[Solved]Shooting at the player

Comments

• acksys

  February 2012 edited February 2012

  Hi sonic,
  
  I have used unit vectors for this purpose in the past.
  
  Assume you have the player at vector coordinates (0, 0, 0) and the enemy at vector coordinates (10, 20, 0).
  
  You know the vector from the enemy to the player (the trajectory down which the bullet must be fired) is (-10, -20, 0). dX = -10, dY = -20, dZ = 0
  
  However, as you said, you wouldn't set the speed of the bullet to that vector
  
  Instead, you can calculate the unit vector, which is defined as a vector of length 1 in the same direction as the original vector.
  
  Calculate the unit vector of the vector (-10, -20, 0). Here is the formula. Just plug in your numbers instead (or see sample code below): http://maxwell.byu.edu/~spencerr/websumm122/node7.html
  
  Now you have a very small vector that points from the enemy to the player. You can multiply the components of this vector by an arbitrary quantity which is the speed of the bullet. This gives you the speed vector which you can apply to the bullet.
  
  Sample code:
  

  // Calculate unit vector for dX, dY
  orxFLOAT rdX = 0;
  orxFLOAT rdY = 0;
  float rprim = pow(dX, 2) + pow(dY, 2);
  
  if (rprim > 0) {
    orxFLOAT r = sqrt(rprim);
    rdX = dX / r;
    rdY = dY / r;
  }
  
  orxVECTOR speed = {0, 0, 0};
  
  // Adjust speed of the projectile by changing value of SPEED
  speed.fX = rdX * SPEED;
  speed.fY = rdY * SPEED;
  

  
  Where dX and dY are values representing the original vector between the source and target objects, and SPEED is a constant representing the desired speed of the projectile.
  
  Maybe there are others ways to do this for well, but this is a very easy method I have used successfully. I hope this helps you.
• faistoiplaisir

  February 2012 edited February 2012

  Hi,
  
  Just a little precision, orxVector.h define some usefull function to do that.
  
  To compute a unit vector (called normalized vector too), you can use orxVector_Normalize().
  
  To apply the speed to your normalized vector, you can use orxVector_Mulf().
  
  It's the same, but just already done in Orx
  
  Cheers.
• sonicbhoc

  February 2012 edited February 2012

  thanks guys!