I wrote some methods to draw a curve through three points. I took the quadratic Bezier equation and solved for the control point, given the two anchor points and time t=0.5.

P(t) = a(1-t)^2 + b(2t(1-t)) + ct^2
P = P(.5) = .25a + .5b + .25c

// solve for b
.5b = P - .25a - .25c
b = 2P - .5(a + c);

=]

MovieClip.prototype.drawCurve3Pts = function (x1, y1, x2, y2, x3, y3) {
	var cx = 2*x2 - .5*(x1 + x3);
	var cy = 2*y2 - .5*(y1 + y3);
	this.moveTo (x1, y1);
	this.curveTo (cx, cy, x3, y3);
}; // Robert Penner

MovieClip.prototype.curveToThru = function (px, py, ax, ay) {
	var cx = 2*px - .5*(this._xpen + ax);
	var cy = 2*py - .5*(this._ypen + ay);
	this.curveTo (cx, cy, ax, ay);
}; // Robert Penner


// MovieClip.curveToThru() depends on these methods
// which override the built-in ones:
/*
var MCP = MovieClip.prototype;

MCP.f6moveTo = MCP.moveTo;
MCP.moveTo = function (x, y) {
	with (this) {
		f6moveTo (x, y);
		_xpen = _xpenStart = x;
		_ypen = _ypenStart = y;
	}
};

MCP.f6lineTo = MCP.lineTo;
MCP.lineTo = function (x, y) {
	with (this) {
		f6lineTo (x, y);
		_xpen = x;
		_ypen = y;
	}
};

MCP.f6curveTo = MCP.curveTo;
MCP.curveTo = function (cx, cy, ax, ay) {
	with (this) {
		f6curveTo (cx, cy, ax, ay);
		_xpen = ax;
		_ypen = ay;
	}
};
*/

Here is an example for the drawCurve3Pts() function:

this.onEnterFrame = function () {
	this.clear();
	this.lineStyle(0);
	this.drawCurve3Pts (100, 100, _xmouse, _ymouse, 400, 400);
};

[colorblind]

Pretty nice equation!

[dbonates]

Very Cool!!! But it only works on MX?? How to do it on Flash 5???

[lifaros]

hi dbdonates

sure, it can be done using flash5.
- the first step will be to download a flash 5 bezier engine (in the flas section)
- then, you will need to apply the penner´s function in order to calc the control point. thats all.!!!

cheers
lifaros

[reefscape]

Nice function,

Would it also be possible to rewrite this so it can be used for any number of points?

Bob

[McLaranium]

do I can see one example onLine? I mean: the result some site or SWF.. mo!

[jassh]

here's an example of the equation online...


http://www.quinlik.com/~jassh/robpenner/


*webspace Courtesy of DavidNetK of Quinlik.Com
Quinlik.Com Genesis Coming Soon!!

[EGOLDY]

[jassh]

here's another example with a twist of a jelly..
err.. i mean jelly effects...

http://quinlik.com/~jassh/robpenner/index2.php

tell me what you think eh !!


-jassh

p/s: Mr. Rob, i hope u dont mind me posting the example



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Quinlik.com Genesis Coming Soon!!!