Description
In this assignment, you will build a Haskell program that uses the [CodeWorld API](https://hackage.haskell.org/package/codeworld-api/docs/CodeWorld.html) to draw colourful shapes on the screen, including lines, polygons, rectangles, circles, and ellipses. {:.msg-info}
**Part A** of the assignment requires you to complete Task 1. **Part B** of the assignment requires you to complete all assigned tasks. As you complete each task (or even each function within a task), you should commit and push your work with a sensible commit message. {:.msg-info} The purpose of Part A is to give you an opportunity to collect feedback on your code and your progress in the course, and for us to give you an indicative mark for your work so far. This will be returned to you before the census date. Part A will be re-marked alongside your Part B submission, giving you a final mark for the assignment. ## Getting Started 1. Fork the assignment repository and create a project for it in IntelliJ IDEA, following the same steps as in [Lab 2](https://cs.anu.edu.au/courses/comp1100/labs/02/#forking-a-project). The assignment repository is at . 2. Add our version of the repository as a remote called `upstream`. This allows us to provide additional fixes if they are required. You do this by going to **VCS \| Git \| Remotes \| Add** in IntelliJ IDEA, and adding a remote called `upstream` with URL `https://gitlab.cecs.anu.edu.au/comp1100/comp1100-assignment1.git`. ## Overview of the Repository Most of your code will be written to Haskell files in the `src/` directory. We are using the [model-view-controller](https://en.wikipedia.org/wiki/Model–view–controller) pattern to structure this assignment. Each file is called a _module_, and we use modules to group related code together and separate unrelated code. ### Model.hs The _model_ is a data type that describes the state of the running program. The program will move to new states (new values of type `Model`) in response to user actions, as defined by the _controller_. ### View.hs The _view_ turns the _model_ into something that can be shown on the screen; in this project, that is the CodeWorld `Picture` type. ### Controller.hs The _controller_ considers user input (and other events), along with the current _model_, and uses that to decide what the new _model_ should be. ### Other Files * `tests/ShapesTest.hs` contains some _unit tests_ – simple checks that verify small parts of your program are working correctly. You are not required to write tests for this assignment, but you might find it useful to do so. * `tests/Testing.hs` is a small testing library used by `tests/ShapesTest.hs`. You are not required to understand it for this assignment. * `app/Main.hs` ties your functions together into the final program that runs. You are not required to understand it. * `comp1100-assignment1.cabal` tells the cabal build tool how to build your assignment. You are not required to understand this file, and we will discuss how to use cabal below. * `Setup.hs` tells cabal that this is a normal package with no unusual build steps. Some complex packages (that we won’t see in this course) need to put more complex code here. You are not required to understand it. ## Overview of Cabal `cabal` is the build tool for Haskell programs and libraries. It provides several useful commands: * `cabal build`: Compile your assignment. * `cabal run shapes`: Build your assignment (if necessary), and run the `shapes` program. * `cabal repl comp1100-assignment1`: Run the GHCi interpreter over your project. This gives you the same ghci environment you use in labs, but with the assignment code loaded. (Aside: REPL is the name for interactive sessions like GHCi – it stands for read-eval-print loop. Many modern languages have REPLs.) * `cabal test`: Build and run the tests. Tests will abort on the first failure, or the first call to a function that is still `undefined`. {:.msg-info} You should execute these cabal commands in the **top-level directory** of your project: `~/comp1100/assignment1` (i.e., the directory you are in when you launch the IntelliJ Terminal tool for your project). ## Overview of the Program You use a web browser to interact with the `shapes` program that you launched with `cabal run shapes`. Once you have completed the assignment, it will respond to the following actions: | Action | Effect | |—————————-|———————————————————————————–| | `Esc` (key) | Clear the canvas | | `M` (key) | Display a mystery image | | `C` (key) | Cycle colour (of shape to draw) | | `T` (key) | Cycle tool (type of shape to draw) | | `Backspace`/`Delete` (key) | Remove the last added shape | | `D` (key) | Print the current `Model` to the terminal (useful for testing) | | Click-drag-release (mouse) | When not drawing polygons, draw a shape between the click-point and release-point | | Click (mouse) | When drawing polygons, add a point to the polygon | | `Spacebar` (key) | Finish drawing a polygon, adding it to the canvas. | ## Task 1: Helper Functions (COMP1100: 20 marks; COMP1130: 10 marks) The easiest way to solve a large problem is often to break it apart into smaller, easier problems. Programming is the same. In this task you will write some helper functions that will make future tasks easier. You can test your implementations by running `cabal test`. The functions you need to write for this task are: * `toolLabel` in `src/View.hs`. This function should return instructions for the user on how to use each `Tool`, according to the following table: | Tool | Label | |—————–|—————————————————-| | `LineTool` | `”Line… click-drag-release”` | | `PolygonTool` | `”Polygon… click 3 or more times then spacebar”` | | `RectangleTool` | `”Rectangle… click-drag-release”` | | `CircleTool` | `”Circle… click-drag-release”` | | `EllipseTool` | `”Ellipse… click-drag-release”` | **Note:** At the time this assignment is released, the course will have only briefly covered lists. You do not need to manipulate lists to write `toolLabel`; you can use a blank pattern (`_`) to ignore them. * `nextColour` in `src/Controller.hs`. This function should return the next colour in our set of `ColourName`s: | Argument | Result | |———-|———-| | `Black` | `Red` | | `Red` | `Orange` | | `Orange` | `Yellow` | | `Yellow` | `Green` | | `Green` | `Blue` | | `Blue` | `Violet` | | `Violet` | `Black` | * `nextTool` in `src/Controller.hs`. This function implements tool-switching, but should not change `Tool` if the user is halfway through an operation: – If the tool is not holding a point (that is, a non-`PolygonTool` tool holding `Nothing` or a `PolygonTool` holding the empty list `[]`), select the next tool in the following sequence: `Line` -> `Polygon` -> `Rectangle` -> `Circle` -> `Ellipse` -> `Line` -> `…`. – If there is a `Point` stored in the given tool (because it’s holding a `Just` value or the list in `PolygonTool` is non-empty), return the argument unchanged. – If this is unclear, study the `nextToolTests` in `test/ShapesTest.hs`. **Note:** At the time this assignment is released, the course will have only briefly covered lists. You can write the `PolygonTool` case for `nextTool` without using list recursion. Use `[]` to match an empty list. In a subsequent case, give the entire list a name like `points` to match any nonempty list. Alternatively, you might use the Prelude function `null`, which returns `True` if a list is empty and `False` if it is not. ***** **Part A ends here.** ***** ### CodeWorld `Picture`, so that it can be displayed on the screen. It currently does not work, because `colourShapesToPicture` is `undefined`. In this task you will fill in that missing piece, building up a function to convert the `[ColourShape]` from your `Model` into a `Picture`. You can test these functions individually by using `cabal repl comp1100-assignment1`, using `drawingOf` to show small pictures on the screen. You can also test everything as a whole by launching the program with `cabal run shapes` and pressing the `M` key to show the mystery image. The functions you need to write for this task are all in `src/View.hs`: * `colourNameToColour`: This function turns your `ColourName` type from the model into a CodeWorld `Colour`. You should check [the CodeWorld documentation](http://hackage.haskell.org/package/codeworld-api-0.2.5/docs/CodeWorld.html#t:Color) for information on colours. * `shapeToPicture`: This function turns your `Shape` type into a CodeWorld `Picture`. You will need to consider the constructors for `Shape` individually, and work out the best way to turn each one into a `Picture`. Here are some hints to help you along: – CodeWorld has no function to draw a single line segment. It does have a function to draw a line made of multiple segments – `polyline`. – Polygons, rectangles, circles and ellipses should be drawn as solid (filled) `Picture`s. – Most of CodeWorld’s functions draw individual shapes centred on the origin – `(0, 0)`. You will need to figure out how to slide (translate) the generated `Picture` so it winds up where it’s supposed to go. Drawing diagrams will help. The `abs` function will also help – it computes the absolute value of its argument (i.e., `abs x == x` if `x > 0`, and `abs x == negate x` otherwise). – Ellipses are specified as two opposite coordinates for a bounding box that wraps the ellipse. CodeWorld has no primitive that draws an ellipse, but an ellipse is a stretched circle. Does CodeWorld have a function to stretch (scale) a `Picture`? – You do not have to completely implement this function before moving onto others. If you have written code to render `Rectangle`s but nothing else, you can create a drawing out of `Rectangle`s only, and check that your other functions work, before returning to finish `shapeToPicture`. * `colourShapeToPicture`: This function should render the `Shape` and colour it using the Colour that corresponds to the given `ColourName`. * `colourShapesToPicture`: This function should turn every `ColourShape` in a list into a single `Picture`. You will need to recurse over the input list. If you have not yet completed Lab 5, you may want to work on other parts of the assignment and come back to this. ## Task 3: Handling Events (COMP1100: 30 marks; COMP1130: 25 marks) It is now time to tackle `handleEvent` in `src/Controller.hs`. CodeWorld calls this function whenever something interesting happens (like a key press, a pointer press, or a pointer release). This function is called with two arguments: * The `Event` that just happened, and * The current `Model` at the time the `Event` happened. `handleEvent` then returns a new `Model` for the program to use moving forward. (Aside: [Elm](https://elm-lang.org) is a functional programming language that uses a similar pattern to build front-end web applications that are compiled to JavaScript.) Let’s trace a simple interaction. If the user wants to draw a *red line* by clicking on the screen at coordinates $$(1, 1)$$ and releasing the mouse at coordinates $$(2, 2)$$. starting at a blank canvas, the state would transition as follows, starting with the initial model: 