# FieldTrip

### From HaskellWiki

(moved torusPair example) |
(fleshed out example some) |
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</haskell> |
</haskell> |
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where <hask>pivot3X</hask> and <hask>move3X</hask> are simple helper functions for 3D transformation, and <hask>plasmat</hask> applies a color with a plastic look (defined in <code>Test.hs</code>). |
where <hask>pivot3X</hask> and <hask>move3X</hask> are simple helper functions for 3D transformation, and <hask>plasmat</hask> applies a color with a plastic look (defined in <code>Test.hs</code>). |
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+ | |||

+ | The <code>[http://code.haskell.org/FieldTrip/doc/html/Graphics-FieldTrip-ParamSurf.html#v%3Atorus torus]</code> function used here is a simple wrapper around a parametric surface defined as follows: |
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+ | <haskell> |
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+ | -- | Torus, given radius of sweep circle and cross section |
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+ | torus :: (Floating s, VectorSpace s, Scalar s ~ s) => s -> s -> Surf s |
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+ | torus sr cr = revolve (const (sr,0) ^+^ cr *^ circle) |
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+ | </haskell> |
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+ | where <hask>revolve</hask> and <hask>circle</hask> are defined in <code>[http://code.haskell.org/FieldTrip/doc/html/Graphics-FieldTrip-ParamSurf.html Graphics.FieldTrip.ParamSurf]</code>, along with other tools for shape generation. |
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+ | The trick to turning this polymorphic <hask>torus</hask> function into a <hask>Geometry3</hask> is to use a derivative tower (from [[vector-space]]) for the type parameter <hask>s</hask>. |
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+ | <haskell> |
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+ | surfG :: Surf (Vector2 R :> R) -> Geometry3 |
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+ | |||

+ | torus :: R -> R -> Geometry3 |
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+ | torus sr cr = surfG (P.torus (pureD sr) (pureD cr)) |
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+ | </haskell> |
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''[fill in more examples]'' |
''[fill in more examples]'' |

## Revision as of 20:08, 10 November 2008

## Contents |

## 1 Abstract

**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.

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

- Join the FieldTrip mailing list.
- Peruse the library documentation.
- Install from Hackage.
- Download the code repository:
. Patches welcome.`darcs get http://code.haskell.org/FieldTrip` - Report bugs and request features on the tracker.
- Examine the version history.

## 2 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 () to embed 2D into 3D.flatG

- 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.

## 3 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 = plasmat col (move3X dx tor)

`Test.hs`

).
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)

`Graphics.FieldTrip.ParamSurf`

, along with other tools for shape generation.
The trick to turning this polymorphic surfG :: Surf (Vector2 R :> R) -> Geometry3 torus :: R -> R -> Geometry3 torus sr cr = surfG (P.torus (pureD sr) (pureD cr))

*[fill in more examples]*

## 4 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`

into ghci, and type

anim3 (spinningG torusPair)