Processing 入门教程（六）宇宙飞船大战外星人

飞船跟随鼠标移动，按 a键 发射子弹 

主类：

float x, y;
//x,y是圆心坐标
float easing = 0.01;
Particle p;

float diameterWidth = 32.0, 
  diameterHeight = 4.0;


void draw_a_UFO(float x, float y)
{
  fill(255, 0, 0);
  ellipse(x, y, diameterWidth / 3, diameterHeight * 2.5);
  fill(0, 255, 0);
  ellipse(x, y, diameterWidth, diameterHeight); 
  int colornum = int(random(0, 255));

  fill(colornum);
  ellipse(x-diameterWidth/2, y, diameterWidth / 3, diameterHeight * 2.5); 
  ellipse(x+diameterWidth/2, y, diameterWidth / 3, diameterHeight * 2.5);
}    

boolean isShoot = false;
boolean isKeyPressedFirst = true;
boolean isFirst = true;
void setup()
{
  size(720, 404);
  smooth();
  x = 0.5 * width;
  y = 0.5 * height;
}
void keyPressed() {
   if (key == 'a') {

   isKeyPressedFirst= true;
  }
  
}
void keyReleased() {
 if (key == 'a') {

    if (isKeyPressedFirst) {
      println("aaa");
      isShoot = true;
      isFirst = true;
      isKeyPressedFirst= false;
    }
  }
}
void draw()
{
  background(0);
  float targetX = mouseX, 
    targetY = mouseY;

  x += (targetX - x) * easing;
  y += (targetY - y) * easing;
  noStroke();
  draw_a_UFO(x, y);
  if (isShoot) { 

    if (isFirst) {
      p  = new Particle(new PVector(x, y));
      isFirst = false;
    }
    p.run();
  }
}

子弹（粒子）类：

class Particle {
  PVector location;
  PVector velocity;
  PVector acceleration;
 
  float lifespan;
  Particle(PVector l) {
    // The acceleration
    acceleration = new PVector(0, 0);
    // circel's x and y ==> range
    velocity = new PVector(0, random(-20, 0));
    // apawn's position
    location = l.copy();
    // the circle life time
    lifespan = 255.0;
  }
  void run() {
    update();
    display();
  }
  void update() {
    velocity.add(acceleration);
    location.add(velocity);
    lifespan-=1.0;
  }
 
  boolean isDead() {
    if (lifespan <= 0) {
      return true;
    } else {
      return false;
    }
  }
  void display() {
    // border
    stroke(0, lifespan);
    // border's weight
    strokeWeight(1);
    float r = random(0,255);
    float g = random(0,255);
    float b = random(0,255);
    // random the circle's color
    fill(r,g,b, lifespan);
    // draw circle
    ellipse(location.x, location.y, 8, 8);
  }
}

效果图如下：