Make lasers flash by screen - randomly

Hey everyone,

Sorry if I post too much here, because Im starting to get the impression I am haha ;)

Anyways, I was wondering if someone could help me. I would like to know how to randomly shoot lasers across the screen.

Now before you all shout how easy that is , let me explain what exactly it is :D


1) Have a movieclip in the library that is of a simple laser (a line)
2) The main movie randomizes a position on the left side of the stage and attaches the movie there
3) It the randomizes a position on the opposite side (right) of the stage and then moves the laser to that position

Thats pretty easy I know, but I still need a little guidance as well as help with having the laser actually POINT in the right direction


Makes me wonder if its even possible in the first place :P

Anyways, thanks everyone :D

I think the random thing to attach isn't too hard.. Just use Math.random()*stage._height. For moving the laser, that should be clear, too..

For the rotation of the laser, you can use some trigeometry.

Here's the code I usually use for that, it detects the angle between to points, and with that, you can change the rotation of the laser to fit your needs:

code:

---

if (point2x<pointx and point2y<pointy) {

			angle = Math.atan(Math.abs(point2y-pointy)/Math.abs(point2x-pointx));

			degrees = angle*pi;

		} else if (point2x<pointx and point2y>pointy) {

			angle = Math.atan(Math.abs(point2y-pointy)/Math.abs(point2x-pointx));

			degrees = angle*pi;

		}

---

EDIT: I made two if's, to check about the angle will be positive or negative, that would be important, depending on the use of the code..

You just need to declar "pi" as Math.PI before using this code..

mfg Dave

PS: If you need better explanation of the code, just post here, please ;)

Hey dave,

Thanks alot for that, Ill give it a try tomorrow. Im about to go home in about a minute from now :D

But thanks alot, this really helps and Ill see what I can do with it tomorrow :)

If you want more than one laser to appear you need to use a loop but if you don't this code should work:

speed = 20;
attachLaser = function () {
// to attach the laser and set position:
d = getNextHighestDepth();
_root.attachMovie("laser", "laser", d);
laser._x = -laser._width;
laser._y = random(Stage.height);
// to set the target location:
xtarget = Stage.width;
ytarget = random(Stage.height);
// to set the rotation:
laser._rotation = (180/Math.PI)*Math.atan2(ytarget-laser._y, xtarget-laser._x);
// to set the speed:
xspeed = (xtarget-laser._x)/speed;
yspeed = (ytarget-laser._y)/speed;
};

// make the laser move and reset when it reaches the target:
onEnterFrame = function () {
if (laser._x >= xtarget) {
laser.removeMovieClip();
attachLaser.call();
} else {
laser._x += xspeed;
laser._y += yspeed;
}
};

Add all this code to the first frame of the stage and it should work if the laser is a MC which has a linkage name of 'laser' and points straight across (left->right) (if it doesn't point straight accross it won't point towards the target).

To change the speed, change the variable 'speed' at the top (to make it faster you have to make the number smaller).

Hey nickfisher, thanks alot :)

Well, thanks to you both , Ill play around with both your ideas and see how they'll fit my needs

Thanks alot :)

Hey,

It works perfectly thank you so much. Ive seen this line (or similar ones) used alot and Ive always wondered what it does.

Im not too good with math, its one of my weak points but if someone could please explain how this rotation part works?

code:

---

laser._rotation = (180/Math.PI)*Math.atan2(ytarget-laser._y, xtarget-laser._x);

---

Thanks :)

I'm not sure either but all I know is that you set which direction to point it at in the brackets at the end. If you set the ytarget and xtarget to _ymouse and _xmouse it will point at the mouse

Copied, hmm? ;)

So, it works like that:

Math.atan2 returns the Bogenmass ( don't know the word in english, sorry.. ) between the point ( arguments ) and the X axis. Your arguments are the distances between the target and the beginning points, with that, you will get the correct value.This value is between -2*pi and 2*pi.

So, you need to multiplicate it with 180/pi ( Convert between "Bogenmass" and angle/deegre ) to get a angle ( or deegres - again my bad english ) value.

If you didn't understood it, just feel free to ask again..
Maybe something is written incorrect, but I'm trying to get my english to a higher standart..

mfg Dave

i tell you what, if my Maths teacher had of said "Pay attention class, if you know maths you can create games" i would be alot happier now.

