Curves: Move constructor/assignment

Add the ability to move `CurvesGeometry` without copying its attributes
and data. The benefit is more intuitive management of the data-block
copying, and less overhead for copying in some cases. The "moved-from"
source is left in an empty but valid state. A test file is added to test
the move constructor.

1 files changed, 3 insertions, 1 deletions

diff --git a/source/blender/makesdna/DNA_curves_types.h b/source/blender/makesdna/DNA_curves_types.h
index 98d2aa4b295..d3e69315265 100644
--- a/source/blender/makesdna/DNA_curves_types.h
+++ b/source/blender/makesdna/DNA_curves_types.h
@@ -69,7 +69,8 @@ typedef struct CurvesGeometry {
   /**
    * The start index of each curve in the point data. The size of each curve can be calculated by
    * subtracting the offset from the next offset. That is valid even for the last curve because
-   * this array is allocated with a length one larger than the number of splines.
+   * this array is allocated with a length one larger than the number of splines. This is allowed
+   * to be null when there are no curves.
    *
    * \note This is *not* stored in #CustomData because its size is one larger than #curve_data.
    */
@@ -77,6 +78,7 @@ typedef struct CurvesGeometry {
 
   /**
    * All attributes stored on control points (#ATTR_DOMAIN_POINT).
+   * This might not contain a layer for positions if there are no points.
    */
   CustomData point_data;