PVector dir; void setup() {  size(500, 500);  rectMode(CENTER);}void draw() {  background(100);　dir = new PVector(mouseX, mouseY).sub(new PVector(pmouseX,pmouseY));  translate(mouseX,mouseY);  rotate(dir.heading());  //rotate(atan2(dir.y,dir.x));  rect(0, 0, 100,50);}

*注：在processing中，物体默认朝向为X轴正方向，即右边。