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callegroallegro5

Creating a projectile trajectory in Allegro

I'm developing a 2D game in C using Allegro 5, where an enemy from a fixed position shoots a projectile at the player's current position. I know I will have to calculate the tangent of an imaginary triangle based on the player's position and the enemy's. However, how can I have the projectile follow a straight line based on that value?

Solution

  • This is a situation where can be easier to work with vectors than angles.

    Some simple math computes the vector between the enemy and the player:

    # Compute the x and y displacement from the enemy to the player
dx = player_x - enemy_x
dy = player_y - enemy_y

# normalize the displacement to get the direction vector 
distance = sqrt(dx * dx + dy * dy)
projectile.dir_x = dx / distance

    ```

    The projectile just needs to follow that vector during the update loop:

    projectile.x += projectile.dir_x * projectile.speed * time_elapsed
projectile.y += projectile.dir_y * projectile.speed * time_elapsed