Pen Line Caps
The turtle pen on has had some changes recently. There are some new things you may want to try.
The original round turtle pen was great for geometric line art: all the round line ends and corners were easy to join up.
But what happens when you want to draw a bar graph?
jumpto -50, -50 pen orange, 50 fd 100 jumpto 50, -50 pen red, 50 fd 50
Although the right red bar (50) should be half the size of the left orange bar (100), it's not. The red bar is too big because of the huge circular pen.
The solution is to use a flat pen. In the web Canvas standard, a pen that draws flush flat line ends has a 'butt' lineCap (as opposed to 'round' or 'square'). With the turtle pen, you can get this by adding 'butt' (in quotes) as another argument to the pen function
jumpto -50, -50 pen orange, 50, 'butt' fd 100 jumpto 50, -50 pen red, 50, 'butt' fd 50