Add hexagon

Descartes.cabal

@@ -52,7 +52,7 @@ extra-doc-files:    CHANGELOG.md
 -- extra-source-files:
 
 common warnings
-    ghc-options: -Wall -Werror
+    ghc-options: -Wall
 
 library
     -- Import common warning flags.
@@ -79,7 +79,7 @@ library
     build-depends:    base ^>=4.18.2.1
 
     -- GHC options for the library
-    ghc-options: -O2
+    ghc-options: -O2 -Werror
 
     -- Directories containing source files.
     hs-source-dirs:   src

README.org

@@ -0,0 +1,17 @@
+#+title: Descartes
+#+author: James Leslie
+[[https://img.shields.io/github/license/jeslie0/descartes.svg]]
+
+#+html: <img src=".img/hexagon.png" width="200px"/>
+
+This is a Haskell wrapper around The University of Edinburgh, School of Informatics' [[https://www.inf.ed.ac.uk/teaching/courses/cp/descartes.html][Descartes Package]]. The Descartes Packages is a small C library that uses [[https://www.libsdl.org/][SDL]] to make a very simple graphics package. It provides a way to make and render points, lines and rectangles on a 500px by 500px grid. It is mainly useful for educational purposes (indeed, I used it in the introductory "Computer Programming" course, back in 2014).
+
+The main reason I made this library was to get a better understanding of Haskell's Foreign Function Interface with C, which turns out to be quite nice and very useable. As such, this repository may be of more use for someone wanting to explore Haskell's FFI functionality, rather than as an actual library.
+
+Note - I only wrote the Haskell code and C wrapper code. Everything in [[file:cbits/descartes/][descartes]] directory is from the Descartes library.
+
+* Dependencies
+The only dependency is SDL. This has been tested with SDL version 1.2.15.
+
+* Modifications
+I made a few minor modifications to the Descartes C library. I changed the title of the graphics window to "Descartes".

test/Main.hs

@@ -1,11 +1,13 @@
 module Main (main) where
 
 import Descartes qualified as D
-import Control.Monad (when)
+import Control.Monad (when, forM_)
+import Data.Complex qualified as C
+import Data.Functor ((<&>))
 
 main :: IO ()
 main = D.withGraphics $ do
-  D.setColour D.Red
+  D.setColour D.Blue
 
   putStrLn "Click twice to draw a line."
   p1 <- D.getPoint
@@ -23,12 +25,36 @@ main = D.withGraphics $ do
 
   D.fillRectangle $ D.rectangle bl tr
 
+  D.setColour D.Green
+  forM_ makeHexagon D.draw
+
+  D.setColour D.Red
   makePath Nothing
 
 
+
 makePath :: Maybe D.Point -> IO ()
 makePath Nothing = D.getPoint >>= \p -> makePath (Just p)
 makePath (Just p) = do
   p' <- D.getPoint
   D.draw $ D.lineSeg p p'
   makePath (Just p')
+
+joinPoints :: [D.Point] -> [D.LineSeg]
+joinPoints [] = []
+joinPoints [p] = []
+joinPoints (p1:p2:ps) = D.lineSeg p1 p2 : joinPoints (p2:ps)
+
+makeHexagon :: [D.LineSeg]
+makeHexagon =
+  let
+    scale f = round $ 166 * (f + 1.5)
+
+    -- We use 7 here so that the last point is equal to the first.
+    powers :: [C.Complex Float] =
+      take 7 $ iterate (\ z -> z * C.mkPolar 1 (pi / 3)) (1.0 C.:+ 0)
+
+    points :: [D.Point] =
+      powers <&> \ z -> D.point (scale . C.realPart $ z) (scale . C.imagPart $ z)
+
+  in joinPoints points