Prcessing课程（angry birds）

// angry birds 


class Bird {
    float x, y, xSpeed, ySpeed, rotation;
    boolean stopped = false;
    
    
    Bird(float xx, float yy) {
        x = xx;
        y =yy;
        
        xSpeed = (mouseX - x) /50.0;
        ySpeed = (mouseY -y) /50.0;
    }
    
    void update() {
        x += xSpeed;
        y += ySpeed;
        ySpeed += GRAV;
        
        if(y > 300) {
            xSpeed = ySpeed = 0;
            stopped = true;
        } else {
            rotation += ROTATE;
        }
    }
    
    void display() {
        translate(x,y);
        image(redImg, 0, 0, 64, 64);
        resetMatrix();
    }
}
    
String redUrl = "https://vignette.wikia.nocookie.net/p__/images/e/e2/Red_bird.png/revision/latest?cb=20150530184407&path-prefix=protagonist";

PImage redImg = loadImage(redUrl);

Bird red;
float GRAV = .05;
float ROTATE = 0.1;

void setup() {
    size(600,400);
    imageMode(CENTER);
    red = new Bird(width/2, 300);
}

void draw() {
    background(128, 196, 255);
    
    fill(0,128,0);
    noStroke();
    rect(0, 300, width, 200);
    
    red.update();
    red.display();
    
    drawTrajectory();
}

void mousePressed() {
    red = new Bird(width/2, 300);
}

void drawTrajectory() {
    Bird tb = new Bird(width/2, 300);
    stroke(0, 128);
    
    while(!tb.stopped) {
        float oldX = tb.x;
        float oldY = tb.y;
        
        tb.update();
        
        line(oldX, oldY, tb.x, tb.y);
    }
    
    noStroke();
    fill(0, 64);
    ellipse(tb.x, tb.y, 30, 30);
}