blending circles

int diam = 175;

float radius = 100; 

int numCircles; 

float[] step;

float incStep, inc; 

int bgColor = 255;

float mx, my;

​

PGraphics pg1, pg2;

​

void setup() {

  size(400, 400);

  noStroke();

  smooth();

  frameRate(200); 

  background(bgColor);

​

  pg1 = createGraphics(width, height);

  pg2 = createGraphics(diam+2, diam+2);

​

  mx = width/2;

  my = height/2;

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  numCircles = 5; 

  step = new float[numCircles];

  for (int i = 0; i < numCircles; i++) {

    step[i] = 0;

  }

  incStep = 0.02;

}

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void draw() {

  background(bgColor);

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  float x, y;

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  pg1.beginDraw();

  pg1.background(0, 0);

  pg1.endDraw(); 

​

  inc = 0.01; 

  for (int i = 0; i < numCircles; i++) {

​

    x = mx + radius * cos(step[i]);

    y = my + radius * sin(step[i]);

    drawEllipse(x, y); 

    x = mx + radius * cos(-step[i]);

    y = my + radius * sin(-step[i]);

    drawEllipse(x, y); 

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    x = mx + radius * cos(step[i]+PI);

    y = my + radius * sin(step[i]+PI);

    drawEllipse(x, y);  

    x = mx + radius * cos(-step[i]-PI);

    y = my + radius * sin(-step[i]-PI);

    drawEllipse(x, y); 

​

    step[i] += inc; 

    inc += incStep;

  }

​

  image(pg1, 0, 0);

}

​

void drawEllipse(float _x, float _y) {

  int sx, sy; 

​

  // only blend the area around the ellipse to speed things up

  sx = (int) (_x - diam/2); 

  sy = (int) (_y - diam/2);

​

  pg2.beginDraw();

  pg2.background(0, 0);

  pg2.noStroke();

  pg2.smooth();

  pg2.fill(255);

  pg2.ellipse(diam/2 + 1, diam/2 + 1, diam, diam);

  pg2.endDraw(); 

​

  pg1.blend(pg2, 0, 0, pg2.width, pg2.height, sx-1, sy-1, pg2.width, pg2.height, EXCLUSION);

}

​

​

​