Lab 9
Repetition, Again

Due: Fri 11/8 at the start of class

Labs are due at the start of class. It is OK if you show up and copy your files to the handin directory at the very beginning of class, but this should take at most a couple of minutes and you should not spend the next lab period finishing up the previous week's lab.

Introduction

Loops provide a powerful shortcut for repetition — instead of cutting and pasting (with lots of small, tedious, error-prone edits) to get multiple copies of something, a loop allows you to repeat things as often as you want with only a few extra lines of code.

This week's lab focuses on breaking up complex pictures into loops, and working with the different loop patterns discussed in class (repeat-as-long-as loops and counting loops; one thing in the loop body, multiple things in the loop body; a single loop variable, multiple loop variables; a single loop, one loop after another, nested loops). Quilts once again provide the source of inspiration.

Successfully completing this lab means that you are able to:

• recognize applications the loop patterns identified above
• implement the loop patterns

Academic Integrity and Collaboration

The short version:

• Help with learning the process of constructing programs is fine; shortcutting the process and arriving at a result that you didn't produce yourself or don't fully understand how to produce is not.

• Always attempt the problem yourself first, using this lab handout, the materials from class posted on the schedule page, and the assigned reading in the textbook.

• Your primary resources for help should be office hours and the Teaching Fellows.

• You may not work with other students to write code together.

• You may not shortcut to a solution by copying code (except as specifically authorized in instructions) or using someone else's program as a guide or to understand what yours should be like even if you don't directly copy anything, You may not be in possession of someone else's program or solution before you have handed in your own.

• You must document any help received (including from TFs) and any resources used other than the textbook and posted course materials. Put comments in your sketch indicating who helped (or the source used) and how / with what.

• Make sure that you understand not only the result achieved, but also how one knows what to do to achieve that result. This gets at the process of writing a sketch — identifying what code elements are needed, filling in the details for a particular task, and pulling it all together.

Review the discussion in previous lab handouts and the full collaboration policy for more details.

Handin

To hand in your work:

• Make sure that your name and a short description of the sketch are included in a comment at the beginning of each sketch.

• Make sure that you've auto-formatted each sketch.

• Copy the entire lab9a, lab9b, lab9c, and lab9d directories from your sketchbook (~/cs120/sketchbook) to your handin directory (found inside /classes/cs120/handin).

Preliminaries

Getting Started

Review the posted slides and examples for identifying loop patterns, as well as the posted slides and examples for repeat-as-long-as loops, counting loops, and nested loops. Keep in mind that considering what changes and how it changes is crucial for deciding on loops — in one loop, whatever changes should change consistently from one repetition to the next.

Also read through all of each exercise before starting it — there's important information about how to do the task after the initial statement.

Then, consider the loop questions to help you build up each loop. It is strongly recommended that you identify at least what is repeated and what changes in comments in your sketch.

"Any Size Window"

The exercises ask you to design your sketches so that they work with any size window. Remember that this means to use the system variables width and height instead of specific numbers when referring to the drawing window dimensions.

Exercises

Put your name and a description of the sketch in comments at the beginning of each sketch. Also don't forget to Auto Format your code before handing it in. (Refer back to lab 2 for more on Auto Format if needed.)

You must use loops wherever it is appropriate to do so! (Reminder: a loop when something repeats more than a few times and there is predictable change from one copy to the next.) You will receive very little credit for producing the right drawing without using loops.

Exercise 1

Create a sketch named lab9a which draws a color variation of the Jacob's Ladder quilt block, as shown. You can choose your own colors, but you should have two light colors and two dark colors and the pattern should be the same as shown — things which are the same color in the picture should be the same color in your sketch.

Design your sketch so that it works with any size window.

To create this sketch:

• Create a new sketch, add your name and a description of the sketch in comments at the beginning, and save your sketch as lab9a.

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  Draw the blue band, which consists of a quad and two triangles as shown. Note: the shapes are outlined in red in the picture to show what to draw; you should make the stroke and fill colors the same so that the blue band looks like a single seamless shape. The black grid is shown to help you figure out coordinates and sizes; you do not need to draw it.

