is the top of your screen.
#include <math.h> // atan2
// you need to way to represent position and directions
struct vector2{
float x;
float y;
} playerPosition, enemyPosition;
float playerRotation;
// setup the instances and values
void setup() {
// Set some default values for the positions
playerPosition.x = 100;
playerPosition.y = 100;
enemyPosition.x = 200;
enemyPosition.y = 300;
}
// called every frame
void update(float delta){
// get the direction vector between the player and the enemy. We can then use this to both calculate the rotation angle between the two as well as move the player towards the enemy.
vector2 dirToEnemy;
dirToEnemy.x = playerPosition.x - enemyPosition.x;
dirToEnemy.y = playerPosition.y - enemyPosition.y;
// move the player towards the enemy
playerPosition.x += dirToEnemy.x * delta * MOVEMENT_SPEED;
playerPosition.y += dirToEnemy.y * delta * MOVEMENT_SPEED;
// get the player angle on the y axis
playerRotation = atan2(-dirToEnemy.y, dirToEnemy.x);
}
void draw(){
// use the playerPosition and playerAngle to render the player
}
Using the above code, you should be able to move your player object around and set the angle of rotation (you need to watch out for radians/degrees of the returned and expected angle values).