Fix: Avoid floating point error in some mesh primitive nodes

Some mesh primitives created using geometry nodes use loops to create
vertices and accumulates positions/angles in FP variables. This allows
rounding errors to accumulate and can introduce significant errors.

To minimize changes from original implementation, variables allowing
errors to accumulate are replaced by: delta * index. Affected Mesh
Primitives nodes are Line, Grid, Cylinder, Circle, Cone, and UV-Sphere.

Differential Revision: https://developer.blender.org/D12136

1 files changed, 1 insertions, 3 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_line.cc b/source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_line.cc
index a193c05daa1..2e6d8ca34c8 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_line.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_mesh_primitive_line.cc
@@ -118,11 +118,9 @@ static Mesh *create_line_mesh(const float3 start, const float3 delta, const int
   short normal[3];
   normal_float_to_short_v3(normal, delta.normalized());
 
-  float3 co = start;
   for (const int i : verts.index_range()) {
-    copy_v3_v3(verts[i].co, co);
+    copy_v3_v3(verts[i].co, start + delta * i);
     copy_v3_v3_short(verts[i].no, normal);
-    co += delta;
   }
 
   fill_edge_data(edges);