Mini-Project 1 : Image composition and decomposition

In the first few days of class, you have received a crash-course introduction to programming in Scheme, in particular with images. Furthermore, you also learned about algorithmic decomposition and its importance in computer programming. In this brief demonstration exercise, we’ll practice these techniques further by playing around with images.

External and internal correctness

In this course, we’re concerned about writing good code. What does that look like? Good programs have two qualities we’re looking after:

• External correctness: Does the program behave correctly according to its specification?
• Internal correctness: Is the program designed well?

External correctness is observable in the sense that we can run a program and determine that its behavior is correct. In contrast, internal correctness concerns the design of our program: Is it readable? Does it follow the design guidelines outlined in the exercise write-up and otherwise adhere to good coding conventions?

External correctness is often a given—we always want to write programs that do the right thing. However, we’ll find in this course that internal correctness is just as important! Computer programs are not just “consumed” by computers Other people will read and even modify our programs. In particular, you will find that in three months (or perhaps sooner), you will feel like “another person”, forgetting what you were thinking when you were designing the program. So it is important that we build habits that are conducive to writing readable code.

Playing around

As we may have discussed previously, programming is not a spectator sport (really, few things are in this world). You need to write programs to learn how to program. You often need to write programs to learn to think computationally. The labs and projects will be you primary vehicle for this sort of practice. This alone may be enough for some of you to master Scheme programming. But for many people, you will need additional practice to truly master these concepts.

One way to do this is through “playing around.” What we mean by this is programming for the purposes of exploring a programming language or its libraries, rather than a specific end-product. This is how many of us approach learning a new language. We may have a few starting points in our back pockets, but as we write, we are less concerned about finishing the task at hand as we are about understanding the new environment. This exploration usually involves investigating and answering questions such as “How do I do X in this language?” or “How does feature X that I don’t understand compare to feature Y that I do understand?” or even “How does this language lead me to think differently about algorithm design?”

Because you are beginning programmers, your questions will likely be markedly simpler: “How can I even make a thing happen?” Hnd “how do I type a thing?”. But nevertheless, “playing around” lets you tackle some of those ideas. You might start with one our lab exercises that you developed with a peer as a starting point and then change the code in ways that are novel to you. Or you might start from scratch and try to reproduce something you have seen or written before. There is no right way to go about “play”. Its the attitude that’s important: one of exploration and asking and answering questions rather than focusing on the final product.

Turn-in details

For this mini project, you will create two files: spaceship.scm and freestyle.scm. The particular contents of each are detailed below. For additional details on turning on this assignment and interpreting your feedback from it, please consult the Gradescope page.

Part the first: Rainbow spaceship

For this first part of the demo, your goal is to define an image called rainbow-spaceship that looks like this:

Here are the details of the rainbow-spaceship image:

• The spaceship composed of a collection of colored stripes, each of which are 100 pixels wide and 25 pixels tall.
• As the spaceship grows in height from left to right, a new colored stripe is added in rainbow order from top to bottom. The order of colors of the rainbow are red, orange, yellow, green, blue, and violet.
• The spaceship then shrinks in height past its center-point, losing a stripe from bottom-to-top order.

The “horizontal pyramid” effect is due to how the image library places sub-images with beside when they are different heights. Smaller images are automatically centered vertically relative to the taller images. For example the left-most red stripe is vertically centered relative to the red-orange two-stack of stripes next to it.

Make sure that the definition of rainbow-spaceship mimics its structure. Also pay special attention to remove redundancy from your code using define and, as appropriate, functions. We do not yet have the machinery to elegantly capture the growing, symmetric nature of the columns of the spaceship. However, note the relationship between the stripes of each successive column. How can you capture this relationship in code?

Please put your definition in the file spaceship.scm

Part the second: Freestyle

Now that you’ve had a taste for manipulating images and using define and functions to reduce redundancy, you will now get the opportunity to play around making images of some complexity. As discussed, this is open-ended: I have no particular image for you to draw and only some requirements about how you design your program. Feel free to try the following starting points:

• Take our image drawing lab and improve on the pictures there.
• Find an image on the Internet and do you best to replicate it using the limited image functions we’ve discussed in the course. Keep in mind that your final image will likely be impressionistic in nature!
• Doodle! Start with a few shapes and try to build up interesting patterns from there.

To encourage you to practice algorithmic decomposition, your program must follow these design requirements:

• Your image should contain no fewer than five smaller sub-images that you identify and codify in your program using the define command. These sub-images should be independent of each other (i.e., not defined in terms of each other), but can then be combined together.
• The names you define should be evocative of what the image is. It should be pithy, a few words at most, but at the same time descriptive. Scheme programming conventions say that these names should be in all lowercase with dashes between words, e.g., names-like-this.
• Your program should include a define that is the overall image, which you should call my-image.

• Your program should include introductory documentation, as below. (All of your Scheme files should include similar documentation.)

  (import image)
  
  ; freestyle.scm
  ;
  ; An amazing image of <....> I've created.
  ;
  ; CSC 151 (22fa)
  ; Mini Project 1, Part 2
  ; Author: Stu Dent
  ; Date: 2022-09-08
  ; Acknowledgements: ...
  
  ; (...code below here...)
  ;
  (define my-image...)
  

Other than this, there are no minimum requirements regarding limits, code size, or complexity. Have fun with it!

Please put your definitions in the file freestyle.scm.

Partial rubric

In grading these assignment, we will look for the following for each level. We may also identify other characteristics that move your work between levels.

You should read through the rubric and verify that your submission meets the rubric.

Redo or above

Submissions that lack any of these characteristics will get an I.

[ ] Includes the specified files (correctly named).
[ ] Includes an appropriate header on each file that indicates the course, author, etc.
[ ] Code runs in Scamper.

Meets expectations or above

Submissions that lack any of these characteristics will get an R.

[ ] In Part 1, creates the correct spaceship.
[ ] In Part 2, includes at least five sub-images.
[ ] In Part 2, includes at least one procedure.

Exemplary / Exceeds expectations

Submissions that lack any of these characteristics will get an M.

[ ] In Part 1, code is concise and avoids repetition.
[ ] In Part 2, image is particularly interesting or creative.