W1503 Lines and Ellipses

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

— Merlin, The Coder

Prerequisites

• 1502 Object Attributes

Research

• Examine the back of a dollar bill. Note the pyramid on the left-hand side.

Experiment

Enter into the Sources directory of the IgisShell-Introduction project.

cd ~/projects/IgisShell-Introduction/Sources/IgisShell/

Open main.swift in emacs.

emacs main.swift

Paint a Single Blue Line

Find the function within the Painter object named "setup". Edit the contents as follows:

    func setup(canvas:Canvas) {
        let lineWidth = LineWidth(width:3)
        canvas.paint(lineWidth)

        let blue = StrokeStyle(color:Color(red:100, green:100, blue:255))
        canvas.paint(blue)

        let lines = Lines(from:Point(x:10, y:50), to:Point(x:100, y:50))
        canvas.paint(lines)
     }

Paint a Triangle

Find the function within the Painter object named "setup". Edit the contents as follows:

    func setup(canvas:Canvas) {
        let lineWidth = LineWidth(width:3)
        canvas.paint(lineWidth)

        let blue = StrokeStyle(color:Color(red:100, green:100, blue:255))
        canvas.paint(blue)

        let lines = Lines(from:Point(x:10, y:50), to:Point(x:100, y:50))
        lines.lineTo(Point(x:55, y:150))
        lines.lineTo(Point(x:10, y:50))
        canvas.paint(lines)
     }

Now, run the program and view in a browser before continuing.

Circumscribe the Triangle with an Ellipse

Find the function within the Painter object named "setup". Edit the contents as follows:

    func setup(canvas:Canvas) {
        let lineWidth = LineWidth(width:3)
        canvas.paint(lineWidth)

        let blue = StrokeStyle(color:Color(red:100, green:100, blue:255))
        canvas.paint(blue)

        let lines = Lines(from:Point(x:110, y:150), to:Point(x:200, y:150))
        lines.lineTo(Point(x:155, y:250))
        lines.lineTo(Point(x:110, y:150))
        canvas.paint(lines)

        let violet = StrokeStyle(color:Color(.blueviolet))
        canvas.paint(violet)

        let ellipse = Ellipse(center:Point(x:155, y:200), radiusX:120, radiusY:55)
        canvas.paint(ellipse)
     }

Exercises

Continuing your previous project:

1. Split your pyramid so that a few rows near the apex are separated from the body of the pyramid
2. Alter the pyramid so that these separated rows (on top) are drawn using a triangle (rather than by a rows of bricks)
3. Inside the triangle, draw an eye
4. Draw the entire pyramid in shades of green. (Use at least three different shades of green.) See this note for more information about colors.