W1501 Introduction to Objects

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

— Merlin, The Coder

Blurry reflection

Prerequisites

• W1412 Constructors

Background

• Read Computer Science I Textbook by Bourke Chapter 10. Encapsulation & Objects
• Review Presentation on Objects

Introduction

We'll begin our exploration of objects using Scenes. Scenes is an object-oriented, event-driven platform that enables us to write server-side Swift code which (rapidly) sends a series of instructions to a browser to generate visual effects, and optionally, an interactive experience. Scenes is built upon another framework called Igis.

Caution

It's important to understand that while most of the objects we'll be using have an associated visual representation, most of the objects that we build and interact with in programming will not have such a representation.

Prepare

Create a new Scenes shell project within your "Experiences" directory:

jane-williams@codermerlin:~$  cd ~/Experiences

jane-williams@codermerlin:~$  git clone https://github.com/TheCoderMerlin/ScenesShellBasic W1501

Getting started with a shell enables us to avoid writing repetitive code commonly required by all similar projects. This type of code is often called boilerplate code.

Enter the Sources/ScenesShell directory of the new project:

jane-williams@codermerlin:~$  cd W1501/Sources/ScenesShell/

Run the program. jane-williams@codermerlin:~$  run

Open a browser (or use a new tab on an already-open browser). Then, go to the URL:

http://www.codermerlin.com/users/user-name/dyn/index.html

NOTE: You MUST change user-name to your actual user name. For example, http://www.codermerlin.com/users/john-williams/dyn/index.html

You'll know you're successful if you see the title bar change to "Coder Merlin: IGIS". (The browser window will be blank because we haven't added any graphics yet.)

Helpful Hint

Helpful hint: It's useful to bookmark this page in your browser.

Hello World

Stop the running program. Return to the console and press ^C (Hold down the CONTROL key and press C)

Open main.swift in emacs.

emacs main.swift

Find the function within the Painter object named "setup". Add a line to create a Text object and then draw (render) that object on the "canvas", an imaginary surface for painting within the browser.

    func setup(canvas:Canvas) {
        let text = Text(location:Point(x:50, y:50), text:"Hello, World!")
        canvas.render(text)
    }

Remember to save the file, then suspend emacs.

Run the program and refresh the browser page.

Observe

Observe, Ponder, and Journal: : Section 1

1. What do you observe?
2. How large is the text?

Stop the running program.

Let's change the font. Resume emacs and edit the line where the text object is instantiated.

    func setup(canvas:Canvas) {
        let text = Text(location:Point(x:50, y:50), text:"Hello, World!")
        text.font = "30pt Arial"
        canvas.render(text)
    }

Remember to save the file, then suspend emacs.

Run the program and refresh the browser page.

Observe

Observe, Ponder, and Journal: : Section 2

1. What do you observe?
2. How large is the text now?

Stop the running program.

Let's add a rectangle around the text. Resume emacs and add the following lines so that the entire function appears as:

    func setup(canvas:Canvas) {
        let text = Text(location:Point(x:50, y:50), text:"Hello, World!")
        text.font = "30pt Arial"
        canvas.render(text)

        let rect = Rect(topLeft:Point(x:20, y:10), size:Size(width:300, height:50))
        let rectangle = Rectangle(rect:rect, fillMode:.stroke)
        canvas.render(rectangle)
    }

Remember to save the file, then suspend emacs.

Run the program and refresh the browser page.

Observe

Observe, Ponder, and Journal: : Section 3

1. What do you observe?
2. What is the purpose of the location parameter in the Text constructor?
3. What is the corresponding parameter named in the Rectangle?
4. What is the difference between a Rect and a Rectangle? Hint: Are you able to render a Rect?

Stop the running program.

Exercises

Exercises

Making use of your accumulated knowledge to date (loops, functions, coding style, etc.) and using only Rectangles and Text on a single canvas:

1. Draw a single rectangle (without any text)
2. Draw a grid (at least 3 x 3)
3. Draw a brick wall (at least 5 x 5)
4. Draw a pyramid constructed of bricks (at least seven rows high)
5. Draw a skyscraper with a large sign on the roof containing your name
6. Draw at least three skyscrapers of different heights on the same Canvas, each containing your name