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ParticleSystem.pde
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ParticleSystem.pde
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/*
Skyline:
Input image: > skylineThreshold means particle freezen when location hit
Input image is transformed slightly:
- bottom pixel in each row in skyline is set to 254
- when a particle reaches bottom pixel, bottom pixel is set to 255 and particle is deleted
(to avoid growing amount of frozen particles)
*/
class ParticleSystem
{
ArrayList<Particle> particles;
PImage sprite;
PVector frameMin = null;
PVector frameMax = null;
PImage skyline;
PVector skylinePosition;
PGraphics layer;
int skylineThreshold = 50;
int stormyness = 0; // [0..255] 0 = off, 255 = max
private float lastTime = 0;
private int[] lowestPointOnSkyline;
private float accumulatedTime = 0;
boolean invisibleSnow = false;
ParticleSystem(PGraphics layer, PImage sprite)
{
this.layer = layer;
this.sprite = sprite;
particles = new ArrayList<Particle>();
lastTime = 0;
//populate();
}
void populate()
{
for (int i=0; i<100; i++)
{
Particle p = new Particle(layer, sprite);
particles.add(p);
p.position = new PVector(i*2, 20);
p.velocity = new PVector(random(0.1, 1), random(0.5, 5));
p.acceleration = new PVector(0, random(0, 0.5));
}
}
// position is upper left corner of image
void setSkyline(PImage skyline, PVector position)
{
this.skyline = skyline;
this.skylinePosition = position;
updateSkyline();
}
void updateSkyline()
{
this.skyline.loadPixels();
lowestPointOnSkyline = new int[this.skyline.width];
Arrays.fill(lowestPointOnSkyline, this.skyline.height);
for (int x = 0; x < this.skyline.width; x++)
{
boolean first = true;
for (int y = this.skyline.height - 1; y >= 0; y--)
{
int loc = y * this.skyline.width + x;
if (red(this.skyline.pixels[loc]) > skylineThreshold)
{
if (first)
{
lowestPointOnSkyline[x] = y;
first = false;
}
}
}
}
}
void addParticle(Particle p)
{
particles.add(p);
}
void update()
{
float time = (float) millis() / 1000.0;
float dt = time - lastTime;
if (lastTime == 0)
dt = 0;
lastTime = time;
update(dt);
}
// dt is difference in time since last time the function was called, given in seconds
void update(float dt)
{
if (dt <= 0)
return;
accumulatedTime += dt;
Iterator<Particle> it = particles.iterator();
while (it.hasNext())
{
Particle particle = it.next();
applyForce(particle);
particle.update(dt);
checkInsideFrame(particle);
checkSkyline(particle);
if (particle.isDead())
{
it.remove();
}
}
}
void draw()
{
imageMode(CENTER);
for (Particle particle: particles)
{
if ( (!invisibleSnow) || (invisibleSnow && particle.frozen))
particle.draw();
}
}
int numParticles()
{
return particles.size();
}
void unfreezeAll()
{
for (Particle particle: particles)
{
particle.frozen = false;
}
}
private void applyForce(Particle particle)
{
//if (stormyness <= 4)
// return;
float scale = (float)stormyness / 255.0;
float sign = particle.position.z < 0 ? -1.0 : 1.0;
float phase = 400.0 * sin (accumulatedTime / 5.0 * 2 * PI) + random(-30, 30);
float amp = scale * 100.0;
float wavelength = 600 + 400 * sin(accumulatedTime / 10.0 * 2 * PI);
PVector f = new PVector(
amp * sign * sin((particle.position.x + phase) / wavelength * 2 * PI),
amp * 0.5 * ( 0.2 + cos((particle.position.x + phase) / wavelength * 2 * PI)));
particle.setForce(f);
particle.velocityBlend = 1.0 - scale;
}
private void checkInsideFrame(Particle particle)
{
if ( (frameMin != null) && (frameMax != null) &&
((particle.position.x < frameMin.x) || (particle.position.y < frameMin.y) ||
(particle.position.x > frameMax.x) || (particle.position.y > frameMax.y)) )
{
particle.dead = true;
//print("-");
}
}
private void checkSkyline(Particle particle)
{
if (this.skyline == null)
return;
float fsx = particle.position.x - skylinePosition.x;
fsx = fsx < 0 ? 0 : fsx > this.skyline.width - 1 ? this.skyline.width - 1 : fsx;
float fsy = particle.position.y - skylinePosition.y;
fsy = fsy < 0 ? 0 : fsy > this.skyline.height - 1 ? this.skyline.height - 1 : fsy;
int sx = round(fsx);
int sy = round(fsy);
int loc = sy * this.skyline.width + sx;
//println("x: " + sx + ", y: " + sy + " - " + loc + " - " + particle.position);
if (red(skyline.pixels[loc]) > skylineThreshold)
{
particle.frozen = true;
for (int y=-1; y<=1; y++)
{
for (int x=-1; x<=1; x++)
{
loc = (sy + y) * this.skyline.width + (sx + x);
if (loc < skyline.pixels.length)
{
skyline.pixels[loc] = 0; // remove pixel in skyline
}
}
}
}
if ( (sx < lowestPointOnSkyline.length) && (sy > lowestPointOnSkyline[sx]))
particle.dead = true; // don't snow past last pixel in row
}
boolean lessThan(PVector v1, PVector v2)
{
return (v1.x < v2.x) && (v1.y < v2.y);
}
boolean greaterThan(PVector v1, PVector v2)
{
return (v1.x > v2.x) && (v1.y > v2.y);
}
}