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Easy math question...

Started by Dookie Jul 16, 2004 at 2:53 PM 3 replies 550+ views

Original Post

Jul 16, 2004 at 2:53 PM

Hey guys. I'm trying to figure out a math problem for my 2D game, but for some reason I'm drawing a blank (not to mention I didn't make a very good grade in geometry class...) I have these: ship_maxVelocity (the fastest this ship will travel) ship_angle (rotational value in radians) ship_velocity[0] (velocity along the 'x' axis, between 'ship_maxVelocity * -1' and 'ship_maxVelocity') ship_velocity[1] (velocity along the 'y' axis, between 'ship_maxVelocity * -1' and 'ship_maxVelocity') And I want to use those to create a single, floating-point forward velocity value that's between ship_maxVelocity * -1 and ship_maxVelocity In other words, if I'm flying backwards in any direction and 'ship_maxVelocity' = 250, then my forward velocity value should be (-250). But if I'm flying forwards in any direction and 'ship_maxVelocity' = 250, then my forward velocity value should be 250. On the same note, if I'm flying sideways then my forward velocity value should be around zero. How should I create my equasion? I'm stumped! Thanks in advance for the help!

ninmonkey

Jul 16, 2004 at 3:00 PM

Have you heard of Vectors? (not the container) I think it's exactly what you want.

Dookie

Jul 16, 2004 at 4:32 PM

The values I've posted ARE vectors (of a rather large magnitude). What sort of vectors are you talking about and, more importantly, how can I get them to do what I want?

Remember, I don't have a whole lot of math background, so you may have to simplify ('dumb it down') what you're talking about.

Thanks!

Zakwayda

Jul 16, 2004 at 4:59 PM

I'm not sure if I understood all that, but...

If ship_velocity.x and y can both be in the range -maxVel, maxVel, your actual velocity can exceed maxVel. I don't know if that's what you want.

So are you just looking for the magnitude of the velocity vector? If so, that would be sqrt(vel.x * vel.x + vel.y * vel.y).

I think what you really want is a unit length direction vector which would be something like [cos(angle), sin(angle)]. Then you would multiply this by a ship_speed variable to get your change in position.

Dookie

Jul 16, 2004 at 6:41 PM

I just figured it out... It would have been easier if I knew how the original programmer had performed his rotation calculations in the first place (it made it hard to get a radian value that I could make a comparison with), but I finally got a function working that gets the values I desire. Pretty cool!

Thanks for the help though. I appreciate it! Maybe I'll have a tougher question in the near future. ;)

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