[Bf-blender-cvs] [7dc4ac71e8d] master: Fix T97278: wrong hair particle shape with kink spiral

[Hallam Roberts]

Commit: 7dc4ac71e8dcbd801ca9d375cdd1bea88e6293ac
Author: Hallam Roberts
Date:   Wed Apr 13 16:23:38 2022 +0200
Branches: master
https://developer.blender.org/rB7dc4ac71e8dcbd801ca9d375cdd1bea88e6293ac

Fix T97278: wrong hair particle shape with kink spiral

Revert change from 3da84d8b that incorrectly used M_PI_4.

Differential Revision: https://developer.blender.org/D14636

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M	source/blender/blenkernel/intern/particle_child.c

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diff --git a/source/blender/blenkernel/intern/particle_child.c b/source/blender/blenkernel/intern/particle_child.c
index 5dba4d3f003..524ee31229b 100644
--- a/source/blender/blenkernel/intern/particle_child.c
+++ b/source/blender/blenkernel/intern/particle_child.c
@@ -85,7 +85,7 @@ static void do_kink_spiral_deform(ParticleKey *state,
      * and goes up to the Golden Spiral for 1.0
      * https://en.wikipedia.org/wiki/Golden_spiral
      */
-    const float b = shape * (1.0f + sqrtf(5.0f)) / (float)M_PI_4;
+    const float b = shape * (1.0f + sqrtf(5.0f)) / (float)M_PI * 0.25f;
     /* angle of the spiral against the curve (rotated opposite to make a smooth transition) */
     const float start_angle = ((b != 0.0f) ? atanf(1.0f / b) : (float)-M_PI_2) +
                               (b > 0.0f ? -(float)M_PI_2 : (float)M_PI_2);