Comments on: Throw a ball with a sling physics Flash tutorial: Part 2 by Kevin Ward

By: edgar

edgar — Wed, 08 Jun 2011 17:52:23 +0000

Good work Kevin, Thanks for sharing

By: William

William — Tue, 15 Jun 2010 20:37:38 +0000

I made an exetremely similar tutorial, only… This my one allows you to move the points on the elastic. Actually they happen to be strikingly similar, I just came across this now.

http://willasss.deviantart.com/art/Tutorial-Ball-Band-Collision-166528666

By: Ahzrael

Ahzrael — Mon, 13 Apr 2009 00:15:55 +0000

This was a nice read, thanks :)

By: brandon

brandon — Mon, 23 Feb 2009 05:54:52 +0000

question i would like to make something similar i would like to make a trowable ball without the sling part and with boundries so that you can trow it with your mouse but i dont want gravity i think you know what i mean try to find a way to do this thanks

By: peter

peter — Fri, 05 Oct 2007 14:44:27 +0000

toworth matthew
its funny how u can write actionscript so well and not know math :) but anyway
i’ve been putting ur codes in a flash movie, and besides the faults u said there is also this one

at least at my flashstage (pro 8)
all the lines like this one give errors, because the asterix * gets changed to a “x”
line1.lineStyle(2,0*000000);

oh and i just noticed, (i was changing the coordinates to get the things in screen) and u have the node2 2 times in the top lines, u create it 2 times? i don’t realy see use for it i deleted it and it still works :) just that u know its double ;)

i placed ur game here
http://users.telenet.be/architectural_inspiration_peter_stals/matthew.swf

By: herman

herman — Mon, 17 Sep 2007 15:55:17 +0000

hey could somebody help me? I don’t understand these lines ->

var xOffset:Number=
Math.cos(angle1+Math.PI/2)*radius;

var yOffset:Number = Math.sin(angle1+Math.PI/2)*radius;

How can you know ,you should add “Math.PI/2″
to get to the right position?

Please tell me the idea !

By: Izy

Izy — Fri, 17 Aug 2007 20:20:40 +0000

You’re very correct. I’ve made some consideration on that, but I didn’t want to take too large a step from Emanuele’s original tutorial.

A good tweak would also be to allow the two points to be at different elevations.

By: Matthew

Matthew — Fri, 17 Aug 2007 19:47:44 +0000

o and also change this:
if (xpos2>xpos1) {
xspeed = 0.3;
}

if (xpos2>xpos1) {
xspeed (plus symbol)= 0.3;
}

By: Matthew

Matthew — Fri, 17 Aug 2007 19:43:17 +0000

oops I just relised it doesnt add the plus symbol for some reason so
in your code change

yspeed = gravity;
ball._y = yspeed;
xspeed *= friction;
ball._x = xspeed;

yspeed (plus symbol)= gravity;
ball._y (plus symbol)= yspeed;
xspeed *= friction;
ball._x (plus symbol)= xspeed;

obviously replaing the (plus symbol) with the actual symbol

also you will need to change any quotation marks to normal ones
just delete them and then put them in again as normal ones

o and gd luck to everyone entering the Jayisgames comp :)

By: Matthew

Matthew — Fri, 17 Aug 2007 18:24:45 +0000

Forgive me if im wrong but because Im only 12 i don’t realy understand the maths that well. So I made a much easier way to do this which although it doesnt look exactly the same you hardly notice it.
Below is the code (if you want to use it just copy it to the main timeline, youll need three balls in your library linkaged as ball,node1 and node2. Also center the registration points of the two nodes and for the ball choose the middles bottom one)

//Attach some movieclips to the stage
var node1:MovieClip = _root.attachMovie(“node1″, “node11″, 3, {_x:50, _y:350});
var node2:MovieClip = _root.attachMovie(“node2″, “node22″, 4, {_x:650, _y:350});
var ball:MovieClip = _root.attachMovie(“ball”, “balll”, 5, {_x:350, _y:200});
var node2:MovieClip = _root.attachMovie(“node2″, “node22″, 4, {_x:650, _y:350});
//The movieclips we will use as lines
var line1:MovieClip = _root.createEmptyMovieClip(“lines1″, 1);
var line2:MovieClip = _root.createEmptyMovieClip(“lines2″, 2);
line1.lineStyle(2,0×000000);
line2.lineStyle(2,0×000000);
line1.moveTo(node1.x,node1.y);
line1.lineTo(node2.x,node2.y);
//Define some variables we can use later on
var friction:Number = 0.99;
var xspeed:Number = 0;
var yspeed:Number = 0;
var gravity:Number = 0.5;
var spring:Number = 1;
var dragging:Boolean = false;
//These are for dragging the ball

ball.onPress = function() {
this.startDrag();
yspeed = 0;
xspeed = 0;
gravity = 0;
spring = 0;
dragging = true;
};

ball.onRelease = function() {
this.stopDrag();
yspeed = 0;
gravity = 0.5;
spring = 1;
dragging = false;
};

//When you click on one of the nodes the ball is placed back in its original position
node1.onRelease = function() {
_root.ball._x = 350;
_root.ball._y = 200;
xspeed = 0;
yspeed = 0;
};
node2.onRelease = function() {
_root.ball._x = 350;
_root.ball._y = 200;
xspeed = 0;
yspeed = 0;
};

//The main function
this.onEnterFrame = function() {
//Moves the ball
yspeed = gravity;
ball._y = yspeed;
xspeed *= friction;
ball._x = xspeed;
line1.clear();
line2.clear();
//If its lower than the node
if (ball._y>node1._y) {
//Check how far to the right and left the nodes are
var xpos1:Number = node1._x-ball._x;
var xpos2:Number = node2._x-ball._x;
xpos1 = -xpos1;
//If your not dragging the ball
if (dragging == false) {
//If it is further to the right than the left
if (xpos1>xpos2) {
//Move it to the left
xspeed -= 0.3;
}
//Other way round
if (xpos2>xpos1) {
xspeed = 0.3;
}
}
//Otherwise it would keep going down
yspeed -= spring;
//Draw the lines again so they are connected to the ball
line1.lineStyle(2,0×000000);
line2.lineStyle(2,0×000000);
line1.moveTo(node1._x,node1._y);
line1.lineTo(ball._x,ball._y);
line2.moveTo(node2._x,node2._y);
line2.lineTo(ball._x,ball._y);

} else {
//If it isnt below the two points draw the line so it connects the two nodes
line1.lineStyle(2,0×000000);
line1.moveTo(node1._x,node1._y);
line1.lineTo(node2._x,node2._y);
}
};