only take up to the max number of joints (#9351)

# Objective

- Meshes with a higher number of joints than `MAX_JOINTS` are crashing
- Fixes partly #9021 (doesn't crash anymore, but the mesh is not
correctly displayed)

## Solution

- Only take up to `MAX_JOINTS` joints when extending the buffer

crates/bevy_gltf/src/loader.rs

@@ -11,7 +11,7 @@ use bevy_log::warn;
 use bevy_math::{Mat4, Vec3};
 use bevy_pbr::{
     AlphaMode, DirectionalLight, DirectionalLightBundle, PbrBundle, PointLight, PointLightBundle,
-    SpotLight, SpotLightBundle, StandardMaterial,
+    SpotLight, SpotLightBundle, StandardMaterial, MAX_JOINTS,
 };
 use bevy_render::{
     camera::{Camera, OrthographicProjection, PerspectiveProjection, Projection, ScalingMode},
@@ -489,6 +489,7 @@ async fn load_gltf<'a, 'b>(
             }
         }
 
+        let mut warned_about_max_joints = HashSet::new();
         for (&entity, &skin_index) in &entity_to_skin_index_map {
             let mut entity = world.entity_mut(entity);
             let skin = gltf.skins().nth(skin_index).unwrap();
@@ -497,6 +498,16 @@ async fn load_gltf<'a, 'b>(
                 .map(|node| node_index_to_entity_map[&node.index()])
                 .collect();
 
+            if joint_entities.len() > MAX_JOINTS && warned_about_max_joints.insert(skin_index) {
+                warn!(
+                    "The glTF skin {:?} has {} joints, but the maximum supported is {}",
+                    skin.name()
+                        .map(|name| name.to_string())
+                        .unwrap_or_else(|| skin.index().to_string()),
+                    joint_entities.len(),
+                    MAX_JOINTS
+                );
+            }
             entity.insert(SkinnedMesh {
                 inverse_bindposes: skinned_mesh_inverse_bindposes[skin_index].clone(),
                 joints: joint_entities,

crates/bevy_pbr/src/render/mesh.rs

@@ -52,7 +52,8 @@ use crate::render::{
 #[derive(Default)]
 pub struct MeshRenderPlugin;
 
-const MAX_JOINTS: usize = 256;
+/// Maximum number of joints supported for skinned meshes.
+pub const MAX_JOINTS: usize = 256;
 const JOINT_SIZE: usize = std::mem::size_of::<Mat4>();
 pub(crate) const JOINT_BUFFER_SIZE: usize = MAX_JOINTS * JOINT_SIZE;
 
@@ -323,6 +324,7 @@ impl SkinnedMeshJoints {
             joints
                 .iter_many(&skin.joints)
                 .zip(inverse_bindposes.iter())
+                .take(MAX_JOINTS)
                 .map(|(joint, bindpose)| joint.affine() * *bindpose),
         );
         // iter_many will skip any failed fetches. This will cause it to assign the wrong bones,