1. `Model [] (LineTool Nothing) Black` 2. The user presses “C” to change the colour from red to black: `Model [] (LineTool Nothing) Red` 4. The user presses the mouse button at $$(1, 1)$$ changing the state to `Model [] (LineTool (Just (1.0,1.0))) Red` 5. The user releases the mouse button at $$(2, 2)$$ changing the state to `Model [(Red,Line (1.0,1.0) (2.0,2.0))] (LineTool Nothing) Red` {:.msg-info} Note that the `Tool` and the `ColourName` do not reset to the default values after a shape has been drawn. However, the `Maybe Point` inside the tool revert to `Nothing`. ### Task 3.1: Handling Mouse Input CodeWorld provides a few different event constructors for mouse input, but the ones we’re interested in are `PointerPress` for when the user clicks, and `PointerRelease` for when the user releases the mouse button. When a `PointerPress` event arrives, you will need to store it in the current `Tool`. For everything except `PolygonTool`, you will store it in the `Maybe Point` argument. For `PolygonTool`, you will add it to the list of vertices. When a `PointerRelease` event arrives, we can ignore it for `PolygonTool` because we’ll finish polygons using the spacebar in Task 3.2. For everything else, a `PointerRelease` means the end of a click-drag-release action, so you should construct the appropriate shape and add it to the `[Shape]` in the `Model`. You should also remove the starting point from the current `Tool`, so that future shapes draw properly too. ### Task 3.2: Handling Key Presses To handle keyboard input, CodeWorld provides a `KeyPress` event. This case is already present in the assignment skeleton, because we have implemented some keyboard functionality already. In the “Overview of the Program” section, we listed the full set of keyboard commands that your program will respond to. You need to implement the missing functionality for these keys: | Key | Effect | |———————-|—————————————————-| | `C` | Cycle colour (of shape to draw) | | `T` | Cycle tool (type of shape to draw) | | `Backspace`/`Delete` | Remove the last added shape | | `Spacebar` | Finish drawing a polygon, adding it to the canvas. | If you have made it this far, you should not need to write a lot of code to implement these. A few hints: * Think back to Task 1. * `Backspace`/`Delete` with no shapes drawn should not crash the program. ## Task 4: Extensions (COMP1130 Only: 30 marks) COMP1100 students are welcome to attempt extensions, but will not attract marks for completing them. COMP1130 students will need to complete **two** of the **five** extensions in the pool below. If you attempt more than two extensions, you must indicate in your report which ones should be marked. Otherwise, we will mark the first extensions that you have attempted, according to the order they appear in this document. If you change the behaviour of tool or colour switching, you may want to adjust the tests in `tests/ShapesTest.hs` so they continue to pass. **Note:** Extension functionalities must be executed through the CodeWorld API just like the rest of the assignment. Interactions should be received through the `handleEvent` function, which you will need to modify. If you need to add fields to the `Model` constructor, please do so after the existing ones: `data Model = Model [ColourShape] Tool ColourName YourField1 YourField2 …`. ### Task 4.1 Allow the user to delete multiple shapes using the mouse. The user should enter some kind of “mouse delete mode”, and then delete multiple shapes at once by pressing the mouse button and dragging a rectangle around them. When the user releases the mouse, any shape that is wholly within the rectangle should be deleted. ### Task 4.2 Add a free-hand drawing tool. When using this tool, moving the mouse with the button pressed should draw short lines or curves, as if a pen is being dragged across the screen. If the button is released, the program should stop drawing. ### Task 4.3 Add the ability to select and delete a shape using the keyboard. How you select shapes, and how you enter and leave “keyboard delete” mode, is all up to you. ### Task 4.4 Preview shapes as the user draws them. If the user has started to draw a shape, then you should show the shape currently being drawn using a hollow (not solid) rectangle, polygon, circle or ellipse. Lines will draw the same way as usual. For polygons, you won’t be able to show a preview until two or more points have been saved. ### Task 4.5 Allow the user to delete all shapes that have something in common. For example, all lines, all orange shapes, or all yellow rectangles. Whether you consider colour, shape, both, or something else as your measure of similarity is up to you. How the user selects what similarities to search for is also up to you. {:.msg-warn} Do not try to claim that “everything is similar to everything else”. That would collapse this problem to “erase the entire canvas”, which is too easy. #### Introduction If you wish to do so you can write an introduction. In it, give: * A brief overview of your program: – how it works; and – what it is designed to do. * If you have changed the way the controls work, or added something that may make your program behave unexpectedly then it would be worth making a note of it here. This section is particularly relevant to more complicated programs (i.e. COMP1130). #### Content Talk about why you structured the program the way you did. Below are some questions you could answer: * Program design – Describe what each relevant function does conceptually. (i.e. how does it get you