supercala

Posted: **Thu Nov 11, 2010 5:11 pm**

So by using some very simple formulas in trig, and getting a bit random here and there you can make a cool star spiral. Experiment with the settings to learn how it is done.

A great online tutorial of sin and cos for radian math and rotation
http://pixwiki.bafsoft.com/mags/5/artic ... sincos.htm

2d Matrix for rotation around origin

2d matrix in inline algebraic form

and remember the change of degrees (360) to radians for the looping in the program

Code: Select all

rotRads=rot*(Math.PI/180);

here is the file in a zip to play with (library has 'mc_star' but you can use any still or animated movieclip you like)

http://www.supercala.net/tuts/flash_rot ... nd-rot.zip

Here is the code

Code: Select all

//-----
function Particle(sPar,sLvl,sX,sY)
	{
	trace("Particle>");
	this.par=sPar;
	this.mc=sPar.attachMovie("mc_star","pt_"+sLvl,sLvl);
	this.mc._alpha=0;
	this.mc.ID=sLvl;
	this.mc._x=sX;
	this.mc._y=sY;
	trace(this.mc);
	}
//-----
ParticleSystem.prototype.initParticles=function(amt)
	{
	trace("initParticles>");
	//
	len=this.parts.length;
	//
	for(a=0;a<len;a++)
		{
		this.parts.pop();
		}
	//
	for(a=0;a<amt;a++)
		{
		trace(this.partBase+a);
		this.parts[a]=new Particle(this.mc,this.partBase+a,0,0);
		trace("^"+this.parts[a].mc);
		}
	}
//-----
ParticleSystem.prototype.initPart=function(sPar)
	{
	dist=this.minDist+Math.floor(Math.random()*this.maxOffset+1);
	sPar.starScale=dist/2;
	sPar._xscale=sPar._yscale=sPar.starScale;
	sPar._x=dist;
	spar._y=0;
	sPar._alpha=0;
	sPar.lifePos=-1;
	sPar.lifeSpan=this.minLife+Math.floor(Math.random()*this.lifeOffset);
	tgt.spd=Math.random()*3;
	}
//-----
ParticleSystem.prototype.anim=function()
	{
	//spread=10;
	trace("anim>");
	amt=this.parts.length;
	//
	for(a=0;a<amt;a++)
		{
		tgt=this.parts[a].mc;
		this.initPart(tgt,dist,0);
		tgt.classPar=this;
		//
		tgt.onEnterFrame=function()
			{
			this.lifePos++;
			oX=this._x;
			oY=this._y;
			rot=this.spd;
			rotRads=rot*(Math.PI/180);
			nX=Math.cos(rotRads)*oX-Math.sin(rotRads)*oY;
			this._x=nX;
			nY=Math.sin(rotRads)*oX+Math.cos(rotRads)*oY;
			this._y=nY;
			//
			if(this.lifePos>this.lifeSpan)
				{
				this._alpha-=5;				
				}
			//
			if(this._alpha<0)
				{
				this.classPar.initPart(this);
				}
			//
			if(this.lifePos<6)
				{
				this._alpha+=20;
				}
			}
		}
	}
//-----
function ParticleSystem(sPar,sLvl,sX,sY)
	{
	this.parts=new Array();
	this.partBase=100;
	this.minDist=100;
	this.maxOffset=170;
	this.minLife=30;
	this.lifeOffset=20;
	trace("ParticleSystem>");
	this.par=sPar;
	this.mc=sPar.createEmptyMovieClip("mach_pSys"+sLvl,sLvl);
	this.mc._x=sX;
	this.mc._y=sY;
	this.initParticles(40);
	trace("?"+this.parts[0].mc);
	this.anim();
	}
//-----
function main()
	{
	pl_center._visible=false;
	pl_backsize1._visible=0;
	T1.test1=new ParticleSystem(T1.root,100,pl_center._x,pl_center._y);
	}
//-----
var T1=new Object();
T1.root=this;
main();

supercala

rotating star sprites (mc) using simple trigonometry sin cos

rotating star sprites (mc) using simple trigonometry sin cos