  
  
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  Draw the dark blue squares.

  
  
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  Draw the white squares.

  
  

Exercise 2

Create a sketch named lab9b which draws a tumbling blocks quilt, as shown. Use quad to draw the diamond shapes. You don't need to match the example exactly in terms of the number of repetitions of the pattern, but the window should be completely filled. You can also choose your own colors, but should use lighter, medium, and darker colors in the configuration shown.

Design your sketch so that it works with any size window.

To create this sketch:

• Create a new sketch, add your name and a description of the sketch in comments at the beginning, and save your sketch as lab9b.

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  Create a function drawBlock which takes the position (x,y) and size s of the block as parameters and draws one block shape as shown. Use quad to draw each diamond shape. Test your function by calling it from draw().

  
  
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  Call drawBlock twice to create the pattern shown. (Note that part of the pattern sticks up past the top of the window — that's fine, you don't have to limit drawing to within the window. Just use drawBlock and let stuff extend past the edge.)

  
  
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  Draw one row of the 2-block pattern.

  
  
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  Complete the quilt by repeating the rows.

  
  

Exercise 3

Create a sketch named lab9c which draws a strip of 16 flying geese as shown. You can choose your own colors, but each group of four triangles should be the same color and the color of successive groups should change smoothly, as shown. (In the example, red increases to the right.)

Recall from lab 8 that the height of each triangle should be twice its width. Design your sketch so that it works with any height of window, but make sure you size the window so that there is room for 16 triangles the height of the window.

To create this sketch:

• Create a new sketch, add your name and a description of the sketch in comments at the beginning, and save your sketch as lab9c.

• Draw a set of four geese. (You can use your solution from lab 8 as a starting point, but you'll need to modify it to draw four geese instead of filling the width of the window.)

  
  

• Draw four sets of four geese. Note: do not simply modify your previous solution to draw 16 geese instead of four! Repeat the drawing of four geese four times.

  
  

• Vary at least one color component with each group of four geese.

  
  

Exercise 4

Create a sketch named lab9d which displays a block star quilt, as shown. (To see the star pattern, focus on the color rather than the white shapes.) You can choose your own colors, but you should vary one color component horizontally and a different one vertically. (In the example, the red decreases to the right and the blue increases going down.)

Design your sketch so that it works with any size window.

Hint: view the pattern as white shapes (squares and quads) drawn on top of a background of colored squares. (The white triangles on the edges are just quads that extend past the edges of the drawing window — you do not need to handle those specially by drawing triangles.) Break your development of the sketch down into three steps: draw the background of squares all the same color, add the color variation, and then draw the white squares and quads.

Extra Credit

You can earn extra credit by going substantially beyond the required elements. Create a new sketch called lab9e with a recognizable scene. (A geometric pattern, such as a quilt, is OK — the idea is that the scene should be deliberately created and have some overall theme rather than just being a jumble of different elements.) Some possibilities for extra credit:

• Showcase different loop patterns, in particular:

  • only one property varies from one repetition to the next
  • more than one property (excluding counters) varies from one repetition to the next
  • a counting loop, where the loop condition is based on the number of times the loop has repeated
  • two or more loops one after another (not nested) are needed to create a single pattern
  • nested loops (or a loop which calls a drawing function containing a loop)

  Be sure to identify the pattern for each loop you use!

• Demonstrate more complex ways in which things change from one repetition to the next. This could include changing things other than position, size, or color (such as orientation — use rotate()) or accelerating/decelerating the change. The "twisted square and variations" and "circular patterns" examples from the extra credit section in lab 8 have some examples of quilt blocks where orientation varies. Another possibility is repetition in space that isn't in a straight line, such as creating a Ferris wheel or water wheel by positioning things around a circle.

• Combine loops and animation and/or interaction, having one or more things drawn with loops that are also animated or interactive. A spinning Ferris wheel or water wheel is one such possibility.

Include a brief description of what you've done for extra credit in a comment at the beginning of your sketch. More creative and challenging elements will earn more points.