书名：代码本色：用编程模拟自然系统
作者：Daniel Shiffman
译者：周晗彬
ISBN：978-7-115-36947-5
目录
1.10 加速度的交互
一、示例代码1-11
例子和引力还有个关键的不同点，引力的大小（加速度的大小）和距离成反比，也就是说，物体离鼠标越近，加速度越大。
示例代码1-11 一组同时朝着鼠标加速的运动物体
Mover[] movers = new Mover[20];
void setup() {
size(640,360);
for (int i = 0; i < movers.length; i++) {
movers[i] = new Mover();
}
}
void draw() {
background(255);
for (int i = 0; i < movers.length; i++) {
movers[i].update();
movers[i].display();
}
}
// mover.pde
class Mover {
// The Mover tracks position, velocity, and acceleration
PVector position;
PVector velocity;
PVector acceleration;
// The Mover's maximum speed
float topspeed;
Mover() {
// Start in the center
position = new PVector(random(width),random(height));
velocity = new PVector(0,0);
topspeed = 5;
}
void update() {
// Compute a vector that points from position to mouse
PVector mouse = new PVector(mouseX,mouseY);
acceleration = PVector.sub(mouse,position);
// Set magnitude of acceleration
//acceleration.setMag(0.2);
acceleration.normalize();
acceleration.mult(0.2);
// Velocity changes according to acceleration
velocity.add(acceleration);
// Limit the velocity by topspeed
velocity.limit(topspeed);
// position changes by velocity
position.add(velocity);
}
void display() {
stroke(0);
strokeWeight(2);
fill(127,200);
ellipse(position.x,position.y,48,48);
}
}
