Processing入門したので対称定規を作ってみた。Processing強力すぎました。協力してくれた @8q に感謝です。

symmetry.pde

void setup(){
  size(640,360);
  background(0);
  frameRate(60);  
  stroke(120,100,210);
}
void draw(){
  if(mouseButton == LEFT){  
    int px1 = pmouseX - width / 2;
    int py = pmouseY - height / 2;
    int px2 = width/2 - pmouseX;
    int x1 = mouseX - width / 2;
    int y = mouseY - height / 2;
    int x2 = width/2 - mouseX;
    translate(width/2,height/2);
    for(int i = 0;i<6;i++){
      rotate(60 * PI / 180);
      line(px1,py,x1,y);
      line(px2,py,x2,y);
    }
  }
  else if(mouseButton == RIGHT){
    clear();
  }
}

symmetry_color.pde

int count = 0;
void setup(){
  size(640,360);
  background(0);
  frameRate(60);  
}
void draw(){
  if(mouseButton == LEFT){  
    int px1 = pmouseX - width / 2;
    int py = pmouseY - height / 2;
    int px2 = width/2 - pmouseX;
    int x1 = mouseX - width / 2;
    int y = mouseY - height / 2;
    int x2 = width/2 - mouseX;
    translate(width/2,height/2);
    for(int i = 0;i<6;i++){
      rotate(60 * PI / 180);
      line(px1,py,x1,y);
      line(px2,py,x2,y);
    }
    count++;
    stroke(255 * abs(cos((float)count/200)), 255 * abs(cos((float)count/100)), 255 * abs(sin((float)count/300)));
  }
  else if(mouseButton == RIGHT){
    clear();
  }
}