HALFEDGE: initial implementation for half-edge data structures
See http://www.flipcode.com/archives/The_Half-Edge_Data_Structure.shtml
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CG2.cabal
31
CG2.cabal
@ -65,6 +65,7 @@ executable Gtk
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Graphics.Diagram.Core
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Graphics.Diagram.Gtk
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Graphics.Diagram.Plotter
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Graphics.HalfEdge
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GUI.Gtk
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MyPrelude
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Parser.Meshparser
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@ -76,6 +77,7 @@ executable Gtk
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-- Other library packages from which modules are imported.
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build-depends: attoparsec >= 0.12.1.1,
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array >= 0.5.0.0,
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base >=4.6,
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bytestring >= 0.10.4.0,
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containers >= 0.5.0.0,
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@ -113,6 +115,7 @@ executable Gif
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Graphics.Diagram.Core
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Graphics.Diagram.Gif
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Graphics.Diagram.Plotter
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Graphics.HalfEdge
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MyPrelude
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Parser.Meshparser
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Parser.PathParser
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@ -124,16 +127,18 @@ executable Gif
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-- Other library packages from which modules are imported.
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build-depends: attoparsec >= 0.12.1.1,
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base >=4.6,
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array >= 0.5.0.0,
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base >=4.6 && <4.8,
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bytestring >= 0.10.4.0,
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containers >= 0.5.0.0,
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dequeue >= 0.1.5,
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diagrams-lib >=1.3,
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diagrams-cairo >=1.3,
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diagrams-contrib >= 1.3.0.0,
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diagrams-lib >=1.2 && <1.3,
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diagrams-cairo >=1.2 && <1.3,
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diagrams-contrib >= 1.1.2.1,
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JuicyPixels >= 3.1.7.1,
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safe >= 0.3.8,
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transformers >=0.4
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multiset-comb >= 0.2.1,
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transformers >=0.4 && <0.5,
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safe >= 0.3.8
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-- Directories containing source files.
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-- hs-source-dirs:
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@ -158,6 +163,7 @@ executable Test
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Graphics.Diagram.Core
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Graphics.Diagram.Gif
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Graphics.Diagram.Plotter
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Graphics.HalfEdge
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MyPrelude
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Parser.Meshparser
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Parser.PathParser
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@ -171,13 +177,18 @@ executable Test
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-- Other library packages from which modules are imported.
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build-depends: attoparsec >= 0.12.1.1,
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base >=4.6,
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array >= 0.5.0.0,
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base >=4.6 && <4.8,
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bytestring >= 0.10.4.0,
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containers >= 0.5.0.0,
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diagrams-lib >=1.3,
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diagrams-cairo >=1.3,
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diagrams-contrib >= 1.3.0.0,
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dequeue >= 0.1.5,
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diagrams-lib >=1.2 && <1.3,
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diagrams-cairo >=1.2 && <1.3,
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diagrams-contrib >= 1.1.2.1,
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JuicyPixels >= 3.1.7.1,
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multiset-comb >= 0.2.1,
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QuickCheck >= 2.4.2,
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transformers >=0.4 && <0.5,
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safe >= 0.3.8
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-- Directories containing source files.
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198
Graphics/HalfEdge.hs
Normal file
198
Graphics/HalfEdge.hs
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@ -0,0 +1,198 @@
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{-# OPTIONS_HADDOCK ignore-exports #-}
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-- |This module provides methods to build a cyclic half-edge data structure
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-- from an already parsed obj mesh file. As such, it depends on details
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-- of the parsed data structures.
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--
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-- In particular, 'indirectHeFaces', 'indirectHeVerts' and 'indirectToDirect'
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-- assume specific structure of some input lists. Check their respective
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-- documentation.
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--
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-- As the data structure has a lot of cross-references and the knots are
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-- not really known at compile-time, we have to use helper data structures
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-- such as arrays, lists or vectors under the hood and tie the knots through
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-- index lookups.
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--
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-- For an explanation of the abstract concept of the half-edge data structure,
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-- check <http://www.flipcode.com/archives/The_Half-Edge_Data_Structure.shtml>
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module Graphics.HalfEdge (
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HeVert(..)
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, HeFace(..)
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, HeEdge(..)
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, buildHeEdge
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, buildHeEdgeFromStr
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) where
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import Algebra.Vector
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import Control.Monad.ST
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import Data.Array.Unboxed
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import Data.Array.ST
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import qualified Data.ByteString.Char8 as B
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import Data.Functor
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import Parser.Meshparser
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import Safe
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-- |The vertex data structure for the half-edge.
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data HeVert a = HeVert {
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vcoord :: a -- the coordinates of the vertex
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, emedge :: HeEdge a -- one of the half-edges emanating from the vertex
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}
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-- |The face data structure for the half-edge.
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data HeFace a = HeFace {
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bordedge :: HeEdge a -- one of the half-edges bordering the face
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}
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-- |The actual half-edge data structure.
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data HeEdge a = HeEdge {
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startvert :: HeVert a -- start-vertex of the half-edge
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, oppedge :: Maybe (HeEdge a) -- oppositely oriented adjacent half-edge
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, edgeface :: HeFace a -- face the half-edge borders
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, nextedge :: HeEdge a -- next half-edge around the face
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}
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-- This is a helper data structure of half-edge edges
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-- for tying the knots in 'indirectToDirect'.
