My First Processing

rotate.pde

float theta = 0;
float sh = 0;

float[] rotate(int a, int b) {
  float c = cos(theta);
  float s = sin(theta);
  return mat(a, b, c, -s, s, c);
}

float[] mat(float a, float b, float A, float B, float C, float D) {
  return new float[]{
    a * A + b * B,
    a * C + b * D
  }; 
}

void setup () {
  size(640, 480);
}

void draw() {
  background(255);
  color(0, 0, 0);
  line(width/2, 0, width/2, height);
  line(0, height/2, width, height/2);
  
  int zero[] = {width/20, height/20};
  color(255, 0, 0);
  for(int i = zero[0] - 4; i < zero[0] + 5; i++) {
    for(int j = zero[1] - 4; j < zero[1] + 5; j++) {
      float v[] = rotate(10*(i - zero[0]), 10*(j - zero[1]));
      ellipse((v[0] * (sh + 1) + zero[0] * 10), (v[1] * (sh + 1) + zero[1] * 10), 1, 1);
    }
  }
}

void mouseMoved() {
  sh = mouseY / 250.0;
  theta = mouseX / 50.0;
}