closer to solving the problems outlined in this assignment spec?) – How do these functions piece together to make the finished program? Why did you design and implement it this way? – What major design choices did *you* make regarding the functions that *you’ve* written, and the overall structure of your program? * Assumptions – Describe assumptions you have made about how a user might use the program, and how this has influenced your design decisions. * Testing – How did you test individual functions? – Be specific about this – the tutors know that you have tested your program, but they want to know *how*. – Describe the tests that prove individual functions on their own behave as expected (i.e. testing a function with different inputs and doing a calculation by hand to check that the outputs are correct). – How did you test the entire program? What tests did you perform to show that the program behaves as expected in all (even unexpected) cases? – Again, be specific – did you check that you can draw shapes from left to right? What about right to left? An ellipse is defined by the two opposite corners of a bounding box – did you check that it fits perfectly within a rectangle drawn from the same two input points? – Have you checked edge cases (this is a computer science term that refers to unexpected or unlikely inputs that may cause a program to crash or behave in strange ways)? It is not likely that someone would try to change the tool halfway through drawing a shape, but it is essential that it has behaviour defined for that scenario. Describe similar tests that you have done to ensure the program can handle all inputs. * Inspiration / external content – What resources did you use when writing your program (e.g., published algorithms)? – If you have used resources such as a webpage describing an algorithm, be sure to cite it properly at the end of your report in a ‘References’ section. References do not count to the maximum word limit. #### Reflection Discuss the reasoning behind your decisions, rather than *what* the decisions were. You can reflect on not only the decisions you made, but the process through which you developed the final program: * Did you encounter any conceptual or technical issues? – If you solved them, describe the relevant details of what happened and how you overcame them. – Sometimes limitations on time or technical skills can limit how much of the assignment can be completed. If you ran into a problem that you could not solve, then your report is the perfect place to describe them. Try to include details such as: – theories as to what caused the problem; – suggestions of things that might have fixed it; and – discussion about what you did try, and the results of these attempts. * What would you have done differently if you were to do it again – What changes to the design and structure you would make if you wrote the program again from scratch? * Are parts of the program confusing for the reader? You can explain them in the report (in this situation you should also make use of comments in your code). * If you collaborated with others, what was the nature of the collaboration? (Note that you are only allowed to collaborate by sharing ideas, not code.) – Collaborating is any discussion or work done together on planning or writing your assignment. * Other info – You may like to briefly discuss details of events which were relevant to your process of design – strange or interesting things that you noticed and fixed along the way. {:.msg-info} This is a list of **suggestions**, not requirements. You should only discuss items from this list if you have something interesting to write. ### Things to avoid in a technical report * Line by line explanations of large portions of code. (If you want to include a specific line of code, be sure to format as described in the “Format” section below.) * Pictures of code or IntelliJ. * Content that is not your own, unless cited. * Grammatical errors or misspellings. Proof-read it before submission. * Informal language – a technical report is a professional document, and as such should avoid things such as: – Unnecessary abbreviations (atm, btw, ps, and so on), emojis, and emoticons; and – Stories / recounts of events not relevant to the development of the program. * Irrelevant diagrams, graphs, and charts. Unnecessary elements will distract from the important content. Keep it succinct and focused. If you need additional help with report writing, the [academic skills writing centre](http://www.anu.edu.au/students/academic-skills/appointments/academic-skills-writing-centre) has a peer writing service and writing coaches. ### Format You are not required to follow any specific style guide (such as APA or Harvard). However, here are some tips which will make your report more pleasant to read, and make more sense to someone with a computer science background. * Colours should be kept minimal. If you need to use colour, make sure it is absolutely necessary. * If you are using graphics, make sure they are *vector* graphics (that stay sharp even as the reader zooms in on them). * Any code, including type/function/module names or file names, that appears in your document should have a monospaced font (such as Consolas, Courier New, Lucida Console, or Monaco) * Other text should be set in serif fonts (popular choices are Times, Palatino, Sabon, Minion, or Caslon). * When available, automatic *ligatures* should be activated. * Do not use underscore to highlight your text. * Text should be at least 1.5 spaced.
