Re: [pygame] trajectory

[James Paige <Bob@xxxxxxxxxxxxxxxxxxx>]

Not built into pygame, but there is a good one on the pygame wiki:

http://pygame.org/wiki/2DVectorClass

On Wed, Jul 20, 2011 at 04:33:16PM +0200, Nathan BIAGINI wrote:
>    There is a pygame object to create a 2d vector?
> 
>    2011/7/20 Joe Ranalli <jranalli@xxxxxxxxx>
> 
>      Yes a vector is probably appropriate.
> 
>      On Wed, Jul 20, 2011 at 10:20 AM, Nathan BIAGINI <nathan.open@xxxxxxxxx>
>      wrote:
> 
>        Ok. But all the calcul of how long the bullet will take to reach the
>        target etc... will be made byn using vector? I mean, using a vector
>        still viable?
> 
>        2011/7/20 Joe Ranalli <jranalli@xxxxxxxxx>
> 
>          It depends what you're trying to do. 
> 
>          If you draw the straight line between the tower and the enemy and
>          use that vector to translate a bullet each tick, the bullets might
>          miss the enemy.  Think about it this way, the bullet moves 2 steps
>          toward the enemy, then the enemy moves 1 step, then the bullet moves
>          2, etc.  Because the enemy moves the bullet will have to change its
>          direction through the flight.  So you could calculate the direction
>          vector between the bullet and the enemy every tick and have the
>          bullet move that direction.  That would make the bullets kind of arc
>          to the target.
> 
>          If you want to have the bullet go straight to the right spot, you
>          need to:
>          1) calculate how long the bullet will take to get to the enemy
>          2) calculate where the enemy will be at that time (newposition)
>          3) calculate how long it will take the bullet to get to newposition
>          4) recalculate newposition based on the new time
> 
>          Technically you could iterate that repeatedly until newposition
>          converges.  Practically, iterating once probably gets you close
>          enough unless the movement is extremely complicated.
> 
>          On Wed, Jul 20, 2011 at 9:14 AM, Nathan BIAGINI
>          <nathan.open@xxxxxxxxx> wrote:
> 
>            Hi everyone,
> 
>            i would like to know what are the common way to handle
>            "trajectory" in a 2d game. In fact, i think of writing a tower
>            defense game and i wonder how to handle the trajectory of the
>            missile launch by the towers. I though of getting the pos of the
>            tower and the target and create a vector between this two
>            entitites to make a sprite translation of this vector but there is
>            maybe some tricky stuff to do it.
> 
>            Thanks in advance and happy game making all :-)