5 files changed, 82 insertions, 11 deletions

diff --git a/gfx/include/gfx/asset.h b/gfx/include/gfx/asset.h
index 9845b03..1a4e551 100644
--- a/gfx/include/gfx/asset.h
+++ b/gfx/include/gfx/asset.h
@@ -86,15 +86,11 @@ typedef struct LoadModelCmd {
   ShaderProgram* shader;
 } LoadModelCmd;
 
-// TODO: We should return const resources. If the client wants a mutable copy,
-//  then let them clone the resource.
-
-/// Load a scene.
-///
-/// Return a top-level node under which scene elements are rooted.
+/// Load a model.
 ///
-/// |parent_node| is made the parent of the returned top-level node. It may be
-/// null.
+/// For animated models, this function returns a (shallow) clone of the model
+/// that is safe to mutate. For static models, this returns the original model
+/// in the cache.
 ///
 /// Currently only supports the GLTF format.
 Model* gfx_load_model(Gfx*, const LoadModelCmd*);
diff --git a/gfx/include/gfx/scene/node.h b/gfx/include/gfx/scene/node.h
index 3877670..d048894 100644
--- a/gfx/include/gfx/scene/node.h
+++ b/gfx/include/gfx/scene/node.h
@@ -85,7 +85,7 @@ void gfx_destroy_node(SceneNode**);
 
 // TODO: Review constness of getters here.
 
-/// Return the node's type.
+/// Get the node's type.
 NodeType gfx_get_node_type(const SceneNode*);
 
 /// Get the node's anima.
@@ -113,6 +113,9 @@ Model* gfx_get_node_model(const SceneNode*);
 /// The node must be of type ObjectNode.
 SceneObject* gfx_get_node_object(const SceneNode*);
 
+/// Get the node's parent.
+const SceneNode* gfx_get_node_parent(const SceneNode*);
+
 /// Get an iterator to the node's first child.
 NodeIter gfx_get_node_child(const SceneNode*);
 
diff --git a/gfx/src/asset/asset_cache.c b/gfx/src/asset/asset_cache.c
index 0320954..e17de9d 100644
--- a/gfx/src/asset/asset_cache.c
+++ b/gfx/src/asset/asset_cache.c
@@ -1,9 +1,15 @@
 #include "asset_cache.h"
 
 #include "scene.h"
+#include "scene/animation_impl.h"
+#include "scene/model_impl.h"
+#include "scene/node_impl.h"
+#include "scene/scene_memory.h"
 #include "texture.h"
+
 #include <gfx/asset.h>
 #include <gfx/gfx.h>
+#include <gfx/scene/node.h>
 #include <gfx_assert.h>
 
 #include <cstring.h>
@@ -97,6 +103,31 @@ static void log_model_loaded(const LoadModelCmd* cmd) {
   }
 }
 
+static Model* clone_model(const Model* model) {
+  assert(model);
+
+  // Only the Anima needs to be (shallow) cloned since everything else in the
+  // model is static. Also note that only the Anima's joints and animation state
+  // need to be cloned; all other members can be shared. So a shallow clone of
+  // the anima is sufficient.
+  const SceneNode* root = mem_get_node(model->root);
+  if (gfx_get_node_type(root) == AnimaNode) {
+    const Anima* anima      = gfx_get_node_anima(root);
+    Anima*       anima_copy = mem_alloc_anima();
+    *anima_copy             = *anima; // Shallow copy.
+
+    SceneNode* root_copy = gfx_clone_scene_shallow(root);
+    root_copy->anima     = mem_get_anima_index(anima_copy);
+    anima_copy->parent   = mem_get_node_index(root_copy);
+
+    Model* copy = mem_alloc_model();
+    copy->root  = mem_get_node_index(root_copy);
+    return copy;
+  } else {
+    return (Model*)model; // Static model, can't be mutated.
+  }
+}
+
 void gfx_init_asset_cache(AssetCache* cache) {
   assert(cache);
   mempool_make(&cache->assets);
@@ -122,7 +153,7 @@ Model* gfx_load_model(Gfx* gfx, const LoadModelCmd* cmd) {
   Asset*         asset = lookup_cache(cache, hash);
   if (asset) {
     log_model_cache_hit(cmd, hash);
-    return asset->model;
+    return clone_model(asset->model);
   }
 
   // Asset not found in the cache.
@@ -136,7 +167,7 @@ Model* gfx_load_model(Gfx* gfx, const LoadModelCmd* cmd) {
     };
     log_model_loaded(cmd);
   }
-  return model;
+  return clone_model(model);
 }
 
 const Texture* gfx_load_texture(Gfx* gfx, const LoadTextureCmd* cmd) {
diff --git a/gfx/src/scene/node.c b/gfx/src/scene/node.c
index c48d3dd..0fbb696 100644
--- a/gfx/src/scene/node.c
+++ b/gfx/src/scene/node.c
@@ -229,6 +229,11 @@ SceneObject* gfx_get_node_object(const SceneNode* node) {
   NODE_GET(node, object, ObjectNode);
 }
 
+const SceneNode* gfx_get_node_parent(const SceneNode* node) {
+  assert(node);
+  return mem_get_node(node->parent);
+}
+
 NodeIter gfx_get_node_child(const SceneNode* node) {
   assert(node);
   return (NodeIter)node->child.val;
@@ -344,3 +349,35 @@ void gfx_log_node_hierarchy(const SceneNode* node) {
   const sstring pad = sstring_make("");
   log_node_hierarchy_rec(node, &pad);
 }
+
+static SceneNode* clone_scene_rec(const SceneNode* node) {
+  assert(node);
+
+  SceneNode* copy = mem_alloc_node();
+  *copy           = *node; // Shallow clone of the node's resource.
+
+  if (node->child.val) {
+    SceneNode* child      = mem_get_node(node->child);
+    SceneNode* child_copy = clone_scene_rec(child);
+    copy->child           = mem_get_node_index(child_copy);
+    child_copy->parent    = mem_get_node_index(copy);
+  }
+
+  if (node->next.val) {
+    SceneNode* next      = mem_get_node(node->next);
+    SceneNode* next_copy = clone_scene_rec(next);
+    copy->next           = mem_get_node_index(next_copy);
+    next_copy->prev      = mem_get_node_index(copy);
+  }
+
+  return copy;
+}
+
+SceneNode* gfx_clone_scene_shallow(const SceneNode* node) {
+  assert(node);
+  // Must be a root node; not allowed to have siblings.
+  assert(!node->prev.val);
+  assert(!node->next.val);
+
+  return clone_scene_rec(node);
+}
diff --git a/gfx/src/scene/node_impl.h b/gfx/src/scene/node_impl.h
index cabdc60..c79f252 100644
--- a/gfx/src/scene/node_impl.h
+++ b/gfx/src/scene/node_impl.h
@@ -34,3 +34,7 @@ typedef struct SceneNode {
 ///
 /// This function is for the library's internal use only.
 void gfx_del_node(node_idx);
+
+/// Return a shallow clone of the scene rooted at the given node.
+/// The given node must have no siblings (must be a root node).
+SceneNode* gfx_clone_scene_shallow(const SceneNode*);