4 files changed, 42 insertions, 4 deletions
diff --git a/src/3d/object.h b/src/3d/object.h
index 0c8edd8..a7ce0b8 100644
--- a/src/3d/object.h
+++ b/src/3d/object.h
@@ -40,11 +40,12 @@ class Object3D {
   bool is_static;
 
   AssetId mesh_asset_id;
+  void* user_data; // For tool-specific data, not for general use
 
   Object3D(ObjectType t = ObjectType::CUBE)
       : position(0, 0, 0), rotation(0, 0, 0, 1), scale(1, 1, 1), type(t),
         color(1, 1, 1, 1), velocity(0, 0, 0), mass(1.0f), restitution(0.5f),
-        is_static(false), mesh_asset_id((AssetId)0) {
+        is_static(false), mesh_asset_id((AssetId)0), user_data(nullptr) {
   }
 
   mat4 get_model_matrix() const {
diff --git a/src/3d/renderer.h b/src/3d/renderer.h
index 5caf19b..5c9fd38 100644
--- a/src/3d/renderer.h
+++ b/src/3d/renderer.h
@@ -65,13 +65,23 @@ class Renderer3D {
   // Set whether to use BVH acceleration
   void SetBvhEnabled(bool enabled) { bvh_enabled_ = enabled; }
 
- private:
   struct MeshGpuData {
     WGPUBuffer vertex_buffer;
     WGPUBuffer index_buffer;
     uint32_t num_indices;
   };
 
+  // HACK for test_mesh tool
+  void override_mesh_buffers(const MeshGpuData* data) {
+    temp_mesh_override_ = data;
+  }
+
+#if !defined(STRIP_ALL)
+  VisualDebug& GetVisualDebug() { return visual_debug_; }
+#endif
+
+ private:
+
   void create_pipeline();
   WGPURenderPipeline create_pipeline_impl(bool use_bvh);
   void create_mesh_pipeline();
@@ -98,6 +108,7 @@ class Renderer3D {
   bool bvh_enabled_ = true;
 
   std::map<AssetId, MeshGpuData> mesh_cache_;
+  const MeshGpuData* temp_mesh_override_ = nullptr; // HACK for test_mesh tool
 
   WGPUTextureView noise_texture_view_ = nullptr;
   WGPUTextureView sky_texture_view_ = nullptr;
diff --git a/src/3d/visual_debug.cc b/src/3d/visual_debug.cc
index 86f12b4..009a1e1 100644
--- a/src/3d/visual_debug.cc
+++ b/src/3d/visual_debug.cc
@@ -107,7 +107,7 @@ void VisualDebug::create_pipeline(WGPUTextureFormat format) {
 #if defined(DEMO_CROSS_COMPILE_WIN32)
   pipeline_desc.vertex.entryPoint = "vs_main";
 #else
-  pipeline_desc.vertex.entryPoint = {"vs_main", 7};
+  pipeline_desc.vertex.entryPoint = str_view("vs_main");
 #endif
   pipeline_desc.vertex.bufferCount = 1;
   pipeline_desc.vertex.buffers = &vertex_layout;
@@ -117,7 +117,7 @@ void VisualDebug::create_pipeline(WGPUTextureFormat format) {
 #if defined(DEMO_CROSS_COMPILE_WIN32)
   fragment_state.entryPoint = "fs_main";
 #else
-  fragment_state.entryPoint = {"fs_main", 7};
+  fragment_state.entryPoint = str_view("fs_main");
 #endif
   fragment_state.targetCount = 1;
 
@@ -203,6 +203,29 @@ void VisualDebug::add_aabb(const vec3& min, const vec3& max,
   }
 }
 
+void VisualDebug::add_mesh_normals(const mat4& transform, uint32_t num_vertices,
+                                   const MeshVertex* vertices) {
+  if (!vertices || num_vertices == 0)
+    return;
+
+  mat4 normal_matrix = mat4::transpose(transform.inverse());
+
+  for (uint32_t i = 0; i < num_vertices; ++i) {
+    const auto& v = vertices[i];
+
+    vec4 p_world = transform * vec4(v.p[0], v.p[1], v.p[2], 1.0f);
+    vec3 n_object = vec3(v.n[0], v.n[1], v.n[2]);
+    vec4 n_world_h = normal_matrix * vec4(n_object.x, n_object.y, n_object.z, 0.0f);
+    vec3 n_world = n_world_h.xyz().normalize();
+
+    lines_.push_back(
+        {p_world.xyz(), p_world.xyz() + n_world * 0.1f, // 0.1 is the length
+         {0.0f, 1.0f, 1.0f}                             // Cyan color
+        });
+  }
+}
+
+
 void VisualDebug::update_buffers(const mat4& view_proj) {
   // Update Uniforms
   wgpuQueueWriteBuffer(wgpuDeviceGetQueue(device_), uniform_buffer_, 0,
diff --git a/src/3d/visual_debug.h b/src/3d/visual_debug.h
index 6173fc4..ebccf45 100644
--- a/src/3d/visual_debug.h
+++ b/src/3d/visual_debug.h
@@ -8,6 +8,7 @@
 
 #include "gpu/gpu.h"
 #include "util/mini_math.h"
+#include "3d/object.h"
 #include <vector>
 
 struct DebugLine {
@@ -27,6 +28,8 @@ class VisualDebug {
 
   void add_aabb(const vec3& min, const vec3& max, const vec3& color);
 
+  void add_mesh_normals(const mat4& transform, uint32_t num_vertices, const MeshVertex* vertices);
+
   // Render all queued primitives and clear the queue
   void render(WGPURenderPassEncoder pass, const mat4& view_proj);