From 5946352ae2cd3ef14d8af07f8d4bd047954b9fd1 Mon Sep 17 00:00:00 2001
From: Campbell Barton <ideasman42@gmail.com>
Date: Fri, 30 Apr 2021 00:22:02 +1000
Subject: Fix T87779: Asymmetric position vertices in circles primitives.

Incrementing a floating point value in a loop resulted in the vertex
locations for circles in primitives being slightly asymmetric.
---
 source/blender/bmesh/operators/bmo_primitive.c | 29 +++++++++++++-------------
 1 file changed, 14 insertions(+), 15 deletions(-)

(limited to 'source/blender/bmesh')

diff --git a/source/blender/bmesh/operators/bmo_primitive.c b/source/blender/bmesh/operators/bmo_primitive.c
index a0a31ab6154..f47c8dfb405 100644
--- a/source/blender/bmesh/operators/bmo_primitive.c
+++ b/source/blender/bmesh/operators/bmo_primitive.c
@@ -867,19 +867,19 @@ void bmo_create_uvsphere_exec(BMesh *bm, BMOperator *op)
   BMIter iter;
   const float axis[3] = {0, 0, 1};
   float vec[3], mat[4][4], cmat[3][3];
-  float phi, phid;
   int a;
 
   BMO_slot_mat4_get(op->slots_in, "matrix", mat);
 
-  phid = 2.0f * (float)M_PI / tot;
+  const float phid = (float)M_PI / tot;
   /* phi = 0.25f * (float)M_PI; */ /* UNUSED */
 
   /* one segment first */
-  phi = 0;
-  phid /= 2;
   for (a = 0; a <= tot; a++) {
     /* Going in this direction, then edge extruding, makes normals face outward */
+    /* Calculate with doubles for higher precision, see: T87779. */
+    const float phi = M_PI * ((double)a / (double)tot);
+
     vec[0] = 0.0;
     vec[1] = dia * sinf(phi);
     vec[2] = dia * cosf(phi);
@@ -891,7 +891,6 @@ void bmo_create_uvsphere_exec(BMesh *bm, BMOperator *op)
       BMO_edge_flag_enable(bm, e, EDGE_ORIG);
     }
 
-    phi += phid;
     preveve = eve;
   }
 
@@ -1272,7 +1271,7 @@ void bmo_create_circle_exec(BMesh *bm, BMOperator *op)
   const bool calc_uvs = (cd_loop_uv_offset != -1) && BMO_slot_bool_get(op->slots_in, "calc_uvs");
 
   BMVert *v1, *lastv1 = NULL, *cent1, *firstv1 = NULL;
-  float vec[3], mat[4][4], phi, phid;
+  float vec[3], mat[4][4];
   int a;
 
   if (!segs) {
@@ -1281,9 +1280,6 @@ void bmo_create_circle_exec(BMesh *bm, BMOperator *op)
 
   BMO_slot_mat4_get(op->slots_in, "matrix", mat);
 
-  phid = 2.0f * (float)M_PI / segs;
-  phi = 0;
-
   if (cap_ends) {
     zero_v3(vec);
     mul_m4_v3(mat, vec);
@@ -1292,8 +1288,11 @@ void bmo_create_circle_exec(BMesh *bm, BMOperator *op)
     BMO_vert_flag_enable(bm, cent1, VERT_MARK);
   }
 
-  for (a = 0; a < segs; a++, phi += phid) {
+  for (a = 0; a < segs; a++) {
     /* Going this way ends up with normal(s) upward */
+
+    /* Calculate with doubles for higher precision, see: T87779. */
+    const float phi = (2.0 * M_PI) * ((double)a / (double)segs);
     vec[0] = -radius * sinf(phi);
     vec[1] = radius * cosf(phi);
     vec[2] = 0.0f;
@@ -1392,7 +1391,7 @@ void bmo_create_cone_exec(BMesh *bm, BMOperator *op)
 {
   BMVert *v1, *v2, *lastv1 = NULL, *lastv2 = NULL, *cent1, *cent2, *firstv1, *firstv2;
   BMFace *f;
-  float vec[3], mat[4][4], phi, phid;
+  float vec[3], mat[4][4];
   const float dia1 = BMO_slot_float_get(op->slots_in, "diameter1");
   const float dia2 = BMO_slot_float_get(op->slots_in, "diameter2");
   const float depth_half = 0.5f * BMO_slot_float_get(op->slots_in, "depth");
@@ -1409,9 +1408,6 @@ void bmo_create_cone_exec(BMesh *bm, BMOperator *op)
 
   BMO_slot_mat4_get(op->slots_in, "matrix", mat);
 
-  phid = 2.0f * (float)M_PI / segs;
-  phi = 0;
-
   if (cap_ends) {
     vec[0] = vec[1] = 0.0f;
     vec[2] = -depth_half;
@@ -1432,7 +1428,10 @@ void bmo_create_cone_exec(BMesh *bm, BMOperator *op)
   const int side_faces_len = segs - 1;
   BMFace **side_faces = MEM_mallocN(sizeof(*side_faces) * side_faces_len, __func__);
 
-  for (int i = 0; i < segs; i++, phi += phid) {
+  for (int i = 0; i < segs; i++) {
+    /* Calculate with doubles for higher precision, see: T87779. */
+    const float phi = (2.0 * M_PI) * ((double)i / (double)segs);
+
     vec[0] = dia1 * sinf(phi);
     vec[1] = dia1 * cosf(phi);
     vec[2] = -depth_half;
-- 
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