I agree with you Mr Malee haha..

As for Dave. Let me try to understand : *Ahem*

code:

---

laser._rotation = (180/Math.PI)*Math.atan2(ytarget-laser._y, xtarget-laser._x); 

---

180/Math.PI - this either returns a negative or positive value, which in turn is the degree/angle in which the laser will fire?
I think I remember this from Math class, something about Radians right?

Math.atan2(ytarget-laser._y, xtarget-laser._x - you then multiply it by Math.atan2, and the arguments (or the stuff in brackets) are the DIFFERENCE between the end and start point?

Is that what Bogenmass means, the difference?

What language is that anyways?

Quote:

---

Originally Posted by Osteel

code:

---

laser._rotation = (180/Math.PI)*Math.atan2(ytarget-laser._y, xtarget-laser._x); 

---

180/Math.PI - this either returns a negative or positive value, which in turn is the degree/angle in which the laser will fire?
I think I remember this from Math class, something about Radians right?

Math.atan2(ytarget-laser._y, xtarget-laser._x - you then multiply it by Math.atan2, and the arguments (or the stuff in brackets) are the DIFFERENCE between the end and start point?

Is that what Bogenmass means, the difference?

What language is that anyways?

---

It is german :)

So, Math.PI just returns PI, and 180/pi is always the same, it should be around 52 or so..

This value is needed to convert radians ( that's what the translator gave me for Bogenmass ) to deegres/angles. And a radian is always between -(2pi) and 2pi..

Math.atan2 is something like that:

Code:

---

  I
  I
  I
  I
  I
  I
  I  W
  I    I  < Z2
0- I____I_____
  (___)
    Z1

---

So, math.atan2 get's the radiant between 0 and W. It uses two parameters, Z1 and Z2. Z1 is the x value of W, and Z2 is the y value of W. With this two parameters, it calculates the radiant between 0 and W.

mfg Dave

OOH, I think Im starting to see what you mean. Too bad I never really paid attention to radians in school, it would have helped haha.



Anyways, I have a totally different question but thought it best to post it here since I write too many threads

I have a moving ship (related to the laser question) and it works fine and all. But I would just like to get it to glide a bit more after you release the "UP" (forward) button.

code:

---

onClipEvent (enterFrame) {

	if (Key.isDown(Key.UP)) {

		speed += 1;

		_root.moving++;

	}

	if (Key.isDown(Key.DOWN)) {

		speed -= .2;

	}

	if (Math.abs(speed)>20) {

		speed *= .7;

	}

	if (Key.isDown(Key.LEFT)) {

		_rotation -= 5;

	}

	if (Key.isDown(Key.RIGHT)) {

		_rotation += 5;

	}

	speed *= .90;

	x = Math.sin(+_rotation*(Math.PI/180))*speed;

	y = Math.cos(+_rotation*(Math.PI/180))*speed*-1;

	_x += x;

	_y += y;

}

---

I was able to accomplish this be changing the speed *= .90; to a higher number, but it also made the ship go extremely fast

If someone could lend assistance ? :D

You simply have to make the speed increase by a lower number (e.g. 0.5) becuase the speed *= .9 plays every frame, even when you're accelerating. The higher the *= value the faster it will move.

Hey nick,

I know what you mean, but Im asking (if its even possible in the first place) to make the speed stay the same way it currently is, but make the glide (when you release UP) a bit 'stronger'

If you use that code up there on an object , you'll see that it does have a small little glide to it.

We're trying to make a game , space related, so the Glide would add more of a 'spacy no-friction' effect

:D

aah,

try this:

if (Key.isDown(Key.UP)) {
speed *= .9;
}else{
speed *= .(whatever value you want goes here eg. 95);
}

Haha, sometimes I feel like an idiot

Thanks alot nick, it works perfectly :)

no problem :thumbsup:

isnt it -2pi and 2pi that radians go to?

Quote:

---

Originally Posted by chuckury

isnt it -2pi and 2pi that radians go to?

---

Oh, yeah, you're right.. Little mistake, I'm going to edit my post, thanks :)

mfg Dave

and they could technically go higher than that for example 720 degrees is 4pi, which of course is the equivalent of 2pi.