W1501 Introduction to Objects

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

— Merlin, The Coder

Research

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

Create

First Steps

Begin a new project.

Create an Igis shell project within your "project" directory.

cd ~/projects
git clone https://github.com/TangoGolfDigital/IgisShellD IgisShell-Introduction

Enter into the Sources directory of the new project.

cd IgisShell-Introduction/Sources/IgisShellD/

Run the program.

./run.sh

Open a browser (or use a new tab on an already-open browser). 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: It's useful to bookmark this page in your browser.

Hello World

Stop the running program with ^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.

What do you observe? 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!", font:"30pt Arial")
        canvas.render(text)
    }

Remember to save the file, then suspend emacs.

Run the program and refresh the browser page.

What do you observe? How large is the text now?

Let's add a rectangle around the text. Interrupt the running program and then 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!", font:"30pt Arial")
        canvas.paint(text)

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

Now, suspend emacs and then run the program again.

swift run

Now, refresh the browser page.

Exercises

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

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