Complete the WQuadtree construction and ray-cast.

src/geometry/wquadtree.rs

@@ -0,0 +1,285 @@
+use crate::geometry::{ColliderHandle, ColliderSet, Ray, AABB};
+use crate::geometry::{WRay, WAABB};
+use crate::math::{Point, Vector};
+use crate::simd::{SimdFloat, SIMD_WIDTH};
+use ncollide::bounding_volume::BoundingVolume;
+use simba::simd::{SimdBool, SimdValue};
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+struct NodeIndex {
+    index: u32, // Index of the addressed node in the `nodes` array.
+    lane: u8,   // SIMD lane of the addressed node.
+}
+
+impl NodeIndex {
+    fn new(index: u32, lane: u8) -> Self {
+        Self { index, lane }
+    }
+
+    fn invalid() -> Self {
+        Self {
+            index: u32::MAX,
+            lane: 0,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+struct WQuadtreeNodeChildren {
+    waabb: WAABB,
+    // Index of the nodes of the 4 nodes represented by self.
+    // If this is a leaf, it contains the proxy ids instead.
+    children: [u32; 4],
+    parent: NodeIndex,
+    leaf: bool, // TODO: pack this with the NodexIndex.lane?
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+struct ColliderNodeIndex {
+    node: NodeIndex,
+    handle: ColliderHandle, // The collider handle. TODO: only set the collider generation here?
+}
+
+impl ColliderNodeIndex {
+    fn invalid() -> Self {
+        Self {
+            node: NodeIndex::invalid(),
+            handle: ColliderSet::invalid_handle(),
+        }
+    }
+}
+
+pub struct WQuadtree {
+    nodes: Vec<WQuadtreeNodeChildren>,
+    dirty: Vec<bool>, // TODO: use a bitvec/Vob and check it does not break cross-platform determinism.
+    proxies: Vec<ColliderNodeIndex>,
+}
+
+impl WQuadtree {
+    pub fn new() -> Self {
+        WQuadtree {
+            nodes: Vec::new(),
+            dirty: Vec::new(),
+            proxies: Vec::new(),
+        }
+    }
+
+    pub fn clear_and_rebuild(&mut self, colliders: &ColliderSet) {
+        self.nodes.clear();
+        self.dirty.clear();
+        self.proxies.clear();
+
+        // Create proxies.
+        let mut indices = Vec::with_capacity(colliders.len());
+        self.proxies = vec![ColliderNodeIndex::invalid(); colliders.len()];
+
+        for (handle, collider) in colliders.iter() {
+            let index = handle.into_raw_parts().0;
+            if self.proxies.len() < index {
+                self.proxies.resize(index + 1, ColliderNodeIndex::invalid());
+            }
+
+            self.proxies[index].handle = handle;
+            indices.push(index);
+        }
+
+        // Compute AABBs.
+        let mut aabbs = vec![AABB::new_invalid(); self.proxies.len()];
+        for (handle, collider) in colliders.iter() {
+            let index = handle.into_raw_parts().0;
+            let aabb = collider.compute_aabb();
+            aabbs[index] = aabb;
+        }
+
+        // Build the tree recursively.
+        let root_node = WQuadtreeNodeChildren {
+            waabb: WAABB::new_invalid(),
+            children: [1, u32::MAX, u32::MAX, u32::MAX],
+            parent: NodeIndex::invalid(),
+            leaf: false,
+        };
+
+        self.nodes.push(root_node);
+        let root_id = NodeIndex::new(0, 0);
+        let (_, aabb) = self.do_recurse_build(&mut indices, &aabbs, root_id);
+        self.nodes[0].waabb = WAABB::from([
+            aabb,
+            AABB::new_invalid(),
+            AABB::new_invalid(),
+            AABB::new_invalid(),
+        ]);
+    }
+
+    fn do_recurse_build(
+        &mut self,
+        indices: &mut [usize],
+        aabbs: &[AABB],
+        parent: NodeIndex,
+    ) -> (u32, AABB) {
+        // Leaf case.
+        if indices.len() <= 4 {
+            let my_id = self.nodes.len();
+            let mut my_aabb = AABB::new_invalid();
+            let mut leaf_aabbs = [AABB::new_invalid(); 4];
+            let mut proxy_ids = [u32::MAX; 4];
+
+            for (k, id) in indices.iter().enumerate() {
+                my_aabb.merge(&aabbs[*id]);
+                leaf_aabbs[k] = aabbs[*id];
+                proxy_ids[k] = *id as u32;
+            }
+
+            let node = WQuadtreeNodeChildren {
+                waabb: WAABB::from(leaf_aabbs),
+                children: proxy_ids,
+                parent,
+                leaf: true,
+            };
+
+            self.nodes.push(node);
+            return (my_id as u32, my_aabb);
+        }
+
+        // Compute the center and variance along each dimension.
+        // In 3D we compute the variance to not-subdivide the dimension with lowest variance.
+        // Therefore variance computation is not needed in 2D because we only have 2 dimension
+        // to split in the first place.
