#ifndef PARTICLE_H
#define PARTICLE_H

#include <math.h>
#include <SDL\SDL.h>
#include <SDL\SDL_gfxPrimitives.h>

#define NUM 75



class Particle
{
public:

	Particle();
	~Particle();

	void reset_particles(int n);
	void update(SDL_Surface* screen);
	void reset_all();
	void attract(struct particles *A, struct particles *B);
	void render(SDL_Surface* screen);



private:

	struct particles
	{
		double mass;
		double x, y;
		long oldX, oldY;
		long xp, yp;
		double ax, ay, vx, vy;
	}p[NUM];

	int cx, cy;


};

#endif

#include "Particle.h"
#include "Globals.h"

Particle::Particle()
{
}

Particle::~Particle()
{
}

void Particle::attract(struct particles *A, struct particles *B)
{
	double distance;
	double dist, distX, distY;
	double transX, transY;

	//increase the vector position of particle by it's velocity it's respected direction
	A->x += A->vx;
	A->y += A->vy;

	//calculate the distance between particles
	distX = A->x - B->x;
	distY = A->y - B->y;
	dist = distX*distX + distY*distY;

	if(dist != 0)
	{
		distance = 1/dist;
	}
	else dist = 0;

	transX = distX*distance;
	transY = distY*distance;

	//accelerate each particle acceleration (m*d)
	A->ax = -1 * B->mass * transX;
	A->ay = -1 * B->mass * transY;

	//increase velocity by acceleration value
	A->vx += A->ax;
	A->vy += A->ay;

	//scale position to the screen
	A->xp = cx + A->x;
	A->yp = cy + A->y;
}

//reset a number of particles
void Particle::reset_particles(int n)
{
	p[n].mass = 0.001;
	p[n].ax = 0;
	p[n].ay = 0;
	p[n].xp = 0;
	p[n].yp = 0;
	p[n].x = rand() % width/4;
	p[n].y = rand() % height/4;
	p[n].vx = 0;
	p[n].vy = 0;
}

void Particle::reset_all()
{
	int n;
	cx = width/2;
	cy = height/2;

	for(n=0; n<NUM; n++)
		resetparticles(n);
}

void Particle::update(SDL_Surface* screen)
{
	int n;
	int i;

	//erase old particle
	for(n=0; n<NUM; n++)
	{
		circleColor(screen, p[n].oldx, p[n].oldy, 5, 33);

		//apply gravity between every particle
		for(i=0; i<NUM; i++)
		{
			if(i != n) attract(&p[n], &p);
		}

		//reset particle if it gets to far away
		if((p[n].xp < 0) || (p[n].xp > 600) || (p[n].yp < 0) || (p[n].yp > 400))
			reset_particles(n);

		//plot new particle
		circleColor(screen, p[n].xp, p[n].yp, 5, 33);

		//keep track of current position
		p[n].oldX = p[n].xp;
		p[n].oldY = p[n].yp;
	}

	//draw primary partice
	circleColor(screen, p[0].xp, p[0].yp, 5, 33);
}

Particle.cpp
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(13) : error C2511: 'void Particle::attract(Particle::particles *,Particle::particles *)' : overloaded member function not found in 'Particle'
        c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(13) : see declaration of 'Particle'
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(70) : error C3861: 'resetparticles': identifier not found
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(81) : error C2039: 'oldx' : is not a member of 'Particle::particles'
        c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(30) : see declaration of 'Particle::particles'
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(81) : error C2039: 'oldy' : is not a member of 'Particle::particles'
        c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.h(30) : see declaration of 'Particle::particles'
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(86) : error C2664: 'Particle::attract' : cannot convert parameter 1 from 'Particle::particles *' to 'particles *'
        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(94) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(94) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(102) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data
c:\documents and settings\c.s.  finch\my documents\visual studio 2008\projects\no bs guide to sdl\part ii\breakout\breakout\particle.cpp(102) : warning C4244: 'argument' : conversion from 'long' to 'Sint16', possible loss of data
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