#include <math.h>#include <stdlib.h>#include <time.h> #include "simulation.h" static int _width, _height;static int _dt;static Particle *_draggedParticle = NULL;static int _radius;static int _dragX, _dragY;static int _mouseX, _mouseY; voidresize(int width, int height){	_width = width;	_height = height;} voidSim_Init(int width, int height, int radius, int dt){	resize(width, height);	_radius = radius;	_dt = dt;} voidSim_Quit(){	_draggedParticle = NULL;} voidSim_Resize(int width, int height){	resize(width, height);} voidSim_Randomize(Particle *particles, int count){	int i; 	time_t t;	srand((unsigned)time(&t)); 	for(i = 0; i < count; i++) {		Particle *p = &particles[i];		p->x = (rand() % _width) - _radius;		p->y = (rand() % _height) - _radius;		p->angle = rand() % 360;		p->xVel = ((double)(rand() % 100) / 1000 + 0.05) * (rand() % 2 ? -1 : 1);		p->yVel = ((double)(rand() % 100) / 1000 + 0.05) * (rand() % 2 ? -1 : 1); 		switch(rand() % 3) {		case 0:			p->r = 0xFF;			p->g = 0;			p->b = 0;			break;		case 1:			p->r = 0.44 * 0xFF;			p->g = 0.87 * 0xFF;			p->b = 0.76 * 0xFF;			break;		case 2:			p->r = 0xFF;			p->g = 0xFF;			p->b = 0xFF;			break;		}		p->a = rand() % 0xFF;	}} intSim_Update(Particle *particles, int count, double deltaTime){	int collided = 0;	int i, j;	double stepTime = deltaTime * 1000 / _dt; 	for(i = 0; i < _dt; i++) { 		for(j = 0; j < count; j++) {			Particle *p = &particles[j]; 			if(_draggedParticle == p) {				p->x = _mouseX + _dragX;				p->y = _mouseY + _dragY;			} else {				if(p->x < 0) {					p->x = 0;					p->xVel *= -1;					collided = 1;				} 				if(p->x > _width - (_radius * 2)) {					p->x = _width - (_radius * 2);					p->xVel *= -1;					collided = 1;				} 				if(p->y < 0) {					p->y = 0;					p->yVel *= -1;					collided = 1;				} 				if(p->y > _height - (_radius * 2)) {					p->y = _height - (_radius * 2);					p->yVel *= -1;					collided = 1;				} 				p->x += p->xVel * stepTime;				p->y += p->yVel * stepTime;			} 			p->angle += 0.1 * stepTime; 			p->a -= 0.1 * stepTime;			if(p->a <= 0) {				p->a = 0xFF;			}		}	} 	return collided;} voidSim_UpdateDrag(int x, int y){	_mouseX = x;	_mouseY = y;} voidSim_BeginDrag(Particle *particles, int count, int x, int y){	int i;	Sim_UpdateDrag(x, y);	for(i = 0; i < count; i++) {		Particle *p = &particles[i];		int radiusSquared = _radius * _radius;		double distSquared = pow(p->x - x + _radius, 2) + pow(p->y - y + _radius, 2);		if(distSquared < radiusSquared) {			_draggedParticle = p;			_dragX = p->x - x;			_dragY = p->y - y;			break;		}	}} voidSim_EndDrag(){	if(_draggedParticle != NULL) {		_draggedParticle->xVel =			((double)(rand() % 100) / 100 + 0.1) * (rand() % 2 ? -1 : 1);		_draggedParticle->yVel =			((double)(rand() % 100) / 100 + 0.1) * (rand() % 2 ? -1 : 1);		_draggedParticle = NULL;	}}