Introduction

This is a demonstration of one way to develop a TK program. It is an incremental approach.

This will be simple drawing program demonstrating a drawing area. With each step you do a few line of code, then test and debug it. It this way you accumulate more and more detail and functionality.

step 1 - write simple requirements

For example:

• There will be a drawing area
• Lines can be drawn on the drawing area
  • When the cursor is over the drawing area and a button held down, draw pixel(s) at that location
  • As the cursor moves a line is drawn
• The drawing area background color can be changed
• The drawing area background color is selected from a minimum of four different colors
• The line drawing color can be changed
• The line drawing color is selected from a minimum of four different colors
• There will be a "quit program" capability
• The drawing areas can be reset to a default background and line color
• Resizing will not be allowed

Note: this is not a set of formal requirements. This is for your use. It is to prevent requirements creep.

Step 2 - design decisions

• Program will be coded in Python 3
• A Canvas widget will be the drawing area
• Buttons will be used to select the drawing area background color
• Buttons will be used to select the line color
• Color buttons background color will be the color
• Color buttons text will define the color
• A button will be used to quit the program
• A button will be used to reset the drawing area
• The left mouse button will be used to draw lines
• Lines will not be strait but ragged as the cursor moves
• The title "Drawing Program" will be a TK label at the top

Note: this is not a formal design. This is for your use. It is to prevent design creep.

Steps 3 - preliminary layout

On paper, draw a layout for the program. For example:

Note: this is not a formal layout. This is for your use. It is to prevent layout changes during development.

Steps 4 - incremental code and testing

Increment 1
Increment 2
Increment 3
Increment 4
Increment 5
Continue adding code and testing

Step 5 - cleanup and comment code, and document program