Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
  • Talk about quiz.
• Optimism
  • A bit about design.
  • A bit about color theory.
  • Exploring some images and design spaces.

Preliminaries

Admin

• New partners!
• Mentor session Monday (tonight) at 7:00 p.m.
• Work returned (I hope): Quiz 3.
• Virtual machine somewhat available. URL to be announced. Get info on using it at http://www.cs.grinnell.edu/~rebelsky/CSC151/UserGuide.md

Upcoming Work

• Exam 1.
  • Exam due in electronic form due Tuesday at 10:30 p.m. (free extension until Wednesday at 10:30 p.m.).
  • Exam due in printed form Wednesday (free extension until Thursday at review time).
  • Required epilogue due Wednesday at 10:30 p.m. (free extension until Wednesday at 11:00 p.m.)
• No lab writeup for today!
• Today will be more of a discussion day. That means we have time for questions on the exam and more at the beginning.
• Reading for Tuesday
  • Raster Graphics: Images from Pixels and Colors
  • RGB Colors

Extra Credit Opportunities

Academic

• Education Film, Wednesday night
• TEDx Grinnell, February 21

Miscellaneous

• Read and comment on the new Grinnell College Guide to Preventing, Reporting, and Responding to Sexual Harassment and Sexual Misconduct. Angela Voos says that she would really like to know what kinds of things might go in an FAQ or instructional video about the reporting process.

Peer Support (Afternoon Section)

• Swimming, Conference Championships, February 13-15, The Osgood

Recommended, But no EC

• 2 <3 GC day on Wednesday.

Questions

What's the difference between a drawing and an image?

A drawing is a conceptual thing; it's a collection of colored ellipses and rectangles. An image, in contrast, is a reference to GIMP's rendering of something visual.

How many tests is enough?

Make sure that you cover all the cases, but each test can cover multiple cases. I would guess that ten different tests would suffice.

Getting the rectangles on top of the image is challenging. Any hints?

See the exam for hints.

_What's the relationship between hshift-drawing and drawing-hshift.

It's just the order of parameters. (hshift-drawing AMT DRAWING) vs. (drawing-hshift DRAWING AMT). It's a matter of taste which you use.

Should we show you our experiments?

Yes.

Copy from the interactions pane. Paste into the definition pane. Select. Then comment out with semicolons (under the Racket menu).

Is there a procedure for finding the center of a shape?

Yes.

http://www.cs.grinnell.edu/~rebelsky/Courses/CSC151/2015S/labs/rackunit-drawings-lab.html

http://www.cs.grinnell.edu/~rebelsky/Courses/CSC151/2015S/eboards.am/extra.03.html

Can we give you multiple versions of a procedure in the hope that you will find one more to your liking?

If you indicate that the less correct ones are incorrect, yes.

About Quiz 3

Problem 1: Find the difference between a number and the square of its square root

    (define error-root-squared
      (lambda (number)
        (- number (square (sqrt number)))))

    (define error-root-squared
      (lambda (x)
        (- x (* (sqrt x) (sqrt x)))))

    (define error-root-squared
      (lambda (val)
        (- val (expt (sqrt val) 2))))

• Remember: The thing you are subtracting from comes on the left.
• We use display rarely.

Problem 2: Given lots of weird code, figure out what it does.

(define circ
  (hshift-drawing 0.5 (vshift-drawing 0.5 drawing-unit-circle)))

• Is this defining a procedure or a value or ...? It's defining a value; a drawing. We would need a lambda for it to be a procedure.
• When you are describing a drawing to someone else, you normally specify a variety of characteristics
  • Position: Left, top, bottom, right
  • Color
  • Type: Rectangle, Ellipse, Group
  • Height and width (given by scaling)
  • Center x and center y

• Given all of that, how would you describe circ?

  • A circle
  • Height and width of 1
  • Center at (0.5,0.5)
  • Top at 0, Left at 0, Bottom at 1, Right at 1

  (define shape (lambda (h v) (hshift-drawing h (vshift-drawing v (hscale-drawing h (vscale-drawing v circ))))))

• Is shape a value or a procedure? It's a procedure - It has a lambda

• Inputs (type): Two real numbers
• Outputs (type): A drawing
• Sample call: (shape 30 70)
• First action: Vertically scale circ by 70. Result is an ellipse, centered at (0.5,35), top is 0, left is 0.
  Height is 70, width is 1.
• Second action. Horizontally scale by 30. Result is an ellipse, centered at (15,35), top is 0, left is 0, height is 70, width is 30.
• Third action. Vertically shift by 70. Change top, bottom, center-y. Result is an ellipse, centered at (15,105), top is 70, left is 0, height is 70, bottom is 140

• Fourth action. Horizontally shift by 30. Results is an ellipse, centered at (45,105), top is 70, left is 30, height is 70, width is 30.

  (define munge! (lambda (image) (drawing-render! (shape (* 1/3 (image-width image)) (* 1/3 (image-height image))) image)))

• Procedure

• Inputs (type): image
• Outputs (type): image
• Sample input: 600 x 450 drawing.
• Compute 1/3 of width - 200
• Compute 1/3 of height - 150
• Call (shape 200 150)

A bit about design

A bit about color theory

Exploring some images and design spaces