paint

Create an abstract image and allow to operate over it.

Usage

It's an interactive program that interprets instructions line by line. To see an example usage just run:

lein run < sample_input.txt

Rationale

Implementation

An image is just represented as a vector of vector of keywords.

The library core.matrix is used for some of of the image manipulations internall, but the type of the matrixes passed around is still always a simple vector of vectors.

Only one function (cli.clj:handle-line) has side effects, because it's using an atom for storing what's the current image we are working on. This was not 100% necessary, but since this program has an implicit global state for the user it made sense to use an atom to store that.

The most complex part was to get the algorithm for filling in a region. This was implemented in filling.clj:fill-coordinates as a recursive function which returns the whole list of coordinates, without actually doing any mutation to the image itself.

This algorithm (inspired from the flood-fill algorithm) moves in the 4 cardinal directions recursively until every part of the image with the same colour has been discovered.

Testing

Tests are written with a mix of core.test and clojure.test.check generative tests. Properties of the system that can for example be tested like this could be for example:

• a new img has all white pixels
• clearing an existing image is the same as creating a new one withe the same dimensions
• every operation is idempotent, so running it more than once on the same image doesn't change that image

There are many different generators composed together to accomplish that, a particularly interesting is gen-image, which allows to generate random images, which however still satisfy the general properties of the system (rectangular matrix and containing colours represented as keywords).

(gen/sample gen-image)
=> ([[:O]] [[:G]] [[:A :E :T] [:S :A :T]] [[:J :W] [:F :X] [:T :J]] [[:C :O :B :S] [:K :B :V :R] [:P :K :O :A]])

Possible improvements

• defprotocol?
• performances with very big images
• multi image with a map in the atom keyed by image id
• better split between show and quit and the other manipulations
• parse arguments could be done with regular expressions instead
• could use swap instead of reset?
• better prompt
• define more colour and not just white
• command function name?

License

Copyright © 2017 Andrea Crotti

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.