hi, well i dont know about any haskell wrapper for openscenegraph. There are some python wrappers. (pyosg, avango). What i want to do is to use haskell for some simple graphics hacking, demo effects and to test ideas. Kind regards, Andreas C.M.Brown wrote:
Andreas-Christoph,
I'm afraid I can't help answering your question, but I was wondering what you were using to create your scene graph? I'm currently having to use OpenSceneGraph in C++, and would be grateful if you knew of some kind of Haskell wrapper for this?
Kind regards, Chris.
On Thu, 23 Oct 2008, Andreas-Christoph Bernstein wrote:
Hi,
Is there a pattern for tree traversal with a state ?
I am developing a small scenegraph represented by a tree. To draw a scenegraph one traverses over the graph starting with a global state. Inner Nodes can overwrite the inherited state for their subtree (e.g. Transformations are accumulated). The accumulated state is then either used immediately to draw the geometry in the leaf nodes, or a secondary data structure is build. This secondary data structure (a list or a tree) can then be sorted for optimal drawing performance.
So i want to do the second and create a list of all leaves with the accumulated global state. To illustrate my problem i appended some code. The idea similar applies to a scenegraph.
So my Question is: Is there allready a pattern for traversal with a state ?
module Main where
produces: Fork (0,"a") (Fork (1,"a") (Leaf (2,"a")) (Leaf (1,"a"))) (Leaf (0,"a"))
newTree :: BTree State newTree = traverse modState globalState sampleTree
produces: [(0,"a"),(1,"a"),(2,"a"),(1,"a"),(0,"a")]
stateList = flattenTree newTree
flattenTree (Leaf x) = [x] flattenTree (Fork x l r) = [x] ++ flattenTree l ++ flattenTree r
type State = (Int, String)
globalState :: State globalState = (0, "a")
State modifiers
data StateMod = ModInt | ModString | ModNop deriving Show
modState :: StateMod -> State -> State modState ModInt (x,w) = (x+1,w) modState ModNop s = s modState ModString (x,w) = (x,'b':w)
data BTree a = Fork a (BTree a) (BTree a) | Leaf a deriving Show
traverses the tree and executes a function which modifies the current state depending on the statemodifier
traverse :: (a -> b -> b) -> b -> BTree a -> BTree b traverse f state (Leaf x) = Leaf (f x state) traverse f state (Fork x l r) = Fork (f x state) newLeft newRight where newLeft = traverse f (f x state) l newRight = traverse f (f x state) r
an example tree
sampleTree :: BTree StateMod sampleTree = Fork ModNop (Fork ModInt (Leaf ModInt) (Leaf ModNop)) (Leaf ModNop)
creates a list from a tree
flattenTree (Leaf x) = [x] flattenTree (Fork x l r) = [x] ++ flattenTree l ++ flattenTree r
Thanks for any help and ideas
Andreas _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners