W1523 Paddle Paddle

Within these castle walls be forged Mavens of Computer Science ...

— Merlin, The Coder

A boy and girl play ping-pong, circa 1950

Prerequisites

• W1522 Ping Then Pong

Background

As we learned in the previous lab, the render event handler is invoked by the system periodically to refresh the canvas. We'll take advantage of this behavior to draw two "paddles"—one on the left and one on the right. We'll also learn how to handle keyboard input.

Experiment

Getting Started

Continue from the previous project; we'll be editing all of our files there. Enter into the the project's Sources directory.

john-williams@codermerlin: cd ~/Experiences/W1521/Sources/ScenesShell/

First Steps

Let's start by adding a new file to our project, Paddle.swift. Open the file for editing.

Add Constructor and Required Methods

Our paddle will be a rectangle. Feel free to use any colors for stroke and fill that you deem appropriate.

import Igis
import Scenes

class Paddle: RenderableEntity {
    var rectangle: Rectangle

    init(rect:Rect) {
        rectangle = Rectangle(rect:rect, fillMode:.fillAndStroke)

        // Using a meaningful name can be helpful for debugging
        super.init(name: "Paddle")
    }

    override func render(canvas:Canvas) {
        let strokeStyle = StrokeStyle(color:Color(.black))
        let fillStyle = FillStyle(color:Color(.white))
        let lineWidth = LineWidth(width:2)
        canvas.render(strokeStyle, fillStyle, lineWidth, rectangle)
    }

    func move(to point:Point) {
        rectangle.rect.topLeft = point
    }

}

Add a Left Paddle to Our InteractionLayer

We'll need to make the following changes to our InteractionLayer class:

1. import the Igis library
2. Add a paddleLeft property and initialize paddleLeft
3. Insert the paddleLeft into the InteractionLayer
4. Set the initial coordinates of paddleLeft in a new, override func preSetup

    import Igis

    let ball = Ball()
    let paddleLeft = Paddle(rect:Rect(size:Size(width:10, height:100)))

    init() {
        // Using a meaningful name can be helpful for debugging 
        super.init(name:"Interaction")

        insert(entity: ball, at: .front)
        ball.changeVelocity(velocityX: 3, velocityY: 5)

        insert(entity: paddleLeft, at: .front)
    }

   override func preSetup(canvasSize: Size, canvas: Canvas) {
        paddleLeft.move(to:Point(x: 10, y: canvasSize.center.y))
   }

Run the program and view in a browser before continuing. Ensure that the application behaves as expected.

Add a Right Paddle to Our InteractionLayer

Using what you've just learned, add a right paddle to the code.

Observe

Observe, Ponder, and Journal: Section 1

Is it necessary to define another class to add another paddle? Why or why not?

Run the program and view in a browser before continuing. Ensure that the application behaves as expected and that a paddle is on the left of the screen and another is on the right.

Add an Event Handler to Process Key Down Events

Add the following method to our InteractionLayer class:

    func onKeyDown(key:String, code:String, ctrlKey:Bool, shiftKey:Bool, altKey:Bool, metaKey:Bool) {
    }

Enable the onKeyDown handler by making the following changes:

class InteractionLayer : Layer, KeyDownHandler

   ...

    override func preSetup(canvasSize: Size, canvas: Canvas) {
        paddleLeft.move(to:Point(x: 10, y: canvasSize.center.y))

        dispatcher.registerKeyDownHandler(handler: self)
    }

    override func postTeardown() {
        dispatcher.unregisterKeyDownHandler(handler: self)
    }

Helpful Hint

Thoroughly review the Scenes Containment Example. How can containment help you provide the required functionality?

Exercises

Exercises

1. Use print statements to investigate the arguments provided to the onKeyDown event handler
2. Select sensible keys to be used to move the left paddle up and down and to move the right paddle up and down
3. Implement the required code to actually move the paddles in accordance with your selected keypresses

•  M1523-28  Complete  Merlin Mission Manager  Mission M1523-28.