A quick buster example

Written by Jeff Heard on July 9th, 2009

Some people have asked of late for examples of Buster.  What follows is the (annotated) code that I used to generate the FDL video of the particles swarming around the lambda in the last post:

module Main where

import qualified Data.Array.IO as A
import Graphics.Rendering.Hieroglyph
import Graphics.Rendering.Hieroglyph.OpenGL
import App.EventBus
import IsoFDL
import Random
import Data.Colour
import Data.Colour.Names
import System.Random
import Control.Concurrent

dim = 480
minSeedCoord = fromIntegral $ quot dim 2 - 80
maxSeedCoord = fromIntegral $ quot dim 2 + 80
minIdealDist = (-100)
maxIdealDist = 100
npts = 100
basestrength = 4 

randomRIOs :: Double -> Double -> IO [Double]
randomRIOs a b = do
    g <- getStdGen
    return $ randomRs (a, b) g

This is the only behaviour we define, adjustLayout, and it runs a single layout iteration over the data.  We take the old locales of points, compute an FDL iteration, take the new locales of points, and produce the event, which is “Visible” (this is important, as Hieroglyph looks for all items in the Visible group, assumes they are o the class Visual, and attempts to render them.  We also produce a re-rendering request, and return the list of rerender and our layout as a future to be used at the appropriate time by the buster framework.  One final thing to note about our event is that it should live for 10 iterations.  Often geometry is persistent, but this was used to give the “contrail” effect to the particles as they move, effectively layering slightly transparent geometry over the top of older slightly transparent geometry to create the effect.

The Hieroglyph code is also fairly straightforward.  We apply linewidth and line color combinators (using the colours in Russell O’Connor’s excellent Data.Colour library) to a list of paths which are slightly exaggerated (that’s the +/-(x1-x0) and +/-(y1-y0) operations on the Points in the path) vectors along the path that was most recently traveled.

adjustLayout :: [Attractor] -> (Arr (Int,Int) Double) -> (Arr Int Double) -> (Arr Int Double) -> Behaviour [EData HieroglyphGLRuntime]
adjustLayout poles dists xs ys b = do
    pts <- externalizeLayout xs ys
    layoutIteration basestrength poles xs ys dists
    pts' <- externalizeLayout xs ys
    event' <- produce "Visible" "" (show . head $ pts') (Iterations 10)
                . (:[])
                . EOther
                . Geometry
                . linewidth 1
                . strokecolour (dissolve 0.3 (opaque darkblue))
                . name "points"
                $ zipWith (\(x0,y0) (x1,y1) -> path{ begin=Point (x0-(x1-x0)) (y0-(y1-y0)), segments=[Line $ Point (x1+(x1-x0)) (y1+(y1-y0))] }) pts pts'
    rerender <- produce "Hieroglyph" "" "Rerender" once []
    future b . return $ [event',rerender]

The next function, behaviour would normally be pure, but because we have some data that is internal to the adjustLayout behaviour, it’s got a do.  One of the things that I will change in the near future about Hieroglyph and OpenGL is to make the events it can respond to more polymorphic.  Currently I require that to use Hieroglyph in OpenGL that the event data type is [EData HieroglyphGLRuntime].  That’s pretty inane if I do say so myself, and in the future, there will be a constraint more along the lines of (HieroglyphInteractiveEventData a) => a rather than a static type to be determined at compile time.  However, with the current state of things, this is our behaviour, and it’s still pretty straightforward.  renderBehaviour depends on the result of adjustLayout.  That’s it.  The <~< establishes the dependency relationship and buster takes care of the rest.  The “poles” are a series of attractors (defined in IsoFDL.hs), which are static fields attached to a fixed point in space, attracting or repelling depending on the constant given them.

behaviour = do
    randomDistances <- randomRIOs minIdealDist maxIdealDist >>= A.newListArray ((0,0),(npts-1,npts-1)) . take (npts^2) . drop (2*npts)
    randomXs <- randomRIOs minSeedCoord maxSeedCoord >>= A.newListArray (0,npts-1) . take npts
    randomYs <- randomRIOs minSeedCoord maxSeedCoord >>= A.newListArray (0,npts-1) . take npts . drop npts

    poles <- mapM (\(x,y) -> compileAttractor . Attractor x y . take npts $ repeat 150)
        [(100,(440-100)), (170,(440-160)), (220,(440-220)), (160,(440-280)),
         (100,(440-320)), (280,(440-280)), (350,(440-320)), (380,(440-300))]

    return $ renderBehaviour <~< adjustLayout poles randomDistances randomXs randomYs

main = behaviour >>= boilerplateOpenGLMain  [initializeBus "Testing Force Directed layouts" dim dim]

Finally, our main function is incredibly simple.  We simply bind the behaviour to the boilerplate buster OpenGL main.  The other argument to boilerplateOpenGLMain is a list of “widgets” to be bound to the bus at the beginning of the application.

1 Comments so far ↓

  1. Russell O'Connor says:

    BTW (dissolve 0.3 (opaque darkblue)) can be written as (darkblue `withOpacity` 0.3) if you prefer.

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