Curves: Remove redundant custom data pointers

These mutable pointers present problems with ownership in relation to
proper copy-on-write for attributes. The simplest solution is to just
remove them and retrieve the layers from  `CustomData` when they are
needed. This also removes the complexity and redundancy of having to
update the pointers as the curves change. A similar change will apply
to meshes and point clouds.

One downside of this change is that it makes random access with RNA
slower. However, it's simple to just use the RNA attribute API instead,
which is unaffected. In this patch I updated Cycles to do that. With
the future attribute CoW changes, this generic approach makes sense
because Cycles can just request ownership of the existing arrays.

Differential Revision: https://developer.blender.org/D15486

1 files changed, 29 insertions, 8 deletions

diff --git a/intern/cycles/blender/curves.cpp b/intern/cycles/blender/curves.cpp
index 263a5fc0e02..c4154bce022 100644
--- a/intern/cycles/blender/curves.cpp
+++ b/intern/cycles/blender/curves.cpp
@@ -630,6 +630,25 @@ static std::optional<BL::FloatAttribute> find_curves_radius_attribute(BL::Curves
   return std::nullopt;
 }
 
+static BL::FloatVectorAttribute find_curves_position_attribute(BL::Curves b_curves)
+{
+  for (BL::Attribute &b_attribute : b_curves.attributes) {
+    if (b_attribute.name() != "position") {
+      continue;
+    }
+    if (b_attribute.domain() != BL::Attribute::domain_POINT) {
+      continue;
+    }
+    if (b_attribute.data_type() != BL::Attribute::data_type_FLOAT_VECTOR) {
+      continue;
+    }
+    return BL::FloatVectorAttribute{b_attribute};
+  }
+  /* The position attribute must exist. */
+  assert(false);
+  return BL::FloatVectorAttribute{b_curves.attributes[0]};
+}
+
 template<typename TypeInCycles, typename GetValueAtIndex>
 static void fill_generic_attribute(BL::Curves &b_curves,
                                    TypeInCycles *data,
@@ -793,16 +812,16 @@ static void attr_create_generic(Scene *scene,
   }
 }
 
-static float4 hair_point_as_float4(BL::Curves b_curves,
+static float4 hair_point_as_float4(BL::FloatVectorAttribute b_attr_position,
                                    std::optional<BL::FloatAttribute> b_attr_radius,
                                    const int index)
 {
-  float4 mP = float3_to_float4(get_float3(b_curves.position_data[index].vector()));
+  float4 mP = float3_to_float4(get_float3(b_attr_position.data[index].vector()));
   mP.w = b_attr_radius ? b_attr_radius->data[index].value() : 0.0f;
   return mP;
 }
 
-static float4 interpolate_hair_points(BL::Curves b_curves,
+static float4 interpolate_hair_points(BL::FloatVectorAttribute b_attr_position,
                                       std::optional<BL::FloatAttribute> b_attr_radius,
                                       const int first_point_index,
                                       const int num_points,
@@ -812,8 +831,8 @@ static float4 interpolate_hair_points(BL::Curves b_curves,
   const int point_a = clamp((int)curve_t, 0, num_points - 1);
   const int point_b = min(point_a + 1, num_points - 1);
   const float t = curve_t - (float)point_a;
-  return lerp(hair_point_as_float4(b_curves, b_attr_radius, first_point_index + point_a),
-              hair_point_as_float4(b_curves, b_attr_radius, first_point_index + point_b),
+  return lerp(hair_point_as_float4(b_attr_position, b_attr_radius, first_point_index + point_a),
+              hair_point_as_float4(b_attr_position, b_attr_radius, first_point_index + point_b),
               t);
 }
 
@@ -846,6 +865,7 @@ static void export_hair_curves(Scene *scene,
 
   hair->reserve_curves(num_curves, num_keys);
 
+  BL::FloatVectorAttribute b_attr_position = find_curves_position_attribute(b_curves);
   std::optional<BL::FloatAttribute> b_attr_radius = find_curves_radius_attribute(b_curves);
 
   /* Export curves and points. */
@@ -864,7 +884,7 @@ static void export_hair_curves(Scene *scene,
 
     /* Position and radius. */
     for (int i = 0; i < num_points; i++) {
-      const float3 co = get_float3(b_curves.position_data[first_point_index + i].vector());
+      const float3 co = get_float3(b_attr_position.data[first_point_index + i].vector());
       const float radius = b_attr_radius ? b_attr_radius->data[first_point_index + i].value() :
                                            0.005f;
       hair->add_curve_key(co, radius);
@@ -921,6 +941,7 @@ static void export_hair_curves_motion(Hair *hair, BL::Curves b_curves, int motio
   int num_motion_keys = 0;
   int curve_index = 0;
 
+  BL::FloatVectorAttribute b_attr_position = find_curves_position_attribute(b_curves);
   std::optional<BL::FloatAttribute> b_attr_radius = find_curves_radius_attribute(b_curves);
 
   for (int i = 0; i < num_curves; i++) {
@@ -936,7 +957,7 @@ static void export_hair_curves_motion(Hair *hair, BL::Curves b_curves, int motio
         int point_index = first_point_index + i;
 
         if (point_index < num_keys) {
-          mP[num_motion_keys] = hair_point_as_float4(b_curves, b_attr_radius, point_index);
+          mP[num_motion_keys] = hair_point_as_float4(b_attr_position, b_attr_radius, point_index);
           num_motion_keys++;
 
           if (!have_motion) {
@@ -956,7 +977,7 @@ static void export_hair_curves_motion(Hair *hair, BL::Curves b_curves, int motio
       for (int i = 0; i < curve.num_keys; i++) {
         const float step = i * step_size;
         mP[num_motion_keys] = interpolate_hair_points(
-            b_curves, b_attr_radius, first_point_index, num_points, step);
+            b_attr_position, b_attr_radius, first_point_index, num_points, step);
         num_motion_keys++;
       }
       have_motion = true;