FieldTrip

Abstract

Torus pair modeled and rendered in FieldTrip

FieldTrip is a library for functional 3D graphics, intended for building static, animated, and interactive 3D geometry, efficient enough for real-time synthesis and display. Our first renderer uses OpenGL, with the usual visual limitations. Since FieldTrip is functional, it is about being rather than doing. One describes what models are, not how to render them.

FieldTrip is work-in-progress. It's being released to show what's going on and see who's interested in collaborating on developing it further.

Besides this wiki page, here are more ways to find out about and get involved with FieldTrip:

• Join the FieldTrip mailing list.
• Visit the Hackage page for library documentation and to download & install.
• Or install with cabal install FieldTrip. See Installation dependencies below.
• Get the code repository: darcs get http://code.haskell.org/FieldTrip
• Report bugs and request features on the tracker.

Basic types

The basic purpose of the core FieldTrip library is to allow a user build 3D geometry, from individual simple shapes to full 3D scenes. The principal types are as follows.

Geometry3

3D geometry. These values can be spatially transformed in space (affinely: scale, rotate, translate) and combined (union).

Surf a = (a,a) -> (a,a,a)

Parametric surfaces, i.e., mappings from 2D to 3D. Normals are constructed automatically and exactly via derivatives, thanks to the vector-space library. These normals are used for shading. For simplicity and composability, surfaces are curved, not faceted.

Surface rendering tessellates adaptively, caching tessellations in an efficient, infinite data structure for reuse. The mechanism for choosing tessellation is a very primitive placeholder. FieldTrip provides some basic shapes of surfaces (spheres, torus, cubes, etc) and many functions for manipulating surfaces, colors, etc.

Geometry2

2D geometry. There's a function (flatG) to embed 2D into 3D.

Image o = (R,R) -> o

A primitive placeholder for functional imagery in the spirit of Pan. The intention is to use this type or

something like it for texture mapping. Much design and implementation work to be done.

Example

The code for the static torus pair shown above:

torusPair :: Geometry3
torusPair = f red (1/2) `mappend` pivot3X (f green (-1/2))
 where
   tor = torus 1 (2/5)
   f :: Col -> R -> Geometry3
   f col dx = materialG (plastic col) (move3X dx tor)

where pivot3X and move3X are simple helper short-hands for 3D transformation.

The torus function used here is a simple wrapper around a parametric surface defined as follows:

-- | Torus, given radius of sweep circle and cross section
torus :: (Floating s, VectorSpace s, Scalar s ~ s) => s -> s -> Surf s
torus sr cr = revolve (const (sr,0) ^+^ cr *^ circle)

where revolve and circle are defined in Graphics.FieldTrip.ParamSurf, along with other tools for shape generation.

The trick to turning this polymorphic torus function into a Geometry3 is to use a derivative tower (from vector-space) for the type parameter s.

surfG :: Surf (Vector2 R :> R) -> Geometry3

torus :: R -> R -> Geometry3
torus sr cr = surfG (P.torus (pureD sr) (pureD cr))

[fill in more examples]

FieldTrip meets Reactive

FieldTrip contains no support for animation, because we intend it to be used with the Reactive functional reactive programming (FRP) library (and possibly other animation frameworks). By design, FieldTrip is completely orthogonal to any formulation or implementation of FRP.

The reactive-fieldtrip project connects Reactive and FieldTrip.

The picture above comes from an animation in reactive-fieldtrip. Load src/Test.hs, as follows:

    ~/Haskell$ cd reactive-fieldtrip/src
    ~/Haskell/reactive-fieldtrip/src$ ghci
    GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help
    Loading package ghc-prim ... linking ... done.
    Loading package integer ... linking ... done.
    Loading package base ... linking ... done.
    Prelude> :l Test
    :l Test
    [1 of 2] Compiling FRP.Reactive.FieldTrip.Adapter ( FRP/Reactive/FieldTrip/Adapter.hs, interpreted )
    [2 of 2] Compiling Test             ( Test.hs, interpreted )
    Ok, modules loaded: FRP.Reactive.FieldTrip.Adapter, Test.

Then run the example:

    *Test> anim3 (const (spinningG torusPair))
    Loading package OpenGL-2.2.1.1 ... linking ... done.
    Loading package syb ... linking ... done.
    Loading package base-3.0.3.0 ... linking ... done.
    [...]
    Loading package reactive-0.9.0 ... linking ... done.
    Loading package FieldTrip-0.2.2 ... linking ... done.
    Loading package reactive-glut-0.0.5 ... linking ... done.

Some videos

• Texture-mapped Earth.
• The torus demo running in GHCi.

Problems and solutions

Installation dependencies

Haskell packages

You'll need the OpenGL and GLUT packages. If you are using synaptics/apt-get, those are called libghc6-opengl-dev and libghc6-glut-dev. If you're using cabal-install, it will take care of the dependencies for you (see "Non-Haskell libraries" below though).

Non-Haskell libraries

Make sure that you have the opengl-dev and glut-dev libraries installed. If you don't have them, there are two ways to fail: Either on the installation of the corresponding Haskell libraries, like this:

    configure: error: no GLUT header found, so this package cannot be built                                                      
    See `config.log' for more details.                                                                                           
    cabal: Error: some packages failed to install:                                                                               
    GLUT-2.1.1.2 failed during the configure step. The exception was:                                                            
    exit: ExitFailure 1

Or, if you do have the Haskell packages and C libraries, but accidentally removed the opengl-dev and glut-dev libraries, you can end up with FieldTrip just producing black windows.

Linking problems on Debian Lenny

You may experience linker problems on Debian Lenny. Running:

> ghc --make -main-is Test Test.hs

can give you:

 Linking Test ...
 /home/ghc/.cabal/lib/reactive-glut-0.1.6/ghc-6.10.1/libHSreactive-glut-0.1.6.a(SimpleGL.o): In function `s5SW_info':
 (.text+0x1654): undefined reference to `glutInitDisplayMode'
 /home/ghc/.cabal/lib/reactive-glut-0.1.6/ghc-6.10.1/libHSreactive-glut-0.1.6.a(SimpleGL.o): In function `s5SW_info':
 (.text+0x1668): undefined reference to `glutInitWindowSize'
 ...

This is a HOpenGL problem and has already been reported here and a solution here. To make a long story short, you need to explicitly link with glut when compiling:

> ghc --make -lglut -main-is Test Test.hs