CSC151.02 2013F, Class 09: An Introduction to the GIMP
======================================================

_Overview_

* Preliminaries
    * Admin.
    * Preparation for quiz / confusing topics / etc.
    * Quiz
* Lab 

_Admin_

* Warning! Friday the 13th falls on a Friday this month.  (Today even.)
* The outline and what we're doing don't match very well today.  We've
  rearranged the course, but I like leaving my old notes around.
* If you're finding this difficult, know that you're not alone - this stuff is 
  challenging.  
* I don't think folks are taking enough advantage of the mentor sessions.
  If you're having difficulty in the class and not going, please drop me
  a note to explain why.
* Reading for Monday: Programming the GIMP Tools
* EC Opportunities:
    * Submit a short paragraph giving reactions/thoughts/etc.  (I don't need
      a summary)
    * CS Table NEXT Friday (Pair programming)
    * Soccer 1:30 pm Saturday against people from a very flat state
    * Other?

_Preparation for Quiz (and other discussion items)_

I have a bit of code to show you that I hope resolves some recent questions.
Then I'll give you ten minutes for additonal questions.

    #lang racket
    (require gigls/unsafe)
    
    ;;; File:
    ;;;   sample.rkt
    ;;; Author:
    ;;;   Samuel A. Rebelsky
    ;;; Summary:
    ;;    A quick sample to illustrate a variety of points about drawings.
    
    ;;; Procedure:
    ;;;   bigred
    ;;; Parameters:
    ;;;   drawing, a drawing
    ;;; Purpose:
    ;;;   To confuse students
    ;;; Produces:
    ;;;   A drawing
    ;;; Props:
    ;;;   Taken from a clicker question designed by SR and JD
    (define bigred
      (lambda (drawing)
        (drawing-recolor drawing "red")
        (drawing-scale drawing 10)))
    
    ;;; Procedure:
    ;;;   preview
    ;;; Parameters:
    ;;;   d, a drawing
    ;;; Purpose:
    ;;;   preview the drawing in a new window
    ;;; Produces:
    ;;;   img, the id of the preview image
    ;;; Preconditions:
    ;;;   (drawing-right d) >= 1
    ;;;   (drawing-bottom d) >= 1
    ;;; Postconditions:
    ;;;   img contains a rendering of d
    (define preview
      (lambda (d)
        (image-show (drawing->image d (drawing-right d) (drawing-bottom d)))))
    
    ;;; Value
    ;;;   d1, a sample drawing
    ;;; Type:
    ;;;   drawing
    ;;; Contents:
    ;;;   A black, 50x50 circle centered at (25,25)
    (define d1
      (drawing-hshift 
       (drawing-vshift
        (drawing-scale drawing-unit-circle 50)
        25)
       25))
    
    ;;; Value:
    ;;;   d2
    ;;; Type:
    ;;;   drawing
    ;;; Contents:
    ;;;   A purple 50x50 circle, centered at (75,75)
    (define d2
      (drawing-hshift 
       (drawing-vshift
        (drawing-scale 
         (drawing-recolor drawing-unit-circle "purple")
         50)
        75)
       75))
    
    ;;; Value:
    ;;;   d3
    ;;; Type:
    ;;;   drawing
    ;;; Contents:
    ;;;   A green rectangle
    (define d3
      (drawing-hshift
       (drawing-vshift
        (drawing-scale
         (drawing-recolor
          drawing-unit-square
          "green")
         30)
        20)
       80))
    
    ;;; Value:
    ;;;   scene
    ;;; Type:
    ;;;   drawing
    ;;; Summary:
    ;;;   A simple scene
    (define scene
      (drawing-group d1 d2 d3))
    
    ;;; Procedure:
    ;;;   drawing-munge
    ;;; Parameters:
    ;;;   drawing, a drawing
    ;;; Purpose:
    ;;;   Create a new drawing, based on the original drawing
    ;;; Produces:
    ;;;   new-drawing, a drawing
    (define drawing-munge
      (lambda (d)
        (drawing-recolor (drawing-scale d 1.1) "blue")))

* Puzzlement about what what happens with parameters and what happens when
  we don't name drawings
* Disappearing values

        3 + (4*5)

  Just as intermediate values in a calculation disappear, so do intermedia
  drawings.

* Behind the scenes: Procedures

* When does order matter?
    * Scale vs. shift (traditionally scale first)
    * Group vs. almost anything

* What's the difference between drawing-bottom and drawing-height

* Where should your detail be: In the parameters or the pre/post?
    * I like detail in the pre/post
    * But documentation is like an essay, not code - it need not be perfertct
      at this stage of your career.  As long as it makes sense, I'll probably
      accept it
    * Is it always possible to express postconditions formally?  NO

* Can we derive immense satisfaction from watching SamR screw up while
  trying to do relatively easy things in DrRacket/Gimp?
    * Yes
    * And you should take that as a moral of "it's okay to screw up"
    * [No, I don't do so intentionally, just to make that point.]

_Quiz_

* Is the code in part 1 in the definitions pane or the interactions pane?
    * It shouldn't matter - It will give the same result either way

Lab 
---

* Quick.