genmesh 0.3.0

A package for generating 3D meshes
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//   Copyright Colin Sherratt 2014
//   
//   Licensed under the Apache License, Version 2.0 (the "License");
//   you may not use this file except in compliance with the License.
//   You may obtain a copy of the License at
//   
//       http://www.apache.org/licenses/LICENSE-2.0
//   
//   Unless required by applicable law or agreed to in writing, software
//   distributed under the License is distributed on an "AS IS" BASIS,
//   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//   See the License for the specific language governing permissions and
//   limitations under the License.

use std::collections::VecDeque;

use Polygon::{ PolyQuad, PolyTri };
use {
    Quad,
    Triangle,
    Polygon,
};

/// provides a way to convert a polygon down to triangles
pub trait EmitTriangles {
    /// The content of each point in the face
    type Vertex;

    /// convert a polygon to one or more triangles, each triangle
    /// is returned by calling `emit`
    fn emit_triangles<F>(&self, mut emit: F) where F: FnMut(Triangle<Self::Vertex>);
}

impl<T: Clone> EmitTriangles for Quad<T> {
    type Vertex = T;

    fn emit_triangles<F>(&self, mut emit: F) where F: FnMut(Triangle<T>) {
        let &Quad{ref x, ref y, ref z, ref w} = self;
        emit(Triangle::new(x.clone(), y.clone(), z.clone()));
        emit(Triangle::new(z.clone(), w.clone(), x.clone()));
    }
}

impl<T: Clone> EmitTriangles for Triangle<T> {
    type Vertex = T;

    fn emit_triangles<F>(&self, mut emit: F) where F: FnMut(Triangle<T>) {
        emit(self.clone());
    }
}

impl<T: Clone> EmitTriangles for Polygon<T> {
    type Vertex = T;

    fn emit_triangles<F>(&self, emit: F) where F: FnMut(Triangle<T>)  {
        match self {
            &PolyTri(ref t) => t.emit_triangles(emit),
            &PolyQuad(ref q) => q.emit_triangles(emit),
        }
    }
}

/// `Triangluate` is a easy to to convert any Polygon stream to
/// a stream of triangles. This is useful since Quads and other geometry
/// are not supported by modern graphics pipelines like OpenGL.
pub trait Triangulate<T, V> {
    /// convert a stream of Polygons to a stream of triangles
    fn triangulate(self) -> TriangulateIterator<T, V>;
}

impl<V, P: EmitTriangles<Vertex=V>, T: Iterator<Item=P>> Triangulate<T, V> for T {
    fn triangulate(self) -> TriangulateIterator<T, V> {
        TriangulateIterator::new(self)
    }
}

/// Used to iterator of polygons into a iterator of triangles
pub struct TriangulateIterator<SRC, V> {
    source: SRC,
    buffer: VecDeque<Triangle<V>>
}

impl<V, U: EmitTriangles<Vertex=V>, SRC: Iterator<Item=U>> TriangulateIterator<SRC, V> {
    fn new(src: SRC) -> TriangulateIterator<SRC, V> {
        TriangulateIterator {
            source: src,
            buffer: VecDeque::new()
        }
    }
}

impl<V, U: EmitTriangles<Vertex=V>, SRC: Iterator<Item=U>> Iterator for TriangulateIterator<SRC, V> {
    type Item = Triangle<V>;

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (n, _) = self.source.size_hint();
        (n, None)
    }

    fn next(&mut self) -> Option<Triangle<V>> {
        loop {
            match self.buffer.pop_front() {
                Some(v) => return Some(v),
                None => ()
            }

            match self.source.next() {
                Some(p) => p.emit_triangles(|v| self.buffer.push_back(v)),
                None => return None
            }
        }
    }
}