% talking points for week 4, GUI programming with wxPython

I've adjusted the original schedule - we're doing Graphics and GUI
programming this week, events and threads next week.  It makes more
sense --- GUIs motivate events, in fact we're starting events this
week.

SNR demo - explain it simulates lab bench equipment (show photo)
Explain scope, frequency analyzer (mention Peter's EEG analyzer)
Show scope and especially freq analyzer as adjust freq, amplitude, noise 
Emphasize real-time response, hard to achieve in web application

Graphics - pictures, images
GUI - graphical user interface, UI that uses graphics and events

You can have graphics without GUI but they often use the same libraries
Graphics can be heavy on geometry, matrix math -- too deep for tonight.
Tonight we'll emphasize GUI programming - libraries, O-O programming, events

This demo uses GNU Radio library - which in turn uses wxPython GUI library.
I am experienced with GNU Radio so that's why I'm discussing wxPython tonight.

Other Python GUI libraries: TKinter (used in Downey textbook), PyQt, PyGTK, ...

All GUI libraries are very complicated, have steep learning curve.

They're all built on top of C/C++ libraries

They all use classes and objects heavily.  Object-oriented programming
as we now know it grew up with GUI programming and was (partly)
motivated by it: Xerox PARC, Alto computer, Smalltalk language.

They are all very complicated and have a steep learning curve.
(show list of classes)

Demo buttoncounter, show code

script code creates app, creates a frame object, calls MainLoop.
MainLoop contains all the event handling, returns when you close app from GUI.

Frame object is top-level window.
Frame object defines all the graphics and also the events and handlers.
Frame __init__ runs once when object created, creates all the graphics
 - in __init__, for loop populates dictionaries of graphic objects

Show wx.Button class - including inheritance

Events:

Frame event handlers run whenever you do something in GUI - click buttons.
 - in OnButton, find source of event and update approprate objects in display

binds (associates) event handler with object - the event handler is a *callback*
   we pass in the handler method as arg, on event the GUI framework will call it

Event is itself an object that gets passed to handler, event object
contains information about source of event.

Does it have to be this complicated?  Compare to HTML form + server code

If time remains, show SNR demo code - it's not much more complicated than
buttoncounter!   That's what I mean by "steep learning curve"

Same basic pattern, several kinds of events,
here no Bind method, instead callback is arg of object initializer

Also in SNR code - BoxSizer layout manager, flowgraph ...

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URLs

http://gnuradio.org/redmine/wiki/gnuradio/TutorialsWritePythonApplications

http://www.wxpython.org/ 

http://wiki.wxpython.org/Getting Started

http://www.zetcode.com/wxpython/ (tutorial)

http://www.wxpython.org/docs/api/  (reference)

http://www.wxpython.org/docs/api/wx.Button-class.html, etc. (detailed ref.)