From 73fa110f21dc671d849152172ab215e9186893eb Mon Sep 17 00:00:00 2001
From: Alex Kocharin <alex@kocharin.ru>
Date: Tue, 2 Apr 2024 16:51:27 +0400
Subject: [PATCH] Add support for unindexed meshes in
 `Collider::from_bevy_mesh`

fixes https://github.com/dimforge/bevy_rapier/issues/490
---
 src/geometry/collider_impl.rs | 37 +++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/geometry/collider_impl.rs b/src/geometry/collider_impl.rs
index d98c980c..cc8752d3 100644
--- a/src/geometry/collider_impl.rs
+++ b/src/geometry/collider_impl.rs
@@ -3,7 +3,7 @@ use na::DVector;
 #[cfg(all(feature = "dim3", feature = "async-collider"))]
 use {
     bevy::prelude::*,
-    bevy::render::mesh::{Indices, VertexAttributeValues},
+    bevy::render::mesh::{Indices, PrimitiveTopology, VertexAttributeValues},
 };
 
 use rapier::prelude::{FeatureId, Point, Ray, SharedShape, Vector, DIM};
@@ -739,7 +739,7 @@ fn extract_mesh_vertices_indices(mesh: &Mesh) -> Option<(Vec<na::Point3<Real>>,
     use rapier::na::point;
 
     let vertices = mesh.attribute(Mesh::ATTRIBUTE_POSITION)?;
-    let indices = mesh.indices()?;
+    let indices = mesh.indices();
 
     let vtx: Vec<_> = match vertices {
         VertexAttributeValues::Float32(vtx) => Some(
@@ -756,11 +756,40 @@ fn extract_mesh_vertices_indices(mesh: &Mesh) -> Option<(Vec<na::Point3<Real>>,
     }?;
 
     let idx = match indices {
-        Indices::U16(idx) => idx
+        Some(Indices::U16(idx)) => idx
             .chunks_exact(3)
             .map(|i| [i[0] as u32, i[1] as u32, i[2] as u32])
             .collect(),
-        Indices::U32(idx) => idx.chunks_exact(3).map(|i| [i[0], i[1], i[2]]).collect(),
+        Some(Indices::U32(idx)) => idx.chunks_exact(3).map(|i| [i[0], i[1], i[2]]).collect(),
+        None => {
+            // Meshes loaded from glTF files may not necessarily have an index buffer
+            // in order to save memory (e.g. files generated by osm2world), in which case
+            // there's predefined algorithm to calculate indices for each topology.
+            match mesh.primitive_topology() {
+                PrimitiveTopology::TriangleList => {
+                    // [[0, 1, 2], [3, 4, 5], [6, 7, 8], ...]
+                    (0..vtx.len() as u32)
+                        .step_by(3)
+                        .map(|i| [i, i + 1, i + 2])
+                        .collect()
+                }
+                PrimitiveTopology::TriangleStrip => {
+                    // [[0, 1, 2], [2, 1, 3], [2, 3, 4], ...]
+                    (0..vtx.len() as u32 - 2)
+                        .map(|i| {
+                            if i % 2 == 0 {
+                                [i, i + 1, i + 2]
+                            } else {
+                                [i + 1, i, i + 2]
+                            }
+                        })
+                        .collect()
+                }
+                // ignore PointList, LineList, LineStrip:
+                // they don't have meaningful colliders
+                _ => return None,
+            }
+        }
     };
 
     Some((vtx, idx))