+        let mut center = Point::origin();
+        #[cfg(feature = "dim3")]
+        let mut variance = Vector::zeros();
+
+        let denom = 1.0 / (indices.len() as f32);
+
+        for i in &*indices {
+            let coords = aabbs[*i].center().coords;
+            center += coords * denom;
+            #[cfg(feature = "dim3")]
+            {
+                variance += coords.component_mul(&coords) * denom;
+            }
+        }
+
+        #[cfg(feature = "dim3")]
+        {
+            variance = variance - center.coords.component_mul(&center.coords);
+        }
+
+        // Find the axis with minimum variance. This is the axis along
+        // which we are **not** subdividing our set.
+        let mut subdiv_dims = [0, 1];
+        #[cfg(feature = "dim3")]
+        {
+            let min = variance.imin();
+            subdiv_dims[0] = (min + 1) % 3;
+            subdiv_dims[1] = (min + 2) % 3;
+        }
+
+        // Split the set along the two subdiv_dims dimensions.
+        // TODO: should we split wrt. the median instead of the average?
+        // TODO: we should ensure each subslice contains at least 4 elements each (or less if
+        // indices has less than 16 elements in the first place.
+        let (left, right) = split_indices_wrt_dim(indices, &aabbs, &center, subdiv_dims[0]);
+
+        let (left_bottom, left_top) = split_indices_wrt_dim(left, &aabbs, &center, subdiv_dims[1]);
+        let (right_bottom, right_top) =
+            split_indices_wrt_dim(right, &aabbs, &center, subdiv_dims[1]);
+
+        // println!(
+        //     "Recursing on children: {}, {}, {}, {}",
+        //     left_bottom.len(),
+        //     left_top.len(),
+        //     right_bottom.len(),
+        //     right_top.len()
+        // );
+
+        let node = WQuadtreeNodeChildren {
+            waabb: WAABB::new_invalid(),
+            children: [0; 4], // Will be set after the recursive call
+            parent,
+            leaf: false,
+        };
+
+        let id = self.nodes.len() as u32;
+        self.nodes.push(node);
+
+        // Recurse!
+        let a = self.do_recurse_build(left_bottom, aabbs, NodeIndex::new(id, 0));
+        let b = self.do_recurse_build(left_top, aabbs, NodeIndex::new(id, 1));
+        let c = self.do_recurse_build(right_bottom, aabbs, NodeIndex::new(id, 2));
+        let d = self.do_recurse_build(right_top, aabbs, NodeIndex::new(id, 3));
+
+        // Now we know the indices of the grand-nodes.
+        self.nodes[id as usize].children = [a.0, b.0, c.0, d.0];
+        self.nodes[id as usize].waabb = WAABB::from([a.1, b.1, c.1, d.1]);
+
+        // TODO: will this chain of .merged be properly optimized?
+        let my_aabb = a.1.merged(&b.1).merged(&c.1).merged(&d.1);
+        (id, my_aabb)
+    }
+
+    pub fn cast_ray(&self, ray: &Ray, max_toi: f32) -> Vec<ColliderHandle> {
+        let mut res = Vec::new();
+
+        if self.nodes.is_empty() {
+            return res;
+        }
+
+        // Special case for the root.
+        let mut stack = vec![0u32];
+        let wray = WRay::splat(*ray);
+        let wmax_toi = SimdFloat::splat(max_toi);
+        while let Some(inode) = stack.pop() {
+            let node = self.nodes[inode as usize];
+            let hits = node.waabb.intersects_ray(&wray, wmax_toi);
+            let bitmask = hits.bitmask();
+
+            for ii in 0..SIMD_WIDTH {
+                if (bitmask & (1 << ii)) != 0 {
+                    if node.leaf {
+                        // We found a leaf!
+                        // Unfortunately, invalid AABBs return a hit as well.
+                        if let Some(proxy) = self.proxies.get(node.children[ii] as usize) {
+                            res.push(proxy.handle);
+                        }
+                    } else {
+                        // Internal node, visit the child.
+                        // Un fortunately, we have this check because invalid AABBs
+                        // return a hit as well.
+                        if node.children[ii] as usize <= self.nodes.len() {
+                            stack.push(node.children[ii]);
+                        }
+                    }
+                }
+            }
+        }
+
+        res
+    }
+}
+
+fn split_indices_wrt_dim<'a>(
+    indices: &'a mut [usize],
+    aabbs: &[AABB],
+    split_point: &Point<f32>,
+    dim: usize,
+) -> (&'a mut [usize], &'a mut [usize]) {
+    let mut icurr = 0;
+    let mut ilast = indices.len() - 1;
+
+    // The loop condition we can just do 0..indices.len()
+    // instead of the test icurr < ilast because we know
+    // we will iterate exactly once per index.
+    for _ in 0..indices.len() {
+        let i = indices[icurr];
+        let center = aabbs[i].center();
+
+        if center[dim] > split_point[dim] {
+            indices.swap(icurr, ilast);
+            ilast -= 1;
+        } else {
+            icurr += 1;
+        }
+    }
+
+    indices.split_at_mut(icurr)
+}