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 Moving from point A to B - Shooting and movement  (Read 726 times) 0 Members and 1 Guest are viewing this topic.
SauronWatchesYou
 « Posted 2014-07-06 07:57:54 »

Hi guys so i'm looking into making my enemy get the position of the player and then fire a bullet towards the previous location and was wondering what the best way to do this was. (My game is a 2D vertical scrolling game and the enemy shoots down towards the player)

I've searched online but i'm a little confused right now. People seem to suggest using trig and was wondering if anyone could point me in the right direction? A common piece of code I found was this:

 1  2  3  4  5  6 `double dx = player.x - enemy.x, dy = player.y - enemy.y;double distance = Math.sqrt(dx*dx + dy*dy);double multiplier = moveSpeedOfEnemy / distance;double velocityX = dx * multiplier, velocityY = dy * multiplier;`

I'll likely have to brush up my maths as this is confusing me but if anyone can explain exactly what I should do and any useful resources then it would be great!

Sorry if the question is a little vague but just ask if you need more info etc

Thank you

Hey, you! Back to work
PandaMoniumHUN

JGO Coder

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White-bearded OGL wizard

 « Reply #1 - Posted 2014-07-06 09:24:59 »

That's actually a pretty good code snippet you found there.

To be honest you don't even need trigonometry for this, just the very basics of linear algebra, mostly vectors.
You can create a vector that points from point A to point B by subtracting all of A's components from all of B's components.
That's what
 `dx`
and
 `dy`
The
 `distance`
is just the distance formula to calculate the distance between the player and the enemy, and the
 `multiplier`
is there to make the projectile go faster as it gets closer to it's target. However, it's a really bad way of achieving acceleration and I wouldn't use that.

To make your enemies fire a bullet at your player's current position you should save the player's actual position (by value and not by reference) and calculate against that like so:
 1  2  3  4 `Vector2f direction = new Vector2f(target.x-position.x, target.y-position.y);direction.normalise(direction);position.x += direction.x*speed*delta;position.y += direction.y*speed*delta;`

 `position`
is just a Vector2f that contains your projectile's current position and
 `target`
is a Vector2f too which contains the projectile's target location.
 `speed`
should be the speed of the projectile.

This is just the basics and the first thing that I would change on this code as soon as you understand what's going on is to add some kind of time based (and definitely not distance based) acceleration.

My Blog | Jumpbutton Studio - INOP Programmer
Can't stress enough: Don't start game development until you haven't got the basics of programming down!
SauronWatchesYou
 « Reply #2 - Posted 2014-07-07 07:27:05 »

Thanks Panda! I really appreciate the detailed response about what each thing is doing. I'm going to go over it a few more times just to make sure I understand it and then will mess around with the code

Hey, you! Back to work
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