Difference between revisions of "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:

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
GHCi, version 6.10.1: http://www.haskell.org/ghc/  :? for help
Prelude> :l Test
:l Test
[2 of 2] Compiling Test             ( Test.hs, interpreted )
```

Then run the example:

```    *Test> anim3 (const (spinningG torusPair))
[...]
```

Problems and solutions

Installation dependencies

You may also need to install libghc6-opengl-dev and libghc6-glut-dev using synaptic or apt-get.

If the opengl-dev or glut-dev libraries are not installed cabal will emit an error message like the one below:

```    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
```