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data IndirectHeEdge = IndirectHeEdge {
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edgeindex :: Int -- edge index
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, svindex :: Int -- index of start-vertice
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, nvindex :: Int -- index of next-vertice
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, indexf :: Int -- index of face
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, offsetedge :: Int -- offset to get the next edge
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}
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-- This is a helper data structure of half-edge vertices
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-- for tying the knots in 'indirectToDirect'.
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data IndirectHeVert = IndirectHeVert {
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emedgeindex :: Int -- emanating edge index (starts at 1)
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, edgelist :: [Int] -- index of edge that points to this vertice
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}
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-- This is a helper data structure of half-edge faces
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-- for tying the knots in 'indirectToDirect'.
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data IndirectHeFace =
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IndirectHeFace (Int, [Int]) -- (faceIndex, [verticeindex])
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-- |Construct the indirect data structure for half-edge faces.
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-- This function assumes that the input faces are parsed exactly like so:
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--
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-- @
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-- f 1 3 4 5
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-- f 4 6 1 3
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-- @
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--
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-- becomes
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--
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-- > [[1,3,4,5],[4,6,1,3]]
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indirectHeFaces :: [[Int]] -- ^ list of faces with their respective
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-- list of vertice-indices
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-> [IndirectHeFace]
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indirectHeFaces = fmap IndirectHeFace . zip [0..]
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-- |Construct the indirect data structure for half-edge edges.
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indirectHeEdges :: [IndirectHeFace] -> [IndirectHeEdge]
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indirectHeEdges = concat . fmap indirectHeEdge
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where
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indirectHeEdge :: IndirectHeFace -> [IndirectHeEdge]
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indirectHeEdge (IndirectHeFace (_, [])) = []
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indirectHeEdge p@(IndirectHeFace (_, pv@(v:_))) = go p 0
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where
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go (IndirectHeFace (_, [])) _
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= []
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-- connect last to first element
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go (IndirectHeFace (fi, [vlast])) ei
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= [IndirectHeEdge ei vlast v fi (negate $ length pv - 1)]
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-- regular non-last element
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go (IndirectHeFace (fi, vfirst:vnext:vrest)) ei
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= (:) (IndirectHeEdge ei vfirst vnext fi 1)
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(go (IndirectHeFace (fi, vnext:vrest)) (ei + 1))
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-- |Construct the indirect data structure for half-edge vertices.
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-- It is assumed that the list of points is indexed in order of their
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-- appearance in the obj mesh file.
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indirectHeVerts :: [a] -- ^ list of points
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-> [IndirectHeEdge] -- ^ list of indirect edges
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-> Array Int IndirectHeVert -- ^ output list, starts at index 1
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indirectHeVerts pts hes'
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= runSTArray $ do
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arr <- newArray (1, length pts) (IndirectHeVert 0 [])
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:: ST s (STArray s Int IndirectHeVert)
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-- build the array
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let go [] _ = return ()
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go (IndirectHeEdge _ _ nv _ offset:hes) i
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= do
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(IndirectHeVert _ xs) <- readArray arr nv
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writeArray arr nv (IndirectHeVert (i + offset) (i:xs))
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go hes (i + 1)
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go hes' 0
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return arr
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-- |Tie the knots!
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-- It is assumed that the list of points is indexed in order of their
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-- appearance in the obj mesh file.
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-- TODO: make this function safe.
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indirectToDirect :: [a] -- ^ list of points
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-> [IndirectHeEdge]
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-> [IndirectHeFace]
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-> Array Int IndirectHeVert -- ^ assumed to start at index 1
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-> HeEdge a
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indirectToDirect pts pe@(e:_) fs vertarr
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= thisEdge e
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where
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thisEdge (IndirectHeEdge ei sv _ fi off)
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= HeEdge (thisVert (vertarr ! sv) sv)
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(getOppEdge sv fi)
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(thisFace (fs !! fi))
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(thisEdge . (!!) pe $ (ei + off))
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thisFace (IndirectHeFace (_, vi:_))
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= HeFace (thisEdge (pe !! vi))
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thisVert (IndirectHeVert eedg _) coordi
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= HeVert (pts !! (coordi - 1))
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(thisEdge (pe !! (eedg - 1)))
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getOppEdge sv fi
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= (\x -> thisEdge (pe !! x))
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<$>
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(headMay
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. filter (\x -> (/=) fi . indexf $ (pe !! x))
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. edgelist
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$ (vertarr ! sv))
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-- |Build the half-edge data structure from a list of points
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-- and from a list of faces.
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-- The points are assumed to have been parsed in order of their appearance
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-- in the .obj mesh file, so that the indices match.
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-- The faces are assumed to have been parsed in order of their appearance
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-- in the .obj mesh file as follows:
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--
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-- @
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-- f 1 3 4 5
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-- f 4 6 1 3
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-- @
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--
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-- becomes
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--
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-- > [[1,3,4,5],[4,6,1,3]]
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buildHeEdge :: [a] -> [[Int]] -> Maybe (HeEdge a)
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buildHeEdge [] _ = Nothing
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buildHeEdge _ [] = Nothing
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buildHeEdge pts fs
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= let faces' = indirectHeFaces fs
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edges' = indirectHeEdges faces'
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verts' = indirectHeVerts pts edges'
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in Just $ indirectToDirect pts edges' faces' verts'
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-- |Build the HeEdge data structure from the .obj mesh file contents.
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buildHeEdgeFromStr :: B.ByteString -- ^ contents of an .obj mesh file
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-> Maybe (HeEdge PT)
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buildHeEdgeFromStr bmesh =
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let pts = meshVertices bmesh
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fs = meshFaces bmesh
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in buildHeEdge pts fs
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