Game Development Stack Exchange is a question and answer site for professional and independent game developers. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

How would I apply gravity to a bullet so that it would drop slightly the longer that it travels?

I somewhat understand how the gravity works, Im just asking for second opinions for more optimized ways of doing this.

VOID update()
    veloc_Y += gravity;//0.5f
    posX += veloc_X;
    posY += veloc_Y;

       if(posY > 650)
           posY = 650.0f;
           veloc_Y = 0.0f;
           on_g = true;//lets my game know im on the ground

so, would I apply gravity to bullet veloc_Y?


b_veloc_Y += gravity;
b_pos_Y += b_veloc_Y;

would this make my bullet drop?

thanks for help in advance

share|improve this question

You'll want to more than just add velocity every frame. That's basic Euler math, but doesn't work properly in a time sliced environment. Specifically, a variable framerate means that you'll get different results.

You'll want to do basic integration. There's a good article that goes into depth on that subject here:

share|improve this answer
Your advice may be true in general, but not really applicable in this particular case. Whatever discrepancies the Euler method has compared to the "true" integration of variables, the difference can be nullified by setting the initial Y velocity equal to -gravity/2. – Pasha S May 22 '13 at 0:26
Great article, but I feel the take-away message should be "use fixed frame rate (for physics), failing that, use integration". The RK4 method is simple but by no means trivial, and most of the time a fixed simulation rate is good enough. @PashaS that's not the only weakness of Euler. – congusbongus May 22 '13 at 0:29

Yes, that's how simplified gravity (or acceleration in general) works. You might want to limit your velocity (and gravity) to something (in reality: terminal velocity), e.g.

b_veloc_Y = std::max(-max_veloc_y, std::min(b_veloc_Y + gravity, max_veloc_y));

You might want to add some friction as well (maybe even make it velocity dependant) to lower acceleration over time.

share|improve this answer
I appreciate that, thank you – Lampr3y May 21 '13 at 14:24
What's the point of introducing air friction in Y direction, but not in X direction? Once you hit the speed limit your bullet just flies in a straight line, which doesn't look very natural. – Pasha S May 21 '13 at 17:33
I only added one dimension, because I thought it's enough to show the basic idea/concept, especially considering the question already started with gravity. – Mario May 22 '13 at 9:33

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.