Core Ideas

Making drawings and art in Kojo with the help of the turtle is easy. You just need to be familiar with the following core ideas:

• Your program (to make a drawing) contains a sequence of lines containing commands. When you run your program, it does its job line by line, carrying out the commands from the top of the program to the bottom.
• As your program runs (line by line, from top to bottom), it draws stuff on the canvas by giving commands to the turtle.
• The clear() command is used at the beginning of a program to clean out the canvas before drawing on it.
• All straight lines on the canvas are made by the forward(numSteps) command, which draws a (straight) line in the direction of the turtle’s nose.
• The right(angle) and left(angle) commands change the direction of the turtle’s nose.
• All curved lines on the canvas are made by the right(angle, radius) and left(angle, radius) commands.
• If you want to move the turtle around the canvas without drawing lines, you have the following options:
  • use the hop(numSteps) command.
  • do a penUp(), do forwards, rights, etc. as desired, and then do a penDown().
  • do a setPosition(x, y).
• You need to know just a handful of turtle commands to make great drawings. These commands are listed on the commands reference page.
• You can use the repeat command to run a bunch of commands many times. This can make your programs shorter and easier to understand.
• If your program does a particular thing many times, you can give this thing a name and teach Kojo a new command with this name - using the def instruction.
• To draw colorful lines, use the setPenColor(color) command.
• To draw colorful filled areas, use the setFillColor(color) command.
• The above couple of commands need you to give them colors as inputs. Colors in Kojo are described in more detail on a separate page, but here’s a quick summary:
  • Use the randomColor or randomColor.fadeOut(fraction) functions to let Kojo choose a random color for you.
  • Use the ColorMaker (abbreviation - cm) - in the following ways:
    • Wherever a color is needed in your program, type cm. (or ColorMaker.) in the script editor and then type Ctrl+Space. This will pop-up a list of pre-defined colors. Select a color from this list and hit enter to get that color into your program.
    • Ctrl+Click on any color in your program to bring up a color chooser. Inside the color chooser, you can visually select a color, or manually modify the hue, saturation, lightness, and/or transparency of your desired color.
• To draw thick or thin lines, use the setPenThickness(thickness) command.

Here is an examples showing some of the above ideas in action:

Code:

clear()
def square() {
    repeat(4) {
        forward(100)
        right(90)
    }
}

clear()
setSpeed(fast)
setPenColor(cm.black)
repeat(20) {
    setFillColor(randomColor.fadeOut(0.5))
    square()
    right(18)
}

Output: