An Introduction to Interactive Programming in Python - Week three

Canvas — Canvas and drawing

The canvas is the area associated with an application where information contain in the application may be drawn.

In SimpleGUI applications, the width and height of the canvas are specified (in pixels) in  create_frame . (A pixel is the smallest unit of area that your computer can draw in.)

The origin for the canvas is the upper left-hand corner.

Positions in the canvas are specified as pairs  [x,y]  where  x  is the horizontal coordinate and  y  is the vertical coordinate.

Lecture examples - Canvas and Drawing

More examples - Structure

Event-driven drawing — Canvas and drawing

Computers refresh their screens around 60 times per sec.

For each application, the computer calls a special event handler, the draw handler, that is registered to the application.

In SimpleGUI, the draw handler is registered via  set_draw_handler .

The draw handler can modify the canvas via simple draw operations defined in SimplGUI

Lecture examples - Canvas and Drawing

More examples - Structure, Echo

String operations — String processing

The function  str  converts other types of data into a string.

The concatenation operator  +  joins two strings to form a single string,

The  i th element of a string  my_string  can be access via  my_string[i] . Note that strings are immutable (cannot be changed).

Substrings of  my_string  can be accessed via slicing .

Lecture examples - Strings, Dollars and Cents One, Dollars and Cents Two

More examples - Operations, Input Checking, Initials

Drawing text — Interactive drawing

The method  draw_text  draws a string when given a position (lower left corner), a font size and a color.

The method  draw_circle  (see "More examples"below) draws a circle at a given point with a given radius in pixels. To draw a point, draw a circle of radius one.

The method  draw_line  (see "More examples"below) draws a line between two points.

The method  draw_polygon  (see "More examples"below) draws a sequence of points (enclosed in square brackets and separated by commas) as a closed polygon.

Colors for drawing methods can be specified as HTML color strings;  "White", "Red", "Green", ...

Lecture examples - Drawing, Interactive Drawing

More examples - Shapes, Pictures, Hidden Picture

Timers — Timers

Timers are another component of SimpleGUI that generate regularly timed events.

Users create a timer using  create_timer  with a specified interval and event handler.

The timer calls its associated event handler regularly at the given interval.

A timer  t  is started with  t.start()  and is stopped by  t.stop() .

Lecture examples - Timers

More examples - Blinking Text, Reaction Time

Programming Tips — Week 3 (pt. 1), Week 3 (pt. 2)
from: https://class.coursera.org/interactivepython-005/wiki/view?page=week3