Code HS Animation Unit

What does this program do?

var ball;

function start(){

ball = new Circle(40);

add(ball);

setTimer(draw, 20);

}

function draw(){

ball.move(2, 2);

}

• Animates a ball by moving it down and to the right once every 20 milliseconds.

  Notes: Correct! setTimer(draw, 20) will result in the function draw being called every 20 milliseconds, and each time it is called it moves the ball down and to the right.

• Animates a ball by moving it up and to the right once every 20 milliseconds

  Notes: setTimer(draw, 20) will result in the function draw being called every 20 milliseconds, and each time it is called it moves the ball down and to the right.

• Animates a ball by moving it down and to the right every 20 seconds

  Notes: setTimer(draw, 20) will result in the function draw being called every 20 milliseconds, and each time it is called it moves the ball down and to the right.

var ball;

function start(){

ball = new Circle(40);

add(ball);

setTimer(draw, 20);

}

function draw(){

ball.move(2, 2);

}

Which of the two statements is true?

• ball is a local variable

• the ball variable in draw is different from the ball variable in start

• ball is a global variable

• ball’s scope includes both start and draw

var ball;

function start(){

ball = new Circle(40);

add(ball);

setTimer(draw, 20);

mouseClickMethod(stopAnimation);

}

function draw(){

ball.move(2, 2);

}

function stopAnimation(e){

//your code here

...

}

Which statement would stop the animation in this program?

• stopTimer(ball.move(2, 2));

• stopTimer(draw);

• stopTimer(draw());

• stopTimer(draw, 20);

1 var ball;

2 var moveCounter = 0;

3 function draw(){

4

5 ball.move(2, 2);

6 moveCounter++;

7

8 if(moveCounter == 25){

9 stopTimer(draw);

10 }

11 }

12

13 function start(){

14 ball = new Circle(40);

15 add(ball);

14 setTimer(draw, 20);

15 }

How many times will the ball be moved before the animation stops?

• 20

• 40

• 2

• 25

Which of the following are techniques that make our code more reusable?

• Using constants instead of magic numbers

• Using specific values in our functions rather than using parameters

• Writing multiple functions that solve small subproblems rather than one function that solves the entire problem.

• Writing as few lines of code as possible

Which function has better reusability?

• function drawCircle(x, y, radius, color){

  var circle = new Circle(radius);

  circle.setPosition(x, y);

  circle.setColor(color);

  add(circle);

  }

• function drawGreenCircleInCenter(radius){

  var circle = new Circle(radius);

  circle.setPosition(getWidth() / 2, getHeight() / 2);

  circle.setColor(Color.green);

  add(circle);

  }

What statement should we use to determine if ball is hitting the bottom edge of the window?

• if(ball.getX() + ball.getRadius() < 0){

  //ball is hitting bottom edge

  }

• if(ball.getY() - ball.getRadius() < 0){

  //ball is hitting bottom edge

  }

• if(ball.getY() + ball.getRadius() > getHeight()){

  //ball is hitting bottom edge

  }

• if(ball.getY() + ball.getRadius() < 0){

  //ball is hitting bottom edge

  }

Which of the following statements will call the function paint every time the mouse is moved?

• mouseMoveMethod(paint, e);

• mouseMoveMethod(paint);

• mouseMoveMethod(paint());

• mouseMoveMethod(paint(e));

What is a callback function?

• A function called at the bottom of the start function

• A function passed to an event handler that is called every time a certain event happens

In the following statement:

mouseMoveMethod(draw);

Which part is the event handler?

• mouseMoveMethod

• draw

• e

• none