Drawing a path circle with actionscript and trigonometria

[albegago]

Hi:

I want animate a dot following a circle path using action script.

(Yeah... its easy to draw a circle path and create a motion tween... but i want to animate it using action script)

Im using this formula:
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var r = 150;
// r is the radius value

mover = function()
{
if( this._x >= -1*r && this._x <= r-1 && this._y >= 0 && this._y <= r)
// x will increase by 2 if the dot is located
// at x=-150 and x<149
// y = 0 and y <= 150
{
this._x +=2;
// increase x by 2 px
this._y = Math.sqrt ((r*r) - (this._x * this._x));
// I determine the y position using the trigonometria circle formula
}
else
{
this._x -=2;
this._y = (Math.sqrt ((r*r) - (this._x * this._x))) * (-1);
// I determine the y position using the trigonometria circle formula
// x will decrease by 2 if the dot is not located
// at x=-150 and x<149
// y = 0 and y <= 150

}

}

c1._x = -1*r;
// The dot is posted at coord x=-150
c1._y = 0;
// The dot is posted at Y=0
c1.onEnterFrame = mover;

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The formula works well... more or less...

check it and see how the dot follow the circle path, put it jumps just in the middle of the circle.

[GrantUnwin]

equation for circle:

(X-a)^2 + (Y-b)^2 = c^2

where:
|-a|=x co-ordinate of centre of circle
|-b|=y co-ordinate of centre of circle
c = radius

set the position of the dot to be the radius distance above the centre point. (this way its definatly on the line). Then move accross the X co-ordinates using the formula to find the Y co-ordinate. Or vice versa. There will be 2 solutions but IF |(X POS - OLD XPOS)| is less than 0.1 then use that 1. if you get me. very early cant be bothered im sure you can figure it out. I hope this was a help.

formula for working out X co=ordinate with Y co-ordinate is:

X = ( SqRt[c^2 - (Y-b)^2] ) + a

where:
|-a|=x co-ordinate of centre of circle
|-b|=y co-ordinate of centre of circle
c = radius
X is X co-ordinate
Y is Y co-ordinate


PS - this is just dodgy maths notation not actionscript