Interaction Design Wiki ･ Programming

Animation

In this simple program, we animate an ellipse to always chase a point defined by the mouse. The ellipse only ever moves a percentage of the distance between it and the target destination in each step.

The PVector object is used to handle the coordinates and the simple math operations.

PVector pos;
PVector targetPos;
PVector mousePos;
void setup() {
  size(1000, 600);
  fill(0);
  pos = new PVector(0, 0);
  targetPos = new PVector(0, 0);
  mousePos = new PVector(width/2, height/2);
}

void draw() {
  background(255);
  targetPos.set(mousePos); 
  targetPos.sub(pos);  // find the vector between mouse position and ellipse position
  targetPos.mult(.2); // each step in the animation will move this percentage of the distance to the target position
  pos.add(targetPos);
  ellipse(pos.x, pos.y, 60, 60);
}
void mousePressed() {
  mousePos.set(mouseX, mouseY);
};

Exercise 10

Add an additional ellipse that follows the mouse at a slower rate than the first ellipse.

Modify the code so that the ellipse always follows the mouse position.

Replace with the ellipse with another shape (like a triangle or even a car) , and keep it pointed towards the mouse.

Exercise Solution Using Arrays

Expand source

PVector[] pos;
PVector[] targetPos;
PVector mousePos;
int arrayLength = 5;
void setup() {
  size(1000, 600);
  fill(0);

  pos = new PVector[arrayLength];
  targetPos = new PVector[arrayLength];

  for (int i = 0; i<pos.length; i++) { 
    pos[i] = new PVector(0, 0);
    targetPos[i] = new PVector(0, 0);
  }
  mousePos = new PVector(width/2, height/2);
}

void draw() {
    mousePos.set(mouseX, mouseY);
  background(255);
  
    for (int i = 0; i<pos.length; i++) { 
        targetPos[i].set(mousePos); 
        targetPos[i].sub(pos[i]);  // find the vector between mouse position and ellipse position
        targetPos[i].mult((i*0.02)+.02); // each step in the animation will move this percentage of the distance to the target position
        pos[i].add(targetPos[i]);
        ellipse(pos[i].x, pos[i].y, 60, 60);
    }
}

Solution using a class.

classExample.zip