Dashed Lines Introduction

PIL (Pillow) has no inbuilt function for drawing dashed lines in its Draw module, necessary for many sketches or drawings. This module was based on a program seen in *Code Review* where a simple case of drawing a dashed line with an equal number of spaces was shown (thankyou Richard Weiss).

There was a variable in the original script that allowed one to start with a space rather than a dash, this is similar to the dashoffset, used in the Canvas, where dash patterns are started after a specified distance. Both these were not thought to be strictly necessary.

We will be using the dash tuple to make various patterns, see later dash tuple

One of the innate problems is that a line drawn on one of the major axes is 1.4 times shorter than the line at 45°. The user usually gives the begin and end points, so how the line changes is not remarked. To start with geometrical solutions are given, finally the problem is tackled using Bresenham's algorithm to draw a line which worked better. Extending this method the lines can be antialiased.