Speed question

myme15 · 2002-06-21T10:08:14

In a 2D game I''m making, I have some alien spaceships that can roatate to any orientation. They need to be able to fire lasers and such from any angle, so the lasers need to be able to move along a ray extending from the alien at a certain angle. I move all the objects in my game by assigning them an x velocity and a y velocity, and adding these velocities to the object''s coordinates each frame. If I have the initial coordinates (x,y) and my angle A, how can I calculate the necessary x and y velocities for a projectile if it needs to move at a certain speed: sqrt((vx^2)+(vy^2)) = speed^2. I have figured out how to do this, but I need to use the sqrt() function in the calculation. I figure that having to calculate many sqrt()s each frame would be a big performance drain, so I need a way to do this without square rooting anything. In Andre LaMothe''s TOTWPG, he has a function called Fast_Distance_2D that speedily approximates sqrt(x^2+y^2). I think my problem can be solved with a similar method, but I have no idea how Fast_Distance_2D works, so I can''t figure it out. Here''s the code for Fast_Distance_2D: int Fast_Distance_2D(int x, int y) { // this function computes the distance from 0,0 to x,y with 3.5% error // first compute the absolute value of x,y x = abs(x); y = abs(y); // compute the minimum of x,y int mn = MIN(x,y); // return the distance return(x+y-(mn>>1)-(mn>>2)+(mn>>4)); } // end Fast_Distance_2D Please help! Things are not what they are.